From 25cb0b2fa389d5effbb846d1538b401f975f1163 Mon Sep 17 00:00:00 2001
From: Ben Surgison <ben.surgison@digital.cabinet-office.gov.uk>
Date: Thu, 8 Jun 2023 15:28:11 +0100
Subject: [PATCH 1/4] Specify plugin dependencies

---
 CHANGELOG.md                                  |   2 +
 .../govuk-prototype-kit.config.json           |   7 +
 __tests__/spec/force-https-redirect.js        |   4 +
 ...=> install-plugin-via-cli-test.cypress.js} |   2 +-
 .../install-plugin-via-ui-test.cypress.js     | 105 +++++++
 cypress/e2e/plugins/plugin-utils.js           |   2 +-
 cypress/events/index.js                       |   2 +-
 .../govuk-prototype-kit.config.json           |  14 +
 .../fixtures/plugins/plugin-fee/package.json  |   7 +
 .../fixtures/plugins/plugin-fee/sass/fee.scss |   4 +
 .../plugins/plugin-fee/templates/fee.njk      |  10 +
 known-plugins.json                            |   4 +
 .../manage-prototype/manage-plugins.js        |  11 +-
 .../manage-prototype/manage-plugins.test.js   |   8 +
 lib/manage-prototype-handlers.js              | 263 ++++++++---------
 lib/manage-prototype-handlers.test.js         | 224 +++++++++------
 lib/manage-prototype-routes.js                |   4 +-
 .../plugin-install-or-uninstall.njk           |  42 ++-
 lib/plugins/packages.js                       | 245 ++++++++++++++++
 lib/plugins/packages.spec.js                  | 264 ++++++++++++++++++
 lib/plugins/plugin-utils.js                   |  14 +
 lib/plugins/plugin-validator.js               |  53 +++-
 lib/plugins/plugin-validator.spec.js          |  64 +++++
 lib/plugins/plugins.js                        |  25 +-
 lib/utils/index.js                            |  26 --
 lib/utils/requestHttps.js                     |  96 +++++++
 26 files changed, 1222 insertions(+), 280 deletions(-)
 rename cypress/e2e/plugins/0-mock-plugin-tests/{install-plugin-test.cypress.js => install-plugin-via-cli-test.cypress.js} (96%)
 create mode 100644 cypress/e2e/plugins/0-mock-plugin-tests/install-plugin-via-ui-test.cypress.js
 create mode 100644 cypress/fixtures/plugins/plugin-fee/govuk-prototype-kit.config.json
 create mode 100644 cypress/fixtures/plugins/plugin-fee/package.json
 create mode 100644 cypress/fixtures/plugins/plugin-fee/sass/fee.scss
 create mode 100644 cypress/fixtures/plugins/plugin-fee/templates/fee.njk
 create mode 100644 lib/plugins/packages.js
 create mode 100644 lib/plugins/packages.spec.js
 create mode 100644 lib/plugins/plugin-utils.js
 create mode 100644 lib/plugins/plugin-validator.spec.js
 create mode 100644 lib/utils/requestHttps.js

diff --git a/CHANGELOG.md b/CHANGELOG.md
index ef5e6322a1..c127259122 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,8 @@
 
 ## Unreleased
 
+- [#2220: Specify plugin dependencies](https://github.com/alphagov/govuk-prototype-kit/pull/2220)
+
 ## 13.9.1
 
 ### Fixes
diff --git a/__tests__/fixtures/mockPlugins/valid-plugin/govuk-prototype-kit.config.json b/__tests__/fixtures/mockPlugins/valid-plugin/govuk-prototype-kit.config.json
index 91f784976d..afec4488ff 100644
--- a/__tests__/fixtures/mockPlugins/valid-plugin/govuk-prototype-kit.config.json
+++ b/__tests__/fixtures/mockPlugins/valid-plugin/govuk-prototype-kit.config.json
@@ -34,5 +34,12 @@
 		"path": "/templates/start-with-step-by-step.html",
 		"type": "nunjucks"
 	  }
+	],
+	"pluginDependencies": [
+	  {
+	    "packageName": "govuk-frontend",
+		  "minVersion": "4.5.0",
+		  "maxVersion": "5.5.0"
+	  }
 	]
   }
\ No newline at end of file
diff --git a/__tests__/spec/force-https-redirect.js b/__tests__/spec/force-https-redirect.js
index 4f002ecd18..e41b9600da 100644
--- a/__tests__/spec/force-https-redirect.js
+++ b/__tests__/spec/force-https-redirect.js
@@ -18,6 +18,10 @@ process.env.KIT_PROJECT_DIR = testDir
 process.env.NODE_ENV = 'production'
 process.env.USE_HTTPS = 'true'
 
+jest.mock('../../lib/plugins/packages.js', () => {
+  return {}
+})
+
 const app = require('../../server.js')
 
 describe('The Prototype Kit - force HTTPS redirect functionality', () => {
diff --git a/cypress/e2e/plugins/0-mock-plugin-tests/install-plugin-test.cypress.js b/cypress/e2e/plugins/0-mock-plugin-tests/install-plugin-via-cli-test.cypress.js
similarity index 96%
rename from cypress/e2e/plugins/0-mock-plugin-tests/install-plugin-test.cypress.js
rename to cypress/e2e/plugins/0-mock-plugin-tests/install-plugin-via-cli-test.cypress.js
index b6575dfacb..37901e1314 100644
--- a/cypress/e2e/plugins/0-mock-plugin-tests/install-plugin-test.cypress.js
+++ b/cypress/e2e/plugins/0-mock-plugin-tests/install-plugin-via-cli-test.cypress.js
@@ -29,7 +29,7 @@ const pluginBazViewMarkup = `
 {% endblock %}
 `
 
-describe('Single Plugin Test', async () => {
+describe('Install Plugin via CLI Test', async () => {
   before(() => {
     uninstallPlugin('plugin-baz')
     createFile(pluginBazView, { data: pluginBazViewMarkup })
diff --git a/cypress/e2e/plugins/0-mock-plugin-tests/install-plugin-via-ui-test.cypress.js b/cypress/e2e/plugins/0-mock-plugin-tests/install-plugin-via-ui-test.cypress.js
new file mode 100644
index 0000000000..7534ab40f1
--- /dev/null
+++ b/cypress/e2e/plugins/0-mock-plugin-tests/install-plugin-via-ui-test.cypress.js
@@ -0,0 +1,105 @@
+const { installPlugin, uninstallPlugin } = require('../../utils')
+const path = require('path')
+const { loadTemplatesPage, managePluginsPagePath, performPluginAction, loadPluginsPage } = require('../plugin-utils')
+
+const panelCompleteQuery = '[aria-live="polite"] #panel-complete'
+const fixtures = path.join(Cypress.config('fixturesFolder'))
+const dependentPlugin = 'plugin-fee'
+const dependentPluginName = 'Plugin Fee'
+const dependentPluginLocation = path.join(fixtures, 'plugins', dependentPlugin)
+const dependencyPlugin = 'govuk-frontend'
+const dependencyPluginName = 'GOV.UK Frontend'
+
+function restore () {
+  installPlugin(dependencyPlugin)
+  uninstallPlugin(dependentPlugin)
+}
+
+describe('Install and uninstall Local Plugin via UI Test', async () => {
+  before(restore)
+  after(restore)
+
+  it(`The ${dependentPlugin} plugin templates are not available`, () => {
+    loadTemplatesPage()
+    cy.get(`[data-plugin-package-name="${dependentPlugin}"]`).should('not.exist')
+  })
+
+  it(`Install the ${dependentPlugin} plugin`, () => {
+    cy.task('waitUntilAppRestarts')
+    cy.visit(`${managePluginsPagePath}/install?package=${encodeURIComponent(dependentPlugin)}&version=${encodeURIComponent(dependentPluginLocation)}`)
+    cy.get('#plugin-action-button').click()
+
+    cy.get(panelCompleteQuery, { timeout: 20000 })
+      .should('be.visible')
+    cy.get('a').contains('Back to plugins').click()
+
+    cy.get(`[data-plugin-package-name="${dependentPlugin}"] button`).contains('Uninstall')
+  })
+
+  it(`The ${dependentPlugin} plugin templates are available`, () => {
+    loadTemplatesPage()
+    cy.get(`[data-plugin-package-name="${dependentPlugin}"]`).should('exist')
+  })
+
+  it('Uninstall the local plugin', () => {
+    loadPluginsPage()
+
+    cy.get(`[data-plugin-package-name="${dependentPlugin}"]`)
+      .scrollIntoView()
+      .find('button')
+      .contains('Uninstall')
+      .click()
+
+    performPluginAction('uninstall', dependentPlugin, dependentPluginName)
+  })
+
+  it(`The ${dependentPlugin} plugin templates are not available`, () => {
+    loadTemplatesPage()
+    cy.get(`[data-plugin-package-name="${dependentPlugin}"]`).should('not.exist')
+  })
+})
+
+describe('Install and uninstall Local Dependent Plugin via UI Test', async () => {
+  before(restore)
+  after(restore)
+
+  it(`The ${dependentPlugin} plugin templates are not available`, () => {
+    loadTemplatesPage()
+    cy.get(`[data-plugin-package-name="${dependentPlugin}"]`).should('not.exist')
+  })
+
+  it(`Uninstall the ${dependencyPlugin} to force the UI to ask for it later`, () => {
+    cy.task('waitUntilAppRestarts')
+    cy.visit(`${managePluginsPagePath}/uninstall?package=${encodeURIComponent(dependencyPlugin)}`)
+    cy.get('#plugin-action-button').click()
+    performPluginAction('uninstall', dependencyPlugin, dependencyPluginName)
+  })
+
+  it(`Install the ${dependentPlugin} plugin and the ${dependencyPlugin}`, () => {
+    cy.task('waitUntilAppRestarts')
+    cy.visit(`${managePluginsPagePath}/install?package=${encodeURIComponent(dependentPlugin)}&version=${encodeURIComponent(dependentPluginLocation)}`)
+    // Should list the dependency plugin
+    cy.get('li').contains(dependencyPluginName)
+    cy.get('#plugin-action-button').click()
+    performPluginAction('install', dependentPlugin, dependentPluginName)
+  })
+
+  it(`The ${dependentPlugin} plugin templates are available`, () => {
+    loadTemplatesPage()
+    cy.get(`[data-plugin-package-name="${dependentPlugin}"]`).should('exist')
+  })
+
+  it('Uninstall the dependency plugin', () => {
+    cy.task('waitUntilAppRestarts')
+    cy.visit(`${managePluginsPagePath}/uninstall?package=${encodeURIComponent(dependencyPlugin)}`)
+    // Should list the dependent plugin
+    cy.get('li').contains(dependentPluginName)
+    cy.get('#plugin-action-button').click()
+    performPluginAction('uninstall', dependencyPlugin, dependencyPluginName)
+  })
+
+  it(`The ${dependentPlugin} plugin templates are not available`, () => {
+    loadTemplatesPage()
+    cy.get(`[data-plugin-package-name="${dependentPlugin}"]`).should('not.exist')
+  })
+})
diff --git a/cypress/e2e/plugins/plugin-utils.js b/cypress/e2e/plugins/plugin-utils.js
index 63c15fa3dd..30129ce235 100644
--- a/cypress/e2e/plugins/plugin-utils.js
+++ b/cypress/e2e/plugins/plugin-utils.js
@@ -28,7 +28,7 @@ async function loadTemplatesPage () {
 function performPluginAction (action, plugin, pluginName) {
   cy.task('log', `The ${plugin} plugin should be displayed`)
   cy.get('h2')
-    .contains(`${capitalize(action)} ${pluginName}`)
+    .contains(pluginName)
 
   const processingText = `${action === 'upgrade' ? 'Upgrad' : action}ing ...`
 
diff --git a/cypress/events/index.js b/cypress/events/index.js
index 4af13a6197..80f8b0b524 100644
--- a/cypress/events/index.js
+++ b/cypress/events/index.js
@@ -24,7 +24,7 @@ const https = require('https')
 // local dependencies
 const { starterDir } = require('../../lib/utils/paths')
 const { sleep } = require('../e2e/utils')
-const { requestHttpsJson } = require('../../lib/utils')
+const { requestHttpsJson } = require('../../lib/utils/requestHttps')
 
 const log = (message) => console.log(`${new Date().toLocaleTimeString()} => ${message}`)
 
