/**
 * 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 {
  IManifest,
  IAdaptation,
  IPeriod,
  IRepresentation,
} from "../../../../manifest";
import type { IBufferedChunk } from "../../../segment_sinks";
import type { IBufferDiscontinuity } from "../types";

/**
 * Check if there is a soon-to-be-encountered discontinuity in the buffer that
 * won't be filled by any future segment.
 * This function will only check discontinuities for the given `checkedRange`.
 *
 * @param {Object} content - The content we are currently loading.
 * @param {Object} checkedRange - The time range that will be checked for
 * discontinuities.
 * Both `nextSegmentStart` and `bufferedSegments` arguments can only refer to
 * that range.
 * @param {number|null} nextSegmentStart - The start time in seconds of the next
 * not-yet-pushed segment that can be pushed, in the limits of `checkedRange`.
 * This includes segments which have not been loaded or pushed yet, but also
 * segments which might be re-downloaded because currently incomplete in the
 * buffer, the point being to know what is the earliest time in the buffer where
 * a segment might be pushed in the future.
 * `null` if no segment in `checkedRange` will be pushed under current buffer's
 * conditions.
 * @param {boolean} hasFinishedLoading - if `true`, all segments for the current
 * Period have been loaded and none will be loaded in the future under the
 * current buffer's state.
 * @param {Array.<Object>} bufferedSegments - Information about every segments
 * currently in the buffer, in chronological order.
 * Only segments overlapping with the given `checkedRange` will be looked at,
 * though the array given can be larger.
 */
export default function checkForDiscontinuity(
  content: {
    adaptation: IAdaptation;
    manifest: IManifest;
    period: IPeriod;
    representation: IRepresentation;
  },
  checkedRange: { start: number; end: number },
  nextSegmentStart: number | null,
  hasFinishedLoading: boolean,
  bufferedSegments: IBufferedChunk[],
): IBufferDiscontinuity | null {
  const { period, adaptation, representation } = content;

  // `bufferedSegments` might also contains segments which are before
  // `checkedRange`.
  // Here we want the first one that goes over `checkedRange.start`, to  see
  // if there's a discontinuity at the beginning in the buffer
  const nextBufferedInRangeIdx = getIndexOfFirstChunkInRange(
    bufferedSegments,
    checkedRange,
  );
  if (nextBufferedInRangeIdx === null) {
    // There's no segment currently buffered for the current range.

    if (nextSegmentStart === null) {
      // No segment to load in that range
      // Check if we are in a discontinuity at the end of the current Period
      if (
        hasFinishedLoading &&
        period.end !== undefined &&
        checkedRange.end >= period.end
      ) {
        return { start: undefined, end: null }; // discontinuity to Period's end
      }

      // Check that there is a discontinuity announced in the Manifest there
      const discontinuityEnd = representation.index.checkDiscontinuity(
        checkedRange.start,
      );
      if (discontinuityEnd !== null) {
        return { start: undefined, end: discontinuityEnd };
      }
    }
    return null;
  }

  const nextBufferedSegment = bufferedSegments[nextBufferedInRangeIdx];

  // Check if there is a hole that won't be filled before `nextSegmentStart`
  if (
    // Next buffered segment starts after the start of the current range
    nextBufferedSegment.bufferedStart !== undefined &&
    nextBufferedSegment.bufferedStart > checkedRange.start &&
    // and no segment will fill in that hole
    (nextSegmentStart === null ||
      nextBufferedSegment.infos.segment.end <= nextSegmentStart)
  ) {
    const discontinuityEnd = nextBufferedSegment.bufferedStart;
    if (
      !hasFinishedLoading &&
      representation.index.awaitSegmentBetween(checkedRange.start, discontinuityEnd) !==
        false
    ) {
      return null;
    }
    log.debug(
      "RS: current discontinuity encountered",
      adaptation.type,
      nextBufferedSegment.bufferedStart,
    );
    return { start: undefined, end: discontinuityEnd };
  }

  // Check if there's a discontinuity BETWEEN segments of the current range
  const nextHoleIdx = getIndexOfFirstDiscontinuityBetweenChunks(
    bufferedSegments,
    checkedRange,
    nextBufferedInRangeIdx + 1,
  );

  // If there was a hole between two consecutives segments, and if this hole
  // comes before the next segment to load, there is a discontinuity (that hole!)
  if (nextHoleIdx !== null) {
    const segmentInfoBeforeHole = bufferedSegments[nextHoleIdx - 1];
    const segmentInfoAfterHole = bufferedSegments[nextHoleIdx];

    if (
      nextSegmentStart === null ||
      segmentInfoAfterHole.infos.segment.end <= nextSegmentStart
    ) {
      if (
        !hasFinishedLoading &&
        representation.index.awaitSegmentBetween(
          segmentInfoBeforeHole.infos.segment.end,
          segmentInfoAfterHole.infos.segment.time,
        ) !== false
      ) {
        return null;
      }
      const start = segmentInfoBeforeHole.bufferedEnd as number;
      const end = segmentInfoAfterHole.bufferedStart as number;
      log.debug("RS: future discontinuity encountered", adaptation.type, start, end);
      return { start, end };
    }
  }

  if (nextSegmentStart === null) {
    // If no hole between segments and no segment to load, check for a
    // discontinuity at the end of the Period

    if (hasFinishedLoading && period.end !== undefined) {
      // Period is finished
      if (checkedRange.end < period.end) {
        // We've not reached the Period's end yet
        return null;
      }

