/*
 * 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 android.util;

import android.content.ContentResolver;
import android.database.ContentObserver;
import android.net.Uri;
import android.os.Handler;

Abstract class for observing changes to a specified setting stored as a comma-separated key value list of parameters. Registers and unregisters a ContentObserver and handles updates when the setting changes. 
Subclasses should pass in the relevant setting's Uri in the constructor and implement update(KeyValueListParser) to receive updates when the value changes. Calls to update(KeyValueListParser) only trigger after calling start(). 
To get the most up-to-date parameter values, first call start() before accessing the values to start observing changes, and then call stop() once finished. 
@hide
/**
 * Abstract class for observing changes to a specified setting stored as a comma-separated key value
 * list of parameters. Registers and unregisters a {@link ContentObserver} and handles updates when
 * the setting changes.
 *
 * <p>Subclasses should pass in the relevant setting's {@link Uri} in the constructor and implement
 * {@link #update(KeyValueListParser)} to receive updates when the value changes.
 * Calls to {@link #update(KeyValueListParser)} only trigger after calling {@link
 * #start()}.
 *
 * <p>To get the most up-to-date parameter values, first call {@link #start()} before accessing the
 * values to start observing changes, and then call {@link #stop()} once finished.
 *
 * @hide
 */
public abstract class KeyValueSettingObserver {
    private static final String TAG = "KeyValueSettingObserver";

    private final KeyValueListParser mParser = new KeyValueListParser(',');

    private final ContentObserver mObserver;
    private final ContentResolver mResolver;
    private final Uri mSettingUri;

    public KeyValueSettingObserver(Handler handler, ContentResolver resolver,
            Uri uri) {
        mObserver = new SettingObserver(handler);
        mResolver = resolver;
        mSettingUri = uri;
    }

    
Starts observing changes for the setting. Pair with stop(). /** Starts observing changes for the setting. Pair with {@link #stop()}. */
    public void start() {
        mResolver.registerContentObserver(mSettingUri, false, mObserver);
        setParserValue();
        update(mParser);
    }

    
Stops observing changes for the setting. /** Stops observing changes for the setting. */
    public void stop() {
        mResolver.unregisterContentObserver(mObserver);
    }

    
Returns the String representation of the setting. Subclasses should implement this for their setting. /**
     * Returns the {@link String} representation of the setting. Subclasses should implement this
     * for their setting.
     */
    public abstract String getSettingValue(ContentResolver resolver);

    
Updates the parser with the current setting value. /** Updates the parser with the current setting value. */
    private void setParserValue() {
        String setting = getSettingValue(mResolver);
        try {
            mParser.setString(setting);
        } catch (IllegalArgumentException e) {
            Slog.e(TAG, "Malformed setting: " + setting);
        }
    }

    
Subclasses should implement this to update references to their parameters. /** Subclasses should implement this to update references to their parameters. */
    public abstract void update(KeyValueListParser parser);

    private class SettingObserver extends ContentObserver {
        private SettingObserver(Handler handler) {
            super(handler);
        }

        @Override
        public void onChange(boolean selfChange) {
            setParserValue();
            update(mParser);
        }
    }
}