// 文件 koa/examples/middleware/app.js
const Koa = require('../../lib/application');

// const Koa = require('koa');
// 这里打个断点
const app = new Koa();
// x-response-time

// 这里打个断点
app.use(async (ctx, next) => {

});

class Emitter{
  // node 内置模块
  constructor(){
  }
}
class Koa extends Emitter{
  constructor(options){
    super();
    options = options || {};
    this.middleware = [];
    this.context = {
      method: 'GET',
      url: '/url',
      body: undefined,
      set: function(key, val){
        console.log('context.set', key, val);
      },
    };
  }
  use(fn){
    this.middleware.push(fn);
    return this;
  }
  listen(){
    const  fnMiddleware = compose(this.middleware);
    const ctx = this.context;
    const handleResponse = () => respond(ctx);
    const onerror = function(){
      console.log('onerror');
    };
    fnMiddleware(ctx).then(handleResponse).catch(onerror);
  }
}
function respond(ctx){
  console.log('handleResponse');
  console.log('response.end', ctx.body);
}

function compose (middleware) {
  if (!Array.isArray(middleware)) throw new TypeError('Middleware stack must be an array!')
  for (const fn of middleware) {
    if (typeof fn !== 'function') throw new TypeError('Middleware must be composed of functions!')
  }

 //  传入对象 context 返回Promise
  return function (context, next) {
    // last called middleware #
    let index = -1
    return dispatch(0)
    function dispatch (i) {
      if (i <= index) return Promise.reject(new Error('next() called multiple times'))
      index = i
      let fn = middleware[i]
      if (i === middleware.length) fn = next
      if (!fn) return Promise.resolve()
      try {
        return Promise.resolve(fn(context, dispatch.bind(null, i + 1)));
      } catch (err) {
        return Promise.reject(err)
      }
    }
  }
}

// 这样就可能更好理解了。
// simpleKoaCompose
const [fn1, fn2, fn3] = this.middleware;
const fnMiddleware = function(context){
    return Promise.resolve(
      fn1(context, function next(){
        return Promise.resolve(
          fn2(context, function next(){
              return Promise.resolve(
                  fn3(context, function next(){
                    return Promise.resolve();
                  })
              )
          })
        )
    })
  );
};
fnMiddleware(ctx).then(handleResponse).catch(onerror);

// application.js 文件
class Application extends Emitter {
  // 代码有简化组合
  listen(){
    const  fnMiddleware = compose(this.middleware);
    if (!this.listenerCount('error')) this.on('error', this.onerror);
    const onerror = err => ctx.onerror(err);
    fnMiddleware(ctx).then(handleResponse).catch(onerror);
  }
  onerror(err) {
    // 代码省略
    // ...
  }
}

module.exports = {
  onerror(){
    // delegate
    // app 是在new Koa() 实例
    this.app.emit('error', err, this);
  }
}

app.use(async (ctx, next) => {
  try {
    await next();
  } catch (err) {
    err.status = err.statusCode || err.status || 500;
    throw err;
  }
});

// Koa 将转换
app.use(function *(next) {
  const start = Date.now();
  yield next;
  const ms = Date.now() - start;
  console.log(`${this.method} ${this.url} - ${ms}ms`);
});

class Koa extends Emitter{
  use(fn) {
    if (typeof fn !== 'function') throw new TypeError('middleware must be a function!');
    if (isGeneratorFunction(fn)) {
      deprecate('Support for generators will be removed in v3. ' +
                'See the documentation for examples of how to convert old middleware ' +
                'https://github.com/koajs/koa/blob/master/docs/migration.md');
      fn = convert(fn);
    }
    debug('use %s', fn._name || fn.name || '-');
    this.middleware.push(fn);
    return this;
  }
}

function convert(){
 return function (ctx, next) {
    return co.call(ctx, mw.call(ctx, createGenerator(next)))
  }
  function * createGenerator (next) {
    return yield next()
  }
}

// 写一个请求简版请求
function request(ms= 1000) {
  return new Promise((resolve) => {
    setTimeout(() => {
      resolve({name: '若川'});
    }, ms);
  });
}

// 获取generator的值
function* generatorFunc(){
  const res = yield request();
  console.log(res, 'generatorFunc-res');
}
generatorFunc(); // 报告，我不会输出你想要的结果的

// await 函数 自动执行
async function asyncFunc(){
    const res = await request();
    console.log(res, 'asyncFunc-res await 函数 自动执行');
}
asyncFunc(); // 输出结果

// 获取generator的值
function* generatorFunc(){
  const res = yield request();
  console.log(res, 'generatorFunc-res');
}

function coSimple(gen){
  gen = gen();
  console.log(gen, 'gen');

  const ret = gen.next();
  const promise = ret.value;
  promise.then(res => {
    gen.next(res);
  });
}
coSimple(generatorFunc);
// 输出了想要的结果
// {name: "若川"}"generatorFunc-res"

const args = Array.prototype.slice.call(arguments, 1);
gen = gen.apply(ctx, args);