diff --git a/cypress/fixtures/plugins/plugin-fee/govuk-prototype-kit.config.json b/cypress/fixtures/plugins/plugin-fee/govuk-prototype-kit.config.json
new file mode 100644
index 0000000000..d08deab419
--- /dev/null
+++ b/cypress/fixtures/plugins/plugin-fee/govuk-prototype-kit.config.json
@@ -0,0 +1,14 @@
+{
+  "templates": [
+    {
+      "name": "Plugin Fee page",
+      "path": "/templates/fee.njk",
+      "type": "nunjucks"
+    }
+  ],
+  "sass": "/sass/fee.scss",
+  "pluginDependencies": [{
+    "packageName": "govuk-frontend",
+    "minVersion": "4.5.0"
+  }]
+}
diff --git a/cypress/fixtures/plugins/plugin-fee/package.json b/cypress/fixtures/plugins/plugin-fee/package.json
new file mode 100644
index 0000000000..8cd96be3f3
--- /dev/null
+++ b/cypress/fixtures/plugins/plugin-fee/package.json
@@ -0,0 +1,7 @@
+{
+  "name": "plugin-fee",
+  "version": "1.0.0",
+  "dependencies": {
+    "govuk-prototype-kit": "file:../../../.."
+  }
+}
diff --git a/cypress/fixtures/plugins/plugin-fee/sass/fee.scss b/cypress/fixtures/plugins/plugin-fee/sass/fee.scss
new file mode 100644
index 0000000000..4b2b144f81
--- /dev/null
+++ b/cypress/fixtures/plugins/plugin-fee/sass/fee.scss
@@ -0,0 +1,4 @@
+.plugin-fee-paragraph {
+  background: #d4351c;
+  color:  #ffdd00;
+}
\ No newline at end of file
diff --git a/cypress/fixtures/plugins/plugin-fee/templates/fee.njk b/cypress/fixtures/plugins/plugin-fee/templates/fee.njk
new file mode 100644
index 0000000000..376fd00812
--- /dev/null
+++ b/cypress/fixtures/plugins/plugin-fee/templates/fee.njk
@@ -0,0 +1,10 @@
+{% extends "layouts/main.html" %}
+
+{% block pageTitle %}
+    GOV.UK page template – {{ serviceName }} – GOV.UK Prototype Kit
+{% endblock %}
+
+{% block content %}
+    <p class="plugin-fee-paragraph">Plugin fee styled paragraph</p>
+
+{% endblock %}
diff --git a/known-plugins.json b/known-plugins.json
index 9ff43b2c43..77eb9cdfe1 100644
--- a/known-plugins.json
+++ b/known-plugins.json
@@ -8,6 +8,10 @@
       "hmrc-frontend",
       "jquery",
       "notifications-node-client"
+    ],
+    "required": [
+      "govuk-prototype-kit",
+      "govuk-frontend"
     ]
   }
 }
diff --git a/lib/assets/javascripts/manage-prototype/manage-plugins.js b/lib/assets/javascripts/manage-prototype/manage-plugins.js
index f12b81a3c5..1dceaaa484 100644
--- a/lib/assets/javascripts/manage-prototype/manage-plugins.js
+++ b/lib/assets/javascripts/manage-prototype/manage-plugins.js
@@ -13,12 +13,16 @@
 
   const show = (id) => {
     const element = document.getElementById(id)
-    element.hidden = false
+    if (element) {
+      element.hidden = false
+    }
   }
 
   const hide = (id) => {
     const element = document.getElementById(id)
-    element.hidden = true
+    if (element) {
+      element.hidden = true
+    }
   }
 
   const showCompleteStatus = () => {
@@ -108,6 +112,9 @@
   }
 
   const performAction = (event) => {
+    hide('dependency-heading')
+    show('plugin-heading')
+
     if (!actionTimeoutId) {
       actionTimeoutId = setTimeout(() => {
         timedOut = true
diff --git a/lib/assets/javascripts/manage-prototype/manage-plugins.test.js b/lib/assets/javascripts/manage-prototype/manage-plugins.test.js
index 3a1a61185f..aa25941c13 100644
--- a/lib/assets/javascripts/manage-prototype/manage-plugins.test.js
+++ b/lib/assets/javascripts/manage-prototype/manage-plugins.test.js
@@ -10,6 +10,8 @@ async function fetchResponse (data) {
 
 const loadedHTML = `
       <div>
+        <div id="dependency-heading"></div>
+        <div id="plugin-heading" hidden=""></div>
         <div id="panel-manual-instructions"></div>
         <div id="panel-processing" hidden=""></div>
         <div id="panel-complete" hidden=""></div>
@@ -20,6 +22,8 @@ const loadedHTML = `
 
 const processingHTML = `
       <div>
+        <div id="dependency-heading" hidden=""></div>
+        <div id="plugin-heading"></div>
         <div id="panel-manual-instructions" hidden=""></div>
         <div id="panel-processing"></div>
         <div id="panel-complete" hidden=""></div>
@@ -30,6 +34,8 @@ const processingHTML = `
 
 const completedHTML = `
       <div>
+        <div id="dependency-heading" hidden=""></div>
+        <div id="plugin-heading"></div>
         <div id="panel-manual-instructions" hidden=""></div>
         <div id="panel-processing" hidden=""></div>
         <div id="panel-complete"></div>
@@ -40,6 +46,8 @@ const completedHTML = `
 
 const errorHTML = `
       <div>
+        <div id="dependency-heading" hidden=""></div>
+        <div id="plugin-heading"></div>
         <div id="panel-manual-instructions" hidden=""></div>
         <div id="panel-processing" hidden=""></div>
         <div id="panel-complete" hidden=""></div>
diff --git a/lib/manage-prototype-handlers.js b/lib/manage-prototype-handlers.js
index cf36dd19c2..538f5f2e0f 100644
--- a/lib/manage-prototype-handlers.js
+++ b/lib/manage-prototype-handlers.js
@@ -1,4 +1,3 @@
-
 // core dependencies
 const path = require('path')
 
@@ -11,10 +10,18 @@ const { doubleCsrf } = require('csrf-csrf')
 const config = require('./config')
 const plugins = require('./plugins/plugins')
 const { exec } = require('./exec')
-const { requestHttpsJson, prototypeAppScripts, sortByObjectKey } = require('./utils')
+const { prototypeAppScripts } = require('./utils')
 const { projectDir, packageDir, appViewsDir } = require('./utils/paths')
 const nunjucksConfiguration = require('./nunjucks/nunjucksConfiguration')
 const syncChanges = require('./sync-changes')
+const {
+  lookupPackageInfo,
+  getInstalledPackages,
+  getAvailablePackages,
+  getDependentPackages,
+  getDependencyPackages,
+  waitForPackagesCache
+} = require('./plugins/packages')
 
 const contextPath = '/manage-prototype'
 
@@ -24,75 +31,22 @@ const appViews = plugins.getAppViews([
   path.join(packageDir, 'lib/final-backup-nunjucks')
 ])
 
-const pkgPath = path.join(projectDir, 'package.json')
-
 let kitRestarted = false
 
 const {
   name: currentKitName,
   version: currentKitVersion
 } = require(path.join(packageDir, 'package.json'))
-const { startPerformanceTimer, endPerformanceTimer } = require('./utils/performance')
-const { verboseLog } = require('./utils/verboseLogger')
-
-const latestReleaseVersions = plugins.getKnownPlugins().available
-  .reduce((releaseVersions, nextPlugin) => {
-    return { ...releaseVersions, [nextPlugin]: 0 }
-  }, { 'govuk-prototype-kit': currentKitVersion })
-
-async function lookupPackageInfo (packageName) {
-  const timer = startPerformanceTimer()
-  try {
-    const packageInfo = await requestHttpsJson(`https://registry.npmjs.org/${encodeURIComponent(packageName)}`)
-    endPerformanceTimer('lookupPackageInfo (success)', timer)
-    return packageInfo
-  } catch (e) {
-    endPerformanceTimer('lookupPackageInfo (failure)', timer)
-    console.log('ignoring error', e.message)
-  }
-}
 
 async function isValidVersion (packageName, version) {
-  const versions = Object.keys(((await lookupPackageInfo(packageName) || {}).versions || {}))
-  const isVersionValid = versions.some(distVersion => distVersion === version)
+  const { versions = [], localVersion } = await lookupPackageInfo(packageName, version)
+  const isVersionValid = [...versions, localVersion].includes(version)
   if (!isVersionValid) {
     console.log('version', version, ' is not valid, valid options are:\n\n', versions)
   }
   return isVersionValid
 }
 
-async function lookupLatestPackageVersion (packageName) {
-  try {
-    const packageInfo = (await lookupPackageInfo(packageName) || {})
-    if (config.getConfig().showPrereleases) {
-      latestReleaseVersions[packageName] = Object.values(packageInfo['dist-tags'])
-        .map(version => ({ version, date: packageInfo.time[version] }))
-        .sort(sortByObjectKey('date'))
-        .at(-1)
-        .version
-    } else {
-      latestReleaseVersions[packageName] = packageInfo['dist-tags'].latest
-    }
-    return latestReleaseVersions[packageName]
-  } catch (e) {
-    verboseLog('Error when looking up latest package')
-    verboseLog(e)
-    return null
-  }
-}
-
-async function updateLatestReleaseVersions () {
-  const timer = startPerformanceTimer()
-  await Promise.all(Object.keys(latestReleaseVersions).map(lookupLatestPackageVersion))
-  endPerformanceTimer('updateLatestReleaseVersions', timer)
-  return latestReleaseVersions
-}
-
-if (!config.getConfig().isTest) {
-  updateLatestReleaseVersions()
-  setInterval(lookupLatestPackageVersion, 1000 * 60 * 20)
-}
-
 function getManagementView (filename) {
   return ['views', 'manage-prototype', filename].join('/')
 }
@@ -174,6 +128,12 @@ function developmentOnlyMiddleware (req, res, next) {
   }
 }
 
+// Middleware to ensure pages load when plugin cache has been initially loaded
+async function pluginCacheMiddleware (req, res, next) {
+  await waitForPackagesCache()
+  next()
+}
+
 const managementLinks = [
   {
     text: 'Home',
@@ -206,12 +166,14 @@ async function getHomeHandler (req, res) {
   const originalHomepage = await fse.readFile(path.join(packageDir, 'prototype-starter', 'app', 'views', 'index.html'), 'utf8')
   const currentHomepage = await readFileIfExists(path.join(appViewsDir, 'index.html'))
 
+  const kitPackage = await lookupPackageInfo('govuk-prototype-kit')
+
   const viewData = {
     currentUrl: req.originalUrl,
     currentSection: pageName,
     links: managementLinks,
-    kitUpgradeAvailable: latestReleaseVersions['govuk-prototype-kit'] !== currentKitVersion,
-    latestAvailableKit: latestReleaseVersions['govuk-prototype-kit'],
+    kitUpgradeAvailable: kitPackage.latestVersion !== currentKitVersion,
+    latestAvailableKit: kitPackage.latestVersion,
     tasks: [
       {
         done: serviceName !== 'Service name goes here' && serviceName !== 'GOV.UK Prototype Kit',
@@ -261,14 +223,14 @@ function getPluginTemplates () {
   return output
 }
 
-function getTemplatesHandler (req, res) {
+async function getTemplatesHandler (req, res) {
   const pageName = 'Templates'
   const availableTemplates = getPluginTemplates()
 
   const commonTemplatesPackageName = '@govuk-prototype-kit/common-templates'
   const govUkFrontendPackageName = 'govuk-frontend'
   let commonTemplatesDetails
-  const installedPlugins = plugins.listInstalledPlugins()
+  const installedPlugins = (await getInstalledPackages()).map((pkg) => pkg.packageName)
   if (installedPlugins.includes(govUkFrontendPackageName) && !installedPlugins.includes(commonTemplatesPackageName)) {
     commonTemplatesDetails = {
       pluginDisplayName: plugins.preparePackageNameForDisplay(commonTemplatesPackageName),
@@ -390,7 +352,7 @@ async function postTemplatesInstallHandler (req, res) {
   }
 
   // Don't allow URI reserved characters (per RFC 3986) in paths
-  if ("!$&'()*+,;=:?#[]@.% ".split('').some((char) => chosenUrl.includes(char))) {
+  if ('!$&\'()*+,;=:?#[]@.% '.split('').some((char) => chosenUrl.includes(char))) {
     renderError('invalid')
     return
   }
@@ -424,83 +386,78 @@ function getTemplatesPostInstallHandler (req, res) {
   })
 }
 
