Add downloads to the deletion helper.

This adds a deletion service to delete files in the Downloads
folder. All of the files there are collected and offered to the
user to delete.

Bug: 28621781
Change-Id: I94431f9abc3a0afa2d07dbab763312c09e830aef

src/com/android/settings/deletionhelper/FetchDownloadsLoader.java

@@ -0,0 +1,96 @@
+/*
+ * 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 com.android.settings.deletionhelper;
+
+import android.content.Context;
+import android.support.annotation.VisibleForTesting;
+import com.android.settings.utils.AsyncLoader;
+
+import java.io.File;
+import java.util.ArrayList;
+
+/**
+ * FetchDownloadsLoader is an asynchronous task which returns files in the Downloads
+ * directory which have not been modified in longer than 90 days.
+ */
+public class FetchDownloadsLoader extends
+        AsyncLoader<FetchDownloadsLoader.DownloadsResult> {
+    private File mDirectory;
+
+    /**
+     * Sets up a FetchDownloadsLoader in any directory.
+     * @param directory The directory to look into.
+     */
+    public FetchDownloadsLoader(Context context, File directory) {
+        super(context);
+        mDirectory = directory;
+    }
+
+    @Override
+    protected void onDiscardResult(DownloadsResult result) {}
+
+    @Override
+    public DownloadsResult loadInBackground() {
+        return collectFiles(mDirectory);
+    }
+
+    @VisibleForTesting
+    static DownloadsResult collectFiles(File dir) {
+        return collectFiles(dir, new DownloadsResult());
+    }
+
+    private static DownloadsResult collectFiles(File dir, DownloadsResult result) {
+        File downloadFiles[] = dir.listFiles();
+        if (downloadFiles == null) {
+        }
+        if (downloadFiles != null && downloadFiles.length > 0) {
+            for (File currentFile : downloadFiles) {
+                if (currentFile.isDirectory()) {
+                    collectFiles(currentFile, result);
+                } else {
+                    if (currentFile.lastModified() < result.youngestLastModified) {
+                        result.youngestLastModified = currentFile.lastModified();
+                    }
+                    result.files.add(currentFile);
+                    result.totalSize += currentFile.length();
+                }
+            }
+        }
+
+        return result;
+    }
+
+    /**
+     * The DownloadsResult is the result of a {@link FetchDownloadsLoader} with the files
+     * and the amount of space they use.
+     */
+    public static class DownloadsResult {
+        public long totalSize;
+        public long youngestLastModified;
+        public ArrayList<File> files;
+
+        public DownloadsResult() {
+            this(0, Long.MAX_VALUE, new ArrayList<File>());
+        }
+
+        public DownloadsResult(long totalSize, long youngestLastModified, ArrayList<File> files) {
+            this.totalSize = totalSize;
+            this.youngestLastModified = youngestLastModified;
+            this.files = files;
+        }
+    }
+}