/*
 * Copyright (C) 2016 The Android Open Source Project
 *
 * 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.
 */
package androidx.media3.exoplayer;

import static java.lang.Math.max;

import androidx.media3.common.util.UnstableApi;

/**
 * Maintains decoder event counts, for debugging purposes only.
 *
 * <p>Counters should be written from the playback thread only. Counters may be read from any
 * thread. To ensure that the counter values are made visible across threads, users of this class
 * should invoke {@link #ensureUpdated()} prior to reading and after writing.
 */
@UnstableApi
public final class DecoderCounters {

  /** The number of times a decoder has been initialized. */
  public int decoderInitCount;
  /** The number of times a decoder has been released. */
  public int decoderReleaseCount;
  /** The number of input buffers queued to the decoder. */
  public int queuedInputBufferCount;
  /**
   * The number of skipped input buffers.
   *
   * <p>A skipped input buffer is an input buffer that was deliberately not queued to the decoder.
   */
  public int skippedInputBufferCount;
  /** The number of rendered output buffers. */
  public int renderedOutputBufferCount;
  /**
   * The number of skipped output buffers.
   *
   * <p>A skipped output buffer is an output buffer that was deliberately not rendered. This
   * includes buffers that were never dequeued from the decoder and instead skipped while 'inside'
   * the codec due to a flush.
   */
  public int skippedOutputBufferCount;
  /**
   * The number of dropped buffers.
   *
   * <p>A dropped buffer is a buffer that was supposed to be decoded/rendered, but was instead
   * dropped because it could not be rendered in time.
   *
   * <p>This includes all of {@link #droppedInputBufferCount} in addition to buffers dropped after
   * being queued to the decoder.
   */
  public int droppedBufferCount;
  /**
   * The number of input buffers dropped.
   *
   * <p>A dropped input buffer is a buffer that was not queued to the decoder because it would not
   * be rendered in time.
   */
  public int droppedInputBufferCount;
  /**
   * The maximum number of dropped buffers without an interleaving rendered output buffer.
   *
   * <p>Skipped buffers are ignored for the purposes of calculating this value.
   */
  public int maxConsecutiveDroppedBufferCount;
  /**
   * The number of times all buffers to a keyframe were dropped.
   *
   * <p>Each time buffers to a keyframe are dropped:
   *
   * <ul>
   *   <li>This counter is incremented by one.
   *   <li>{@link #droppedInputBufferCount} is incremented by the number of buffers dropped from the
   *       source to advance to the keyframe.
   *   <li>{@link #droppedBufferCount} is incremented by the sum of the number of buffers dropped
   *       from the source to advance to the keyframe and the number of buffers 'inside' the
   *       decoder.
   * </ul>
   */
  public int droppedToKeyframeCount;
  /**
   * The sum of the video frame processing offsets in microseconds.
   *
   * <p>The processing offset for a video frame is the difference between the time at which the
   * frame became available to render, and the time at which it was scheduled to be rendered. A
   * positive value indicates the frame became available early enough, whereas a negative value
   * indicates that the frame wasn't available until after the time at which it should have been
   * rendered.
   *
   * <p>Note: Use {@link #addVideoFrameProcessingOffset(long)} to update this field instead of
   * updating it directly.
   */
  public long totalVideoFrameProcessingOffsetUs;
  /**
   * The number of video frame processing offsets added.
   *
   * <p>Note: Use {@link #addVideoFrameProcessingOffset(long)} to update this field instead of
   * updating it directly.
   */
  public int videoFrameProcessingOffsetCount;

  /**
   * Should be called to ensure counter values are made visible across threads. The playback thread
   * should call this method after updating the counter values. Any other thread should call this
   * method before reading the counters.
   */
  public synchronized void ensureUpdated() {
    // Do nothing. The use of synchronized ensures a memory barrier should another thread also
    // call this method.
  }

  /**
   * Merges the counts from {@code other} into this instance.
   *
   * @param other The {@link DecoderCounters} to merge into this instance.
   */
  public void merge(DecoderCounters other) {
    decoderInitCount += other.decoderInitCount;
    decoderReleaseCount += other.decoderReleaseCount;
    queuedInputBufferCount += other.queuedInputBufferCount;
    skippedInputBufferCount += other.skippedInputBufferCount;
    renderedOutputBufferCount += other.renderedOutputBufferCount;
    skippedOutputBufferCount += other.skippedOutputBufferCount;
    droppedBufferCount += other.droppedBufferCount;
    droppedInputBufferCount += other.droppedInputBufferCount;
    maxConsecutiveDroppedBufferCount =
        max(maxConsecutiveDroppedBufferCount, other.maxConsecutiveDroppedBufferCount);
    droppedToKeyframeCount += other.droppedToKeyframeCount;
    addVideoFrameProcessingOffsets(
        other.totalVideoFrameProcessingOffsetUs, other.videoFrameProcessingOffsetCount);
  }

  /**
   * Adds a video frame processing offset to {@link #totalVideoFrameProcessingOffsetUs} and
   * increases {@link #videoFrameProcessingOffsetCount} by one.
   *
   * <p>Convenience method to ensure both fields are updated when adding a single offset.
   *
   * @param processingOffsetUs The video frame processing offset in microseconds.
   */
  public void addVideoFrameProcessingOffset(long processingOffsetUs) {
    addVideoFrameProcessingOffsets(processingOffsetUs, /* count= */ 1);
  }

  private void addVideoFrameProcessingOffsets(long totalProcessingOffsetUs, int count) {
    totalVideoFrameProcessingOffsetUs += totalProcessingOffsetUs;
    videoFrameProcessingOffsetCount += count;
  }
}