-function removeDuplicates (val, index, arr) {
-  return !arr.includes(val, index + 1)
-}
-
-async function getPluginDetails () {
-  const pkg = fse.readJsonSync(pkgPath)
-  const installed = plugins.listInstalledPlugins()
-  return Promise.all(installed.concat(plugins.getKnownPlugins().available)
-    .filter(removeDuplicates)
-    .map(async (packageName) => {
-      // Only those plugins not referenced locally can be looked up
-      const reference = pkg.dependencies[packageName] || ''
-      const installedLocally = reference.startsWith('file:')
-      const latestVersion = !installedLocally && await lookupLatestPackageVersion(packageName)
-      return {
-        packageName,
-        latestVersion,
-        installedLocally
-      }
-    })
-    .map(async (packageDetails) => {
-      const pack = await packageDetails
-      Object.assign(pack, plugins.preparePackageNameForDisplay(pack.packageName), {
-        installLink: `${contextPath}/plugins/install?package=${encodeURIComponent(pack.packageName)}`,
-        installCommand: `npm install ${pack.packageName}`,
-        upgradeCommand: pack.latestVersion && `npm install ${pack.packageName}@${pack.latestVersion}`,
-        uninstallCommand: `npm uninstall ${pack.packageName}`
-      })
-      if (installed.includes(pack.packageName)) {
-        const pluginPkgPath = path.join(projectDir, 'node_modules', pack.packageName, 'package.json')
-        const pluginPkg = await fse.pathExists(pluginPkgPath) ? await fse.readJson(pluginPkgPath) : {}
-        pack.installedVersion = pluginPkg.version
-        const mandatoryPlugins = ['govuk-prototype-kit']
-        if (!config.getConfig().allowGovukFrontendUninstall) {
-          mandatoryPlugins.push('govuk-frontend')
-        }
-        if (!mandatoryPlugins.includes(pack.packageName)) {
-          pack.uninstallLink = `${contextPath}/plugins/uninstall?package=${encodeURIComponent(pack.packageName)}`
-        }
-      }
-      if (pack.latestVersion && pack.installedVersion && pack.installedVersion !== pack.latestVersion) {
-        pack.upgradeLink = `${contextPath}/plugins/upgrade?package=${encodeURIComponent(pack.packageName)}`
-      }
-      return pack
-    }))
+function buildPluginData (pluginData) {
+  if (pluginData === undefined) {
+    return
+  }
+  const {
+    packageName,
+    installed,
+    installedLocally,
+    latestVersion,
+    installedVersion,
+    required,
+    localVersion
+  } = pluginData
+  const preparedPackageNameForDisplay = plugins.preparePackageNameForDisplay(packageName)
+  return {
+    ...preparedPackageNameForDisplay,
+    packageName,
+    latestVersion,
+    installedLocally,
+    installLink: `${contextPath}/plugins/install?package=${encodeURIComponent(packageName)}`,
+    installCommand: `npm install ${packageName}`,
+    upgradeLink: installed && !installedLocally && latestVersion !== installedVersion ? `${contextPath}/plugins/upgrade?package=${encodeURIComponent(packageName)}` : undefined,
+    upgradeCommand: latestVersion && `npm install ${packageName}@${latestVersion}`,
+    uninstallLink: installed && !required ? `${contextPath}/plugins/uninstall?package=${encodeURIComponent(packageName)}${installedLocally ? `&version=${encodeURIComponent(localVersion)}` : ''}` : undefined,
+    uninstallCommand: `npm uninstall ${packageName}`,
+    installedVersion
+  }
 }
 
 async function prepareForPluginPage () {
-  const all = await getPluginDetails()
-
   const installedOut = {}
   const availableOut = {}
   const output = [installedOut, availableOut]
 
+  const installedPlugins = await getInstalledPackages()
+  const availablePlugins = await getAvailablePackages()
+
   installedOut.name = 'Installed'
-  installedOut.plugins = []
+  installedOut.plugins = installedPlugins.map(buildPluginData)
   installedOut.status = 'installed'
   availableOut.name = 'Available'
-  availableOut.plugins = []
+  availableOut.plugins = availablePlugins.map(buildPluginData)
   availableOut.status = 'available'
 
-  all.forEach(packageInfo => {
-    if (packageInfo.installedVersion) {
-      installedOut.plugins.push(packageInfo)
-    } else if (packageInfo.latestVersion) {
-      availableOut.plugins.push(packageInfo)
-    }
-  })
-
   return output
 }
 
 function getCommand (mode, chosenPlugin) {
-  let { upgradeCommand, installCommand, uninstallCommand, version } = chosenPlugin
+  let {
+    upgradeCommand,
+    installCommand,
+    uninstallCommand,
+    version,
+    dependencyPlugins,
+    dependentPlugins
+  } = chosenPlugin
+  const dependents = dependentPlugins?.map(({ packageName }) => packageName).join(' ')
+  const dependencies = dependencyPlugins?.map(({ packageName }) => packageName).join(' ')
+
   if (version && installCommand) {
-    installCommand = installCommand + `@${version}`
+    installCommand += `@${version}`
+  }
+
+  if (dependents) {
+    uninstallCommand += ' ' + dependents
+  }
+
+  if (dependencies) {
+    installCommand += ' ' + dependencies
+    upgradeCommand += ' ' + dependencies
   }
+
   switch (mode) {
     case 'upgrade':
       return upgradeCommand + ' --save-exact'
@@ -554,28 +511,58 @@ async function getPluginsHandler (req, res) {
 }
 
 async function getPluginForRequest (req) {
-  const searchPackage = req.query.package || req.body.package
+  const packageName = req.query.package || req.body.package
   const version = req.query.version || req.body.version
+  const { mode } = req.params
   let chosenPlugin
-  if (searchPackage) {
-    const pluginDetails = await getPluginDetails()
-    chosenPlugin = pluginDetails.find(({ packageName }) => packageName === searchPackage)
-    if (chosenPlugin && version) {
-      if (await isValidVersion(searchPackage, version)) {
+
+  if (packageName) {
+    chosenPlugin = buildPluginData(await lookupPackageInfo(packageName, version))
+    if (!chosenPlugin) {
+      return // chosen plugin will be invalid
+    }
+    if (version) {
+      if (await isValidVersion(packageName, version)) {
         chosenPlugin.version = version
+      } else if (chosenPlugin.installedLocally) {
+        chosenPlugin.version = chosenPlugin.installedVersion
       } else {
         return // chosen plugin will be invalid
       }
     }
   }
+
+  const dependentPlugins = mode === 'uninstall'
+    ? (await getDependentPackages(chosenPlugin.packageName))
+        .filter(({ installed }) => installed)
+        .map(buildPluginData)
+    : []
+
+  if (dependentPlugins.length) {
+    chosenPlugin.dependentPlugins = dependentPlugins
+  }
+
+  const dependencyPlugins = mode !== 'uninstall'
+    ? (await getDependencyPackages(chosenPlugin.packageName, version))
+        .filter(({ installed }) => !installed)
+        .map(buildPluginData)
+    : []
+
+  if (dependencyPlugins.length) {
+    chosenPlugin.dependencyPlugins = dependencyPlugins
+  }
+
   return chosenPlugin
 }
 
-function modeIsComplete (mode, { installedVersion, latestVersion, version }) {
+function modeIsComplete (mode, { installedVersion, latestVersion, version, installedLocally }) {
   switch (mode) {
-    case 'upgrade': return installedVersion === latestVersion
-    case 'install': return version ? installedVersion === version : !!installedVersion
-    case 'uninstall': return !installedVersion
+    case 'upgrade':
+      return installedVersion === latestVersion
+    case 'install':
+      return installedLocally || (version ? installedVersion === version : !!installedVersion)
+    case 'uninstall':
+      return !installedVersion
   }
 }
 
@@ -605,6 +592,17 @@ async function getPluginsModeHandler (req, res) {
 
   const returnLink = req.query.returnTo === 'templates' ? templatesReturnLink : pluginsReturnLink
 
+  const fullPluginName = `${chosenPlugin.name}${chosenPlugin.version ? ` version ${chosenPlugin.version} ` : ''}${chosenPlugin.scope ? ` from ${chosenPlugin.scope}` : ''}`
+
+  const pluginHeading = `${verb.title} ${fullPluginName}`
+  let dependencyHeading = ''
+
+  if (chosenPlugin?.dependentPlugins?.length) {
+    dependencyHeading = `Other plugins need ${fullPluginName}`
+  } else if (chosenPlugin?.dependencyPlugins?.length) {
+    dependencyHeading = `${fullPluginName} needs other plugins`
+  }
+
   res.render(getManagementView('plugin-install-or-uninstall.njk'), {
     currentSection: 'Plugins',
     pageName,
@@ -612,6 +610,8 @@ async function getPluginsModeHandler (req, res) {
     links: managementLinks,
     chosenPlugin,
     command: getCommand(mode, chosenPlugin),
+    pluginHeading,
+    dependencyHeading,
     verb,
     isSameOrigin,
     returnLink
@@ -717,6 +717,7 @@ module.exports = {
   getPasswordHandler,
   postPasswordHandler,
   developmentOnlyMiddleware,
+  pluginCacheMiddleware,
   getHomeHandler,
   getTemplatesHandler,
   getTemplatesViewHandler,
diff --git a/lib/manage-prototype-handlers.test.js b/lib/manage-prototype-handlers.test.js
index 2e6948a69f..81ce29a022 100644
--- a/lib/manage-prototype-handlers.test.js
+++ b/lib/manage-prototype-handlers.test.js
@@ -9,9 +9,12 @@ const nunjucksConfiguration = require('./nunjucks/nunjucksConfiguration')
 
 // local dependencies
 const config = require('./config')
-const utils = require('./utils')
+const { requestHttpsJson } = require('./utils/requestHttps')
 const exec = require('./exec')
 const plugins = require('./plugins/plugins')
+const packages = require('./plugins/packages')
+const projectPackage = require('../package.json')
+const knownPlugins = require('../known-plugins.json')
 
 const {
   setKitRestarted,
@@ -35,6 +38,17 @@ const {
 const { projectDir } = require('./utils/paths')
 
 // mocked dependencies
+jest.mock('../package.json', () => {
+  return {
+    dependencies: {}
+  }
+})
+// mocked dependencies
+jest.mock('../known-plugins.json', () => {
+  return {
+    plugins: {}
+  }
+})
 jest.mock('fs-extra', () => {
   return {
     readFile: jest.fn().mockResolvedValue(''),
@@ -42,9 +56,7 @@ jest.mock('fs-extra', () => {
     ensureDir: jest.fn().mockResolvedValue(true),
     exists: jest.fn().mockResolvedValue(true),
     existsSync: jest.fn().mockReturnValue(true),
-    pathExists: jest.fn().mockResolvedValue(true),
     pathExistsSync: jest.fn().mockReturnValue(true),
-    readJson: jest.fn().mockResolvedValue({}),
     readJsonSync: jest.fn().mockReturnValue({})
   }
 })
@@ -57,20 +69,51 @@ jest.mock('./nunjucks/nunjucksConfiguration', () => {
 })
 jest.mock('./utils', () => {
   return {
-    encryptPassword: jest.fn().mockReturnValue('encrypted password'),
+    encryptPassword: jest.fn().mockReturnValue('encrypted password')
+  }
+})
+jest.mock('./utils/requestHttps', () => {
+  return {
     requestHttpsJson: jest.fn()
   }
 })
 jest.mock('./plugins/plugins', () => {
   return {
+    ...jest.requireActual('./plugins/plugins'),
     getAppViews: jest.fn(),
     getAppConfig: jest.fn(),
-    getByType: jest.fn(),
-    listInstalledPlugins: jest.fn(),
-    getKnownPlugins: jest.fn().mockReturnValue({ available: [] }),
-    preparePackageNameForDisplay: jest.fn()
+    getByType: jest.fn()
   }
 })
+
+jest.mock('./plugins/packages', () => {
+  const availablePackage = {
+    packageName: 'test-package',
+    installed: false,
+    available: true,
+    required: false,
+    latestVersion: '2.0.0',
+    versions: [
+      '2.0.0',
+      '1.0.0'
+    ],
+    packageJson: {}
+  }
+  return {
+    lookupPackageInfo: jest.fn().mockImplementation((packageName) => {
+      if (packageName === availablePackage.packageName) {
+        return availablePackage
+      } else {
+        return undefined
+      }
+    }),
+    getInstalledPackages: jest.fn().mockResolvedValue([]),
+    getAvailablePackages: jest.fn().mockResolvedValue([availablePackage]),
+    getDependentPackages: jest.fn().mockResolvedValue([]),
+    getDependencyPackages: jest.fn().mockResolvedValue([])
+  }
+})
+
 jest.mock('./exec', () => {
   return {
     exec: jest.fn().mockReturnValue({ finally: jest.fn() })
@@ -153,10 +196,11 @@ describe('manage-prototype-handlers', () => {
   })
 
   it('getHomeHandler', async () => {
+    packages.lookupPackageInfo.mockResolvedValue({ packageName: 'govuk-prototype-kit', latestVersion: '1.0.0' })
     await getHomeHandler(req, res)
     expect(res.render).toHaveBeenCalledWith(
       'views/manage-prototype/index.njk',
-      expect.objectContaining({ currentSection: 'Home' })
+      expect.objectContaining({ currentSection: 'Home', latestAvailableKit: '1.0.0' })
     )
   })
 
