/**
 * 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 { IRepresentationIndex, ISegment } from "../../../manifest";
import type { ILocalIndex, ILocalIndexSegment } from "./types";

export default class LocalRepresentationIndex implements IRepresentationIndex {
  private _index: ILocalIndex;
  private _representationId: string;
  constructor(index: ILocalIndex, representationId: string) {
    this._index = index;
    this._representationId = representationId;
  }

  /**
   * @returns {Object}
   */
  getInitSegment(): ISegment | null {
    return {
      id: `${this._representationId}_init`,
      isInit: true,
      time: 0,
      end: 0,
      duration: 0,
      timescale: 1,
      url: null,
      complete: true,
      privateInfos: {
        localManifestInitSegment: { load: this._index.loadInitSegment },
      },
    };
  }

  /**
   * @param {Number} up
   * @param {Number} duration
   * @returns {Array.<Object>}
   */
  getSegments(up: number, duration: number): ISegment[] {
    const startTime = up;
    const endTime = up + duration;
    const wantedSegments: ILocalIndexSegment[] = [];
    for (const segment of this._index.segments) {
      const segmentStart = segment.time;
      if (endTime <= segmentStart) {
        break;
      }
      const segmentEnd = segment.time + segment.duration;
      if (segmentEnd > startTime) {
        wantedSegments.push(segment);
      }
    }

    return wantedSegments.map((wantedSegment) => {
      return {
        id: `${this._representationId}_${wantedSegment.time}`,
        isInit: false,
        time: wantedSegment.time,
        end: wantedSegment.time + wantedSegment.duration,
        duration: wantedSegment.duration,
        timescale: 1,
        timestampOffset: wantedSegment.timestampOffset,
        url: null,
        complete: true,
        privateInfos: {
          localManifestSegment: {
            load: this._index.loadSegment,
            segment: wantedSegment,
          },
        },
      };
    });
  }

  /**
   * @returns {Number|undefined}
   */
  getFirstAvailablePosition(): number | undefined {
    if (this._index.segments.length === 0) {
      return undefined;
    }
    const firstSegment = this._index.segments[0];
    return firstSegment.time;
  }

  /**
   * @returns {Number|undefined}
   */
  getLastAvailablePosition(): number | undefined {
    if (this._index.segments.length === 0) {
      return undefined;
    }
    const lastSegment = this._index.segments[this._index.segments.length - 1];
    return lastSegment.time + lastSegment.duration;
  }

  /**
   * Returns the expected ending position of this RepresentationIndex.
   * `undefined` if unknown.
   * @returns {number|undefined}
   */
  getEnd(): number | undefined {
    if (this._index.isFinished) {
      return this.getLastAvailablePosition();
    }

    const { incomingRanges, segments } = this._index;
    if (incomingRanges === undefined || incomingRanges.length === 0) {
      // If incomingRanges is empty but not finished... It's ambiguous.
      return undefined;
    }
    const lastIncomingRange = incomingRanges[incomingRanges.length - 1];
    const futureEnd = lastIncomingRange.end;
    if (segments.length === 0) {
      return futureEnd;
    }
    const lastSegment = this._index.segments[this._index.segments.length - 1];
    return Math.max(lastSegment.time + lastSegment.duration, futureEnd);
  }

  /**
   * Returns:
   *   - `true` if in the given time interval, at least one new segment is
   *     expected to be available in the future.
   *   - `false` either if all segments in that time interval are already
   *     available for download or if none will ever be available for it.
   *   - `undefined` when it is not possible to tell.
   * @param {number} start
   * @param {number} end
   * @returns {boolean|undefined}
   */
  awaitSegmentBetween(start: number, end: number): boolean | undefined {
    if (this.isStillAwaitingFutureSegments()) {
      return false;
    }
    if (this._index.incomingRanges === undefined) {
      return undefined;
    }
    return this._index.incomingRanges.some(
      (range) => range.start < end && range.end > start,
    );
  }

  /**
   * @returns {Boolean}
   */
  shouldRefresh(): false {
    return false;
  }

  /**
   * @returns {Boolean}
   */
  isSegmentStillAvailable(): true {
    return true;
  }

  isStillAwaitingFutureSegments(): boolean {
    return !this._index.isFinished;
  }

  /**
   * @returns {Boolean}
   */
  canBeOutOfSyncError(): false {
    return false;
  }

  /**
   * @returns {null}
   */
  checkDiscontinuity(): null {
    return null;
  }

  /**
   * @returns {Boolean}
   */
  isInitialized(): true {
    return true;
  }

  initialize(): void {
    log.error("A `LocalRepresentationIndex` does not need to be initialized");
  }

  addPredictedSegments(): void {
    log.warn("Cannot add predicted segments to a `LocalRepresentationIndex`");
  }

  /**
   * Returns the `duration` of each segment in the context of its Manifest (i.e.
   * as the Manifest anounces them, actual segment duration may be different due
   * to approximations), in seconds.
   *
   * NOTE: we could here do a median or a mean but I chose to be lazy (and
   * more performant) by returning the duration of the first element instead.
   * As `isPrecize` is `false`, the rest of the code should be notified that
   * this is only an approximation.
   * @returns {number}
   */
  getTargetSegmentDuration(): { duration: number; isPrecize: boolean } | undefined {
    if (this._index.segments.length === 0) {
      return undefined;
    }
    return {
      duration: this._index.segments[0].duration,
      isPrecize: false,
    };
  }

  _replace(newIndex: LocalRepresentationIndex): void {
    this._index.segments = newIndex._index.segments;
    this._index.loadSegment = newIndex._index.loadSegment;
    this._index.loadInitSegment = newIndex._index.loadInitSegment;
  }

  _update(newIndex: LocalRepresentationIndex): void {
    const newSegments = newIndex._index.segments;
    if (newSegments.length <= 0) {
      return;
    }
    const insertNewIndexAtPosition = (pos: number): void => {
      this._index.segments.splice(pos, oldIndexLength - pos, ...newSegments);
      this._index.loadSegment = newIndex._index.loadSegment;
      this._index.loadInitSegment = newIndex._index.loadInitSegment;
    };
    const oldIndexLength = this._index.segments.length;
    const newIndexStart = newSegments[0].time;
    for (let i = oldIndexLength - 1; i >= 0; i--) {
      const currSegment = this._index.segments[i];
      if (currSegment.time === newIndexStart) {
        return insertNewIndexAtPosition(i);
      } else if (currSegment.time < newIndexStart) {
        if (currSegment.time + currSegment.duration > newIndexStart) {
          // the new Manifest overlaps a previous segment (weird). Remove the latter.
          log.warn(
            "Local RepresentationIndex: Manifest update removed" + " previous segments",
          );
          return insertNewIndexAtPosition(i);
        }
        return insertNewIndexAtPosition(i + 1);
      }
    }

    // if we got here, it means that every segments in the previous manifest are
    // after the new one. This is unusual.
    // Either the new one has more depth or it's an older one.
    const oldIndexEnd =
      this._index.segments[oldIndexLength - 1].time +
      this._index.segments[oldIndexLength - 1].duration;
    const newIndexEnd =
      newSegments[newSegments.length - 1].time +
      newSegments[newSegments.length - 1].duration;
    if (oldIndexEnd >= newIndexEnd) {
      return;
    }
    return this._replace(newIndex);
  }
}