<script>
// 实现带有并发控制的promise.all，返回的结果顺序需要和传入的promise顺序一致
// myAll(promises, parallelLimit);
// myAll([promise1, promise2, promise3], 2)
const promise1  = function() {
  return new Promise((resolve, reject) => {
    console.log('promise1执行了');
    setTimeout(() => {
      console.log('promise1');
      resolve(1);
    }, 3000)
  });
}

const promise2  = function() {
  return new Promise((resolve, reject) => {
    console.log('promise2执行了');
    setTimeout(() => {
      console.log('promise2');
      resolve(2);
    }, 5000)
  });
}

const promise3  = function() {
  console.log('promise3执行了');
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      console.log('promise3');
      resolve(3);
    }, 1000)
  });
}

// const b = a();
// b.then(res => {
//   console.log(res);
// });


// 实现带有并发控制的promise.all，返回的结果顺序需要和传入的promise顺序一致
// myAll(promises, parallelLimit);
// myAll([promise1, promise2, promise3], 2)

function myAll(promises = [], parallelLimit) {
  let result = [],
    runCount = 0,
    queue = [];

  return new Promise((resolve, reject) => {
    const runPromise = (promiseFn, i) => {
      if (runCount < parallelLimit) {
        const promise = promiseFn();
        runCount += 1;
        promise.then(res => {
          console.log(`promise${i + 1}完成了`);
          result[i] = res;
          runCount -= 1;
          if (runCount === 0) {
            resolve(result);
          } else {
            if (queue.length) {
              const { promiseFn, i} = queue.shift();
              runPromise(promiseFn, i);
            }
          }
        });
      } else {
        queue.push({
          promiseFn: promiseFn,
          i: i,
        })
      }
    };
    for (let i = 0; i < promises.length; i++) {
      const promiseFn = promises[i];
      if (typeof promiseFn === 'function') {
        runPromise(promiseFn, i);
      }
    }
  });

  // 通过队列和递归的方法实现
  // return new Promise((resolve, reject) => {
  //   for (let i = 0; i < promises.length; i++) {
  //     const promiseFn = promises[i];
  //     if (typeof promiseFn === 'function') {
  //       queue.push({
  //         promiseFn: promiseFn,
  //         i: i,
  //       })
  //     }
  //   }
  //   const runPromise = () => {
  //     if (runCount < parallelLimit) {
  //       if (queue.length) {
  //         const { promiseFn, i} = queue.shift();
  //         const promise = promiseFn();
  //         runCount += 1;
  //         promise.then(res => {
  //           console.log(`promise${i + 1}完成了`);
  //           result[i] = res;
  //           runCount -= 1;
  //           if (runCount === 0) {
  //             resolve(result);
  //           } else {
  //             runPromise();
  //           }
  //         });
  //         runPromise();
  //       }
  //     }
  //   };
  //   runPromise();
  // });
}

const promises = [promise1, promise2, promise3];
myAll(promises, 2).then(res => {
  console.log(res);
});
</script>