@@ -199,8 +243,6 @@ describe('manage-prototype-handlers', () => {
           path: templatePath
         }
       }])
-      plugins.preparePackageNameForDisplay.mockReturnValue(pluginDisplayName)
-      plugins.listInstalledPlugins.mockReturnValue([])
       nunjucksConfiguration.getNunjucksAppEnv.mockImplementation(() => ({
         render: () => view
       }))
@@ -367,31 +409,31 @@ describe('manage-prototype-handlers', () => {
       name: pluginDisplayName.name,
       packageName,
       uninstallCommand: `npm uninstall ${packageName}`,
-      upgradeCommand: `npm install ${packageName}@${latestVersion}`,
-      installedLocally: false
+      upgradeCommand: `npm install ${packageName}@${latestVersion}`
     }
 
     beforeEach(() => {
-      plugins.listInstalledPlugins.mockReturnValue([])
-      plugins.preparePackageNameForDisplay.mockReturnValue(pluginDisplayName)
-      plugins.getKnownPlugins.mockReturnValue({ available: [packageName] })
+      knownPlugins.plugins = { available: [packageName] }
+      projectPackage.dependencies = {}
       const versions = {}
       versions[latestVersion] = {}
       versions[previousVersion] = {}
-      utils.requestHttpsJson.mockResolvedValue({
+      requestHttpsJson.mockResolvedValue({
+        name: packageName,
         'dist-tags': {
           latest: latestVersion,
           'latest-1': previousVersion
         },
         versions
       })
-      fse.readJsonSync.mockReturnValue({
-        dependencies: {}
-      })
+      // mocking the reading of the local package.json
+      fse.readJsonSync.mockReturnValue(undefined)
+      packages.lookupPackageInfo.mockResolvedValue(Promise.resolve(availablePlugin))
       res.json = jest.fn().mockReturnValue({})
     })
 
     it('getPluginsHandler', async () => {
+      fse.readJsonSync.mockReturnValue(undefined)
       req.query.mode = 'install'
       await getPluginsHandler(req, res)
       expect(res.render).toHaveBeenCalledWith(
@@ -428,71 +470,6 @@ describe('manage-prototype-handlers', () => {
       )
     })
 
-    describe('postPluginsStatusHandler', () => {
-      let pkg
-
-      beforeEach(() => {
-        req.params.mode = 'install'
-        req.query.package = packageName
-        pkg = {
-          name: packageName,
-          version: latestVersion,
-          dependencies: { [packageName]: latestVersion }
-        }
-        fse.readJson.mockResolvedValue(pkg)
-        fse.readJsonSync.mockReturnValue(pkg)
-      })
-
-      it('is processing', async () => {
-        await postPluginsStatusHandler(req, res)
-        expect(res.json).toHaveBeenCalledWith(
-          expect.objectContaining({
-            status: 'processing'
-          })
-        )
-      })
-
-      it('is completed', async () => {
-        plugins.listInstalledPlugins.mockReturnValue([packageName])
-        setKitRestarted(true)
-        await postPluginsStatusHandler(req, res)
-        expect(res.json).toHaveBeenCalledWith(
-          expect.objectContaining({
-            status: 'completed'
-          })
-        )
-      })
-
-      it('uninstall local plugin is completed', async () => {
-        const localPlugin = 'local-plugin'
-        req.params.mode = 'uninstall'
-        req.query.package = localPlugin
-        pkg.dependencies[localPlugin] = 'file:../../local-plugin'
-        plugins.listInstalledPlugins.mockReturnValue([localPlugin])
-        setKitRestarted(true)
-        await postPluginsStatusHandler(req, res)
-        expect(res.json).toHaveBeenCalledWith(
-          expect.objectContaining({
-            status: 'completed'
-          })
-        )
-      })
-    })
-
-    describe('postPluginsModeMiddleware', () => {
-      it('with AJAX', async () => {
-        req.headers['content-type'] = 'application/json'
-        await postPluginsModeMiddleware(req, res, next)
-        expect(next).toHaveBeenCalled()
-      })
-
-      it('without AJAX', async () => {
-        req.headers['content-type'] = 'document/html'
-        await postPluginsModeMiddleware(req, res, next)
-        expect(res.redirect).toHaveBeenCalledWith(req.originalUrl)
-      })
-    })
-
     describe('postPluginsModeHandler', () => {
       beforeEach(() => {
         req.params.mode = 'install'
@@ -513,6 +490,11 @@ describe('manage-prototype-handlers', () => {
       })
 
       it('processing specific version', async () => {
+        packages.lookupPackageInfo.mockResolvedValue({
+          packageName: 'test-package',
+          installed: false,
+          versions: ['1.0.0']
+        })
         req.body.version = previousVersion
         const installSpecificCommand = availablePlugin.installCommand + `@${previousVersion}`
         await postPluginsModeHandler(req, res)
@@ -528,6 +510,7 @@ describe('manage-prototype-handlers', () => {
       })
 
       it('error invalid package', async () => {
+        packages.lookupPackageInfo.mockResolvedValue(undefined)
         req.body.package = 'invalid-package'
         await postPluginsModeHandler(req, res)
         expect(exec.exec).not.toHaveBeenCalled()
@@ -550,7 +533,6 @@ describe('manage-prototype-handlers', () => {
       })
 
       it('is passed on to the postPluginsStatusHandler when status matches mode during upgrade from 13.1 to 13.2.4 and upwards', async () => {
-        plugins.listInstalledPlugins.mockReturnValue([packageName])
         req.params.mode = 'status'
         setKitRestarted(true)
         await postPluginsModeHandler(req, res)
@@ -558,6 +540,62 @@ describe('manage-prototype-handlers', () => {
         // req.params.mode should change to upgrade
         expect(req.params.mode).toEqual('upgrade')
 
+        expect(res.json).toHaveBeenCalledWith(
+          expect.objectContaining({
+            status: 'processing'
+          })
+        )
+      })
+    })
+
+    describe('postPluginsStatusHandler', () => {
+      let pkg
+
+      beforeEach(() => {
+        req.params.mode = 'install'
+        req.query.package = packageName
+        pkg = {
+          name: packageName,
+          version: latestVersion,
+          dependencies: { [packageName]: latestVersion }
+        }
+        fse.readJsonSync.mockReturnValue(pkg)
+      })
+
+      it('is processing', async () => {
+        await postPluginsStatusHandler(req, res)
+        expect(res.json).toHaveBeenCalledWith(
+          expect.objectContaining({
+            status: 'processing'
+          })
+        )
+      })
+
+      it('is completed', async () => {
+        packages.lookupPackageInfo.mockResolvedValue({
+          packageName: 'test-package',
+          installedVersion: '2.0.0'
+        })
+        setKitRestarted(true)
+        await postPluginsStatusHandler(req, res)
+        expect(res.json).toHaveBeenCalledWith(
+          expect.objectContaining({
+            status: 'completed'
+          })
+        )
+      })
+
+      it('uninstall local plugin is completed', async () => {
+        const localPlugin = 'local-plugin'
+        req.params.mode = 'uninstall'
+        req.query.package = localPlugin
+        pkg.dependencies[localPlugin] = 'file:../../local-plugin'
+        packages.lookupPackageInfo.mockResolvedValue({
+          packageName: 'test-package',
+          installed: false
+        })
+        setKitRestarted(true)
+        await postPluginsStatusHandler(req, res)
         expect(res.json).toHaveBeenCalledWith(
           expect.objectContaining({
             status: 'completed'
@@ -565,5 +603,19 @@ describe('manage-prototype-handlers', () => {
         )
       })
     })
+
+    describe('postPluginsModeMiddleware', () => {
+      it('with AJAX', async () => {
+        req.headers['content-type'] = 'application/json'
+        await postPluginsModeMiddleware(req, res, next)
+        expect(next).toHaveBeenCalled()
+      })
+
+      it('without AJAX', async () => {
+        req.headers['content-type'] = 'document/html'
+        await postPluginsModeMiddleware(req, res, next)
+        expect(res.redirect).toHaveBeenCalledWith(req.originalUrl)
+      })
+    })
   })
 })
diff --git a/lib/manage-prototype-routes.js b/lib/manage-prototype-routes.js
index 1d4f601170..6f0a787d74 100644
--- a/lib/manage-prototype-routes.js
+++ b/lib/manage-prototype-routes.js
@@ -22,7 +22,7 @@ const {
   getPluginsModeHandler,
   postPluginsModeMiddleware,
   postPluginsModeHandler,
-  postPluginsStatusHandler
+  postPluginsStatusHandler, pluginCacheMiddleware
 } = require('./manage-prototype-handlers')
 const path = require('path')
 const { getInternalGovukFrontendDir } = require('./utils')
@@ -54,6 +54,8 @@ router.post('/password', postPasswordHandler)
 // view when the prototype is not running in development
 router.use(developmentOnlyMiddleware)
 
+router.use(pluginCacheMiddleware)
+
 router.get('/', getHomeHandler)
 
 router.get('/templates', getTemplatesHandler)
diff --git a/lib/nunjucks/views/manage-prototype/plugin-install-or-uninstall.njk b/lib/nunjucks/views/manage-prototype/plugin-install-or-uninstall.njk
index b7523eaf5a..ccc29d9a7a 100644
--- a/lib/nunjucks/views/manage-prototype/plugin-install-or-uninstall.njk
+++ b/lib/nunjucks/views/manage-prototype/plugin-install-or-uninstall.njk
@@ -7,9 +7,15 @@
 
       <h1 class="govuk-heading-l">Plugins</h1>
 
-      <h2 class="govuk-heading-m">
-        {{ verb.title }} {{ chosenPlugin.name }} {% if chosenPlugin.version %} version {{ chosenPlugin.version }} {% endif %} {% if chosenPlugin.scope %} from {{ chosenPlugin.scope }} {% endif %}
-      </h2>
+      <div id="plugin-heading" {% if dependencyHeading %}hidden class="js-hidden"{% endif %} >
+        <h2 class="govuk-heading-m">{{ pluginHeading }}</h2>
+      </div>
+
+      {% if dependencyHeading %}
+      <div id="dependency-heading">
+        <h2 class="govuk-heading-m">{{ dependencyHeading }}</h2>
+      </div>
+      {% endif %}
 
       <div id="panel-manual-instructions" class="govuk-prototype-kit-manage-prototype-plugin-instructions js-hidden">
         <p>
@@ -28,7 +34,35 @@
 
