Introduce concept of DockUser

Dreams and docking often refers to "user zero" or "system user".
But more generally, the special user for dreams or switching-to-on-docking
need not be user 0, and in fact won't be in certain modes. So this needs updating.

Test: the files mentioned in the topic
Bug: 257333623
Change-Id: If068aa79a770bed4abf3f7ca1859a95cd1eb4ecd

src/com/android/settings/users/TimeoutToDockUserSettings.java

@@ -0,0 +1,122 @@
+/*
+ * Copyright (C) 2022 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.users;
+
+import static android.provider.Settings.Secure.TIMEOUT_TO_DOCK_USER;
+
+import android.app.settings.SettingsEnums;
+import android.content.Context;
+import android.graphics.drawable.Drawable;
+import android.os.UserHandle;
+import android.provider.Settings;
+
+import com.android.settings.R;
+import com.android.settings.widget.RadioButtonPickerFragment;
+import com.android.settingslib.widget.CandidateInfo;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Setting screen that lists options for users to configure whether to automatically switch to the
+ * Dock User when the device is docked, and if so duration of the timeout.
+ */
+public class TimeoutToDockUserSettings extends RadioButtonPickerFragment {
+    // Index of the default key of the timeout setting if it hasn't been changed by the user.
+    public static final int DEFAULT_TIMEOUT_SETTING_VALUE_INDEX = 0;
+
+    // Labels of the options, for example, "never", "after 5 minutes".
+    private String[] mEntries;
+
+    // Values and keys of the options.
+    private String[] mValues;
+
+    @Override
+    public int getMetricsCategory() {
+        return SettingsEnums.TIMEOUT_TO_USER_ZERO;
+    }
+
+    @Override
+    protected int getPreferenceScreenResId() {
+        return R.xml.user_timeout_to_dock_user_settings;
+    }
+
+    @Override
+    public void onAttach(Context context) {
+        super.onAttach(context);
+
+        mEntries = getContext().getResources().getStringArray(
+                R.array.switch_to_dock_user_when_docked_timeout_entries);
+        mValues = getContext().getResources().getStringArray(
+                R.array.switch_to_dock_user_when_docked_timeout_values);
+    }
+
+    @Override
+    protected List<? extends CandidateInfo> getCandidates() {
+        final List<CandidateInfo> candidates = new ArrayList<>();
+
+        if (mEntries == null || mValues == null) {
+            return candidates;
+        }
+
+        for (int i = 0; i < mValues.length; i++) {
+            candidates.add(new TimeoutCandidateInfo(mEntries[i], mValues[i], true));
+        }
+
+        return candidates;
+    }
+
+    @Override
+    protected String getDefaultKey() {
+        final String defaultKey = Settings.Secure.getStringForUser(
+                getContext().getContentResolver(), TIMEOUT_TO_DOCK_USER, UserHandle.myUserId());
+        return defaultKey != null ? defaultKey : mValues[DEFAULT_TIMEOUT_SETTING_VALUE_INDEX];
+    }
+
+    @Override
+    protected boolean setDefaultKey(String key) {
+        Settings.Secure.putStringForUser(getContext().getContentResolver(), TIMEOUT_TO_DOCK_USER,
+                key, UserHandle.myUserId());
+        return true;
+    }
+
+    private static class TimeoutCandidateInfo extends CandidateInfo {
+        private final CharSequence mLabel;
+        private final String mKey;
+
+        TimeoutCandidateInfo(CharSequence label, String key, boolean enabled) {
+            super(enabled);
+            mLabel = label;
+            mKey = key;
+        }
+
+        @Override
+        public CharSequence loadLabel() {
+            return mLabel;
+        }
+
+        @Override
+        public Drawable loadIcon() {
+            return null;
+        }
+
+        @Override
+        public String getKey() {
+            return mKey;
+        }
+    }
+}