const http = require('http')
function compose(middlewareList) {
  return function (ctx) {
    function dispatch (i) {
      const fn = middlewareList[i]
      try {
        return Promise.resolve(fn(ctx, dispatch.bind(null, i + 1)))
      } catch (err) {
        Promise.reject(err)
      }
    } 
    return dispatch(0)
  }
}
class App {
  constructor(){
    this.middlewares = []
  }
  use(fn){
    this.middlewares.push(fn)
    return this
  }
  handleRequest(ctx, middleware) {
    return middleware(ctx)
  }
  createContext (req, res) {
    const ctx = {
      req,
      res
    }
    return ctx
  }
  callback () {
    const fn = compose(this.middlewares)
    return (req, res) => {
      const ctx = this.createContext(req, res)
      return this.handleRequest(ctx, fn)
    }
  }
  listen(...args) {
    const server = http.createServer(this.callback())
    return server.listen(...args)
  }
}
module.exports = App