// new Promise((resolve, reject) => {
//   resolve('1')
// })

// promise 三种状态，从pending变为其他两种状态，一旦改变就不会再变化了
const PENDING = 'pending';
const FULFILLED = 'fulfilled';
const REJECTED = 'rejected';

class MyPromise {
  constructor(executor) {
    // 捕获执行器中的报错
    try{
      executor(this.resolve, this.reject)
    } catch(e) {
      this.reject(e)
    }
  }

  status = PENDING;
  value = undefined;
  reason = undefined;
  successCallback = [];
  failCallback = [];

  // 在executor中被调用 需要用箭头函数绑定当前实例的this
  resolve = (value) => {
    // 状态从pending只能改变一次
    if (this.status !== PENDING) return
    this.status = FULFILLED
    // 成功的值，作为成功callback的参数
    this.value = value
    // executor异步时，改变状态后，调用回调函数
    // this.successCallback && this.successCallback(value)
    while(this.successCallback.length) {
      this.successCallback.shift()()
    }
  }
  // 在executor中被调用 需要用箭头函数绑定当前实例的this
  reject = (reason) => {
    // 状态从pending只能改变一次
    if (this.status !== PENDING) return
    this.status = REJECTED
    // 失败的值，作为失败callback的参数
    this.reason = reason
    // executor异步时，改变状态后，调用回调函数
    // this.failCallback && this.failCallback(reason)
    while(this.failCallback.length) {
      this.failCallback.shift()()
    }
  }
  then(successCallback, failCallback) {
    // 如果没有声明成功失败回调时，默认把成功值跟失败原因继续传递
    successCallback = successCallback ? successCallback : value => value;
    failCallback = failCallback ? failCallback : reason => {throw reason};
    let newPromise = new MyPromise((resolve ,reject) => {
      if (this.status === FULFILLED) {
        // 用setTimeout异步，才能获取new出来的对象传递给下面的代码处理
        setTimeout(() => {
          try {
            // 捕获回调执行中的报错
            let result = successCallback(this.value)
            // 根据返回值判断类型再处理
            handleReturn(newPromise,result, resolve, reject)
          } catch(e) {
            reject(e)
          }
          
        }, 0)
      } else if(this.status === REJECTED) {
        // 用setTimeout异步，才能获取new出来的对象传递给下面的代码处理
        setTimeout(() => {
          try {
            // 捕获回调执行中的报错
            let result = failCallback(this.reason)
            // 根据返回值判断类型再处理
            handleReturn(newPromise,result, resolve, reject)
          } catch(e) {
            reject(e)
          }
          
        }, 0)
      } else {
        // 处理executor异步情况,且注册了多个回调时
        this.successCallback.push(() => {
          setTimeout(() => {
            try {
              // 捕获回调执行中的报错
              let result = successCallback(this.value)
              // 根据返回值判断类型再处理
              handleReturn(newPromise,result, resolve, reject)
            } catch(e) {
              reject(e)
            }
            
          }, 0)
        });
        this.failCallback.push(() => {
          // 用setTimeout异步，才能获取new出来的对象传递给下面的代码处理
          setTimeout(() => {
            try {
              // 捕获回调执行中的报错
              let result = failCallback(this.reason)
              // 根据返回值判断类型再处理
              handleReturn(newPromise,result, resolve, reject)
            } catch(e) {
              reject(e)
            }
            
          }, 0)
        });
      }
    });
    
    return newPromise;
  }

  finally(callback) {
    return this.then(value=> {
      return MyPromise.resolve(callback()).then(()=>value);
    }, reason => {
      return MyPromise.resolve(callback()).then(() => {throw reason})
    })
  }

  catch(callback) {
    return this.then(undefined, callback)
  }

  static all(array) {
    let result = [];
    let index = 0;
    
    return new MyPromise((resolve, reject) => {
      function addData (key, value) {
        result[key] = value;
        index++;
        // 当array中有异步操作时，等待完成后再resolve
        if (index === array.length) {
          resolve(result)
        }
      }
      for (let i = 0; i < array.length; i++) {
        let current = array[i];
        if (current instanceof MyPromise) {
          current.then(value => addData(i, value), reason => reject(reason))
        } else {
          addData(i, array[i])
        }
      }
    })
  }

  static resolve(value) {
    if (value instanceof MyPromise) {
      return value
    } else {
      return new MyPromise(resolve => resolve(value))
    }
  }

  static race(array) {
    return new MyPromise((resolve,reject) => {
      for(let item of array) {
        if(item instanceof MyPromise) {
          item.then(value => resolve(value)).catch(reason => reject(reason))
        } else {
          resolve(item)
        }
      }
    })
  }
}

function handleReturn(newPromise, result, resolve, reject) {
  if (newPromise === result) {
    return reject(new TypeError('Chaining cycle detected for promise #<Promise>'))
  }
  if (result instanceof MyPromise) {
    result.then(resolve, reject)
  } else {
    resolve(result)
  }
}