content: /*
   * Copyright (C) 2019 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 com.google.android.exoplayer2.extractor.ts;
  
  import static java.lang.Math.min;
  import static java.lang.annotation.ElementType.TYPE_USE;
  
  import androidx.annotation.IntDef;
  import androidx.annotation.Nullable;
  import com.google.android.exoplayer2.C;
  import com.google.android.exoplayer2.Format;
  import com.google.android.exoplayer2.audio.Ac4Util;
  import com.google.android.exoplayer2.audio.Ac4Util.SyncFrameInfo;
  import com.google.android.exoplayer2.extractor.ExtractorOutput;
  import com.google.android.exoplayer2.extractor.TrackOutput;
  import com.google.android.exoplayer2.extractor.ts.TsPayloadReader.TrackIdGenerator;
  import com.google.android.exoplayer2.util.Assertions;
  import com.google.android.exoplayer2.util.MimeTypes;
  import com.google.android.exoplayer2.util.ParsableBitArray;
  import com.google.android.exoplayer2.util.ParsableByteArray;
  import java.lang.annotation.Documented;
  import java.lang.annotation.Retention;
  import java.lang.annotation.RetentionPolicy;
  import java.lang.annotation.Target;
  import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
  import org.checkerframework.checker.nullness.qual.RequiresNonNull;
  
  /** Parses a continuous AC-4 byte stream and extracts individual samples. */
  public final class Ac4Reader implements ElementaryStreamReader {
  
    @Documented
    @Retention(RetentionPolicy.SOURCE)
    @Target(TYPE_USE)
    @IntDef({STATE_FINDING_SYNC, STATE_READING_HEADER, STATE_READING_SAMPLE})
    private @interface State {}
  
    private static final int STATE_FINDING_SYNC = 0;
    private static final int STATE_READING_HEADER = 1;
    private static final int STATE_READING_SAMPLE = 2;
  
    private final ParsableBitArray headerScratchBits;
    private final ParsableByteArray headerScratchBytes;
    @Nullable private final String language;
  
    private @MonotonicNonNull String formatId;
    private @MonotonicNonNull TrackOutput output;
  
    private @State int state;
    private int bytesRead;
  
    // Used to find the header.
    private boolean lastByteWasAC;
    private boolean hasCRC;
  
    // Used when parsing the header.
    private long sampleDurationUs;
    private @MonotonicNonNull Format format;
    private int sampleSize;
  
    // Used when reading the samples.
    private long timeUs;
  
    /** Constructs a new reader for AC-4 elementary streams. */
    public Ac4Reader() {
      this(null);
    }
  
    /**
     * Constructs a new reader for AC-4 elementary streams.
     *
     * @param language Track language.
     */
    public Ac4Reader(@Nullable String language) {
      headerScratchBits = new ParsableBitArray(new byte[Ac4Util.HEADER_SIZE_FOR_PARSER]);
      headerScratchBytes = new ParsableByteArray(headerScratchBits.data);
      state = STATE_FINDING_SYNC;
      bytesRead = 0;
      lastByteWasAC = false;
      hasCRC = false;
      timeUs = C.TIME_UNSET;
      this.language = language;
    }
  
    @Override
    public void seek() {
      state = STATE_FINDING_SYNC;
      bytesRead = 0;
      lastByteWasAC = false;
      hasCRC = false;
      timeUs = C.TIME_UNSET;
    }
  
    @Override
    public void createTracks(ExtractorOutput extractorOutput, TrackIdGenerator idGenerator) {
      idGenerator.generateNewId();
      formatId = idGenerator.getFormatId();
      output = extractorOutput.track(idGenerator.getTrackId(), C.TRACK_TYPE_AUDIO);
    }
  
    @Override
    public void packetStarted(long pesTimeUs, @TsPayloadReader.Flags int flags) {
      if (pesTimeUs != C.TIME_UNSET) {
        timeUs = pesTimeUs;
      }
    }
  
