class AsyncQueue<T> {
    waitingEnqueue = new Array<() => void>()
    waitingDequeue = new Array<() => void>()
    enqueuePointer = 0
    dequeuePointer = 0
    queue = Array<T>()
    maxSize = 1

    async enqueue(x: T) {
        if ((this.queue.length + 1) > this.maxSize || this.waitingDequeue.length > 0) {
            this.dequeuePointer += 1
            await new Promise(r => this.waitingDequeue.unshift(r))
            this.waitingDequeue.pop()
        }

        this.queue.unshift(x)

        if (this.enqueuePointer > 0) {
            this.waitingEnqueue[this.enqueuePointer-1]()
            this.enqueuePointer -= 1
        }
    }

    async dequeue() {
        if (this.queue.length == 0 || this.waitingEnqueue.length > 0) {
            this.enqueuePointer += 1
            await new Promise(r => this.waitingEnqueue.unshift(r))
            this.waitingEnqueue.pop()
        }

        if (this.dequeuePointer > 0) {
            this.waitingDequeue[this.dequeuePointer - 1]()
            this.dequeuePointer -= 1
        }

        return this.queue.pop()!
    }
}