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ModeShape implementation of the JCR API
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/*
 * ModeShape (http://www.modeshape.org)
 *
 * 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.modeshape.jcr.value;

import java.util.Set;
import org.modeshape.common.annotation.Immutable;
import org.modeshape.common.annotation.ThreadSafe;

/**
 * Registry of namespaces, which are used to provide isolated and independent domains for {@link Name names}.
 */
@ThreadSafe
public interface NamespaceRegistry {

    public static interface Holder {
        NamespaceRegistry getNamespaceRegistry();
    }

    /**
     * Return the namespace URI that is currently mapped to the empty prefix, or null if there is no current default namespace.
     * 
     * @return the namespace URI that represents the default namespace, or null if there is no default namespace
     */
    String getDefaultNamespaceUri();

    /**
     * Get the namespace URI for the supplied prefix.
     * 
     * @param prefix the namespace prefix
     * @return the namespace URI for the supplied prefix, or null if there is no namespace currently registered to use that prefix
     * @throws IllegalArgumentException if the prefix is null
     */
    String getNamespaceForPrefix( String prefix );

    /**
     * Return the prefix used for the supplied namespace URI.
     * 
     * @param namespaceUri the namespace URI
     * @param generateIfMissing true if the namespace URI has not already been registered and the method should auto-register the
     *        namespace with a generated prefix, or false if the method should never auto-register the namespace
     * @return the prefix currently being used for the namespace, or null if the namespace has not been registered
     *         and generateIfMissing is false
     * @throws IllegalArgumentException if the namespace URI is null
     * @see #isRegisteredNamespaceUri(String)
     */
    String getPrefixForNamespaceUri( String namespaceUri,
                                     boolean generateIfMissing );

    /**
     * Return whether there is a registered prefix for the supplied namespace URI.
     * 
     * @param namespaceUri the namespace URI
     * @return true if the supplied namespace has been registered with a prefix, or false otherwise
     * @throws IllegalArgumentException if the namespace URI is null
     */
    boolean isRegisteredNamespaceUri( String namespaceUri );

    /**
     * Register a new namespace using the supplied prefix, returning the namespace URI previously registered under that prefix.
     * 
     * @param prefix the prefix for the namespace, or null if a namesapce prefix should be generated automatically
     * @param namespaceUri the namespace URI
     * @return the namespace URI that was previously registered with the supplied prefix, or null if the prefix was not previously
     *         bound to a namespace URI
     * @throws IllegalArgumentException if the namespace URI is null
     */
    String register( String prefix,
                     String namespaceUri );

    void register( Iterable namespaces );

    /**
     * Unregister the namespace with the supplied URI.
     * 
     * @param namespaceUri the namespace URI
     * @return true if the namespace was removed, or false if the namespace was not registered
     * @throws IllegalArgumentException if the namespace URI is null
     * @throws NamespaceException if there is a problem unregistering the namespace
     */
    boolean unregister( String namespaceUri );

    /**
     * Obtain the set of namespaces that are registered.
     * 
     * @return the set of
     */
    Set getRegisteredNamespaceUris();

    /**
     * Obtain a snapshot of all of the {@link Namespace namespaces} registered at the time this method is called. The resulting
     * set is immutable, and will not reflect changes made to the registry.
     * 
     * @return an immutable set of {@link Namespace} objects reflecting a snapshot of the registry; never null
     */
    Set getNamespaces();

    /**
     * Representation of a single namespace at a single point in time. This object does not change to reflect changes made to the
     * {@link NamespaceRegistry registry}.
     * 
     * @see NamespaceRegistry#getNamespaces()
     * @author Randall Hauch
     */
    @Immutable
    interface Namespace extends Comparable {
        /**
         * Get the prefix for the namespace
         * 
         * @return the prefix; never null but possibly the empty string
         */
        String getPrefix();

        /**
         * Get the URI for the namespace
         * 
         * @return the namespace URI; never null but possibly the empty string
         */
        String getNamespaceUri();
    }

}