/*
 * 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.drm;

import static androidx.media3.common.util.Assertions.checkArgument;
import static androidx.media3.common.util.Assertions.checkNotNull;
import static androidx.media3.common.util.Assertions.checkState;
import static androidx.media3.common.util.Assertions.checkStateNotNull;
import static java.lang.annotation.ElementType.TYPE_USE;

import android.annotation.SuppressLint;
import android.media.ResourceBusyException;
import android.os.Handler;
import android.os.Looper;
import android.os.Message;
import android.os.SystemClock;
import androidx.annotation.IntDef;
import androidx.annotation.Nullable;
import androidx.media3.common.C;
import androidx.media3.common.DrmInitData;
import androidx.media3.common.DrmInitData.SchemeData;
import androidx.media3.common.Format;
import androidx.media3.common.MimeTypes;
import androidx.media3.common.PlaybackException;
import androidx.media3.common.util.Log;
import androidx.media3.common.util.UnstableApi;
import androidx.media3.common.util.Util;
import androidx.media3.exoplayer.analytics.PlayerId;
import androidx.media3.exoplayer.drm.DrmSession.DrmSessionException;
import androidx.media3.exoplayer.drm.ExoMediaDrm.OnEventListener;
import androidx.media3.exoplayer.upstream.DefaultLoadErrorHandlingPolicy;
import androidx.media3.exoplayer.upstream.LoadErrorHandlingPolicy;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Sets;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.lang.annotation.Documented;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.UUID;
import org.checkerframework.checker.nullness.qual.EnsuresNonNull;
import org.checkerframework.checker.nullness.qual.MonotonicNonNull;

/**
 * A {@link DrmSessionManager} that supports playbacks using {@link ExoMediaDrm}.
 *
 * <p>This implementation supports pre-acquisition of sessions using {@link
 * #preacquireSession(DrmSessionEventListener.EventDispatcher, Format)}.
 */
@UnstableApi
public class DefaultDrmSessionManager implements DrmSessionManager {

  /**
   * Builder for {@link DefaultDrmSessionManager} instances.
   *
   * <p>See {@link #Builder} for the list of default values.
   */
  public static final class Builder {

    private final HashMap<String, String> keyRequestParameters;
    private UUID uuid;
    private ExoMediaDrm.Provider exoMediaDrmProvider;
    private boolean multiSession;
    private @C.TrackType int[] useDrmSessionsForClearContentTrackTypes;
    private boolean playClearSamplesWithoutKeys;
    private LoadErrorHandlingPolicy loadErrorHandlingPolicy;
    private long sessionKeepaliveMs;

    /**
     * Creates a builder with default values. The default values are:
     *
     * <ul>
     *   <li>{@link #setKeyRequestParameters keyRequestParameters}: An empty map.
     *   <li>{@link #setUuidAndExoMediaDrmProvider UUID}: {@link C#WIDEVINE_UUID}.
     *   <li>{@link #setUuidAndExoMediaDrmProvider ExoMediaDrm.Provider}: {@link
     *       FrameworkMediaDrm#DEFAULT_PROVIDER}.
     *   <li>{@link #setMultiSession multiSession}: {@code false}.
     *   <li>{@link #setUseDrmSessionsForClearContent useDrmSessionsForClearContent}: No tracks.
     *   <li>{@link #setPlayClearSamplesWithoutKeys playClearSamplesWithoutKeys}: {@code true}.
     *   <li>{@link #setLoadErrorHandlingPolicy LoadErrorHandlingPolicy}: {@link
     *       DefaultLoadErrorHandlingPolicy}.
     *   <li>{@link #setSessionKeepaliveMs sessionKeepaliveMs}: {@link
     *       #DEFAULT_SESSION_KEEPALIVE_MS}.
     * </ul>
     */
    public Builder() {
      keyRequestParameters = new HashMap<>();
      uuid = C.WIDEVINE_UUID;
      exoMediaDrmProvider = FrameworkMediaDrm.DEFAULT_PROVIDER;
      useDrmSessionsForClearContentTrackTypes = new int[0];
      playClearSamplesWithoutKeys = true;
      loadErrorHandlingPolicy = new DefaultLoadErrorHandlingPolicy();
      sessionKeepaliveMs = DEFAULT_SESSION_KEEPALIVE_MS;
    }

    /**
     * Sets the key request parameters to pass as the last argument to {@link
     * ExoMediaDrm#getKeyRequest(byte[], List, int, HashMap)}. May be null if not parameters need to
     * be passed.
     *
     * <p>Custom data for PlayReady should be set under {@link #PLAYREADY_CUSTOM_DATA_KEY}.
     *
     * @param keyRequestParameters A map with parameters.
     * @return This builder.
     */
    @CanIgnoreReturnValue
    public Builder setKeyRequestParameters(@Nullable Map<String, String> keyRequestParameters) {
      this.keyRequestParameters.clear();
      if (keyRequestParameters != null) {
        this.keyRequestParameters.putAll(keyRequestParameters);
      }
      return this;
    }

