// Copyright (c) 2020, Compiler Explorer Authors
// All rights reserved.
//
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import {executionAsyncId} from 'async_hooks';

import {default as Queue} from 'p-queue';
import PromClient from 'prom-client';

// globals as essentially the compilation queue is a singleton, and if we make them members of the queue, tests fail as
// when we create a second queue, the previous counters are still registered.
const queueEnqueued = new PromClient.Counter({
    name: 'ce_compilation_queue_enqueued_total',
    help: 'Total number of jobs enqueued',
});
const queueDequeued = new PromClient.Counter({
    name: 'ce_compilation_queue_dequeued_total',
    help: 'Total number of jobs dequeued',
});
const queueCompleted = new PromClient.Counter({
    name: 'ce_compilation_queue_completed_total',
    help: 'Total number of jobs completed',
});

export type Job<TaskResultType> = () => PromiseLike<TaskResultType>;

export class CompilationQueue {
    private readonly _running: Set<number> = new Set();
    private readonly _queue: Queue;

    constructor(concurrency: number, timeout: number) {
        this._queue = new Queue({
            concurrency,
            timeout,
            throwOnTimeout: true,
        });
    }

    static fromProps(ceProps) {
        return new CompilationQueue(ceProps('maxConcurrentCompiles', 1), ceProps('compilationEnvTimeoutMs'));
    }

    enqueue<Result>(job: Job<Result>): PromiseLike<Result> {
        const enqueueAsyncId = executionAsyncId();
        // If we're asked to enqueue a job when we're already in a async queued job context, just run it.
        // This prevents a deadlock.
        if (this._running.has(enqueueAsyncId)) return job();
        queueEnqueued.inc();
        return this._queue.add(() => {
            queueDequeued.inc();
            const jobAsyncId = executionAsyncId();
            if (this._running.has(jobAsyncId)) throw new Error('somehow we entered the context twice');
            try {
                this._running.add(jobAsyncId);
                return job();
            } finally {
                this._running.delete(jobAsyncId);
                queueCompleted.inc();
            }
        }) as PromiseLike<Result>; // TODO(supergrecko): investigate why this assert is needed
    }

    status(): {busy: boolean; pending: number; size: number} {
        const pending = this._queue.pending;
        const size = this._queue.size;
        return {
            busy: pending > 0 || size > 0,
            pending,
            size,
        };
    }
}