/*******************************************************************************
 * Copyright (c) 2000, 2009 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.core.runtime;

/**
 * An extension declared in a plug-in.
 * All information 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 objects, the most common case is code in a plug-in dealing
 * with extensions contributed to one of the extension points it declares.
 * Code in a plug-in that has declared that it is not dynamic aware (or not
 * declared anything) can 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 when accessing the extension
 * objects because they become invalid if the contributing 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 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 IExtension {
	/**
	 * Returns all configuration elements declared by this extension.
	 * These elements are a direct reflection of the configuration
	 * markup supplied in the manifest (<code>plugin.xml</code>)
	 * file for the plug-in that declares this extension.
	 * Returns an empty array if this extension does not declare any
	 * configuration elements.
	 *
	 * @return the configuration elements declared by this extension
	 * @throws InvalidRegistryObjectException if this extension is no longer valid
	 */
	public IConfigurationElement[] getConfigurationElements() throws InvalidRegistryObjectException;

	/**
	 * Returns the namespace for this extension. This value can be used
	 * in various global facilities to discover this extension's provider.
	 *
	 * @return the namespace for this extension
	 * @throws InvalidRegistryObjectException if this extension 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>
	 */
	@Deprecated
	public String getNamespace() throws InvalidRegistryObjectException;

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	 * @throws InvalidRegistryObjectException if this extension is no longer valid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

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

	/**
	 * Returns the unique identifier of the extension point
	 * to which this extension should be contributed.
	 *
	 * @return the unique identifier of the relevant extension point
	 * @throws InvalidRegistryObjectException if this extension is no longer valid
	 */
	public String getExtensionPointUniqueIdentifier() throws InvalidRegistryObjectException;

	/**
	 * Returns a displayable label for this extension.
	 * Returns the empty string if no label for this extension
	 * 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,
	 *    possibly the empty string
	 * @throws InvalidRegistryObjectException if this extension is no longer valid
	 */
	public String getLabel() throws InvalidRegistryObjectException;

	/**
	 * When multi-language support is enabled, this method returns a displayable label for this
	 * extension in the specified locale. Returns the empty string if no label for this extension
	 * 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,
	 *    possibly the empty string
	 * @throws InvalidRegistryObjectException if this extension is no longer valid
	 * @see IExtensionRegistry#isMultiLanguage()
	 * @since 3.5
	 */
	public String getLabel(String locale) throws InvalidRegistryObjectException;

	/**
	 * Returns the simple identifier of this extension, or <code>null</code>
	 * if this extension does not have an identifier.
	 * This identifier is specified in the plug-in manifest (<code>plugin.xml</code>)
	 * file as a non-empty string containing no period characters
	 * (<code>'.'</code>) and must be unique within the namespace.
	 *
	 * @return the simple identifier of the extension (e.g. <code>"main"</code>)
	 *  or <code>null</code>
	 * @throws InvalidRegistryObjectException if this extension is no longer valid
	 */
	public String getSimpleIdentifier() throws InvalidRegistryObjectException;

	/**
	 * Returns the unique identifier of this extension, or <code>null</code>
	 * if this extension does not have an identifier.
	 * If available, this identifier is unique within the plug-in registry, and
	 * is composed of the namespace where this extension
	 * was declared and this extension's simple identifier.
	 *
	 * @return the unique identifier of the extension
	 *    (e.g. <code>"com.example.acme.main"</code>), or <code>null</code>
	 * @throws InvalidRegistryObjectException if this extension is no longer valid
	 */
	public String getUniqueIdentifier() throws InvalidRegistryObjectException;

	@Override
	public boolean equals(Object o);

	/**
	 * Returns whether this extension 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();
}