    /**
     * Sets the UUID of the DRM scheme and the {@link ExoMediaDrm.Provider} to use.
     *
     * @param uuid The UUID of the DRM scheme.
     * @param exoMediaDrmProvider The {@link ExoMediaDrm.Provider}.
     * @return This builder.
     */
    @CanIgnoreReturnValue
    public Builder setUuidAndExoMediaDrmProvider(
        UUID uuid, ExoMediaDrm.Provider exoMediaDrmProvider) {
      this.uuid = checkNotNull(uuid);
      this.exoMediaDrmProvider = checkNotNull(exoMediaDrmProvider);
      return this;
    }

    /**
     * Sets whether this session manager is allowed to acquire multiple simultaneous sessions.
     *
     * <p>Users should pass false when a single key request will obtain all keys required to decrypt
     * the associated content. {@code multiSession} is required when content uses key rotation.
     *
     * @param multiSession Whether this session manager is allowed to acquire multiple simultaneous
     *     sessions.
     * @return This builder.
     */
    @CanIgnoreReturnValue
    public Builder setMultiSession(boolean multiSession) {
      this.multiSession = multiSession;
      return this;
    }

    /**
     * Sets whether this session manager should attach {@link DrmSession DrmSessions} to the clear
     * sections of the media content.
     *
     * <p>Using {@link DrmSession DrmSessions} for clear content avoids the recreation of decoders
     * when transitioning between clear and encrypted sections of content.
     *
     * @param useDrmSessionsForClearContentTrackTypes The track types ({@link C#TRACK_TYPE_AUDIO}
     *     and/or {@link C#TRACK_TYPE_VIDEO}) for which to use a {@link DrmSession} regardless of
     *     whether the content is clear or encrypted.
     * @return This builder.
     * @throws IllegalArgumentException If {@code useDrmSessionsForClearContentTrackTypes} contains
     *     track types other than {@link C#TRACK_TYPE_AUDIO} and {@link C#TRACK_TYPE_VIDEO}.
     */
    @CanIgnoreReturnValue
    public Builder setUseDrmSessionsForClearContent(
        @C.TrackType int... useDrmSessionsForClearContentTrackTypes) {
      for (@C.TrackType int trackType : useDrmSessionsForClearContentTrackTypes) {
        checkArgument(trackType == C.TRACK_TYPE_VIDEO || trackType == C.TRACK_TYPE_AUDIO);
      }
      this.useDrmSessionsForClearContentTrackTypes =
          useDrmSessionsForClearContentTrackTypes.clone();
      return this;
    }

    /**
     * Sets whether clear samples within protected content should be played when keys for the
     * encrypted part of the content have yet to be loaded.
     *
     * @param playClearSamplesWithoutKeys Whether clear samples within protected content should be
     *     played when keys for the encrypted part of the content have yet to be loaded.
     * @return This builder.
     */
    @CanIgnoreReturnValue
    public Builder setPlayClearSamplesWithoutKeys(boolean playClearSamplesWithoutKeys) {
      this.playClearSamplesWithoutKeys = playClearSamplesWithoutKeys;
      return this;
    }

    /**
     * Sets the {@link LoadErrorHandlingPolicy} for key and provisioning requests.
     *
     * @param loadErrorHandlingPolicy A {@link LoadErrorHandlingPolicy}.
     * @return This builder.
     */
    @CanIgnoreReturnValue
    public Builder setLoadErrorHandlingPolicy(LoadErrorHandlingPolicy loadErrorHandlingPolicy) {
      this.loadErrorHandlingPolicy = checkNotNull(loadErrorHandlingPolicy);
      return this;
    }

    /**
     * Sets the time to keep {@link DrmSession DrmSessions} alive when they're not in use.
     *
     * <p>It can be useful to keep sessions alive during playback of short clear sections of media
     * (e.g. ad breaks) to avoid opening new DRM sessions (and re-requesting keys) at the transition
     * back into secure content. This assumes the secure sections before and after the clear section
     * are encrypted with the same keys.
     *
     * <p>Defaults to {@link #DEFAULT_SESSION_KEEPALIVE_MS}. Pass {@link C#TIME_UNSET} to disable
     * keep-alive.
     *
     * @param sessionKeepaliveMs The time to keep {@link DrmSession}s alive before fully releasing,
     *     in milliseconds. Must be &gt; 0 or {@link C#TIME_UNSET} to disable keep-alive.
     * @return This builder.
     */
    @CanIgnoreReturnValue
    public Builder setSessionKeepaliveMs(long sessionKeepaliveMs) {
      checkArgument(sessionKeepaliveMs > 0 || sessionKeepaliveMs == C.TIME_UNSET);
      this.sessionKeepaliveMs = sessionKeepaliveMs;
      return this;
    }

    /** Builds a {@link DefaultDrmSessionManager} instance. */
    public DefaultDrmSessionManager build(MediaDrmCallback mediaDrmCallback) {
      return new DefaultDrmSessionManager(
          uuid,
          exoMediaDrmProvider,
          mediaDrmCallback,
          keyRequestParameters,
          multiSession,
          useDrmSessionsForClearContentTrackTypes,
          playClearSamplesWithoutKeys,
          loadErrorHandlingPolicy,
          sessionKeepaliveMs);
    }
  }

