/* @flow */

import map from './map.js';

const debug = require('debug')('yarn');

export default class BlockingQueue {
  constructor(alias: string, maxConcurrency?: number = Infinity) {
    this.concurrencyQueue = [];
    this.maxConcurrency = maxConcurrency;
    this.runningCount = 0;
    this.warnedStuck = false;
    this.alias = alias;
    this.first = true;

    this.running = map();
    this.queue = map();

    (this: any).stuckTick = this.stuckTick.bind(this);
  }

  concurrencyQueue: Array<() => void>;
  warnedStuck: boolean;
  maxConcurrency: number;
  runningCount: number;
  stuckTimer: ?number;
  alias: string;
  first: boolean;

  queue: {
    [key: string]: Array<{
      factory: () => Promise<any>,
      resolve: (val: any) => void,
      reject: Function,
    }>,
  };

  running: {
    [key: string]: boolean,
  };

  stillActive() {
    if (this.stuckTimer) {
      clearTimeout(this.stuckTimer);
    }

    this.stuckTimer = setTimeout(this.stuckTick, 5000);

    // We need to check the existense of unref because of https://github.com/facebook/jest/issues/4559
    // $FlowFixMe: Node's setInterval returns a Timeout, not a Number
    this.stuckTimer.unref && this.stuckTimer.unref();
  }

  stuckTick() {
    if (this.runningCount === 1) {
      this.warnedStuck = true;
      debug(
        `The ${JSON.stringify(this.alias)} blocking queue may be stuck. 5 seconds ` +
          `without any activity with 1 worker: ${Object.keys(this.running)[0]}`,
      );
    }
  }

  push<T>(key: string, factory: () => Promise<T>): Promise<T> {
    if (this.first) {
      this.first = false;
    } else {
      this.stillActive();
    }

    return new Promise((resolve, reject) => {
      // we're already running so push ourselves to the queue
      const queue = (this.queue[key] = this.queue[key] || []);
      queue.push({factory, resolve, reject});

      if (!this.running[key]) {
        this.shift(key);
      }
    });
  }

  shift(key: string) {
    if (this.running[key]) {
      delete this.running[key];
      this.runningCount--;
      clearTimeout(this.stuckTimer);

      if (this.warnedStuck) {
        this.warnedStuck = false;
        debug(`${JSON.stringify(this.alias)} blocking queue finally resolved. Nothing to worry about.`);
      }
    }

    const queue = this.queue[key];
    if (!queue) {
      return;
    }

    const {resolve, reject, factory} = queue.shift();
    if (!queue.length) {
      delete this.queue[key];
    }

    const next = () => {
      this.shift(key);
      this.shiftConcurrencyQueue();
    };

    const run = () => {
      this.running[key] = true;
      this.runningCount++;

      factory()
        .then(function(val): null {
          resolve(val);
          next();
          return null;
        })
        .catch(function(err) {
          reject(err);
          next();
        });
    };

    this.maybePushConcurrencyQueue(run);
  }

  maybePushConcurrencyQueue(run: () => void) {
    if (this.runningCount < this.maxConcurrency) {
      run();
    } else {
      this.concurrencyQueue.push(run);
    }
  }

  shiftConcurrencyQueue() {
    if (this.runningCount < this.maxConcurrency) {
      const fn = this.concurrencyQueue.shift();
      if (fn) {
        fn();
      }
    }
  }
}
