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chrome/android/java/src/org/chromium/chrome/browser/download/ui/DownloadItemSelectionDelegate.java

Index: chrome/android/java/src/org/chromium/chrome/browser/download/ui/DownloadItemSelectionDelegate.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/download/ui/DownloadItemSelectionDelegate.java b/chrome/android/java/src/org/chromium/chrome/browser/download/ui/DownloadItemSelectionDelegate.java
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+++ b/chrome/android/java/src/org/chromium/chrome/browser/download/ui/DownloadItemSelectionDelegate.java
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+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.chrome.browser.download.ui;
+
+import org.chromium.base.ObserverList;
+import org.chromium.chrome.browser.download.ui.DownloadHistoryAdapter.SubsectionHeader;
+import org.chromium.chrome.browser.widget.selection.SelectionDelegate;
+
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+/**
+ * Separately maintains the selected state of the {@link SubsectionHeader}s in addition to the other
+ * selected items. Notifies the {@link OfflineGroupHeaderView}s about any change in the selected
+ * state of the headers.
+ */
+public class DownloadItemSelectionDelegate extends SelectionDelegate<DownloadHistoryItemWrapper> {
+    /** Observer interface to be notified of selection changes for {@link SubsectionHeader}s. */
+    public interface SubsectionHeaderSelectionObserver {
+        /**
+         * Called when the set of selected subsection headers has changed.
+         * @param selectedHeaders The set of currently selected headers.
+         */
+        public void onSubsectionHeaderSelectionStateChanged(Set<SubsectionHeader> selectedHeaders);
+    }
+
+    private final Set<SubsectionHeader> mSelectedHeaders = new HashSet<>();
+    private final ObserverList<SubsectionHeaderSelectionObserver> mObservers = new ObserverList<>();
+    private DownloadHistoryAdapter mAdapter;
+
+    /**
+     * Adds an observer to be notified of selection changes for subsection headers.
+     * @param observer The observer to add.
+     */
+    public void addObserver(SubsectionHeaderSelectionObserver observer) {
+        mObservers.addObserver(observer);
+    }
+
+    /**
+     * Removes an observer.
+     * @param observer The observer to remove.
+     */
+    public void removeObserver(SubsectionHeaderSelectionObserver observer) {
+        mObservers.removeObserver(observer);
+    }
+
+    /**
+     * Initializes the selection delegate with the required dependencies. Registers an observer to
+     * be notified of selection changes for the download items of the adapter.
+     * @param adapter The associated download history adapter.
+     */
+    public void initialize(DownloadHistoryAdapter adapter) {
+        mAdapter = adapter;
+        addObserver(new SelectionObserver<DownloadHistoryItemWrapper>() {
+            @Override
+            public void onSelectionStateChange(List<DownloadHistoryItemWrapper> selectedItems) {
+                for (SubsectionHeader header : mAdapter.getSubsectionHeaders()) {
+                    boolean isChecked = true;
+
+                    // A header should get selected if all the associated items are selected
+                    // irrespective of whether it is currently expanded or collapsed.
+                    for (DownloadHistoryItemWrapper subItem : header.getItems()) {
+                        if (!selectedItems.contains(subItem)) {
+                            isChecked = false;
+                            break;
+                        }
+                    }
+                    setSelectionForHeader(header, isChecked);
+                }
+
+                notifySubsectionHeaderSelectionStateChanged();
+            }
+        });
+    }
+
+    /**
+     * True if the header is currently selected. False otherwise.
+     * @param header The given header.
+     * @return Whether the header is selected.
+     */
+    public boolean isHeaderSelected(SubsectionHeader header) {
+        return mSelectedHeaders.contains(header);
+    }
+
+    /**
+     * Toggles selection for a given subsection and sets the associated items to the correct
+     * selection state.
+     * @param header The header for the subsection being toggled.
+     * @return True if the header is selected after the toggle, false otherwise.
+     */
+    public boolean toggleSelectionForSubsection(SubsectionHeader header) {
+        boolean newSelectedState = !isHeaderSelected(header);
+        setSelectionForHeader(header, newSelectedState);
+
+        for (DownloadHistoryItemWrapper item : header.getItems()) {
+            if (newSelectedState != isItemSelected(item)) {
+                toggleSelectionForItem(item);
+            }
+        }
+
+        return isHeaderSelected(header);
+    }
+
+    /**
+     * Sets the selection state for a given header. Doesn't affect the associated items. This method
+     * is supposed to be called if the header needs to be toggled as a result of selecting or
+     * deselecting one of the associated items. In case of a long press on the header, don't call
+     * this method, call {@link #toggleSelectionForSubsection(SubsectionHeader)} instead directly.
+     * @param header The given {@link SubsectionHeader}.
+     * @param selected The new selected state.
+     */
+    public void setSelectionForHeader(SubsectionHeader header, boolean selected) {
+        if (selected) {
+            mSelectedHeaders.add(header);
+        } else {
+            mSelectedHeaders.remove(header);
+        }
+    }
+
+    private void notifySubsectionHeaderSelectionStateChanged() {
+        for (SubsectionHeaderSelectionObserver observer : mObservers) {
+            observer.onSubsectionHeaderSelectionStateChanged(mSelectedHeaders);
+        }
+    }
+}