  /**
   * Signals that the {@link Format#drmInitData} passed to {@link #acquireSession} does not contain
   * scheme data for the required UUID.
   */
  public static final class MissingSchemeDataException extends Exception {

    private MissingSchemeDataException(UUID uuid) {
      super("Media does not support uuid: " + uuid);
    }
  }

  /**
   * A key for specifying PlayReady custom data in the key request parameters passed to {@link
   * Builder#setKeyRequestParameters(Map)}.
   */
  public static final String PLAYREADY_CUSTOM_DATA_KEY = "PRCustomData";

  /**
   * Determines the action to be done after a session acquired. One of {@link #MODE_PLAYBACK},
   * {@link #MODE_QUERY}, {@link #MODE_DOWNLOAD} or {@link #MODE_RELEASE}.
   */
  @Documented
  @Retention(RetentionPolicy.SOURCE)
  @Target(TYPE_USE)
  @IntDef({MODE_PLAYBACK, MODE_QUERY, MODE_DOWNLOAD, MODE_RELEASE})
  public @interface Mode {}

  /**
   * Loads and refreshes (if necessary) a license for playback. Supports streaming and offline
   * licenses.
   */
  public static final int MODE_PLAYBACK = 0;

  /** Restores an offline license to allow its status to be queried. */
  public static final int MODE_QUERY = 1;

  /** Downloads an offline license or renews an existing one. */
  public static final int MODE_DOWNLOAD = 2;

  /** Releases an existing offline license. */
  public static final int MODE_RELEASE = 3;

  /** Number of times to retry for initial provisioning and key request for reporting error. */
  public static final int INITIAL_DRM_REQUEST_RETRY_COUNT = 3;

  /** Default value for {@link Builder#setSessionKeepaliveMs(long)}. */
  public static final long DEFAULT_SESSION_KEEPALIVE_MS = 5 * 60 * C.MILLIS_PER_SECOND;

  private static final String TAG = "DefaultDrmSessionMgr";

  private final UUID uuid;
  private final ExoMediaDrm.Provider exoMediaDrmProvider;
  private final MediaDrmCallback callback;
  private final HashMap<String, String> keyRequestParameters;
  private final boolean multiSession;
  private final @C.TrackType int[] useDrmSessionsForClearContentTrackTypes;
  private final boolean playClearSamplesWithoutKeys;
  private final ProvisioningManagerImpl provisioningManagerImpl;
  private final LoadErrorHandlingPolicy loadErrorHandlingPolicy;
  private final ReferenceCountListenerImpl referenceCountListener;
  private final long sessionKeepaliveMs;

  private final List<DefaultDrmSession> sessions;
  private final Set<PreacquiredSessionReference> preacquiredSessionReferences;
  private final Set<DefaultDrmSession> keepaliveSessions;

  private int prepareCallsCount;
  @Nullable private ExoMediaDrm exoMediaDrm;
  @Nullable private DefaultDrmSession placeholderDrmSession;
  @Nullable private DefaultDrmSession noMultiSessionDrmSession;
  private @MonotonicNonNull Looper playbackLooper;
  private @MonotonicNonNull Handler playbackHandler;
  private int mode;
  @Nullable private byte[] offlineLicenseKeySetId;
  private @MonotonicNonNull PlayerId playerId;

  /* package */ @Nullable volatile MediaDrmHandler mediaDrmHandler;

  private DefaultDrmSessionManager(
      UUID uuid,
      ExoMediaDrm.Provider exoMediaDrmProvider,
      MediaDrmCallback callback,
      HashMap<String, String> keyRequestParameters,
      boolean multiSession,
      @C.TrackType int[] useDrmSessionsForClearContentTrackTypes,
      boolean playClearSamplesWithoutKeys,
      LoadErrorHandlingPolicy loadErrorHandlingPolicy,
      long sessionKeepaliveMs) {
    checkNotNull(uuid);
    checkArgument(!C.COMMON_PSSH_UUID.equals(uuid), "Use C.CLEARKEY_UUID instead");
    this.uuid = uuid;
    this.exoMediaDrmProvider = exoMediaDrmProvider;
    this.callback = callback;
    this.keyRequestParameters = keyRequestParameters;
    this.multiSession = multiSession;
    this.useDrmSessionsForClearContentTrackTypes = useDrmSessionsForClearContentTrackTypes;
    this.playClearSamplesWithoutKeys = playClearSamplesWithoutKeys;
    this.loadErrorHandlingPolicy = loadErrorHandlingPolicy;
    provisioningManagerImpl = new ProvisioningManagerImpl();
    referenceCountListener = new ReferenceCountListenerImpl();
    mode = MODE_PLAYBACK;
    sessions = new ArrayList<>();
    preacquiredSessionReferences = Sets.newIdentityHashSet();
    keepaliveSessions = Sets.newIdentityHashSet();
    this.sessionKeepaliveMs = sessionKeepaliveMs;
  }