       <div class="js-visible" aria-live="polite">
 
-        {% if not isSameOrigin %}
+        {% if chosenPlugin.dependencyPlugins|length or chosenPlugin.dependentPlugins|length %}
+          <div id="plugin-action-confirmation">
+
+          <ul class="govuk-list govuk-list--bullet">
+            {% for plugin in chosenPlugin.dependencyPlugins %}
+              <li>{{ plugin.name }}{% if plugin.scope %} from {{ plugin.scope }} {% endif %}</li>
+            {% endfor %}
+            {% for plugin in chosenPlugin.dependentPlugins %}
+              <li>{{ plugin.name }}{% if plugin.scope %} from {{ plugin.scope }} {% endif %}</li>
+            {% endfor %}
+          </ul>
+
+          <p class="govuk-body">
+            {% if verb.para == 'uninstall' %}
+              If you uninstall {{ chosenPlugin.name }}, these plugins will no longer work.
+            {% else %}
+              To {{ verb.para }} {{ chosenPlugin.name }} you also need to {{ verb.para }} these plugins.
+            {% endif %}
+          </p>
+          <div class="govuk-button-group">
+            {{ govukButton({
+              text: verb.title + ' these plugins',
+              attributes: { id: "plugin-action-button" }
+            }) }}
+
+            <a class="govuk-link" href="{{ returnLink.href }}">Cancel {{ verb.para }}</a>
+          </div>
+        </div>
+        {% elseif not isSameOrigin %}
           <div id="plugin-action-confirmation">
             <p class="govuk-body">
               Are you sure you want to {{ verb.para }} this plugin?
diff --git a/lib/plugins/packages.js b/lib/plugins/packages.js
new file mode 100644
index 0000000000..d1c4422a83
--- /dev/null
+++ b/lib/plugins/packages.js
@@ -0,0 +1,245 @@
+// core dependencies
+const path = require('path')
+
+// npm dependencies
+const fse = require('fs-extra')
+
+// local dependencies
+const { startPerformanceTimer, endPerformanceTimer } = require('../utils/performance')
+const { packageDir, projectDir } = require('../utils/paths')
+const { requestHttpsJson } = require('../utils/requestHttps')
+const { verboseLog } = require('../utils/verboseLogger')
+const knownPlugins = require(path.join(packageDir, 'known-plugins.json'))
+const projectPackage = require(path.join(projectDir, 'package.json'))
+const config = require('../config')
+const { getConfigForPackage } = require('../utils/requestHttps')
+const { getProxyPluginConfig } = require('./plugin-utils')
+
+let packageTrackerInterval
+
+const packagesCache = {}
+
+async function startPackageTracker () {
+  await updatePackagesInfo()
+  packageTrackerInterval = setInterval(updatePackagesInfo, 36000)
+}
+
+async function updatePackagesInfo () {
+  const availablePlugins = knownPlugins?.plugins?.available || []
+  const packagesRequired = [...availablePlugins, ...Object.keys(projectPackage.dependencies)]
+  return Promise.all(packagesRequired.map(async (packageName) => refreshPackageInfo(packageName)))
+}
+
+async function readJson (filename) {
+  return await fse.pathExists(filename) ? fse.readJson(filename) : undefined
+}
+
+async function requestRegistryInfo (packageName) {
+  const timer = startPerformanceTimer()
+  try {
+    const registryInfoUrl = `https://registry.npmjs.org/${encodeURIComponent(packageName)}`
+    verboseLog(`looking up ${registryInfoUrl}`)
+    const registryInfo = await requestHttpsJson(registryInfoUrl)
+    verboseLog(`retrieved ${registryInfoUrl}`)
+    endPerformanceTimer('lookupPackageInfo (success)', timer)
+    return registryInfo
+  } catch (e) {
+    endPerformanceTimer('lookupPackageInfo (failure)', timer)
+    verboseLog('ignoring error', e.message)
+    return undefined
+  }
+}
+
+async function refreshPackageInfo (packageName, version) {
+  const packageDir = path.join(projectDir, 'node_modules', packageName)
+  const pluginConfigFile = path.join(packageDir, 'govuk-prototype-kit.config.json')
+
+  const requiredPlugins = knownPlugins?.plugins?.required || []
+
+  const required = (!(packageName === 'govuk-frontend' && config.getConfig().allowGovukFrontendUninstall)) && requiredPlugins.includes(packageName)
+
+  let [
+    packageJson,
+    pluginConfig,
+    registryInfo
+  ] = await Promise.all([
+    readJson(path.join(packageDir, 'package.json')),
+    readJson(pluginConfigFile),
+    requestRegistryInfo(packageName)
+  ])
+
+  if ([packageJson, pluginConfig, registryInfo, version].every(val => !val)) {
+    return undefined
+  }
+
+  const latestVersion = registryInfo ? registryInfo['dist-tags']?.latest : undefined
+  const versions = registryInfo ? Object.keys(registryInfo.versions) : []
+
+  const installedPackageVersion = projectPackage.dependencies[packageName]
+  const installed = !!installedPackageVersion
+  const installedLocally = installedPackageVersion?.startsWith('file:')
+
+  let localVersion
+
+  if (!installed) {
+    // Retrieve the packageJson and pluginConfig from the registry if possible
+    if (registryInfo) {
+      packageJson = registryInfo?.versions ? registryInfo?.versions[latestVersion] : undefined
+      pluginConfig = await getConfigForPackage(packageName)
+    } else if (version) {
+      packageJson = await readJson(path.join(path.relative(projectDir, version), 'package.json'))
+      pluginConfig = await readJson(path.join(path.relative(projectDir, version), 'govuk-prototype-kit.config.json'))
+      if (packageJson) {
+        localVersion = version
+      } else {
+        return undefined
+      }
+    }
+  }
+
+  const available = !!knownPlugins?.plugins?.available.includes(packageName)
+
+  if (!pluginConfig && getProxyPluginConfig(packageName)) {
+    // Use the proxy pluginConfig if exists when no other plugin config can be found
+    pluginConfig = getProxyPluginConfig(packageName)
+  }
+
+  const { version: installedVersion } = installed ? packageJson : {}
+  if (installedLocally) {
+    localVersion = path.resolve(installedPackageVersion.replace('file:', ''))
+  }
+
+  const pluginDependencies = pluginConfig?.pluginDependencies
+
+  const packageInfo = {
+    packageName,
+    installed,
+    installedVersion,
+    installedLocally,
+    available,
+    required,
+    latestVersion,
+    versions,
+    packageJson,
+    pluginConfig,
+    pluginDependencies,
+    localVersion,
+    installedPackageVersion
+  }
+
+  // Remove all undefined properties and save to cache
+  packagesCache[packageName] = Object.fromEntries(Object.entries(packageInfo).filter(([_, value]) => value !== undefined))
+}
+
+async function lookupPackageInfo (packageName, version) {
+  if (!packagesCache[packageName]) {
+    await refreshPackageInfo(packageName, version)
+  }
+  return packagesCache[packageName]
+}
+
+const basePlugins = config.getConfig().basePlugins
+
+function emphasizeBasePlugins (plugins, nextPlugin) {
+  if (basePlugins.includes(nextPlugin.packageName)) {
+    return [nextPlugin, ...plugins]
+  } else {
+    return [...plugins, nextPlugin]
+  }
+}
+
+function packageNameSort (pkgA, pkgB) {
+  const nameA = pkgA.packageName.toLowerCase()
+  const nameB = pkgB.packageName.toLowerCase()
+  if (nameA > nameB) return 1
+  if (nameA < nameB) return -1
+  return 0
+}
+
+async function getInstalledPackages () {
+  if (!Object.keys(packagesCache).length) {
+    await startPackageTracker()
+  }
+  await waitForPackagesCache()
+  return Object.values(packagesCache)
+    .filter(({ installed }) => installed)
+    .sort(packageNameSort)
+    .reduce(emphasizeBasePlugins, [])
+}
+
+async function getAvailablePackages () {
+  if (!Object.keys(packagesCache).length) {
+    await startPackageTracker()
+  }
+  await waitForPackagesCache()
+  return Object.values(packagesCache)
+    .filter(({ available, installed }) => available && !installed)
+    .sort(packageNameSort)
+    .reduce(emphasizeBasePlugins, [])
+}
+
+function sleep (ms) {
+  return new Promise((resolve) => setTimeout(resolve, ms))
+}
+
+async function waitForPackagesCache () {
+  let numberOfRetries = 20
+  let waiting = !packageTrackerInterval
+  while (waiting) {
+    // If the packageTrackerInterval has been set, then packages cache has been populated at least once
+    waiting = !packageTrackerInterval && numberOfRetries > 0
+    numberOfRetries--
+    if (numberOfRetries === 0) {
+      console.log('Failed to load the package cache')
+    } else {
+      await sleep(250)
+    }
+  }
+}
+
+async function getDependentPackages (packageName) {
+  if (!Object.keys(packagesCache).length) {
+    await startPackageTracker()
+  }
+  await waitForPackagesCache()
+  return Object.values(packagesCache)
+    .filter(({ pluginDependencies }) => pluginDependencies?.some((pluginDependency) => pluginDependency === packageName || pluginDependency.packageName === packageName))
+}
+
+async function getDependencyPackages (packageName, version) {
+  if (!Object.keys(packagesCache).length) {
+    await startPackageTracker()
+  }
+  await waitForPackagesCache()
+  const pkg = await lookupPackageInfo(packageName, version)
+  return !pkg?.pluginDependencies
+    ? []
+    : await Promise.all(pkg.pluginDependencies.map((pluginDependency) => {
+      return typeof pluginDependency === 'string' ? lookupPackageInfo(pluginDependency) : lookupPackageInfo(pluginDependency.packageName)
+    }))
+}
+
+if (!config.getConfig().isTest) {
+  startPackageTracker()
+}
+
+function setPackagesCache (packagesInfo) {
+  // Only used for unit tests
+  while (packagesCache.length) {
+    packagesCache.pop()
+  }
+  packagesInfo.forEach((packageInfo) => {
+    packagesCache[packageInfo.packageName] = packageInfo
+  })
+  packageTrackerInterval = true
+}
+
+module.exports = {
+  setPackagesCache, // Only for unit testing purposes
+  waitForPackagesCache,
+  lookupPackageInfo,
+  getInstalledPackages,
+  getAvailablePackages,
+  getDependentPackages,
+  getDependencyPackages
+}
diff --git a/lib/plugins/packages.spec.js b/lib/plugins/packages.spec.js
new file mode 100644
index 0000000000..468db75538
--- /dev/null
+++ b/lib/plugins/packages.spec.js
@@ -0,0 +1,264 @@
+/* eslint-env jest */
+
+jest.mock('fs-extra')
+jest.mock('../utils/requestHttps')
+
+// node dependencies
+const path = require('path')
+
+// npm dependencies
+const fse = require('fs-extra')
+
+// local dependencies
+const packages = require('./packages')
+const { lookupPackageInfo } = packages
+const requestHttps = require('../utils/requestHttps')
+const {
+  getInstalledPackages,
+  setPackagesCache,
+  getAvailablePackages,
+  getDependentPackages,
+  getDependencyPackages
+} = require('./packages')
+const registryUrl = 'https://registry.npmjs.org/'
+
+jest.mock('../../package.json', () => {
+  return {
+    dependencies: {
+      '@govuk-prototype-kit/common-templates': '1.0.0'
+    }
+  }
+})
+
+describe('packages', () => {
+  beforeEach(() => {
+    setPackagesCache([])
+  })
+
+  afterEach(() => {
+    jest.restoreAllMocks()
+  })
+
+  describe('get packages', () => {
+    const availableInstalledPackage = {
+      packageName: 'available-installed-package',
+      installed: true,
+      available: true
+    }
+    const availableUninstalledPackage = {
+      packageName: 'available-uninstalled-package',
+      installed: false,
+      available: true
+    }
+    const unavailableInstalledPackage = {
+      packageName: 'unavailable-installed-package',
+      installed: true,
+      available: false,
+      pluginDependencies: [availableInstalledPackage]
+    }
+    const unavailableUninstalledPackage = {
+      packageName: 'unavailable-uninstalled-package',
+      installed: false,
+      available: false,
+      pluginDependencies: [availableUninstalledPackage]
+    }
+
+    beforeEach(() => {
+      setPackagesCache([
+        availableInstalledPackage,
+        availableUninstalledPackage,
+        unavailableInstalledPackage,
+        unavailableUninstalledPackage])
+    })
+
+    describe('getInstalledPackages', () => {
+      it('', async () => {
+        const installedPackages = await getInstalledPackages()
+        expect(installedPackages).toEqual([availableInstalledPackage, unavailableInstalledPackage])
+      })
+    })
+
+    describe('getAvailablePackages', () => {
+      it('', async () => {
+        const availablePackages = await getAvailablePackages()
+        expect(availablePackages).toEqual([availableUninstalledPackage])
+      })
+    })
+
+    describe('getDependentPackages', () => {
+      it('', async () => {
+        const dependentPackages = await getDependentPackages(availableInstalledPackage.packageName)
+        expect(dependentPackages).toEqual([unavailableInstalledPackage])
+      })
+    })
+
+    describe('getDependencyPackages', () => {
+      it('', async () => {
+        const dependencyPackages = await getDependencyPackages(unavailableUninstalledPackage.packageName)
+        expect(dependencyPackages).toEqual([availableUninstalledPackage])
+      })
+    })
+  })
+
+  describe('lookupPackageInfo', () => {
+    let packageJson, pluginJson
+
+    async function mockReadJson (fullFileName) {
+      const fileName = fullFileName.substring(fullFileName.lastIndexOf(path.sep) + 1)
+      if (fileName === 'package.json') {
+        return packageJson
+      } else if (fileName === 'govuk-prototype-kit.config.json') {
+        return pluginJson
+      }
+    }
+
+    beforeEach(() => {
+      packageJson = {
+        local: true,
+        version: '1.0.0'
+      }
+      pluginJson = {
+        loaded: true
+      }
+      jest.spyOn(requestHttps, 'requestHttpsJson').mockImplementation(async (url) => {
+        switch (decodeURIComponent(url.replace(registryUrl, ''))) {
+          case 'jquery':
+            return {
+              'dist-tags': { latest: '2.0.0' },
+              versions: {
+                '1.0.0': { version: '1.0.0' },
+                '2.0.0': { version: '2.0.0' }
+              }
+            }
+          case '@govuk-prototype-kit/common-templates':
+            return {
+              'dist-tags': { latest: '1.0.1' },
+              versions: {
+                '1.0.0': { version: '1.0.0' },
+                '1.0.1': { version: '1.0.1' }
+              }
+            }
+          case '@govuk-prototype-kit/task-list':
+            return {
+              'dist-tags': { latest: '1.0.0' },
+              versions: {
+                '1.0.0': { version: '1.0.0' }
+              }
+            }
+          default:
+            return undefined
+        }
+      })
+    })
+
+    it('lookup installed approved plugin', async () => {
+      const packageName = '@govuk-prototype-kit/common-templates'
+
+      jest.spyOn(fse, 'pathExists').mockResolvedValue(true)
+      jest.spyOn(fse, 'readJson').mockImplementation(mockReadJson)
+
+      const packageInfo = await lookupPackageInfo(packageName)
+
+      expect(requestHttps.requestHttpsJson).toHaveBeenCalledWith(registryUrl + encodeURIComponent(packageName))
+
+      expect(packageInfo).toEqual({
+        packageName,
+        available: true,
+        installed: true,
+        installedLocally: false,
+        installedPackageVersion: '1.0.0',
+        installedVersion: '1.0.0',
+        latestVersion: '1.0.1',
+        required: false,
+        packageJson: {
+          local: true,
+          version: '1.0.0'
+        },
+        pluginConfig: {
+          loaded: true
+        },
+        versions: [
+          '1.0.0',
+          '1.0.1'
+        ]
+      })
+    })
+
+    it('lookup uninstalled approved plugin', async () => {
+      const packageName = '@govuk-prototype-kit/task-list'
+      const packageInfo = await lookupPackageInfo(packageName)
+
+      expect(requestHttps.requestHttpsJson).toHaveBeenCalledWith(registryUrl + encodeURIComponent(packageName))
+
+      expect(packageInfo).toEqual({
+        packageName,
+        available: true,
+        installed: false,
+        latestVersion: '1.0.0',
+        required: false,
+        packageJson: {
+          version: '1.0.0'
+        },
+        versions: [
+          '1.0.0'
+        ]
+      })
+    })
+
+    it('lookup uninstalled approved proxy plugin', async () => {
+      const packageName = 'jquery'
+      const packageInfo = await lookupPackageInfo(packageName)
+
+      expect(requestHttps.requestHttpsJson).toHaveBeenCalledWith(registryUrl + encodeURIComponent(packageName))
+
+      expect(packageInfo).toEqual({
+        packageName,
+        available: true,
+        installed: false,
+        latestVersion: '2.0.0',
+        required: false,
+        packageJson: {
+          version: '2.0.0'
+        },
+        pluginConfig: {
+          assets: [
+            '/dist'
+          ],
+          scripts: [
+            '/dist/jquery.js'
+          ]
+        },
+        versions: [
+          '1.0.0',
+          '2.0.0'
+        ]
+      })
+    })
+
+    it('lookup uninstalled local plugin', async () => {
+      const packageName = 'local-plugin'
+      const version = '/local/folder/local-plugin'
+      jest.spyOn(fse, 'pathExists').mockResolvedValue(true)
+      jest.spyOn(fse, 'readJson').mockImplementation(mockReadJson)
+      const packageInfo = await lookupPackageInfo(packageName, version)
+
+      expect(requestHttps.requestHttpsJson).toHaveBeenCalledWith(registryUrl + encodeURIComponent(packageName))
+
+      expect(packageInfo).toEqual({
+        available: false,
+        installed: false,
+        localVersion: version,
+        packageJson: {
+          local: true,
+          version: '1.0.0'
+        },
+        packageName,
+        pluginConfig: {
+          loaded: true
+        },
+        required: false,
+        versions: []
+      })
+    })
+  })
+})
diff --git a/lib/plugins/plugin-utils.js b/lib/plugins/plugin-utils.js
new file mode 100644
index 0000000000..2e579c387b
--- /dev/null
+++ b/lib/plugins/plugin-utils.js
@@ -0,0 +1,14 @@
+// This allows npm modules to act as if they are plugins by providing the plugin config for them
+function getProxyPluginConfig (packageName) {
+  const proxyPluginConfig = {
+    jquery: {
+      scripts: ['/dist/jquery.js'],
+      assets: ['/dist']
+    }
+  }
+  return proxyPluginConfig[packageName] ? { ...proxyPluginConfig[packageName] } : undefined
+}
+
+module.exports = {
+  getProxyPluginConfig
+}
diff --git a/lib/plugins/plugin-validator.js b/lib/plugins/plugin-validator.js
index 7ada59841b..f521f0ba9c 100644
--- a/lib/plugins/plugin-validator.js
+++ b/lib/plugins/plugin-validator.js
@@ -14,7 +14,8 @@ function getKnownKeys () {
     'sass',
     'scripts',
     'stylesheets',
-    'templates'
+    'templates',
+    'pluginDependencies'
   ]
   return knownKeys
 }
@@ -50,7 +51,7 @@ function validateConfigKeys (pluginConfig) {
   const knownKeys = getKnownKeys()
   const invalidKeys = []
 
