const http = require('http');

const compose = require('./compose');

class Koa {

  constructor() {

    this.ctx = {};

    this.middleWares = [];

  }

  use(fn) {

    this.middleWares.push(fn);

  }

  handler(ctx, fnMiddleware) {

    fnMiddleware(ctx);

  }

  callback() {

    const fn = compose(this.middleWares);

    const handleRequest = () => {

      this.handler(this.ctx, fn);

    };

    return handleRequest;

  }

  listen(...args) {

    const server = http.createServer(this.callback());

    server.listen(...args);

  }

}

module.exports = Koa;

function compose(middleWare) {

  return function fnMiddleWare(ctx) {

    function dispatch(i) {

      const fn = middleWare[i];

      if (!fn) return Promise.resolve();

      try {

        return Promise.resolve(fn(ctx, dispatch.bind(null, i + 1)));

      } catch (error) {

        return Promise.reject(error);

      }

    }

    return dispatch(0);

  };

}

module.exports = compose;