  /**
   * Sets the mode, which determines the role of sessions acquired from the instance. This must be
   * called before {@link #acquireSession(DrmSessionEventListener.EventDispatcher, Format)} is
   * called.
   *
   * <p>By default, the mode is {@link #MODE_PLAYBACK} and a streaming license is requested when
   * required.
   *
   * <p>{@code mode} must be one of these:
   *
   * <ul>
   *   <li>{@link #MODE_PLAYBACK}: If {@code offlineLicenseKeySetId} is null then a streaming
   *       license is requested. Otherwise, the offline license is restored.
   *   <li>{@link #MODE_QUERY}: {@code offlineLicenseKeySetId} cannot be null. The offline license
   *       is restored to allow its status to be queried.
   *   <li>{@link #MODE_DOWNLOAD}: If {@code offlineLicenseKeySetId} is null then an offline license
   *       is requested. Otherwise, the offline license is renewed.
   *   <li>{@link #MODE_RELEASE}: {@code offlineLicenseKeySetId} cannot be null. The offline license
   *       is released.
   * </ul>
   *
   * @param mode The mode to be set.
   * @param offlineLicenseKeySetId The key set id of the license to be used with the given mode.
   */
  public void setMode(@Mode int mode, @Nullable byte[] offlineLicenseKeySetId) {
    checkState(sessions.isEmpty());
    if (mode == MODE_QUERY || mode == MODE_RELEASE) {
      checkNotNull(offlineLicenseKeySetId);
    }
    this.mode = mode;
    this.offlineLicenseKeySetId = offlineLicenseKeySetId;
  }

  // DrmSessionManager implementation.

  @Override
  public final void prepare() {
    verifyPlaybackThread(/* allowBeforeSetPlayer= */ true);
    if (prepareCallsCount++ != 0) {
      return;
    }
    if (exoMediaDrm == null) {
      exoMediaDrm = exoMediaDrmProvider.acquireExoMediaDrm(uuid);
      exoMediaDrm.setOnEventListener(new MediaDrmEventListener());
    } else if (sessionKeepaliveMs != C.TIME_UNSET) {
      // Re-acquire the keepalive references for any sessions that are still active.
      for (int i = 0; i < sessions.size(); i++) {
        sessions.get(i).acquire(/* eventDispatcher= */ null);
      }
    }
  }

  @Override
  public final void release() {
    verifyPlaybackThread(/* allowBeforeSetPlayer= */ true);
    if (--prepareCallsCount != 0) {
      return;
    }
    // Release all keepalive acquisitions if keepalive is enabled.
    if (sessionKeepaliveMs != C.TIME_UNSET) {
      // Make a local copy, because sessions are removed from this.sessions during release (via
      // callback).
      List<DefaultDrmSession> sessions = new ArrayList<>(this.sessions);
      for (int i = 0; i < sessions.size(); i++) {
        sessions.get(i).release(/* eventDispatcher= */ null);
      }
    }
    releaseAllPreacquiredSessions();

    maybeReleaseMediaDrm();
  }

  @Override
  public void setPlayer(Looper playbackLooper, PlayerId playerId) {
    initPlaybackLooper(playbackLooper);
    this.playerId = playerId;
  }

  @Override
  public DrmSessionReference preacquireSession(
      @Nullable DrmSessionEventListener.EventDispatcher eventDispatcher, Format format) {
    // Don't verify the playback thread, preacquireSession can be called from any thread.
    checkState(prepareCallsCount > 0);
    checkStateNotNull(playbackLooper);
    PreacquiredSessionReference preacquiredSessionReference =
        new PreacquiredSessionReference(eventDispatcher);
    preacquiredSessionReference.acquire(format);
    return preacquiredSessionReference;
  }

  @Override
  @Nullable
  public DrmSession acquireSession(
      @Nullable DrmSessionEventListener.EventDispatcher eventDispatcher, Format format) {
    verifyPlaybackThread(/* allowBeforeSetPlayer= */ false);
    checkState(prepareCallsCount > 0);
    checkStateNotNull(playbackLooper);
    return acquireSession(
        playbackLooper,
        eventDispatcher,
        format,
        /* shouldReleasePreacquiredSessionsBeforeRetrying= */ true);
  }

  // Must be called on the playback thread.
  @Nullable
  private DrmSession acquireSession(
      Looper playbackLooper,
      @Nullable DrmSessionEventListener.EventDispatcher eventDispatcher,
      Format format,
      boolean shouldReleasePreacquiredSessionsBeforeRetrying) {
    maybeCreateMediaDrmHandler(playbackLooper);

    if (format.drmInitData == null) {
      // Content is not encrypted.
      return maybeAcquirePlaceholderSession(
          MimeTypes.getTrackType(format.sampleMimeType),
          shouldReleasePreacquiredSessionsBeforeRetrying);
    }