-  const validKeysPluginConfig = Object.fromEntries(Object.entries(pluginConfig).filter(([key, value]) => {
+  const validKeysPluginConfig = Object.fromEntries(Object.entries(pluginConfig).filter(([key]) => {
     if (knownKeys.includes(key)) {
       return true
     }
@@ -66,6 +67,29 @@ function validateConfigKeys (pluginConfig) {
   return validKeysPluginConfig
 }
 
+function validatePluginDependency (key, configEntry) {
+  if (typeof configEntry === 'string') {
+    return
+  }
+  // Can be a string, but if an object, the packageName must be a string
+  if (!Object.keys(configEntry).includes('packageName')) {
+    errors.push(`In section ${key}, the packageName property should exist`)
+    return
+  }
+  const { packageName, minVersion, maxVersion } = configEntry
+  if (typeof packageName !== 'string') {
+    errors.push(`In section ${key}, the packageName '${packageName}' should be a valid package name`)
+  }
+  // The minVersion is optional but must be a string if entered
+  if (Object.keys(configEntry).includes('minVersion') && typeof minVersion !== 'string') {
+    errors.push(`In section ${key}, the minVersion '${minVersion}' should be a valid version`)
+  }
+  // The maxVersion is optional but must be a string if entered
+  if (Object.keys(configEntry).includes('maxVersion') && typeof maxVersion !== 'string' && typeof maxVersion !== 'undefined') {
+    errors.push(`In section ${key}, the maxVersion '${maxVersion}' should be a valid version if entered`)
+  }
+}
+
 function validateConfigPaths (pluginConfig, executionPath) {
   console.log('Validating whether config paths meet criteria.')
   const keysToValidate = Object.keys(pluginConfig)
@@ -77,15 +101,17 @@ function validateConfigPaths (pluginConfig, executionPath) {
       criteriaConfig = [criteriaConfig]
     }
 
-    criteriaConfig.forEach((configEntry, index) => {
+    criteriaConfig.forEach((configEntry) => {
       try {
-        if (typeof configEntry === 'string' && configEntry[0] === '/') {
-          checkPathExists(executionPath, configEntry, key)
+        if (key === 'pluginDependencies') {
+          validatePluginDependency(key, configEntry)
         } else if ((key === 'templates' && configEntry.path[0] === '/') ||
           (key === 'scripts' && configEntry.path !== undefined && configEntry.path[0] === '/')) {
           checkPathExists(executionPath, configEntry.path, key)
-        } else if ((key === 'nunjucksMacros')) {
+        } else if (key === 'nunjucksMacros') {
           checkNunjucksMacroExists(executionPath, configEntry.importFrom, pluginConfig.nunjucksPaths)
+        } else if (typeof configEntry === 'string' && configEntry[0] === '/') {
+          checkPathExists(executionPath, configEntry, key)
         } else {
           // Find the path for the ones that can be objects
           const invalidPath = (key === 'templates' || (key === 'scripts' && configEntry.path !== undefined))
@@ -145,6 +171,19 @@ async function validatePlugin (executionPath) {
   }
 }
 
+function clearErrors () {
+  while (errors.length) {
+    errors.pop()
+  }
+}
+
+function getErrors () {
+  return [...errors]
+}
+
 module.exports = {
-  validatePlugin
+  clearErrors,
+  getErrors,
+  validatePlugin,
+  validatePluginDependency
 }
diff --git a/lib/plugins/plugin-validator.spec.js b/lib/plugins/plugin-validator.spec.js
new file mode 100644
index 0000000000..9d3247d15a
--- /dev/null
+++ b/lib/plugins/plugin-validator.spec.js
@@ -0,0 +1,64 @@
+const { validatePluginDependency, clearErrors, getErrors } = require('./plugin-validator')
+
+describe('plugin-validator', () => {
+  beforeEach(() => {
+    clearErrors()
+  })
+
+  describe('validatePluginDependency', () => {
+    it('should be valid with a string', () => {
+      validatePluginDependency('pluginDependencies', 'test-package')
+      expect(getErrors()).toEqual([])
+    })
+
+    it('should be valid when an object with only the pluginName as a property', () => {
+      validatePluginDependency('pluginDependencies', { packageName: 'test-package' })
+      expect(getErrors()).toEqual([])
+    })
+
+    it('should be invalid when an object without the pluginName as a property', () => {
+      validatePluginDependency('pluginDependencies', {})
+      expect(getErrors()).toEqual([
+        'In section pluginDependencies, the packageName property should exist'
+      ])
+    })
+
+    it('should be invalid when an object when the pluginName is not a string', () => {
+      validatePluginDependency('pluginDependencies', { packageName: null })
+      expect(getErrors()).toEqual([
+        'In section pluginDependencies, the packageName \'null\' should be a valid package name'
+      ])
+    })
+
+    it('should be valid when an object with both the pluginName and minVersion as properties', () => {
+      validatePluginDependency('pluginDependencies', { packageName: 'test-package', minVersion: '1.0.0' })
+      expect(getErrors()).toEqual([])
+    })
+
+    it('should be valid when an object with both the pluginName and maxVersion as properties', () => {
+      validatePluginDependency('pluginDependencies', { packageName: 'test-package', maxVersion: '2.0.0' })
+      expect(getErrors()).toEqual([])
+    })
+
+    it('should be valid when an object with the pluginName, minVersion and maxVersion as properties', () => {
+      validatePluginDependency('pluginDependencies', {
+        packageName: 'test-package',
+        minVersion: '1.0.0',
+        maxVersion: '2.0.0'
+      })
+      expect(getErrors()).toEqual([])
+    })
+
+    it('should be invalid the minVersion or maxVersion are not strings', () => {
+      validatePluginDependency('pluginDependencies', {
+        packageName: 'test-package',
+        minVersion: null,
+        maxVersion: 100
+      })
+      expect(getErrors()).toEqual([
+        'In section pluginDependencies, the minVersion \'null\' should be a valid version',
+        'In section pluginDependencies, the maxVersion \'100\' should be a valid version if entered'
+      ])
+    })
+  })
+})
diff --git a/lib/plugins/plugins.js b/lib/plugins/plugins.js
index 2c1dd0461c..c2d8b32101 100644
--- a/lib/plugins/plugins.js
+++ b/lib/plugins/plugins.js
@@ -43,9 +43,9 @@ const fse = require('fs-extra')
 
 // local dependencies
 const appConfig = require('../config')
-const { projectDir, packageDir, shadowNunjucksDir } = require('../utils/paths')
+const { projectDir, shadowNunjucksDir } = require('../utils/paths')
 const { startPerformanceTimer, endPerformanceTimer } = require('../utils/performance')
-const knownPlugins = require(path.join(packageDir, 'known-plugins.json'))
+const { getProxyPluginConfig } = require('./plugin-utils')
 
 const pkgPath = path.join(projectDir, 'package.json')
 
@@ -61,13 +61,6 @@ const objectMap = (object, mapFn) => Object.keys(object).reduce((result, key) =>
 const getPathFromProjectRoot = (...all) => path.join(...[projectDir].concat(all))
 const pathToPluginConfigFile = packageName => getPathFromProjectRoot('node_modules', packageName, 'govuk-prototype-kit.config.json')
 
-const moduleToPluginConversion = {
-  jquery: {
-    scripts: ['/dist/jquery.js'],
-    assets: ['/dist']
-  }
-}
-
 const readJsonFile = (filePath) => JSON.parse(fs.readFileSync(filePath, 'utf8'))
 
 function getPluginConfig (packageName) {
@@ -77,9 +70,10 @@ function getPluginConfig (packageName) {
     endPerformanceTimer('getPluginConfig (fileSystem)', timer)
     return readJsonFile(pluginConfigFile)
   }
-  if (moduleToPluginConversion[packageName]) {
+  const proxyPluginConfig = getProxyPluginConfig(packageName)
+  if (proxyPluginConfig) {
     endPerformanceTimer('getPluginConfig (backup)', timer)
-    return moduleToPluginConversion[packageName]
+    return proxyPluginConfig
   }
   endPerformanceTimer('getPluginConfig (empty)', timer)
   return {}
@@ -102,10 +96,6 @@ function throwIfBadFilepath (subject) {
 // Check for `basePlugins` in config.js. If it's not there, default to `govuk-frontend`
 const getBasePlugins = () => appConfig.getConfig().basePlugins
 
-function getKnownPlugins () {
-  return knownPlugins.plugins
-}
-
 /**
  * Get all npm dependencies
  *
@@ -252,9 +242,6 @@ function preparePackageNameForDisplay (packageName, version) {
   return packageNameDetails
 }
 
-const listInstalledPlugins = () => getPackageNamesInOrder()
-  .filter((packageName) => Object.keys(getPluginConfig(packageName)).length || getKnownPlugins().available.includes(packageName))
-
 function expandToIncludeShadowNunjucks (arr) {
   const out = []
   arr.forEach(orig => {
@@ -374,8 +361,6 @@ function legacyGovukFrontendFixesNeeded () {
 // Exports
 const self = module.exports = {
   preparePackageNameForDisplay,
-  listInstalledPlugins,
-  getKnownPlugins,
   getByType,
   getPublicUrls,
   getFileSystemPaths,
diff --git a/lib/utils/index.js b/lib/utils/index.js
index 311e8a1e11..594172d3ec 100644
--- a/lib/utils/index.js
+++ b/lib/utils/index.js
@@ -3,7 +3,6 @@
 const crypto = require('crypto')
 const fs = require('fs')
 const fsp = fs.promises
-const https = require('https')
 const path = require('path')
 const { existsSync } = require('fs')
 
@@ -197,30 +196,6 @@ function encryptPassword (password) {
   return hash.digest('hex')
 }
 
