feat: upgrade to support new version of log4

- Rewrite with ES2015 syntax
- Rely on log4-nodejs utils
- Cover with tests

BREAKING CHANGE:
- Drop support for log4 v2
- Drop support for Node.js v4
- Switch formatter to rely on log4-nodejs utils
- Change presentation of prefixes

index.js

@@ -1,34 +1,39 @@
 "use strict";
 
-if (!process.env.AWS_EXECUTION_ENV) return; // Do not proceed in non AWS lambda env
+const d               = require("d")
+    , rootLogger      = require("log4")
+    , emitter         = require("log4/writer-utils/emitter")
+    , registerMaster  = require("log4/writer-utils/register-master")
+    , setupVisibility = require("log4/writer-utils/setup-visibility")
+    , formatMessage   = require("log4-nodejs/utils/format-message")
+    , levelPrefixes   = require("log4-nodejs/utils/level-prefixes");
 
-var format          = require("util").format
-  , logger          = require("log4")
-  , setupVisibility = require("log4/setup-visibility");
+const setupPrefixes = levelLogger => {
+	levelLogger.levelMessagePrefix = levelPrefixes[levelLogger.level];
+	Object.defineProperty(
+		levelLogger, "namespaceMessagePrefix", d.gs(function () { return this.namespace; })
+	);
+};
 
-var conf = Object.create(null);
+module.exports = () => {
+	// Ensure it's the only log4 writer initialzed in a process
+	registerMaster();
 
-// Setup visibility
-// Resolve from LOG_* env vars
-logger.predefinedLevels.forEach(function (level) {
-	var varName = "LOG_" + level.toUpperCase();
-	if (process.env[varName]) conf[level] = process.env[varName].split(",");
-});
-// Eventually support as fallback DEBUG env var
-if (!conf.debug && process.env.DEBUG) conf.debug = process.env.DEBUG.split(",");
-// Do not show debug level logs by default
-if (!conf.debug) conf.debug = [];
-conf.debug.unshift("-*");
-setupVisibility(conf);
+	// Read logs visiblity settings from env variables
+	setupVisibility(
+		process.env.LOG_LEVEL, (process.env.LOG_DEBUG || process.env.DEBUG || "").split(",")
+	);
 
-// Log
-logger.emitter.on("log", function (event) {
-	var currentLogger = event.logger;
-	var prefix = "[" + currentLogger.level + "]";
-	if (currentLogger.ns) prefix += "[" + currentLogger.ns + "]";
-	prefix += " ";
-	event.messagePrefix = prefix;
-	if (module.exports.prefixDecorator) prefix = module.exports.prefixDecorator(prefix);
-	event.messageText = format.apply(null, event.messageTokens);
-	console.log(prefix + event.messageText);
-});
+	// Resolve level and namespace log message prefixes
+	// - for already initialized loggers
+	rootLogger.getAllInitializedLevels().forEach(setupPrefixes);
+	// - for loggers to be initialized
+	emitter.on("init", event => { if (!event.logger.namespace) setupPrefixes(event.logger); });
+
+	// Write logs to stderr
+	emitter.on("log", event => {
+		if (!event.logger.isEnabled) return;
+		formatMessage(event);
+		console.error(event.message);
+	});
+};

package.json

@@ -18,14 +18,24 @@
     "url": "git://github.com/medikoo/log4-aws-lambda.git"
   },
   "dependencies": {
-    "log4": "1"
+    "d": "1",
+    "log4-nodejs": "1"
   },
   "devDependencies": {
-    "eslint": "^4.5",
-    "eslint-config-medikoo-es5": "^1.4.3"
+    "cjs-module": "^1.3",
+    "eslint": "^4.19.1",
+    "eslint-config-medikoo": "^1.35",
+    "istanbul": "^0.4.5",
+    "log4": "2",
+    "process-utils": "^1.1",
+    "tape": "^4.9",
+    "tape-index": "2"
+  },
+  "peerDependencies": {
+    "log4": "2"
   },
   "eslintConfig": {
-    "extends": "medikoo-es5",
+    "extends": "medikoo",
     "root": true,
     "env": {
       "node": true
@@ -35,7 +45,10 @@
     }
   },
   "scripts": {
-    "lint": "eslint --ignore-path=.gitignore ."
+    "coverage": "tape-index && istanbul cover test.index.js",
+    "check-coverage": "npm run coverage && istanbul check-coverage --statements 100 --function 100 --branches 100 --lines 100",
+    "lint": "eslint --ignore-path=.gitignore .",
+    "test": "tape-index && node test.index.js"
   },
   "license": "ISC"
 }

test/index.js

@@ -0,0 +1,36 @@
+"use strict";
+
+const test            = require("tape")
+    , requireUncached = require("cjs-module/require-uncached")
+    , overrideEnv     = require("process-utils/override-env");
+
+test("log4-aws-lambda", t => {
+	const { log, initializeWriter } = overrideEnv(() =>
+		requireUncached(
+			[
+				require.resolve("log4"), require.resolve("log4/writer-utils/emitter"),
+				require.resolve("log4/writer-utils/register-master"),
+				require.resolve("log4/writer-utils/setup-visibility"), require.resolve("../")
+			],
+			() => ({ log: require("log4"), initializeWriter: require("../") })
+		));
+	initializeWriter();
+	const originalWrite = console.error;
+	let isInvoked = false;
+	console.error = string => {
+		t.equal(
+			string,
+			`${ log.error.get("elo").levelMessagePrefix } ${
+				log.error.get("elo").namespaceMessagePrefix
+			} foo bar`,
+			"Should write logs for enabled loggers to stderr"
+		);
+		isInvoked = true;
+	};
+	log("not enabled");
+	t.equal(isInvoked, false, "Should not write logs of disabled loggers");
+	log.error.get("elo")("foo bar");
+	t.equal(isInvoked, true, "Should write logs immediately");
+	console.error = originalWrite;
+	t.end();
+});