/*
 * Copyright (C) 2009 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.marvin.talkback;

import java.util.HashMap;

/**
 * This class represents an utterance composed of text to be spoken
 * and meta data about how this text to be spoken. The utterances
 * are cached in a pool of instances to be reused as an optimization
 * to reduce new object instantiation.
 *
 * @author svetoslavganov@google.com (Svetoslav Ganov)
 *
 */
public class Utterance {

    /**
     * Key for obtaining the queuing meta-data property.
     */
    public static final String KEY_METADATA_QUEUING = "queuing";

    /**
     * The maximal size of the pool with cached utterances.
     */
    private static final int MAX_POOL_SIZE = 3;

    /**
     * Mutex lock for accessing the utterance pool.
     */
    private static final Object sPoolLock = new Object();

    /**
     * Pool of cached utterances.
     */
    private static Utterance sPool;

    /**
     * The current size of the utterance pool.
     */
    private static int sPoolSize;

    /**
     * The next cached utterance
     */
    private Utterance mNext;

    /**
     * Denotes if an utterance is currently in the cache pool.
     */
    private boolean mIsInPool;

    /**
     * The text of the utterance.
     */
    private final StringBuilder mText = new StringBuilder();

    /**
     * Meta-data of how the utterance should be spoken.
     */
    private final HashMap<String, Object> mMetadata = new HashMap<String, Object>();

    /**
     * Creates a new instance.
     */
    private Utterance() {
       /* do nothing - reducing constructor visibility */ 
    }

    /**
     * Returns a cached instance if such is available or a new
     * one is instantiated.
     *
     * @return An instance.
     */
    public static Utterance obtain() {
        return obtain("");
    }

    /**
     * Returns a cached instance if such is available or a new
     * one is instantiated and sets its <code>text</code>.
     *
     * @param text The text of the returned utterance.
     * @return An instance.
     */
    public static Utterance obtain(String text) {
        synchronized (sPoolLock) {
            if (sPool != null) {
                Utterance utterance = sPool;
                sPool = sPool.mNext;
                sPoolSize--;
                utterance.mNext = null;
                utterance.mIsInPool = false;
                return utterance;
            }
            return new Utterance();
        }
    }

    /**
     * Gets the text of this utterance.
     *
     * @return The utterance text.
     */
    public StringBuilder getText() {
        return mText;
    }

    /**
     * Gets the mets-data of this utterance.
     *
     * @return The utterance meta-data.
     */
    public HashMap<String, Object> getMetadata() {
        return mMetadata;
    }

    /**
     * Return an instance back to be reused.
     * <p>
     * <b>Note: You must not touch the object after calling this function.</b>
     */
    public void recycle() {
        if (mIsInPool) {
            return;
        }
        clear();
        synchronized (sPoolLock) {
            if (sPoolSize <= MAX_POOL_SIZE) {
                mNext = sPool;
                sPool = this;
                mIsInPool = true;
                sPoolSize++;
            }
        }
    }

    /**
     * Clears the state of this instance.
     */
    private void clear() {
        mText.delete(0, mText.length());
        mMetadata.clear();
    }
}