// 多个yeild，传参情况
function* generatorFunc(suffix = ''){
  const res = yield request();
  console.log(res, 'generatorFunc-res' + suffix);

  const res2 = yield request();
  console.log(res2, 'generatorFunc-res-2' + suffix);
}

function coSimple(gen){
  const ctx = this;
  const args = Array.prototype.slice.call(arguments, 1);
  gen = gen.apply(ctx, args);
  console.log(gen, 'gen');

  const ret = gen.next();
  const promise = ret.value;
  promise.then(res => {
    const ret = gen.next(res);
    const promise = ret.value;
      promise.then(res => {
        gen.next(res);
      });
  });
}

coSimple(generatorFunc, ' 哎呀，我真的是后缀');

function* generatorFunc(suffix = ''){
  const res = yield request();
  console.log(res, 'generatorFunc-res' + suffix);

  const res2 = yield request();
  console.log(res2, 'generatorFunc-res-2' + suffix);

  const res3 = yield request();
  console.log(res3, 'generatorFunc-res-3' + suffix);

  const res4 = yield request();
  console.log(res4, 'generatorFunc-res-4' + suffix);
}

function coSimple(gen){
  const ctx = this;
  const args = Array.prototype.slice.call(arguments, 1);
  gen = gen.apply(ctx, args);
  console.log(gen, 'gen');

  return new Promise((resolve, reject) => {

    onFulfilled();

    function onFulfilled(res){
      const ret = gen.next(res);
      next(ret);
    }

    function next(ret) {
      const promise = ret.value;
      promise && promise.then(onFulfilled);
    }

  });
}

coSimple(generatorFunc, ' 哎呀，我真的是后缀');

function co(gen) {
  var ctx = this;
  var args = slice.call(arguments, 1)

  // we wrap everything in a promise to avoid promise chaining,
  // which leads to memory leak errors.
  // see https://github.com/tj/co/issues/180
  return new Promise(function(resolve, reject) {
    // 把参数传递给gen函数并执行
    if (typeof gen === 'function') gen = gen.apply(ctx, args);
    // 如果不是函数 直接返回
    if (!gen || typeof gen.next !== 'function') return resolve(gen);

    onFulfilled();

    /**
     * @param {Mixed} res
     * @return {Promise}
     * @api private
     */

    function onFulfilled(res) {
      var ret;
      try {
        ret = gen.next(res);
      } catch (e) {
        return reject(e);
      }
      next(ret);
    }

    /**
     * @param {Error} err
     * @return {Promise}
     * @api private
     */

    function onRejected(err) {
      var ret;
      try {
        ret = gen.throw(err);
      } catch (e) {
        return reject(e);
      }
      next(ret);
    }

    /**
     * Get the next value in the generator,
     * return a promise.
     *
     * @param {Object} ret
     * @return {Promise}
     * @api private
     */

    // 反复执行调用自己
    function next(ret) {
      // 检查当前是否为 Generator 函数的最后一步，如果是就返回
      if (ret.done) return resolve(ret.value);
      // 确保返回值是promise对象。
      var value = toPromise.call(ctx, ret.value);
      // 使用 then 方法，为返回值加上回调函数，然后通过 onFulfilled 函数再次调用 next 函数。
      if (value && isPromise(value)) return value.then(onFulfilled, onRejected);
      // 在参数不符合要求的情况下（参数非 Thunk 函数和 Promise 对象），将 Promise 对象的状态改为 rejected，从而终止执行。
      return onRejected(new TypeError('You may only yield a function, promise, generator, array, or object, '
        + 'but the following object was passed: "' + String(ret.value) + '"'));
    }
  });
}

// 这样就可能更好理解了。
// simpleKoaCompose
const [fn1, fn2, fn3] = this.middleware;
const fnMiddleware = function(context){
    return Promise.resolve(
      fn1(context, function next(){
        return Promise.resolve(
          fn2(context, function next(){
              return Promise.resolve(
                  fn3(context, function next(){
                    return Promise.resolve();
                  })
              )
          })
        )
    })
  );
};
fnMiddleware(ctx).then(handleResponse).catch(onerror);

ctx.onerror = function {
  this.app.emit('error', err, this);
};
  listen(){
    const  fnMiddleware = compose(this.middleware);
    if (!this.listenerCount('error')) this.on('error', this.onerror);
    const onerror = err => ctx.onerror(err);
    fnMiddleware(ctx).then(handleResponse).catch(onerror);
  }
  onerror(err) {
    // 代码省略
    // ...
  }