/*******************************************************************************
 * Copyright (c) 2000, 2009 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 * 
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.core.runtime;

/**
 * An extension point declared in a plug-in.
 * Except for the list of extensions plugged in to it, the information 
 * available for an extension point is obtained from the declaring plug-in's 
 * manifest (<code>plugin.xml</code>) file.
 * <p>
 * These registry objects are intended for relatively short-term use. Clients that 
 * deal with these objects must be aware that they may become invalid if the 
 * declaring plug-in is updated or uninstalled. If this happens, all methods except
 * {@link #isValid()} will throw {@link InvalidRegistryObjectException}.
 * For extension point objects, the most common case is code in a plug-in dealing
 * with one of the extension points it declares. These extension point objects are
 * guaranteed to be valid while the plug-in is active. Code in a plug-in that has
 * declared that it is not dynamic aware (or not declared anything) can also safely
 * ignore this issue, since the registry would not be modified while it is
 * active. However, code in a plug-in that declares that it is dynamic aware
 * must be careful if it access the extension point object of a different plug-in,
 * because it's at risk if that other plug-in is removed. Similarly,
 * tools that analyze or display the extension registry are vulnerable.
 * Client code can pre-test for invalid objects by calling {@link #isValid()},
 * which never throws this exception. However, pre-tests are usually not sufficient
 * because of the possibility of the extension point object becoming invalid as a
 * result of a concurrent activity. At-risk clients must treat 
 * <code>InvalidRegistryObjectException</code> as if it were a checked exception.
 * Also, such clients should probably register a listener with the extension registry
 * so that they receive notification of any changes to the registry.
 * </p><p>
 * This interface can be used without OSGi running.
 * </p><p>
 * This interface is not intended to be implemented by clients.
 * </p>
 * @noimplement This interface is not intended to be implemented by clients.
 */
public interface IExtensionPoint {
	/**
	 * Returns all configuration elements from all extensions configured
	 * into this extension point. Returns an empty array if this extension 
	 * point has no extensions configured, or none of the extensions 
	 * contain configuration elements.
	 *
	 * @return the configuration elements for all extension configured 
	 *   into this extension point
	 * @throws InvalidRegistryObjectException if this extension point is no longer valid
	 */
	public IConfigurationElement[] getConfigurationElements() throws InvalidRegistryObjectException;

	/**
	 * Returns the namespace for this extension point. This value can be used
	 * in various global facilities to discover this extension point's provider.
	 * 
	 * @return the namespace for this extension point
	 * @throws InvalidRegistryObjectException if this extension point is no longer valid
	 * @see IExtensionRegistry
	 * @since 3.0
	 * @deprecated As namespace is no longer restricted to the contributor name, 
	 * 	use {@link #getNamespaceIdentifier()} to obtain namespace name or {@link #getContributor()}
	 * 	to get the name of the contributor of this registry element.  
	 * <p>
	 * In the past namespace was dictated by the name of the bundle. If bundle <code>org.abc</code> 
	 * contributed registry element with Id of <code>MyId</code>, the namespace of 
	 * the element was always set to <code>org.abc</code>, producing the qualified name of 
	 * <code>org.abc.MyId</code>.
	 * </p><p>
	 * The namespace used to be the same as the bundle name. As a result, the {@link #getNamespace()} 
	 * method was used both to obtain the name of the bundle and to obtain the namespace of a registry 
	 * element.
	 * </p><p>
	 * Since 3.2, the extension registry allows elements to specify qualified name. The extension point 
	 * of the plug-in <code>org.abc</code> could specify <code>org.zzz.MyExtPoint</code> as 
	 * an Id. In this case, namespace name is <code>org.zzz</code>, but the contributor 
	 * name is <code>org.abc</code>.  
	 * </p><p>
	 * (The use of a simple Id is still a preferred way. Whenever possible, specify only the simple 
	 * Id and let runtime take care of the rest.)
	 * </p><p>
	 * If your code used the {@link #getNamespace()} to obtain the name of the contributing bundle, 
	 * use {@link #getContributor()}. The typical usage pattern here is to find a bundle name to obtain 
	 * some information from the corresponding OSGi bundle. For example, deducing the file location 
	 * specified as a relative path to the bundle install location would fall into this group.
	 * </p><p>
	 * If your code used the {@link #getNamespace()} to obtain the namespace of the registry element, 
	 * use {@link #getNamespaceIdentifier()}. Typically, this is the case when code is trying to process 
	 * registry elements belonging to some logical group. For example, processing notifications for all 
	 * elements belonging to the <code>org.abc</code> namespace would fall into this category.
	 * </p>
	 */
	public String getNamespace() throws InvalidRegistryObjectException;

