/*
 * Copyright (C) 2005-2010 Alfresco Software Limited.
 *
 * This file is part of Alfresco
 *
 * Alfresco is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Alfresco is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with Alfresco. If not, see <http://www.gnu.org/licenses/>.
 */
package org.alfresco.repo.admin.registry;

import java.io.Serializable;
import java.util.Collection;

/**
 * Interface for service providing access to key-value pairs for storage
 * of system-controlled metadata.
 * 
 * @author Derek Hulley
 */
public interface RegistryService
{
    /**
     * Assign a value to the registry key, which must be of the form <b>/a/b/c</b>.
     * 
     * @param key           the registry key.
     * @param value         any value that can be stored in the repository.
     */
    void addProperty(RegistryKey key, Serializable value);
    
    /**
     * @param key           the registry key.
     * @return              Returns the value stored in the key or <tt>null</tt> if
     *                      no value exists at the path and name provided
     * 
     * @see #addProperty(String, Serializable)
     */
    Serializable getProperty(RegistryKey key);
    
    /**
     * Fetches all child elements for the given path.  The key's property should be
     * <tt>null</tt> as it is completely ignored.
     * <code><pre>
     *    ...
     *    registryService.addValue(KEY_A_B_C_1, VALUE_ONE);
     *    registryService.addValue(KEY_A_B_C_2, VALUE_TWO);
     *    ...
     *    assertTrue(registryService.getChildElements(KEY_A_B_null).contains("C"));
     *    ...
     * </pre></code>
     * 
     * @param key           the registry key with the path.  The last element in the path
     *                      will be ignored, and can be any acceptable value localname or <tt>null</tt>.
     * @return              Returns all child elements (not values) for the given key, ignoring
     *                      the last element in the key.
     * 
     * @see RegistryKey#getPath()
     */
    Collection<String> getChildElements(RegistryKey key);
    
    /**
     * Copies the path or value from the source to the target location.  The source and target
     * keys <b>must</b> be both either path-specific or property-specific.  If the source doesn't
     * exist, then nothing will be done; there is no guarantee that the target will exist after
     * the call.
     * <p>
     * This is essentially a merge operation.  Use {@link #delete(RegistryKey) delete} first
     * if the target must be cleaned.
     * 
     * @param sourceKey     the source registry key to take values from
     * @param targetKey     the target registyr key to move the path or value to
     */
    void copy(RegistryKey sourceKey, RegistryKey targetKey);
    
    /**
     * Delete the path element or value described by the key.  If the key points to nothing,
     * then nothing is done.
     * <code>delete(/a/b/c)</code> will remove value <b>c</b> from path <b>/a/b</b>.<br/>
     * <code>delete(/a/b/null)</code> will remove node <b>/a/b</b> along with all values and child
     * elements.
     * 
     * @param key           the path or value to delete
     */
    void delete(RegistryKey key);
}