    @Nullable List<SchemeData> schemeDatas = null;
    if (offlineLicenseKeySetId == null) {
      schemeDatas = getSchemeDatas(checkNotNull(format.drmInitData), uuid, false);
      if (schemeDatas.isEmpty()) {
        final MissingSchemeDataException error = new MissingSchemeDataException(uuid);
        Log.e(TAG, "DRM error", error);
        if (eventDispatcher != null) {
          eventDispatcher.drmSessionManagerError(error);
        }
        return new ErrorStateDrmSession(
            new DrmSessionException(error, PlaybackException.ERROR_CODE_DRM_CONTENT_ERROR));
      }
    }

    @Nullable DefaultDrmSession session;
    if (!multiSession) {
      session = noMultiSessionDrmSession;
    } else {
      // Only use an existing session if it has matching init data.
      session = null;
      for (DefaultDrmSession existingSession : sessions) {
        if (Util.areEqual(existingSession.schemeDatas, schemeDatas)) {
          session = existingSession;
          break;
        }
      }
    }

    if (session == null) {
      // Create a new session.
      session =
          createAndAcquireSessionWithRetry(
              schemeDatas,
              /* isPlaceholderSession= */ false,
              eventDispatcher,
              shouldReleasePreacquiredSessionsBeforeRetrying);
      if (!multiSession) {
        noMultiSessionDrmSession = session;
      }
      sessions.add(session);
    } else {
      session.acquire(eventDispatcher);
    }

    return session;
  }

  @Override
  public @C.CryptoType int getCryptoType(Format format) {
    verifyPlaybackThread(/* allowBeforeSetPlayer= */ false);
    @C.CryptoType int cryptoType = checkNotNull(exoMediaDrm).getCryptoType();
    if (format.drmInitData == null) {
      int trackType = MimeTypes.getTrackType(format.sampleMimeType);
      return Util.linearSearch(useDrmSessionsForClearContentTrackTypes, trackType) != C.INDEX_UNSET
          ? cryptoType
          : C.CRYPTO_TYPE_NONE;
    } else {
      return canAcquireSession(format.drmInitData) ? cryptoType : C.CRYPTO_TYPE_UNSUPPORTED;
    }
  }

  // Internal methods.

  @Nullable
  private DrmSession maybeAcquirePlaceholderSession(
      int trackType, boolean shouldReleasePreacquiredSessionsBeforeRetrying) {
    ExoMediaDrm exoMediaDrm = checkNotNull(this.exoMediaDrm);
    boolean avoidPlaceholderDrmSessions =
        exoMediaDrm.getCryptoType() == C.CRYPTO_TYPE_FRAMEWORK
            && FrameworkCryptoConfig.WORKAROUND_DEVICE_NEEDS_KEYS_TO_CONFIGURE_CODEC;
    // Avoid attaching a session to sparse formats.
    if (avoidPlaceholderDrmSessions
        || Util.linearSearch(useDrmSessionsForClearContentTrackTypes, trackType) == C.INDEX_UNSET
        || exoMediaDrm.getCryptoType() == C.CRYPTO_TYPE_UNSUPPORTED) {
      return null;
    }
    if (placeholderDrmSession == null) {
      DefaultDrmSession placeholderDrmSession =
          createAndAcquireSessionWithRetry(
              /* schemeDatas= */ ImmutableList.of(),
              /* isPlaceholderSession= */ true,
              /* eventDispatcher= */ null,
              shouldReleasePreacquiredSessionsBeforeRetrying);
      sessions.add(placeholderDrmSession);
      this.placeholderDrmSession = placeholderDrmSession;
    } else {
      placeholderDrmSession.acquire(/* eventDispatcher= */ null);
    }
    return placeholderDrmSession;
  }

  private boolean canAcquireSession(DrmInitData drmInitData) {
    if (offlineLicenseKeySetId != null) {
      // An offline license can be restored so a session can always be acquired.
      return true;
    }
    List<SchemeData> schemeDatas = getSchemeDatas(drmInitData, uuid, true);
    if (schemeDatas.isEmpty()) {
      if (drmInitData.schemeDataCount == 1 && drmInitData.get(0).matches(C.COMMON_PSSH_UUID)) {
        // Assume scheme specific data will be added before the session is opened.
        Log.w(
            TAG, "DrmInitData only contains common PSSH SchemeData. Assuming support for: " + uuid);
      } else {
        // No data for this manager's scheme.
        return false;
      }
    }
    String schemeType = drmInitData.schemeType;
    if (schemeType == null || C.CENC_TYPE_cenc.equals(schemeType)) {
      // If there is no scheme information, assume patternless AES-CTR.
      return true;
    } else if (C.CENC_TYPE_cbcs.equals(schemeType)) {
      // Support for cbcs (AES-CBC with pattern encryption) was added in API 24. However, the
      // implementation was not stable until API 25.
      return Util.SDK_INT >= 25;
    } else if (C.CENC_TYPE_cbc1.equals(schemeType) || C.CENC_TYPE_cens.equals(schemeType)) {
      // Support for cbc1 (AES-CTR with pattern encryption) and cens (AES-CBC without pattern
      // encryption) was also added in API 24 and made stable from API 25, however support was
      // removed from API 30. Since the range of API levels for which these modes are usable is too
      // small to be useful, we don't indicate support on any API level.
      return false;
    }
    // Unknown schemes, assume one of them is supported.
    return true;
  }