-function requestHttpsJson (url) {
-  return new Promise((resolve, reject) => {
-    https.get(url, (res) => {
-      const dataParts = []
-
-      const statusCode = res.statusCode
-      if (statusCode < 200 || statusCode >= 300) {
-        const error = new Error(`Bad response from [${url}]`)
-        error.statusCode = statusCode
-        error.code = 'EBADRESPONSE'
-        reject(error)
-      }
-      res.on('end', () => {
-        resolve(JSON.parse(dataParts.join('')))
-      })
-      res.on('data', (d) => {
-        dataParts.push(d)
-      })
-    }).on('error', (e) => {
-      reject(e)
-    })
-  })
-}
-
 function sessionFileStoreQuietLogFn (message) {
   if (message.endsWith('Deleting expired sessions')) {
     // session-file-store logs every time it prunes files for expired sessions,
@@ -312,7 +287,6 @@ module.exports = {
   sleep,
   waitUntilFileExists,
   encryptPassword,
-  requestHttpsJson,
   sessionFileStoreQuietLogFn,
   searchAndReplaceFiles,
   recursiveDirectoryContentsSync,
diff --git a/lib/utils/requestHttps.js b/lib/utils/requestHttps.js
new file mode 100644
index 0000000000..80b36e52d3
--- /dev/null
+++ b/lib/utils/requestHttps.js
@@ -0,0 +1,96 @@
+const https = require('https')
+const zlib = require("zlib")
+const tar = require('tar-stream')
+const {startPerformanceTimer, endPerformanceTimer} = require("./performance")
+const path = require("path")
+const {tmpDir} = require("./paths")
+const {exists, readJson, ensureDir, writeJson} = require("fs-extra")
+
+async function getConfigForPackage(packageName) {
+  const timer = startPerformanceTimer()
+
+  const cacheFileDirectory = path.join(tmpDir, 'caches')
+  const cacheFileReference = path.join(cacheFileDirectory, 'getConfigForPackage.json')
+  let cache = {}
+
+  await ensureDir(cacheFileDirectory)
+  if (await exists(cacheFileReference)) {
+    cache = await readJson(cacheFileReference)
+  }
+
+  let registry
+
+  try {
+    registry = await requestHttpsJson(`https://registry.npmjs.org/${encodeURIComponent(packageName)}`)
+  } catch (e) {
+    endPerformanceTimer('getConfigForPackage (bad status)', timer)
+
+    return undefined
+  }
+  const latestTag = registry['dist-tags']?.latest
+
+function requestHttpsJson (url) {
+  return new Promise((resolve, reject) => {
+    https.get(url, (response) => {
+
+      const statusCode = response.statusCode
+
+      if (statusCode < 200 || statusCode >= 300) {
+        const error = new Error(`Bad response from [${url}]`)
+        error.statusCode = statusCode
+        error.code = 'EBADRESPONSE'
+        reject(error)
+      }
+
+      prepareFn(options, response, resolve, reject)
+    }).on('error', (e) => {
+      reject(e)
+    })
+  })
+}
+
+const requestHttpsJson = setupRequestFunction((options, response, resolve) => {
+  const dataParts = []
+  response.on('end', () => {
+    const data = dataParts.join('')
+    if (data.startsWith('{')) {
+      resolve(JSON.parse(data))
+    } else {
+      resolve()
+    }
+  })
+  response.on('data', (d) => {
+    dataParts.push(d)
+  })
+})
+
+const findFileInHttpsTgz = setupRequestFunction((options, response, resolve) => {
+  const extract = tar.extract();
+  const data = [];
+
+  extract.on('entry', function (header, stream, cb) {
+    stream.on('data', function (chunk) {
+      if (header.name === options.fileToFind) {
+        data.push(chunk.toString())
+      }
+    })
+  })
+
+  extract.on('finish', function () {
+    const result = data.join('');
+    if (options.prepare) {
+      resolve(options.prepare(result))
+    } else {
+      resolve(result)
+    }
+  })
+
+  response
+    .pipe(zlib.createGunzip())
+    .pipe(extract)
+})
+
+module.exports = {
+  requestHttpsJson,
+  getConfigForPackage
+}

From 0552d91e74becd319e8a7f6d16a93c3504d386bc Mon Sep 17 00:00:00 2001
From: Natalie Carey <natalie.carey@digital.cabinet-office.gov.uk>
Date: Mon, 19 Jun 2023 22:21:39 +0100
Subject: [PATCH 2/4] Handling malformed JSON in cache file. Added cache for
 config lookup.

---
 .../plugin-install-or-uninstall.njk           |  6 +-
 lib/utils/requestHttps.js                     | 48 +++++++++--
 npm-shrinkwrap.json                           | 84 ++++++++++++++++++-
 package.json                                  |  4 +-
 proof-of-concept.js                           | 19 +++++
 5 files changed, 149 insertions(+), 12 deletions(-)
 create mode 100644 proof-of-concept.js

diff --git a/lib/nunjucks/views/manage-prototype/plugin-install-or-uninstall.njk b/lib/nunjucks/views/manage-prototype/plugin-install-or-uninstall.njk
index ccc29d9a7a..a01a082f3b 100644
--- a/lib/nunjucks/views/manage-prototype/plugin-install-or-uninstall.njk
+++ b/lib/nunjucks/views/manage-prototype/plugin-install-or-uninstall.njk
@@ -47,11 +47,7 @@
           </ul>
 
           <p class="govuk-body">
-            {% if verb.para == 'uninstall' %}
-              If you uninstall {{ chosenPlugin.name }}, these plugins will no longer work.
-            {% else %}
-              To {{ verb.para }} {{ chosenPlugin.name }} you also need to {{ verb.para }} these plugins.
-            {% endif %}
+            To {{ verb.para }} {{ chosenPlugin.name }} you also need to {{ verb.para }} {% if chosenPlugin.dependentPlugins | length > 1 %}these plugins{% else %}this plugin{% endif %}.
           </p>
           <div class="govuk-button-group">
             {{ govukButton({
diff --git a/lib/utils/requestHttps.js b/lib/utils/requestHttps.js
index 80b36e52d3..3af2126d23 100644
--- a/lib/utils/requestHttps.js
+++ b/lib/utils/requestHttps.js
@@ -15,7 +15,11 @@ async function getConfigForPackage(packageName) {
 
   await ensureDir(cacheFileDirectory)
   if (await exists(cacheFileReference)) {
-    cache = await readJson(cacheFileReference)
+    try {
+      cache = await readJson(cacheFileReference)
+    } catch (e) {
+      writeJson(cacheFileReference, {})
+    }
   }
 
   let registry
@@ -29,10 +33,38 @@ async function getConfigForPackage(packageName) {
   }
   const latestTag = registry['dist-tags']?.latest
 
-function requestHttpsJson (url) {
-  return new Promise((resolve, reject) => {
-    https.get(url, (response) => {
+  if (cache[packageName] && cache[packageName][latestTag]) {
+    endPerformanceTimer('getConfigForPackage (from cache)', timer)
+    return cache[packageName][latestTag]
+  }
+
+  if (!latestTag) {
+    endPerformanceTimer('getConfigForPackage (no latest tag)', timer)
+    return
+  }
+
+  const url = registry.versions[latestTag].dist.tarball
+  const result = await findFileInHttpsTgz(url, {
+    fileToFind: 'package/govuk-prototype-kit.config.json',
+    prepare: str => {
+      if (str && str.startsWith('{')) {
+        const result = JSON.parse(str)
+        cache[packageName] = cache[packageName] || {}
+        cache[packageName][latestTag] = result
+        writeJson(cacheFileReference, cache)
+        return result
+      }
+    }
+  })
+
+  endPerformanceTimer('getConfigForPackage', timer)
+
+  return result
+}
 
+function setupRequestFunction(prepareFn, badStatusFn) {
+  return (url, options) => new Promise((resolve, reject) => {
+    https.get(url, (response) => {
       const statusCode = response.statusCode
 
       if (statusCode < 200 || statusCode >= 300) {
@@ -70,10 +102,16 @@ const findFileInHttpsTgz = setupRequestFunction((options, response, resolve) =>
 
   extract.on('entry', function (header, stream, cb) {
     stream.on('data', function (chunk) {
-      if (header.name === options.fileToFind) {
+      if (header.name == options.fileToFind) {
         data.push(chunk.toString())
       }
     })
+
+    stream.on('end', function () {
+      cb()
+    })
+
+    stream.resume()
   })
 
