/**
 * 并行异步队列
 * 首次上传时占用最大的并行请求数
 * 后续当每个之前的请求结束后，继续执行下一个请求
 * 应用场景：分片文件上传
 *
 */
class WraperTask {
    task;
    finished;
    taskIndex;
    constructor(task, finished, taskIndex?) {
        this.task = task;
        this.finished = finished;
        this.taskIndex = taskIndex;
    }
}
class Task {
    maxParalleTask;
    taskResolve;
    queueResolve;
    taskQueue;
    currentTaskIndex;
    currentCount;
    /**
     *
     * @param {number} maxParalleTask 最大并行数量
     * @param {func} taskResolve 单个 task 的 resolve
     * @param {func} queueResolve 所有 task 完成的 resolve
     */
    constructor(maxParalleTask, taskResolve, queueResolve) {
        this.maxParalleTask = maxParalleTask;
        this.taskResolve = taskResolve;
        this.queueResolve = queueResolve;
        this.reset();
    }

    push(asyncTask) {
        return this.taskQueue.push(new WraperTask(asyncTask, false));
    }

    getTaskQueue() {
        return this.taskQueue.length;
    }

    getUnfinishedTaskQueue() {
        return this.taskQueue.reduce(function(accumulator, currentValue) {
            accumulator = currentValue.finished ? accumulator : accumulator.concat(currentValue);
            return accumulator;
        }, []);
    }

    paralleTask() {
        this.taskQueue
            .slice(0, Math.min(this.taskQueue.length, this.maxParalleTask) - 1)
            .forEach((singleTask, index) => {
                singleTask.taskIndex = index;
                singleTask.task().then(args => this._resolve(args, singleTask));
                this.currentTaskIndex += 1;
                this.currentCount += 1;
            });
    }

    _resolve(args, singleTask) {
        singleTask.finished = true;
        this.currentCount -= 1;
        if (this.taskResolve) {
            this.taskResolve(args);
        }
        // not finished
        console.log(`this.getUnfinishedTaskQueue`, this.getUnfinishedTaskQueue());
        if (this.getUnfinishedTaskQueue().length !== 0) {
            console.log('next task');
            if (this.currentCount < this.maxParalleTask) {
                this.dispatchNextTask();
            }
            return;
        }
        // finished
        if (this.queueResolve) {
            this.queueResolve();
        }
        this.reset();
    }

    dispatchNextTask() {
        const singleTask = this.taskQueue[this.currentTaskIndex];
        if (singleTask && singleTask.task) {
            singleTask.task().then(args => this._resolve(args, singleTask));
            this.currentTaskIndex += 1;
            this.currentCount += 1;
        }
    }

    reset() {
        this.taskQueue = [];
        this.currentTaskIndex = 0; // 执行到第几个 task
        this.currentCount = 0; // 当前执行的 task 的总数
    }
}

function handleAll() {
    console.log('all task resolved');
}
function handleResolve(data) {
    console.log('task resolved', data);
}

function MockTest() {
    let task = new Task(4, handleResolve, handleAll);
    for (let i = 0; i < 10; i++) {
        task.push(signleTask);
    }
    function signleTask() {
        return new Promise((resolve, reject) => {
            setTimeout(() => {
                resolve(Math.random());
            }, Math.random() * 10000);
        });
    }

    task.paralleTask();
}

MockTest();