  @EnsuresNonNull({"this.playbackLooper", "this.playbackHandler"})
  private synchronized void initPlaybackLooper(Looper playbackLooper) {
    if (this.playbackLooper == null) {
      this.playbackLooper = playbackLooper;
      this.playbackHandler = new Handler(playbackLooper);
    } else {
      checkState(this.playbackLooper == playbackLooper);
      checkNotNull(playbackHandler);
    }
  }

  private void maybeCreateMediaDrmHandler(Looper playbackLooper) {
    if (mediaDrmHandler == null) {
      mediaDrmHandler = new MediaDrmHandler(playbackLooper);
    }
  }

  private DefaultDrmSession createAndAcquireSessionWithRetry(
      @Nullable List<SchemeData> schemeDatas,
      boolean isPlaceholderSession,
      @Nullable DrmSessionEventListener.EventDispatcher eventDispatcher,
      boolean shouldReleasePreacquiredSessionsBeforeRetrying) {
    DefaultDrmSession session =
        createAndAcquireSession(schemeDatas, isPlaceholderSession, eventDispatcher);
    // If we're short on DRM session resources, first try eagerly releasing all our keepalive
    // sessions and then retry the acquisition.
    if (acquisitionFailedIndicatingResourceShortage(session) && !keepaliveSessions.isEmpty()) {
      releaseAllKeepaliveSessions();
      undoAcquisition(session, eventDispatcher);
      session = createAndAcquireSession(schemeDatas, isPlaceholderSession, eventDispatcher);
    }

    // If the acquisition failed again due to continued resource shortage, and
    // shouldReleasePreacquiredSessionsBeforeRetrying is true, try releasing all pre-acquired
    // sessions and then retry the acquisition.
    if (acquisitionFailedIndicatingResourceShortage(session)
        && shouldReleasePreacquiredSessionsBeforeRetrying
        && !preacquiredSessionReferences.isEmpty()) {
      releaseAllPreacquiredSessions();
      if (!keepaliveSessions.isEmpty()) {
        // Some preacquired sessions released above are now in their keepalive timeout phase. We
        // release the keepalive references immediately.
        releaseAllKeepaliveSessions();
      }
      undoAcquisition(session, eventDispatcher);
      session = createAndAcquireSession(schemeDatas, isPlaceholderSession, eventDispatcher);
    }
    return session;
  }

  private static boolean acquisitionFailedIndicatingResourceShortage(DrmSession session) {
    if (session.getState() != DrmSession.STATE_ERROR) {
      return false;
    }
    @Nullable Throwable cause = checkNotNull(session.getError()).getCause();
    return cause instanceof ResourceBusyException
        || DrmUtil.isFailureToConstructResourceBusyException(cause);
  }

  /**
   * Undoes the acquisitions from {@link #createAndAcquireSession(List, boolean,
   * DrmSessionEventListener.EventDispatcher)}.
   */
  private void undoAcquisition(
      DrmSession session, @Nullable DrmSessionEventListener.EventDispatcher eventDispatcher) {
    session.release(eventDispatcher);
    if (sessionKeepaliveMs != C.TIME_UNSET) {
      session.release(/* eventDispatcher= */ null);
    }
  }

  private void releaseAllKeepaliveSessions() {
    // Make a local copy, because sessions are removed from this.keepaliveSessions during
    // release (via callback).
    ImmutableSet<DefaultDrmSession> keepaliveSessions = ImmutableSet.copyOf(this.keepaliveSessions);
    for (DrmSession keepaliveSession : keepaliveSessions) {
      keepaliveSession.release(/* eventDispatcher= */ null);
    }
  }

  private void releaseAllPreacquiredSessions() {
    // Make a local copy, because sessions are removed from this.preacquiredSessionReferences
    // during release (via callback).
    ImmutableSet<PreacquiredSessionReference> preacquiredSessionReferences =
        ImmutableSet.copyOf(this.preacquiredSessionReferences);
    for (PreacquiredSessionReference preacquiredSessionReference : preacquiredSessionReferences) {
      preacquiredSessionReference.release();
    }
  }

  /**
   * Creates a new {@link DefaultDrmSession} and acquires it on behalf of the caller (passing in
   * {@code eventDispatcher}).
   *
   * <p>If {@link #sessionKeepaliveMs} != {@link C#TIME_UNSET} then acquires it again to allow the
   * manager to keep it alive (passing in {@code eventDispatcher=null}.
   */
  private DefaultDrmSession createAndAcquireSession(
      @Nullable List<SchemeData> schemeDatas,
      boolean isPlaceholderSession,
      @Nullable DrmSessionEventListener.EventDispatcher eventDispatcher) {
    checkNotNull(exoMediaDrm);
    // Placeholder sessions should always play clear samples without keys.
    boolean playClearSamplesWithoutKeys = this.playClearSamplesWithoutKeys | isPlaceholderSession;
    DefaultDrmSession session =
        new DefaultDrmSession(
            uuid,
            exoMediaDrm,
            /* provisioningManager= */ provisioningManagerImpl,
            referenceCountListener,
            schemeDatas,
            mode,
            playClearSamplesWithoutKeys,
            isPlaceholderSession,
            offlineLicenseKeySetId,
            keyRequestParameters,
            callback,
            checkNotNull(playbackLooper),
            loadErrorHandlingPolicy,
            checkNotNull(playerId));
    // Acquire the session once on behalf of the caller to DrmSessionManager - this is the
    // reference 'assigned' to the caller which they're responsible for releasing. Do this first,
    // to ensure that eventDispatcher receives all events related to the initial
    // acquisition/opening.
    session.acquire(eventDispatcher);
    if (sessionKeepaliveMs != C.TIME_UNSET) {
      // Acquire the session once more so the Manager can keep it alive.
      session.acquire(/* eventDispatcher= */ null);
    }
    return session;
  }