   extract.on('finish', function () {
diff --git a/npm-shrinkwrap.json b/npm-shrinkwrap.json
index 6babb7abae..f6ae1a25b2 100644
--- a/npm-shrinkwrap.json
+++ b/npm-shrinkwrap.json
@@ -30,8 +30,10 @@
         "require-dir": "^1.2.0",
         "sass": "^1.57.1",
         "sync-request": "^6.1.0",
+        "tar-stream": "^3.1.2",
         "universal-analytics": "^0.5.3",
-        "uuid": "^9.0.0"
+        "uuid": "^9.0.0",
+        "zlib": "^1.0.5"
       },
       "bin": {
         "govuk-prototype-kit": "bin/cli"
@@ -2514,6 +2516,11 @@
         "follow-redirects": "^1.14.0"
       }
     },
+    "node_modules/b4a": {
+      "version": "1.6.4",
+      "resolved": "https://registry.npmjs.org/b4a/-/b4a-1.6.4.tgz",
+      "integrity": "sha512-fpWrvyVHEKyeEvbKZTVOeZF3VSKKWtJxFIxX/jaVPf+cLbGUSitjb49pHLqPV2BUNNZ0LcoeEGfE/YCpyDYHIw=="
+    },
     "node_modules/babel-jest": {
       "version": "29.3.1",
       "resolved": "https://registry.npmjs.org/babel-jest/-/babel-jest-29.3.1.tgz",
@@ -5788,6 +5795,11 @@
       "integrity": "sha512-f3qQ9oQy9j2AhBe/H9VC91wLmKBCCU/gDOnKNAYG5hswO7BLKj09Hc5HYNz9cGI++xlpDCIgDaitVs03ATR84Q==",
       "dev": true
     },
+    "node_modules/fast-fifo": {
+      "version": "1.2.0",
+      "resolved": "https://registry.npmjs.org/fast-fifo/-/fast-fifo-1.2.0.tgz",
+      "integrity": "sha512-NcvQXt7Cky1cNau15FWy64IjuO8X0JijhTBBrJj1YlxlDfRkJXNaK9RFUjwpfDPzMdv7wB38jr53l9tkNLxnWg=="
+    },
     "node_modules/fast-glob": {
       "version": "3.2.12",
       "resolved": "https://registry.npmjs.org/fast-glob/-/fast-glob-3.2.12.tgz",
@@ -10498,6 +10510,11 @@
         }
       ]
     },
+    "node_modules/queue-tick": {
+      "version": "1.0.1",
+      "resolved": "https://registry.npmjs.org/queue-tick/-/queue-tick-1.0.1.tgz",
+      "integrity": "sha512-kJt5qhMxoszgU/62PLP1CJytzd2NKetjSRnyuj31fDd3Rlcz3fzlFdFLD1SItunPwyqEOkca6GbV612BWfaBag=="
+    },
     "node_modules/random-bytes": {
       "version": "1.0.0",
       "resolved": "https://registry.npmjs.org/random-bytes/-/random-bytes-1.0.0.tgz",
@@ -11415,6 +11432,15 @@
         "node": ">= 0.10.0"
       }
     },
+    "node_modules/streamx": {
+      "version": "2.15.0",
+      "resolved": "https://registry.npmjs.org/streamx/-/streamx-2.15.0.tgz",
+      "integrity": "sha512-HcxY6ncGjjklGs1xsP1aR71INYcsXFJet5CU1CHqihQ2J5nOsbd4OjgjHO42w/4QNv9gZb3BueV+Vxok5pLEXg==",
+      "dependencies": {
+        "fast-fifo": "^1.1.0",
+        "queue-tick": "^1.0.1"
+      }
+    },
     "node_modules/string_decoder": {
       "version": "1.1.1",
       "resolved": "https://registry.npmjs.org/string_decoder/-/string_decoder-1.1.1.tgz",
@@ -11730,6 +11756,15 @@
         "get-port": "^3.1.0"
       }
     },
+    "node_modules/tar-stream": {
+      "version": "3.1.2",
+      "resolved": "https://registry.npmjs.org/tar-stream/-/tar-stream-3.1.2.tgz",
+      "integrity": "sha512-rEZHMKQop/sTykFtONCcOxyyLA+9hriHJlECxfh4z+Nfew87XGprDLp9RYFCd7yU+z3ePXfHlPbZrzgSLvc16A==",
+      "dependencies": {
+        "b4a": "^1.6.4",
+        "streamx": "^2.15.0"
+      }
+    },
     "node_modules/test-exclude": {
       "version": "6.0.0",
       "resolved": "https://registry.npmjs.org/test-exclude/-/test-exclude-6.0.0.tgz",
@@ -12611,6 +12646,15 @@
       "funding": {
         "url": "https://github.com/sponsors/sindresorhus"
       }
+    },
+    "node_modules/zlib": {
+      "version": "1.0.5",
+      "resolved": "https://registry.npmjs.org/zlib/-/zlib-1.0.5.tgz",
+      "integrity": "sha512-40fpE2II+Cd3k8HWTWONfeKE2jL+P42iWJ1zzps5W51qcTsOUKM5Q5m2PFb0CLxlmFAaUuUdJGc3OfZy947v0w==",
+      "hasInstallScript": true,
+      "engines": {
+        "node": ">=0.2.0"
+      }
     }
   },
   "dependencies": {
@@ -14507,6 +14551,11 @@
         "follow-redirects": "^1.14.0"
       }
     },
+    "b4a": {
+      "version": "1.6.4",
+      "resolved": "https://registry.npmjs.org/b4a/-/b4a-1.6.4.tgz",
+      "integrity": "sha512-fpWrvyVHEKyeEvbKZTVOeZF3VSKKWtJxFIxX/jaVPf+cLbGUSitjb49pHLqPV2BUNNZ0LcoeEGfE/YCpyDYHIw=="
+    },
     "babel-jest": {
       "version": "29.3.1",
       "resolved": "https://registry.npmjs.org/babel-jest/-/babel-jest-29.3.1.tgz",
@@ -16888,6 +16937,11 @@
       "integrity": "sha512-f3qQ9oQy9j2AhBe/H9VC91wLmKBCCU/gDOnKNAYG5hswO7BLKj09Hc5HYNz9cGI++xlpDCIgDaitVs03ATR84Q==",
       "dev": true
     },
+    "fast-fifo": {
+      "version": "1.2.0",
+      "resolved": "https://registry.npmjs.org/fast-fifo/-/fast-fifo-1.2.0.tgz",
+      "integrity": "sha512-NcvQXt7Cky1cNau15FWy64IjuO8X0JijhTBBrJj1YlxlDfRkJXNaK9RFUjwpfDPzMdv7wB38jr53l9tkNLxnWg=="
+    },
     "fast-glob": {
       "version": "3.2.12",
       "resolved": "https://registry.npmjs.org/fast-glob/-/fast-glob-3.2.12.tgz",
@@ -20317,6 +20371,11 @@
       "resolved": "https://registry.npmjs.org/queue-microtask/-/queue-microtask-1.2.3.tgz",
       "integrity": "sha512-NuaNSa6flKT5JaSYQzJok04JzTL1CA6aGhv5rfLW3PgqA+M2ChpZQnAC8h8i4ZFkBS8X5RqkDBHA7r4hej3K9A=="
     },
+    "queue-tick": {
+      "version": "1.0.1",
+      "resolved": "https://registry.npmjs.org/queue-tick/-/queue-tick-1.0.1.tgz",
+      "integrity": "sha512-kJt5qhMxoszgU/62PLP1CJytzd2NKetjSRnyuj31fDd3Rlcz3fzlFdFLD1SItunPwyqEOkca6GbV612BWfaBag=="
+    },
     "random-bytes": {
       "version": "1.0.0",
       "resolved": "https://registry.npmjs.org/random-bytes/-/random-bytes-1.0.0.tgz",
@@ -20992,6 +21051,15 @@
         "limiter": "^1.0.5"
       }
     },
+    "streamx": {
+      "version": "2.15.0",
+      "resolved": "https://registry.npmjs.org/streamx/-/streamx-2.15.0.tgz",
+      "integrity": "sha512-HcxY6ncGjjklGs1xsP1aR71INYcsXFJet5CU1CHqihQ2J5nOsbd4OjgjHO42w/4QNv9gZb3BueV+Vxok5pLEXg==",
+      "requires": {
+        "fast-fifo": "^1.1.0",
+        "queue-tick": "^1.0.1"
+      }
+    },
     "string_decoder": {
       "version": "1.1.1",
       "resolved": "https://registry.npmjs.org/string_decoder/-/string_decoder-1.1.1.tgz",
@@ -21227,6 +21295,15 @@
         "get-port": "^3.1.0"
       }
     },
+    "tar-stream": {
+      "version": "3.1.2",
+      "resolved": "https://registry.npmjs.org/tar-stream/-/tar-stream-3.1.2.tgz",
+      "integrity": "sha512-rEZHMKQop/sTykFtONCcOxyyLA+9hriHJlECxfh4z+Nfew87XGprDLp9RYFCd7yU+z3ePXfHlPbZrzgSLvc16A==",
+      "requires": {
+        "b4a": "^1.6.4",
+        "streamx": "^2.15.0"
+      }
+    },
     "test-exclude": {
       "version": "6.0.0",
       "resolved": "https://registry.npmjs.org/test-exclude/-/test-exclude-6.0.0.tgz",
@@ -21892,6 +21969,11 @@
       "resolved": "https://registry.npmjs.org/yocto-queue/-/yocto-queue-0.1.0.tgz",
       "integrity": "sha512-rVksvsnNCdJ/ohGc6xgPwyN8eheCxsiLM8mxuE/t/mOVqJewPuO1miLpTHQiRgTKCLexL4MeAFVagts7HmNZ2Q==",
       "dev": true
+    },
+    "zlib": {
+      "version": "1.0.5",
+      "resolved": "https://registry.npmjs.org/zlib/-/zlib-1.0.5.tgz",
+      "integrity": "sha512-40fpE2II+Cd3k8HWTWONfeKE2jL+P42iWJ1zzps5W51qcTsOUKM5Q5m2PFb0CLxlmFAaUuUdJGc3OfZy947v0w=="
     }
   }
 }
diff --git a/package.json b/package.json
index af8825e30e..4b798da425 100644
--- a/package.json
+++ b/package.json
@@ -78,8 +78,10 @@
     "require-dir": "^1.2.0",
     "sass": "^1.57.1",
     "sync-request": "^6.1.0",
+    "tar-stream": "^3.1.2",
     "universal-analytics": "^0.5.3",
-    "uuid": "^9.0.0"
+    "uuid": "^9.0.0",
+    "zlib": "^1.0.5"
   },
   "devDependencies": {
     "cheerio": "^1.0.0-rc.12",
diff --git a/proof-of-concept.js b/proof-of-concept.js
new file mode 100644
index 0000000000..c28342f15a
--- /dev/null
+++ b/proof-of-concept.js
@@ -0,0 +1,19 @@
+const {startPerformanceTimer, endPerformanceTimer} = require("./lib/utils/performance")
+const {getConfigForPackage} = require("./lib/utils/requestHttps");
+
+async function demo(packageName) {
+  await getConfigForPackage(packageName);
+
+  console.log('got result for ', packageName)
+}
+
+(async () => {
+  const timer = startPerformanceTimer()
+  await demo('govuk-prototype-kit')
+  await demo('hmrc-frontend')
+  await demo('govuk-frontend')
+  await demo('@x-govuk/edit-prototype-in-browser')
+  await demo('nhsuk-frontend')
+  await demo('lkasdjflkajsdflkfjsad')
+  endPerformanceTimer('Demo', timer)
+})()

From 43375064716ce156313d0f266a8ee2f3cb532d35 Mon Sep 17 00:00:00 2001
From: Ben Surgison <ben.surgison@digital.cabinet-office.gov.uk>
Date: Tue, 4 Jul 2023 15:24:09 +0100
Subject: [PATCH 3/4] Remove duplicate and prevent circular dependency

---
 lib/utils/requestHttps.js | 65 +++++++++++++++++++++++----------------
 proof-of-concept.js       | 19 ------------
 2 files changed, 39 insertions(+), 45 deletions(-)
 delete mode 100644 proof-of-concept.js

diff --git a/lib/utils/requestHttps.js b/lib/utils/requestHttps.js
index 3af2126d23..9b60d729d6 100644
--- a/lib/utils/requestHttps.js
+++ b/lib/utils/requestHttps.js
@@ -1,12 +1,13 @@
 const https = require('https')
-const zlib = require("zlib")
+const zlib = require('zlib')
 const tar = require('tar-stream')
-const {startPerformanceTimer, endPerformanceTimer} = require("./performance")
-const path = require("path")
-const {tmpDir} = require("./paths")
-const {exists, readJson, ensureDir, writeJson} = require("fs-extra")
+const { startPerformanceTimer, endPerformanceTimer } = require('./performance')
+const path = require('path')
+const { tmpDir } = require('./paths')
+const { exists, readJson, ensureDir, writeJson } = require('fs-extra')
+const { verboseLog } = require('./verboseLogger')
 
-async function getConfigForPackage(packageName) {
+async function getConfigForPackage (packageName) {
   const timer = startPerformanceTimer()
 
   const cacheFileDirectory = path.join(tmpDir, 'caches')
@@ -44,25 +45,29 @@ async function getConfigForPackage(packageName) {
   }
 
   const url = registry.versions[latestTag].dist.tarball
-  const result = await findFileInHttpsTgz(url, {
-    fileToFind: 'package/govuk-prototype-kit.config.json',
-    prepare: str => {
-      if (str && str.startsWith('{')) {
-        const result = JSON.parse(str)
-        cache[packageName] = cache[packageName] || {}
-        cache[packageName][latestTag] = result
-        writeJson(cacheFileReference, cache)
-        return result
+  try {
+    const result = await findFileInHttpsTgz(url, {
+      fileToFind: 'package/govuk-prototype-kit.config.json',
+      prepare: str => {
+        if (str && str.startsWith('{')) {
+          const result = JSON.parse(str)
+          cache[packageName] = cache[packageName] || {}
+          cache[packageName][latestTag] = result
+          writeJson(cacheFileReference, cache)
+          return result
+        }
       }
-    }
-  })
+    })
 
-  endPerformanceTimer('getConfigForPackage', timer)
+    endPerformanceTimer('getConfigForPackage', timer)
 
-  return result
+    return result
+  } catch (e) {
+    endPerformanceTimer('getConfigForPackage (error-in-findFileInHttpsTgz)', timer)
+  }
 }
 
-function setupRequestFunction(prepareFn, badStatusFn) {
+function setupRequestFunction (prepareFn, badStatusFn) {
   return (url, options) => new Promise((resolve, reject) => {
     https.get(url, (response) => {
       const statusCode = response.statusCode
@@ -97,12 +102,12 @@ const requestHttpsJson = setupRequestFunction((options, response, resolve) => {
 })
 
 const findFileInHttpsTgz = setupRequestFunction((options, response, resolve) => {
-  const extract = tar.extract();
-  const data = [];
+  const extract = tar.extract()
+  const data = []
 
   extract.on('entry', function (header, stream, cb) {
     stream.on('data', function (chunk) {
-      if (header.name == options.fileToFind) {
+      if (header.name === options.fileToFind) {
         data.push(chunk.toString())
       }
     })
@@ -111,11 +116,15 @@ const findFileInHttpsTgz = setupRequestFunction((options, response, resolve) =>
       cb()
     })
 
+    stream.on('error', function (e) {
+      verboseLog('Error from tar.extract stream', e)
+    })
+
     stream.resume()
   })
 
   extract.on('finish', function () {
-    const result = data.join('');
+    const result = data.join('')
     if (options.prepare) {
       resolve(options.prepare(result))
     } else {
@@ -124,8 +133,12 @@ const findFileInHttpsTgz = setupRequestFunction((options, response, resolve) =>
   })
 
   response
-    .pipe(zlib.createGunzip())
-    .pipe(extract)
+    .on('error', (e) => verboseLog('Error from response', e))
+    .pipe(zlib.createGunzip().on('error', (e) => verboseLog('Error from gunzip', e)))
+    .pipe(extract.on('error', (e) => verboseLog('Error from extract', e)))
+    .on('error', function (e) {
+      verboseLog('Error from within .tgz pipe', e)
+    })
 })
 
 module.exports = {
diff --git a/proof-of-concept.js b/proof-of-concept.js
deleted file mode 100644
index c28342f15a..0000000000
--- a/proof-of-concept.js
+++ /dev/null
@@ -1,19 +0,0 @@
-const {startPerformanceTimer, endPerformanceTimer} = require("./lib/utils/performance")
-const {getConfigForPackage} = require("./lib/utils/requestHttps");
-
-async function demo(packageName) {
-  await getConfigForPackage(packageName);
-
-  console.log('got result for ', packageName)
-}
-
-(async () => {
-  const timer = startPerformanceTimer()
-  await demo('govuk-prototype-kit')
-  await demo('hmrc-frontend')
-  await demo('govuk-frontend')
-  await demo('@x-govuk/edit-prototype-in-browser')
-  await demo('nhsuk-frontend')
-  await demo('lkasdjflkajsdflkfjsad')
-  endPerformanceTimer('Demo', timer)
-})()

From 015d0eacfebed481841760cc1676d848ad73113a Mon Sep 17 00:00:00 2001
From: Ben Surgison <ben.surgison@digital.cabinet-office.gov.uk>
Date: Tue, 4 Jul 2023 15:26:36 +0100
Subject: [PATCH 4/4] Lint

---
 lib/utils/requestHttps.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/utils/requestHttps.js b/lib/utils/requestHttps.js
index 9b60d729d6..16720fd2f9 100644
--- a/lib/utils/requestHttps.js
+++ b/lib/utils/requestHttps.js
@@ -67,7 +67,7 @@ async function getConfigForPackage (packageName) {
   }
 }
 
-function setupRequestFunction (prepareFn, badStatusFn) {
+function setupRequestFunction (prepareFn) {
   return (url, options) => new Promise((resolve, reject) => {
     https.get(url, (response) => {
       const statusCode = response.statusCode