Transaction.java

/*
 * Digital Audio Access Protocol (DAAP) Library
 * Copyright (C) 2004-2010 Roger Kapsi
 *
 * 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 org.ardverk.daap;

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

/**
 * The Transaction object is the handle for a transaction. Methods off the
 * transaction handle are used to abort and commit the transaction.
 * 
 * @author Roger Kapsi
 */
public class Transaction {

    protected final Map<Object, List<Txn>> txnMap 
        = new HashMap<Object, List<Txn>>();
    
    protected final Library library;
    
    protected boolean open = false;
    
    protected Transaction(Library library) {
        this.library = library;
        this.open = true;
    }

    public Library getLibrary() {
        return library;
    }

    /**
     * Returns <code>true</code> if this Transaction is open what means that it
     * hasn't been commited yet.
     * 
     * @return <code>true</code> if this Transaction is open
     */
    public synchronized boolean isOpen() {
        return open;
    }

    /**
     * Commit this Transaction
     */
    public synchronized void commit() {
        if (!isOpen())
            throw new DaapException("Transaction is not open");

        try {
            if (!txnMap.isEmpty()) {
                synchronized (library) {
                    for (List<Txn> list : txnMap.values()) {
                        for (Txn txn : list) {
                            txn.commit(this);
                        }
                    }
                    library.commit(this);
                }
            }
        } finally {
            close();
        }
    }

    /**
     * Rollback this Transaction
     */
    public synchronized void rollback() {
        if (!isOpen())
            throw new DaapException("Transaction is not open");

        try {
            if (!txnMap.isEmpty()) {
                synchronized (library) {
                    for (List<Txn> list : txnMap.values()) {
                        for (Txn txn : list) {
                            txn.rollback(this);
                        }
                    }
                    library.rollback(this);
                }
            }
        } finally {
            close();
        }
    }

    /**
     * Attaches Object and Txn to this Transaction. Object must be an instance
     * of Song, Playlist, Database or Library!
     */
    protected synchronized void addTxn(Object obj, Txn txn) {
        // if (!isOpen()) {
        // throw new DaapException("Transaction is not open");
        // }

        List<Txn> list = txnMap.get(obj);
        if (list == null || list == Collections.EMPTY_LIST) {
            list = new ArrayList<Txn>();
            txnMap.put(obj, list);
        }
        list.add(txn);
    }

    /**
     * Attach Object to Transaction. This is necessary for Objects that were
     * constructed/modified independently from this transaction.
     */
    @SuppressWarnings("unchecked")
    protected synchronized void attach(Object obj) {
        if (!txnMap.containsKey(obj)) {
            txnMap.put(obj, Collections.EMPTY_LIST);
        }
    }

    /**
     * Returns true if Library or one of its Databases was modified
     */
    @SuppressWarnings("unchecked")
    protected synchronized boolean modified(Library library) {
        if (txnMap.containsKey(library)) {
            return true;
        }

        for (Database database : library.getDatabases()) {
            if (modified(database)) {
                txnMap.put(library, Collections.EMPTY_LIST);
                return true;
            }
        }
        return false;
    }

    /**
     * Returns true if Database or one of its Playlists was modified
     */
    @SuppressWarnings("unchecked")
    protected synchronized boolean modified(Database database) {
        if (txnMap.containsKey(database)) {
            return true;
        }

        Iterator<Playlist> it = database.getPlaylists().iterator();
        while (it.hasNext()) {
            if (modified(it.next())) {
                txnMap.put(database, Collections.EMPTY_LIST);
                return true;
            }
        }

        return false;
    }

    /**
     * Returns true if Playlist or one of its Songs was modified
     */
    protected synchronized boolean modified(Playlist playlist) {
        if (txnMap.containsKey(playlist)) {
            return true;
        }

        for (Song song : playlist.getSongs()) {
            if (modified(song)) {
                List<Txn> empty = Collections.emptyList();
                txnMap.put(playlist, empty);
                return true;
            }
        }

        return false;
    }

    /**
     * Returns true if Song was modified
     */
    protected synchronized boolean modified(Song song) {
        return txnMap.containsKey(song);
    }

    /**
     * Cleanup
     */
    protected void close() {
        if (open) {

            library.close(this);

            open = false;

            if (txnMap != null) {
                txnMap.clear();
            }
        }
    }

    @Override
    public String toString() {
        return "Transaction: " + library;
    }
}