    @Override
    public void consume(ParsableByteArray data) {
      Assertions.checkStateNotNull(output); // Asserts that createTracks has been called.
      while (data.bytesLeft() > 0) {
        switch (state) {
          case STATE_FINDING_SYNC:
            if (skipToNextSync(data)) {
              state = STATE_READING_HEADER;
              headerScratchBytes.getData()[0] = (byte) 0xAC;
              headerScratchBytes.getData()[1] = (byte) (hasCRC ? 0x41 : 0x40);
              bytesRead = 2;
            }
            break;
          case STATE_READING_HEADER:
            if (continueRead(data, headerScratchBytes.getData(), Ac4Util.HEADER_SIZE_FOR_PARSER)) {
              parseHeader();
              headerScratchBytes.setPosition(0);
              output.sampleData(headerScratchBytes, Ac4Util.HEADER_SIZE_FOR_PARSER);
              state = STATE_READING_SAMPLE;
            }
            break;
          case STATE_READING_SAMPLE:
            int bytesToRead = min(data.bytesLeft(), sampleSize - bytesRead);
            output.sampleData(data, bytesToRead);
            bytesRead += bytesToRead;
            if (bytesRead == sampleSize) {
              if (timeUs != C.TIME_UNSET) {
                output.sampleMetadata(timeUs, C.BUFFER_FLAG_KEY_FRAME, sampleSize, 0, null);
                timeUs += sampleDurationUs;
              }
              state = STATE_FINDING_SYNC;
            }
            break;
          default:
            break;
        }
      }
    }
  
    @Override
    public void packetFinished() {
      // Do nothing.
    }
  
    /**
     * Continues a read from the provided {@code source} into a given {@code target}. It's assumed
     * that the data should be written into {@code target} starting from an offset of zero.
     *
     * @param source The source from which to read.
     * @param target The target into which data is to be read.
     * @param targetLength The target length of the read.
     * @return Whether the target length was reached.
     */
    private boolean continueRead(ParsableByteArray source, byte[] target, int targetLength) {
      int bytesToRead = min(source.bytesLeft(), targetLength - bytesRead);
      source.readBytes(target, bytesRead, bytesToRead);
      bytesRead += bytesToRead;
      return bytesRead == targetLength;
    }
  
    /**
     * Locates the next syncword, advancing the position to the byte that immediately follows it. If a
     * syncword was not located, the position is advanced to the limit.
     *
     * @param pesBuffer The buffer whose position should be advanced.
     * @return Whether a syncword position was found.
     */
    private boolean skipToNextSync(ParsableByteArray pesBuffer) {
      while (pesBuffer.bytesLeft() > 0) {
        if (!lastByteWasAC) {
          lastByteWasAC = (pesBuffer.readUnsignedByte() == 0xAC);
          continue;
        }
        int secondByte = pesBuffer.readUnsignedByte();
        lastByteWasAC = secondByte == 0xAC;
        if (secondByte == 0x40 || secondByte == 0x41) {
          hasCRC = secondByte == 0x41;
          return true;
        }
      }
      return false;
    }
  
    /** Parses the sample header. */
    @RequiresNonNull("output")
    private void parseHeader() {
      headerScratchBits.setPosition(0);
      SyncFrameInfo frameInfo = Ac4Util.parseAc4SyncframeInfo(headerScratchBits);
      if (format == null
          || frameInfo.channelCount != format.channelCount
          || frameInfo.sampleRate != format.sampleRate
          || !MimeTypes.AUDIO_AC4.equals(format.sampleMimeType)) {
        format =
            new Format.Builder()
                .setId(formatId)
                .setSampleMimeType(MimeTypes.AUDIO_AC4)
                .setChannelCount(frameInfo.channelCount)
                .setSampleRate(frameInfo.sampleRate)
                .setLanguage(language)
                .build();
        output.format(format);
      }
      sampleSize = frameInfo.frameSize;
      // In this class a sample is an AC-4 sync frame, but Format#sampleRate specifies the number of
      // PCM audio samples per second.
      sampleDurationUs = C.MICROS_PER_SECOND * frameInfo.sampleCount / format.sampleRate;
    }
  }
  