/**
 * Copyright 2015 CANAL+ Group
 *
 * 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 log from "../../../log";
import type { CancellationSignal } from "../../../utils/task_canceller";
import type {
  ISegmentFetcher,
  ISegmentFetcherCallbacks,
  ISegmentLoaderContent,
} from "./segment_fetcher";
import type { ITaskFn, ITaskPrioritizerCallbacks } from "./task_prioritizer";
import type TaskPrioritizer from "./task_prioritizer";

/**
 * This function basically put in relation:
 *   - an `ISegmentFetcher`, which will be used to perform the segment requests
 *   - a `TaskPrioritizer`, which will handle the priority of a segment request
 *
 * and returns functions to fetch segments with a given priority.
 * @param {Object} prioritizer
 * @param {Object} fetcher
 * @returns {Object}
 */
export default function applyPrioritizerToSegmentFetcher<TSegmentDataType>(
  prioritizer: TaskPrioritizer<void>,
  fetcher: ISegmentFetcher<TSegmentDataType>,
): IPrioritizedSegmentFetcher<TSegmentDataType> {
  /**
   * Map Promises returned by the `createRequest` method into the actual tasks
   * used by the `TaskPrioritizer`, allowing to update task priorities just by
   * using the Promise.
   */
  const taskHandlers = new WeakMap<Promise<void>, ITaskFn<void>>();

  return {
    /**
     * Create a Segment request with a given priority.
     * @param {Object} content - content to request
     * @param {Number} priority - priority at which the content should be requested.
     * Lower number == higher priority.
     * @param {Object} callbacks
     * @param {Object} cancelSignal
     * @returns {Promise}
     */
    createRequest(
      content: ISegmentLoaderContent,
      priority: number,
      callbacks: IPrioritizedSegmentFetcherCallbacks<TSegmentDataType>,
      cancelSignal: CancellationSignal,
    ): Promise<void> {
      const givenTask = (innerCancelSignal: CancellationSignal) => {
        return fetcher(content, callbacks, innerCancelSignal);
      };
      const ret = prioritizer.create(givenTask, priority, callbacks, cancelSignal);
      taskHandlers.set(ret, givenTask);
      return ret;
    },

    /**
     * Update the priority of a pending request, created through
     * `createRequest`.
     * @param {Promise} task - The Promise returned by `createRequest`.
     * @param {Number} priority - The new priority value.
     */
    updatePriority(task: Promise<void>, priority: number): void {
      const correspondingTask = taskHandlers.get(task);
      if (correspondingTask === undefined) {
        log.warn("Fetchers: Cannot update the priority of a request: task not found.");
        return;
      }
      prioritizer.updatePriority(correspondingTask, priority);
    },
  };
}

/** Oject returned by `applyPrioritizerToSegmentFetcher`. */
export interface IPrioritizedSegmentFetcher<TSegmentDataType> {
  /** Create a new request for a segment with a given priority. */
  createRequest: (
    content: ISegmentLoaderContent,
    priority: number,
    callbacks: IPrioritizedSegmentFetcherCallbacks<TSegmentDataType>,
    cancellationSignal: CancellationSignal,
  ) => Promise<void>;

  /** Update priority of a request created through `createRequest`. */
  updatePriority: (task: Promise<void>, priority: number) => void;
}

/** Callbacks awaited by `applyPrioritizerToSegmentFetcher`. */
export type IPrioritizedSegmentFetcherCallbacks<TSegmentDataType> =
  ISegmentFetcherCallbacks<TSegmentDataType> & ITaskPrioritizerCallbacks;