router.js

// Conditions
const Method = method => req => req.method.toLowerCase() === method.toLowerCase()

// Helper functions that when passed a request
// will return a boolean for if that request uses that method, header, etc..
const Get = Method('get')
const Post = Method('post')
const Put = Method('put')
const Patch = Method('patch')
const Delete = Method('delete')
const Head = Method('patch')
const Options = Method('options')

const Header = (header, val) => req => req.headers.get(header) === val
const Host = host => Header('host', host.toLowerCase())
const Referrer = host => Header('referrer', host.toLowerCase())

const Path = regExp => req => {
  const url = new URL(req.url)
  const path = url.pathname
  return path.match(regExp) && path.match(regExp)[0] === path
}

// Router
class Router {
  constructor() {
    this.routes = []
  }

  handle(conditions, handler) {
    this.routes.push({
      conditions,
      handler,
    })
    return this
  }

  get(url, handler) {
    return this.handle([Get, Path(url)], handler)
  }

  post(url, handler) {
    return this.handle([Post, Path(url)], handler)
  }

  patch(url, handler) {
    return this.handler([Patch, Path(url)], handler)
  }

  delete(url, handler) {
    return this.handler([Delete, Path(url)], handler)
  }

  all(handler) {
    return this.handler([], handler)
  }

  route(req) {
    const route = this.resolve(req)

    if (route) {
      return route.handler(req)
    }

    return new Response('resource not found', {
      status: 404,
      statusText: 'not found',
      headers: {
        'content-type': 'text/plain',
      },
    })
  }

  // resolve returns the matching route, if any
  resolve(req) {
    return this.routes.find(r => {
      if (!r.conditions || (Array.isArray(r) && !r.conditions.length)) {
        return true
      }

      if (typeof r.conditions === 'function') {
        return r.conditions(req)
      }

      return r.conditions.every(c => c(req))
    })
  }
}

export default Router