  private void maybeReleaseMediaDrm() {
    if (exoMediaDrm != null
        && prepareCallsCount == 0
        && sessions.isEmpty()
        && preacquiredSessionReferences.isEmpty()) {
      // This manager and all its sessions are fully released so we can release exoMediaDrm.
      checkNotNull(exoMediaDrm).release();
      exoMediaDrm = null;
    }
  }

  private void verifyPlaybackThread(boolean allowBeforeSetPlayer) {
    if (allowBeforeSetPlayer && playbackLooper == null) {
      Log.w(
          TAG,
          "DefaultDrmSessionManager accessed before setPlayer(), possibly on the wrong thread.",
          new IllegalStateException());
    } else if (Thread.currentThread() != checkNotNull(playbackLooper).getThread()) {
      Log.w(
          TAG,
          "DefaultDrmSessionManager accessed on the wrong thread.\nCurrent thread: "
              + Thread.currentThread().getName()
              + "\nExpected thread: "
              + playbackLooper.getThread().getName(),
          new IllegalStateException());
    }
  }

  /**
   * Extracts {@link SchemeData} instances suitable for the given DRM scheme {@link UUID}.
   *
   * @param drmInitData The {@link DrmInitData} from which to extract the {@link SchemeData}.
   * @param uuid The UUID.
   * @param allowMissingData Whether a {@link SchemeData} with null {@link SchemeData#data} may be
   *     returned.
   * @return The extracted {@link SchemeData} instances, or an empty list if no suitable data is
   *     present.
   */
  private static List<SchemeData> getSchemeDatas(
      DrmInitData drmInitData, UUID uuid, boolean allowMissingData) {
    // Look for matching scheme data (matching the Common PSSH box for ClearKey).
    List<SchemeData> matchingSchemeDatas = new ArrayList<>(drmInitData.schemeDataCount);
    for (int i = 0; i < drmInitData.schemeDataCount; i++) {
      SchemeData schemeData = drmInitData.get(i);
      boolean uuidMatches =
          schemeData.matches(uuid)
              || (C.CLEARKEY_UUID.equals(uuid) && schemeData.matches(C.COMMON_PSSH_UUID));
      if (uuidMatches && (schemeData.data != null || allowMissingData)) {
        matchingSchemeDatas.add(schemeData);
      }
    }
    return matchingSchemeDatas;
  }

  @SuppressLint("HandlerLeak")
  private class MediaDrmHandler extends Handler {

    public MediaDrmHandler(Looper looper) {
      super(looper);
    }

    @Override
    public void handleMessage(Message msg) {
      byte[] sessionId = (byte[]) msg.obj;
      if (sessionId == null) {
        // The event is not associated with any particular session.
        return;
      }
      for (DefaultDrmSession session : sessions) {
        if (session.hasSessionId(sessionId)) {
          session.onMediaDrmEvent(msg.what);
          return;
        }
      }
    }
  }

  private class ProvisioningManagerImpl implements DefaultDrmSession.ProvisioningManager {

    private final Set<DefaultDrmSession> sessionsAwaitingProvisioning;
    @Nullable private DefaultDrmSession provisioningSession;

    public ProvisioningManagerImpl() {
      sessionsAwaitingProvisioning = new HashSet<>();
    }

    @Override
    public void provisionRequired(DefaultDrmSession session) {
      sessionsAwaitingProvisioning.add(session);
      if (provisioningSession != null) {
        // Provisioning is already in-flight.
        return;
      }
      provisioningSession = session;
      session.provision();
    }

    @Override
    public void onProvisionCompleted() {
      provisioningSession = null;
      ImmutableList<DefaultDrmSession> sessionsToNotify =
          ImmutableList.copyOf(sessionsAwaitingProvisioning);
      // Clear the list before calling onProvisionComplete in case provisioning is re-requested.
      sessionsAwaitingProvisioning.clear();
      for (DefaultDrmSession session : sessionsToNotify) {
        session.onProvisionCompleted();
      }
    }

