# All files / util async_queue.ts

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     /**
     * Copyright 2017 Google Inc.
     *
     * Licensed under the Apache License, Version 2.0 (the "License");
     * you may not use this file except in compliance with the License.
     * You may obtain a copy of the License at
     *
     *   http://www.apache.org/licenses/LICENSE-2.0
     *
     * Unless required by applicable law or agreed to in writing, software
     * distributed under the License is distributed on an "AS IS" BASIS,
     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     * See the License for the specific language governing permissions and
     * limitations under the License.
     */

    import { assert, fail } from './assert';
    import * as log from './log';
    import { AnyJs } from './misc';
    import { Deferred, CancelablePromise } from './promise';
    import { Code, FirestoreError } from './error';

    // tslint:disable-next-line:no-any Accept any return type from setTimeout().
    type TimerHandle = any;

    /**
     * Wellknown "timer" IDs used when scheduling delayed operations on the
     * AsyncQueue. These IDs can then be used from tests to check for the presence
     * of operations or to run them early.
     *
     * The string values are used when encoding these timer IDs in JSON spec tests.
     */
    export enum TimerId {
      /** All can be used with runDelayedOperationsEarly() to run all timers. */
      All = 'all',

      /**
       * The following 4 timers are used in persistent_stream.ts for the listen and
       * write streams. The "Idle" timer is used to close the stream due to
       * inactivity. The "ConnectionBackoff" timer is used to restart a stream once
       * the appropriate backoff delay has elapsed.
       */
      ListenStreamIdle = 'listen_stream_idle',
      ListenStreamConnectionBackoff = 'listen_stream_connection_backoff',
      WriteStreamIdle = 'write_stream_idle',
      WriteStreamConnectionBackoff = 'write_stream_connection_backoff',

      /**
       * A timer used in online_state_tracker.ts to transition from
       * OnlineState.Unknown to Offline after a set timeout, rather than waiting
       * indefinitely for success or failure.
       */
      OnlineStateTimeout = 'online_state_timeout'
    }

    /**
     * Represents an operation scheduled to be run in the future on an AsyncQueue.
     *
     * It is created via DelayedOperation.createAndSchedule().
     *
     * Supports cancellation (via cancel()) and early execution (via skipDelay()).
     */
    class DelayedOperation<T> implements CancelablePromise<T> {
      // handle for use with clearTimeout(), or null if the operation has been
      // executed or canceled already.
      private timerHandle: TimerHandle | null;

      private readonly deferred = new Deferred<T>();

      private constructor(
        private readonly asyncQueue: AsyncQueue,
        readonly timerId: TimerId,
        readonly targetTimeMs: number,
        private readonly op: () => Promise<T>,
        private readonly removalCallback: (op: DelayedOperation<T>) => void
      ) {
        // It's normal for the deferred promise to be canceled (due to cancellation)
        // and so we attach a dummy catch callback to avoid
        // 'UnhandledPromiseRejectionWarning' log spam.
        this.deferred.promise.catch(err => {});
      }

      /**
       * Creates and returns a DelayedOperation that has been scheduled to be
       * executed on the provided asyncQueue after the provided delayMs.
       *
       * @param asyncQueue The queue to schedule the operation on.
       * @param id A Timer ID identifying the type of operation this is.
       * @param delayMs The delay (ms) before the operation should be scheduled.
       * @param op The operation to run.
       * @param removalCallback A callback to be called synchronously once the
       *   operation is executed or canceled, notifying the AsyncQueue to remove it
       *   from its delayedOperations list.
       *   PORTING NOTE: This exists to prevent making removeDelayedOperation() and
       *   the DelayedOperation class public.
       */
      static createAndSchedule<T>(
        asyncQueue: AsyncQueue,
        timerId: TimerId,
        delayMs: number,
        op: () => Promise<T>,
        removalCallback: (op: DelayedOperation<T>) => void
      ): DelayedOperation<T> {
        const targetTime = Date.now() + delayMs;
        const delayedOp = new DelayedOperation(
          asyncQueue,
          timerId,
          targetTime,
          op,
          removalCallback
        );
        delayedOp.start(delayMs);
        return delayedOp;
      }

      /**
       * Starts the timer. This is called immediately after construction by
       * createAndSchedule().
       */
      private start(delayMs: number): void {
        this.timerHandle = setTimeout(() => this.handleDelayElapsed(), delayMs);
      }

      /**
       * Queues the operation to run immediately (if it hasn't already been run or
       * canceled).
       */
      skipDelay(): void {
        return this.handleDelayElapsed();
      }

      /**
       * Cancels the operation if it hasn't already been executed or canceled. The
       * promise will be rejected.
       *
       * As long as the operation has not yet been run, calling cancel() provides a
       * guarantee that the operation will not be run.
       */
      cancel(reason?: string): void {
        if (this.timerHandle !== null) {
          this.clearTimeout();
          this.deferred.reject(
            new FirestoreError(
              Code.CANCELLED,
              'Operation cancelled' + (reason ? ': ' + reason : '')
            )
          );
        }
      }

