Extract base class from DashDownloaderFactory

This base class will be used to extend HlsDownloaderFactory from.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=160523335

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

+/*
+ * Copyright (C) 2017 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.source.offline;
+
+import android.support.annotation.Nullable;
+import com.google.android.exoplayer2.upstream.DataSink;
+import com.google.android.exoplayer2.upstream.DataSource;
+import com.google.android.exoplayer2.upstream.DataSource.Factory;
+import com.google.android.exoplayer2.upstream.cache.Cache;
+import com.google.android.exoplayer2.util.ClosedSource;
+import com.google.android.exoplayer2.util.PriorityTaskManager;
+
+/**
+ * A factory class that produces {@link Downloader}.
+ */
+@ClosedSource(reason = "Not ready yet")
+public abstract class DownloaderFactory<T extends Downloader<?, ?>> {
+
+  private final Factory upstreamDataSourceFactory;
+  private final Factory cacheReadDataSourceFactory;
+  private final DataSink.Factory cacheWriteDataSinkFactory;
+
+  protected final Cache cache;
+  protected final PriorityTaskManager priorityTaskManager;
+
+  /**
+   * Constructs a DashDownloaderFactory.
+   *
+   * @param cache Cache instance to be used to store downloaded data.
+   * @param upstreamDataSourceFactory A {@link Factory} for downloading data.
+   */
+  public DownloaderFactory(Cache cache, Factory upstreamDataSourceFactory) {
+    this(cache, upstreamDataSourceFactory, null, null, null);
+  }
+
+  /**
+   * Constructs a DashDownloaderFactory.
+   *
+   * @param cache Cache instance to be used to store downloaded data.
+   * @param upstreamDataSourceFactory A {@link Factory} for downloading data.
+   * @param cacheReadDataSourceFactory A {@link Factory} for reading data from the cache.
+   *     If null, null is passed to {@link Downloader} constructor.
+   * @param cacheWriteDataSinkFactory A {@link DataSink.Factory} for writing data to the cache. If
+   *     null, null is passed to {@link Downloader} constructor.
+   * @param priorityTaskManager If one is given then the download priority is set lower than
+   *     loading. If null, null is passed to {@link Downloader} constructor.
+   */
+  public DownloaderFactory(Cache cache, Factory upstreamDataSourceFactory,
+      @Nullable Factory cacheReadDataSourceFactory,
+      @Nullable DataSink.Factory cacheWriteDataSinkFactory,
+      @Nullable PriorityTaskManager priorityTaskManager) {
+    this.cache = cache;
+    this.upstreamDataSourceFactory = upstreamDataSourceFactory;
+    this.cacheReadDataSourceFactory = cacheReadDataSourceFactory;
+    this.cacheWriteDataSinkFactory = cacheWriteDataSinkFactory;
+    this.priorityTaskManager = priorityTaskManager;
+  }
+
+  /**
+   * Creates a {@link Downloader} with the given manifest.
+   *
+   * @param manifestUri The URI of the manifest of the DASH to be downloaded.
+   * @return A {@link Downloader}.
+   */
+  public final T create(String manifestUri) {
+    return create(manifestUri,
+        upstreamDataSourceFactory != null ? upstreamDataSourceFactory.createDataSource() : null,
+        cacheReadDataSourceFactory != null ? cacheReadDataSourceFactory.createDataSource() : null,
+        cacheWriteDataSinkFactory != null ? cacheWriteDataSinkFactory.createDataSink() : null);
+  }
+
+  protected abstract T create(String manifestUri, DataSource upstreamDataSource,
+      DataSource cacheReadDataSource, DataSink cacheWriteDataSink);
+
+}