      // Check if the last buffered segment ends before this Period's end
      // In which case there is a discontinuity between those
      const lastBufferedInPeriodIdx = getIndexOfLastChunkInPeriod(
        bufferedSegments,
        period.end,
      );
      if (lastBufferedInPeriodIdx !== null) {
        const lastSegment = bufferedSegments[lastBufferedInPeriodIdx];
        if (
          lastSegment.bufferedEnd !== undefined &&
          lastSegment.bufferedEnd < period.end
        ) {
          log.debug(
            "RS: discontinuity encountered at the end of the current period",
            adaptation.type,
            lastSegment.bufferedEnd,
            period.end,
          );
          return { start: lastSegment.bufferedEnd, end: null };
        }
      }
    }

    // At last, check if we don't have a discontinuity at the end of the current
    // range, announced in the Manifest, that is too big to be detected through
    // the previous checks.

    if (period.end !== undefined && checkedRange.end >= period.end) {
      return null; // The previous checks should have taken care of those
    }

    for (let bufIdx = bufferedSegments.length - 1; bufIdx >= 0; bufIdx--) {
      const bufSeg = bufferedSegments[bufIdx];
      if (bufSeg.bufferedStart === undefined) {
        break;
      }

      if (bufSeg.bufferedStart < checkedRange.end) {
        if (bufSeg.bufferedEnd !== undefined && bufSeg.bufferedEnd < checkedRange.end) {
          const discontinuityEnd = representation.index.checkDiscontinuity(
            checkedRange.end,
          );
          if (discontinuityEnd !== null) {
            return { start: bufSeg.bufferedEnd, end: discontinuityEnd };
          }
        }
        return null;
      }
    }
  }
  return null;
}

/**
 * Returns the index of the first element in `bufferedChunks` that is part of
 * `range` (starts before it ends and ends after it starts).
 *
 * Returns `null` if no element is found in that range or if we cannot know the
 * index of the first element in it.
 * @param {Array.<Object>} bufferedChunks
 * @param {Object} range
 * @returns {number|null}
 */
function getIndexOfFirstChunkInRange(
  bufferedChunks: IBufferedChunk[],
  range: { start: number; end: number },
): number | null {
  for (let bufIdx = 0; bufIdx < bufferedChunks.length; bufIdx++) {
    const bufSeg = bufferedChunks[bufIdx];
    if (
      bufSeg.bufferedStart === undefined ||
      bufSeg.bufferedEnd === undefined ||
      bufSeg.bufferedStart >= range.end
    ) {
      return null;
    }
    if (bufSeg.bufferedEnd > range.start) {
      return bufIdx;
    }
  }
  return null;
}

/**
 * Returns the index of the first element in `bufferedChunks` which is not
 * immediately consecutive to the one before it.
 *
 * `startFromIndex` is the index of the first segment that will be checked with
 * the element coming before it. As such, it has to be superior to 0.
 *
 * If the element at `startFromIndex` comes immediately after the one before it,
 * the element at `startFromIndex + 1` will be checked instead and so on until a
 * segment completely out of `checkedRange` (which starts after it) is detected.
 *
 * If no hole between elements is found, `null` is returned.
 * @param {Array.<Object>} bufferedChunks
 * @param {Object} range
 * @param {number} startFromIndex
 * @returns {number|null}
 */
function getIndexOfFirstDiscontinuityBetweenChunks(
  bufferedChunks: IBufferedChunk[],
  range: { start: number; end: number },
  startFromIndex: number,
): number | null {
  if (startFromIndex <= 0) {
    log.error("RS: Asked to check a discontinuity before the first chunk.");
    return null;
  }
  for (let bufIdx = startFromIndex; bufIdx < bufferedChunks.length; bufIdx++) {
    const currSegment = bufferedChunks[bufIdx];
    const prevSegment = bufferedChunks[bufIdx - 1];

    // Exit as soon we miss information or when we go further than `checkedRange`
    if (
      currSegment.bufferedStart === undefined ||
      prevSegment.bufferedEnd === undefined ||
      currSegment.bufferedStart >= range.end
    ) {
      return null;
    }

    // If there is a hole between two consecutive buffered segment
    if (currSegment.bufferedStart - prevSegment.bufferedEnd > 0) {
      return bufIdx;
    }
  }
  return null;
}

/**
 * Returns the index of the last element in `bufferedChunks` that is part of
 * `range` (starts before it ends and ends after it starts).
 *
 * Returns `null` if no element is found in that range or if we cannot know the
 * index of the last element in it.
 * @param {Array.<Object>} bufferedChunks
 * @param {number} periodEnd
 * @returns {number|null}
 */
function getIndexOfLastChunkInPeriod(
  bufferedChunks: IBufferedChunk[],
  periodEnd: number,
): number | null {
  for (let bufIdx = bufferedChunks.length - 1; bufIdx >= 0; bufIdx--) {
    const bufSeg = bufferedChunks[bufIdx];
    if (bufSeg.bufferedStart === undefined) {
      return null;
    }
    if (bufSeg.bufferedStart < periodEnd) {
      return bufIdx;
    }
  }
  return null;
}