Add DownloadActionUtil class

PiperOrigin-RevId: 224647076

library/core/src/main/java/com/google/android/exoplayer2/offline/DownloadActionUtil.java

+/*
+ * Copyright (C) 2018 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.offline;
+
+import com.google.android.exoplayer2.util.Assertions;
+import java.util.ArrayDeque;
+import java.util.ArrayList;
+import java.util.HashSet;
+
+/** {@link DownloadAction} related utility methods. */
+public class DownloadActionUtil {
+
+  private DownloadActionUtil() {}
+
+  /**
+   * Merge {@link DownloadAction}s in {@code actionQueue} to minimum number of actions.
+   *
+   * <p>All actions must have the same type and must be for the same media.
+   *
+   * @param actionQueue Queue of actions. Must not be empty.
+   * @return The first action in the queue.
+   */
+  public static DownloadAction mergeActions(ArrayDeque<DownloadAction> actionQueue) {
+    DownloadAction removeAction = null;
+    DownloadAction downloadAction = null;
+    HashSet<StreamKey> keys = new HashSet<>();
+    boolean downloadAllTracks = false;
+    DownloadAction firstAction = Assertions.checkNotNull(actionQueue.peek());
+
+    while (!actionQueue.isEmpty()) {
+      DownloadAction action = actionQueue.remove();
+      Assertions.checkState(action.type.equals(firstAction.type));
+      Assertions.checkState(action.isSameMedia(firstAction));
+      if (action.isRemoveAction) {
+        removeAction = action;
+        downloadAction = null;
+        keys.clear();
+        downloadAllTracks = false;
+      } else {
+        if (!downloadAllTracks) {
+          if (action.keys.isEmpty()) {
+            downloadAllTracks = true;
+            keys.clear();
+          } else {
+            keys.addAll(action.keys);
+          }
+        }
+        downloadAction = action;
+      }
+    }
+
+    if (removeAction != null) {
+      actionQueue.add(removeAction);
+    }
+    if (downloadAction != null) {
+      actionQueue.add(
+          DownloadAction.createDownloadAction(
+              downloadAction.type,
+              downloadAction.uri,
+              new ArrayList<>(keys),
+              downloadAction.customCacheKey,
+              downloadAction.data));
+    }
+    return Assertions.checkNotNull(actionQueue.peek());
+  }
+}