    @Override
    public void onProvisionError(Exception error, boolean thrownByExoMediaDrm) {
      provisioningSession = null;
      ImmutableList<DefaultDrmSession> sessionsToNotify =
          ImmutableList.copyOf(sessionsAwaitingProvisioning);
      // Clear the list before calling onProvisionError in case provisioning is re-requested.
      sessionsAwaitingProvisioning.clear();
      for (DefaultDrmSession session : sessionsToNotify) {
        session.onProvisionError(error, thrownByExoMediaDrm);
      }
    }

    public void onSessionFullyReleased(DefaultDrmSession session) {
      sessionsAwaitingProvisioning.remove(session);
      if (provisioningSession == session) {
        provisioningSession = null;
        if (!sessionsAwaitingProvisioning.isEmpty()) {
          // Other sessions were waiting for the released session to complete a provision operation.
          // We need to have one of those sessions perform the provision operation instead.
          provisioningSession = sessionsAwaitingProvisioning.iterator().next();
          provisioningSession.provision();
        }
      }
    }
  }

  private class ReferenceCountListenerImpl implements DefaultDrmSession.ReferenceCountListener {

    @Override
    public void onReferenceCountIncremented(DefaultDrmSession session, int newReferenceCount) {
      if (sessionKeepaliveMs != C.TIME_UNSET) {
        // The session has been acquired elsewhere so we want to cancel our timeout.
        keepaliveSessions.remove(session);
        checkNotNull(playbackHandler).removeCallbacksAndMessages(session);
      }
    }

    @Override
    public void onReferenceCountDecremented(DefaultDrmSession session, int newReferenceCount) {
      if (newReferenceCount == 1 && prepareCallsCount > 0 && sessionKeepaliveMs != C.TIME_UNSET) {
        // Only the internal keep-alive reference remains, so we can start the timeout. We only
        // do this if the manager isn't released, because a released manager has already released
        // all its internal session keep-alive references.
        keepaliveSessions.add(session);
        checkNotNull(playbackHandler)
            .postAtTime(
                () -> session.release(/* eventDispatcher= */ null),
                session,
                /* uptimeMillis= */ SystemClock.uptimeMillis() + sessionKeepaliveMs);
      } else if (newReferenceCount == 0) {
        // This session is fully released.
        sessions.remove(session);
        if (placeholderDrmSession == session) {
          placeholderDrmSession = null;
        }
        if (noMultiSessionDrmSession == session) {
          noMultiSessionDrmSession = null;
        }
        provisioningManagerImpl.onSessionFullyReleased(session);
        if (sessionKeepaliveMs != C.TIME_UNSET) {
          checkNotNull(playbackHandler).removeCallbacksAndMessages(session);
          keepaliveSessions.remove(session);
        }
      }
      maybeReleaseMediaDrm();
    }
  }

  private class MediaDrmEventListener implements OnEventListener {

    @Override
    public void onEvent(
        ExoMediaDrm md, @Nullable byte[] sessionId, int event, int extra, @Nullable byte[] data) {
      checkNotNull(mediaDrmHandler).obtainMessage(event, sessionId).sendToTarget();
    }
  }

  /**
   * An implementation of {@link DrmSessionReference} that lazily acquires the underlying {@link
   * DrmSession}.
   *
   * <p>A new instance is needed for each reference (compared to maintaining exactly one instance
   * for each {@link DrmSession}) because each associated {@link
   * DrmSessionEventListener.EventDispatcher} might be different. The {@link
   * DrmSessionEventListener.EventDispatcher} is required to implement the zero-arg {@link
   * DrmSessionReference#release()} method.
   */
  private class PreacquiredSessionReference implements DrmSessionReference {

    @Nullable private final DrmSessionEventListener.EventDispatcher eventDispatcher;

    @Nullable private DrmSession session;
    private boolean isReleased;

    /**
     * Constructs an instance.
     *
     * @param eventDispatcher The {@link DrmSessionEventListener.EventDispatcher} passed to {@link
     *     #acquireSession(DrmSessionEventListener.EventDispatcher, Format)}.
     */
    public PreacquiredSessionReference(
        @Nullable DrmSessionEventListener.EventDispatcher eventDispatcher) {
      this.eventDispatcher = eventDispatcher;
    }

    /**
     * Acquires the underlying session.
     *
     * <p>Must be called at most once. Can be called from any thread.
     */
    public void acquire(Format format) {
      checkNotNull(playbackHandler)
          .post(
              () -> {
                if (prepareCallsCount == 0 || isReleased) {
                  // The manager has been fully released or this reference has already been
                  // released. Abort the acquisition attempt.
                  return;
                }
                this.session =
                    acquireSession(
                        checkNotNull(playbackLooper),
                        eventDispatcher,
                        format,
                        /* shouldReleasePreacquiredSessionsBeforeRetrying= */ false);
                preacquiredSessionReferences.add(this);
              });
    }

    @Override
    public void release() {
      // Ensure the underlying session is released immediately if we're already on the playback
      // thread, to allow a failed session opening to be immediately retried.
      Util.postOrRun(
          checkNotNull(playbackHandler),
          () -> {
            if (isReleased) {
              return;
            }
            if (session != null) {
              session.release(eventDispatcher);
            }
            preacquiredSessionReferences.remove(this);
            isReleased = true;
          });
    }
  }
}