      // Promise implementation.
      readonly [Symbol.toStringTag]: 'Promise';
      then = this.deferred.promise.then.bind(this.deferred.promise);
      catch = this.deferred.promise.catch.bind(this.deferred.promise);

      private handleDelayElapsed(): void {
        this.asyncQueue.enqueue(() => {
          if (this.timerHandle !== null) {
            this.clearTimeout();
            return this.op().then(result => {
              return this.deferred.resolve(result);
            });
          } else {
            return Promise.resolve();
          }
        });
      }

      private clearTimeout() {
        Eif (this.timerHandle !== null) {
          this.removalCallback(this);
          clearTimeout(this.timerHandle);
          this.timerHandle = null;
        }
      }
    }

    export class AsyncQueue {
      // The last promise in the queue.
      private tail: Promise<AnyJs | void> = Promise.resolve();

      // Operations scheduled to be queued in the future. Operations are
      // automatically removed after they are run or canceled.
      private delayedOperations: Array<DelayedOperation<AnyJs>> = [];

      // visible for testing
      failure: Error;

      // Flag set while there's an outstanding AsyncQueue operation, used for
      // assertion sanity-checks.
      private operationInProgress = false;

      /**
       * Adds a new operation to the queue. Returns a promise that will be resolved
       * when the promise returned by the new operation is (with its value).
       */
      enqueue<T>(op: () => Promise<T>): Promise<T> {
        this.verifyNotFailed();
        const newTail = this.tail.then(() => {
          this.operationInProgress = true;
          return op()
            .catch(error => {
              this.failure = error;
              this.operationInProgress = false;
              const message = error.stack || error.message || '';
              log.error('INTERNAL UNHANDLED ERROR: ', message);

              // Escape the promise chain and throw the error globally so that
              // e.g. any global crash reporting library detects and reports it.
              // (but not for simulated errors in our tests since this breaks mocha)
              Iif (message.indexOf('Firestore Test Simulated Error') < 0) {
                setTimeout(() => {
                  throw error;
                }, 0);
              }

              // Re-throw the error so that this.tail becomes a rejected Promise and
              // all further attempts to chain (via .then) will just short-circuit
              // and return the rejected Promise.
              throw error;
            })
            .then(result => {
              this.operationInProgress = false;
              return result;
            });
        });
        this.tail = newTail;
        return newTail;
      }

      /**
       * Schedules an operation to be queued on the AsyncQueue once the specified
       * `delayMs` has elapsed. The returned CancelablePromise can be used to cancel
       * the operation prior to its running.
       */
      enqueueAfterDelay<T>(
        timerId: TimerId,
        delayMs: number,
        op: () => Promise<T>
      ): CancelablePromise<T> {
        this.verifyNotFailed();

        // While not necessarily harmful, we currently don't expect to have multiple
        // ops with the same timer id in the queue, so defensively reject them.
        assert(
          !this.containsDelayedOperation(timerId),
          `Attempted to schedule multiple operations with timer id ${timerId}.`
        );

        const delayedOp = DelayedOperation.createAndSchedule(
          this,
          timerId,
          delayMs,
          op,
          op => this.removeDelayedOperation(op)
        );
        this.delayedOperations.push(delayedOp);

        return delayedOp;
      }

      private verifyNotFailed(): void {
        if (this.failure) {
          fail(
            'AsyncQueue is already failed: ' +
              (this.failure.stack || this.failure.message)
          );
        }
      }

      /**
       * Verifies there's an operation currently in-progress on the AsyncQueue.
       * Unfortunately we can't verify that the running code is in the promise chain
       * of that operation, so this isn't a foolproof check, but it should be enough
       * to catch some bugs.
       */
      verifyOperationInProgress(): void {
        assert(
          this.operationInProgress,
          'verifyOpInProgress() called when no op in progress on this queue.'
        );
      }

      /**
       * Waits until all currently queued tasks are finished executing. Delayed
       * operations are not run.
       */
      drain(): Promise<void> {
        return this.enqueue(() => Promise.resolve());
      }

      /**
       * For Tests: Determine if a delayed operation with a particular TimerId
       * exists.
       */
      containsDelayedOperation(timerId: TimerId): boolean {
        return this.delayedOperations.findIndex(op => op.timerId === timerId) >= 0;
      }

      /**
       * For Tests: Runs some or all delayed operations early.
       *
       * @param lastTimerId Delayed operations up to and including this TimerId will
       *  be drained. Throws if no such operation exists. Pass TimerId.All to run
       *  all delayed operations.
       * @returns a Promise that resolves once all operations have been run.
       */
      runDelayedOperationsEarly(lastTimerId: TimerId): Promise<void> {
        // Note that draining may generate more delayed ops, so we do that first.
        return this.drain().then(() => {
          assert(
            lastTimerId === TimerId.All ||
              this.containsDelayedOperation(lastTimerId),
            `Attempted to drain to missing operation ${lastTimerId}`
          );

          // Run ops in the same order they'd run if they ran naturally.
          this.delayedOperations.sort((a, b) => a.targetTimeMs - b.targetTimeMs);

          for (const op of this.delayedOperations) {
            op.skipDelay();
            if (lastTimerId !== TimerId.All && op.timerId === lastTimerId) {
              break;
            }
          }

          return this.drain();
        });
      }

      /** Called once a DelayedOperation is run or canceled. */
      private removeDelayedOperation<T>(op: DelayedOperation<T>) {
        // NOTE: indexOf / slice are O(n), but delayedOperations is expected to be small.
        const index = this.delayedOperations.indexOf(op);
        assert(index >= 0, 'Delayed operation not found.');
        this.delayedOperations.splice(index, 1);
      }
    }