	/**
	 * Returns the namespace name for this extension point.
	 * 
	 * @return the namespace name for this extension point
	 * @throws InvalidRegistryObjectException if this extension point is no longer valid
	 * @since org.eclipse.equinox.registry 3.2	 
	 */
	public String getNamespaceIdentifier() throws InvalidRegistryObjectException;

	/**
	 * Returns the contributor of this extension point.
	 * 
	 * @return the contributor for this extension point
	 * @throws InvalidRegistryObjectException if this extension point is no longer valid
	 * @since org.eclipse.equinox.registry 3.2	 
	 */
	public IContributor getContributor() throws InvalidRegistryObjectException;

	/**
	 * Returns the extension with the given unique identifier configured into
	 * this extension point, or <code>null</code> if there is no such extension.
	 * Since an extension might not have an identifier, some extensions
	 * can only be found via the <code>getExtensions</code> method.
	 *
	 * @param extensionId the unique identifier of an extension 
	 *		(e.g. <code>"com.example.acme.main"</code>).
	 * @return an extension, or <code>null</code>
	 * @throws InvalidRegistryObjectException if this extension point is no longer valid
	 */
	public IExtension getExtension(String extensionId) throws InvalidRegistryObjectException;

	/**
	 * Returns all extensions configured into this extension point.
	 * Returns an empty array if this extension point has no extensions.
	 *
	 * @return the extensions configured into this extension point
	 * @throws InvalidRegistryObjectException if this extension point is no longer valid
	 */
	public IExtension[] getExtensions() throws InvalidRegistryObjectException;

	/**
	 * Returns a displayable label for this extension point.
	 * Returns the empty string if no label for this extension point
	 * is specified in the plug-in manifest file.
	 * <p> Note that any translation specified in the plug-in manifest
	 * file is automatically applied.
	 * </p>
	 *
	 * @return a displayable string label for this extension point,
	 *    possibly the empty string
	 * @throws InvalidRegistryObjectException if this extension point is no longer valid
	 */
	public String getLabel() throws InvalidRegistryObjectException;

	/**
	 * When multi-language support is enabled, this method returns a displayable label 
	 * for this extension point in the specified locale.
	 * Returns the empty string if no label for this extension point
	 * is specified in the plug-in manifest file.
	 * <p> 
	 * The locale matching tries to find the best match between available translations and 
	 * the requested locale, falling back to a more generic locale ("en") when the specific 
	 * locale ("en_US") is not available. 
	 * </p><p>
	 * If multi-language support is not enabled, this method is equivalent to the method 
	 * {@link #getLabel()}.
	 * </p>
	 * @param locale the requested locale
	 * @return a displayable string label for this extension point,
	 *    possibly the empty string
	 * @throws InvalidRegistryObjectException if this extension point is no longer valid
	 * @see IExtensionRegistry#isMultiLanguage()
	 * @since 3.5
	 */
	public String getLabel(String locale) throws InvalidRegistryObjectException;

	/**
	 * Returns reference to the extension point schema. The schema 
	 * reference is returned as a URL path relative to the plug-in 
	 * installation URL. 
	 * Returns the empty string if no schema for this extension point
	 * is specified in the plug-in manifest file.
	 *
	 * @return a relative URL path, or an empty string
	 * @throws InvalidRegistryObjectException if this extension point is no longer valid
	 */
	public String getSchemaReference() throws InvalidRegistryObjectException;

	/**
	 * Returns the simple identifier of this extension point.
	 * This identifier is a non-empty string containing no
	 * period characters (<code>'.'</code>) and is guaranteed
	 * to be unique within the namespace.
	 *
	 * @return the simple identifier of the extension point (e.g. <code>"builders"</code>)
	 * @throws InvalidRegistryObjectException if this extension point is no longer valid
	 */
	public String getSimpleIdentifier() throws InvalidRegistryObjectException;

	/**
	 * Returns the unique identifier of this extension point.
	 * This identifier is unique within the plug-in registry, and
	 * is composed of the namespace for this extension point 
	 * and this extension point's simple identifier.
	 * 
	 *
	 * @return the unique identifier of the extension point
	 *    (e.g. <code>"org.eclipse.core.resources.builders"</code>)
	 * @throws InvalidRegistryObjectException if this extension point is no longer valid
	 */
	public String getUniqueIdentifier() throws InvalidRegistryObjectException;

	/* (non-javadoc) 
	 * @see Object#equals(java.lang.Object)
	 */
	public boolean equals(Object o);

	/**
	 * Returns whether this extension point object is valid.
	 * 
	 * @return <code>true</code> if the object is valid, and <code>false</code>
	 * if it is no longer valid
	 * @since 3.1
	 */
	public boolean isValid();
}
