// Copyright (c) 2020, Compiler Explorer Authors
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
//     * Redistributions of source code must retain the above copyright notice,
//       this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above copyright
//       notice, this list of conditions and the following disclaimer in the
//       documentation and/or other materials provided with the distribution.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
// POSSIBILITY OF SUCH DAMAGE.

import {executionAsyncId} from 'node:async_hooks';

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

import {PropertyGetter} from './properties.interfaces.js';

// 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 whose promise settled (fulfilled or rejected); a wedged job never counts',
});
const queueStale = new PromClient.Counter({
    name: 'ce_compilation_queue_stale_total',
    help: 'Total number of jobs abandoned before starting as they were stale',
});

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

export type EnqueueOptions = {
    abandonIfStale?: boolean;
    highPriority?: boolean;
};

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

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

    static fromProps(ceProps: PropertyGetter) {
        return new CompilationQueue(
            ceProps('maxConcurrentCompiles', 1),
            ceProps('compilationEnvTimeoutMs', 300_000),
            ceProps('compilationStaleAfterMs', 60_000),
        );
    }

    enqueue<Result>(job: Job<Result>, options?: EnqueueOptions): PromiseLike<Result> {
        const enqueueAsyncId = executionAsyncId();
        const enqueuedAt = Date.now();

        // 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(
            () => {
                const dequeuedAt = Date.now();
                queueDequeued.inc();
                if (options?.abandonIfStale && dequeuedAt > enqueuedAt + this._staleAfterMs) {
                    queueCompleted.inc();
                    queueStale.inc();
                    const queueTimeSecs = (dequeuedAt - enqueuedAt) / 1000;
                    const limitSecs = this._staleAfterMs / 1000;
                    throw new Error(
                        `Compilation was in the queue too long (${queueTimeSecs.toFixed(1)}s > ${limitSecs.toFixed(
                            1,
                        )}s)`,
                    );
                }
                const jobAsyncId = executionAsyncId();
                if (this._running.has(jobAsyncId)) {
                    throw new Error('somehow we entered the context twice');
                }
                try {
                    this._running.add(jobAsyncId);
                    const result = job();
                    // Count completion when the job settles (even by rejection), not when it
                    // merely returns its promise. Deliberately not awaited here: a job that
                    // never settles must not hold _running (and so status().busy) forever.
                    Promise.resolve(result).then(
                        () => queueCompleted.inc(),
                        () => queueCompleted.inc(),
                    );
                    return result;
                } finally {
                    this._running.delete(jobAsyncId);
                }
            },
            {priority: options?.highPriority ? 100 : 0},
        );
    }

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