/*******************************************************************************
 * 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;

/**
 * A configuration element, with its attributes and children, directly reflects
 * the content and structure of the extension section within the declaring
 * plug-in's manifest (<code>plugin.xml</code>) file.
 * <p>
 * This interface also provides a way to create executable extension objects.
 * </p>
 * <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 configuration element 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 and configuration element 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 or configuration element 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 IConfigurationElement {
	/**
	 * Creates and returns a new instance of the executable extension identified by
	 * the named attribute of this configuration element. The named attribute value
	 * must contain a fully qualified name of a Java class. The class can either
	 * refer to a class implementing the executable extension or to a factory
	 * capable of returning the executable extension.
	 * <p>
	 * The specified class is instantiated using its 0-argument public constructor.
	 * <p>
	 * Then the following checks are done:<br>
	 * If the specified class implements the {@link IExecutableExtension} interface,
	 * the method
	 * {@link IExecutableExtension#setInitializationData(IConfigurationElement, String, Object)}
	 * is called, passing to the object the configuration information that was used
	 * to create it.
	 * <p>
	 * If the specified class implements {@link IExecutableExtensionFactory}
	 * interface, the method {@link IExecutableExtensionFactory#create()} is
	 * invoked.
	 * </p>
	 * <p>
	 * Unlike other methods on this object, invoking this method may activate the
	 * plug-in.
	 * </p>
	 *
	 * @param propertyName the name of the property
	 * @return the executable instance
	 * @exception CoreException if an instance of the executable extension could not
	 *                          be created for any reason
	 * @see IExecutableExtension#setInitializationData(IConfigurationElement,
	 *      String, Object)
	 * @see IExecutableExtensionFactory
	 * @throws InvalidRegistryObjectException if this configuration element is no
	 *                                        longer valid
	 */
	public Object createExecutableExtension(String propertyName) throws CoreException;

	/**
	 * Returns the named attribute of this configuration element, or
	 * <code>null</code> if none.
	 * <p>
	 * The names of configuration element attributes are the same as the attribute
	 * names of the corresponding XML element. For example, the configuration markup
	 * </p>
	 * 
	 * <pre>
	 * &lt;bg pattern="stripes"/&gt;
	 * </pre>
	 * <p>
	 * corresponds to a configuration element named <code>"bg"</code> with an
	 * attribute named <code>"pattern"</code> with attribute value
	 * <code>"stripes"</code>.
	 * </p>
	 * <p>
	 * Note that any translation specified in the plug-in manifest file is
	 * automatically applied.
	 * </p>
	 *
	 * @param name the name of the attribute
	 * @return attribute value, or <code>null</code> if none
	 * @throws InvalidRegistryObjectException if this configuration element is no
	 *                                        longer valid
	 */
	public String getAttribute(String name) throws InvalidRegistryObjectException;

	/**
	 * When multi-language support is enabled, this method returns the named
	 * attribute of this configuration element in the specified locale, or
	 * <code>null</code> if none.
	 * <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 #getAttribute(String)}.
	 * </p>
	 * 
	 * @param attrName the name of the attribute
	 * @param locale   the requested locale
	 * @return attribute value, or <code>null</code> if none
	 * @throws InvalidRegistryObjectException if this configuration element is no
	 *                                        longer valid
	 * @see #getAttribute(String)
	 * @see IExtensionRegistry#isMultiLanguage()
	 * @since org.eclipse.equinox.registry 3.5
	 */
	public String getAttribute(String attrName, String locale) throws InvalidRegistryObjectException;

	/**
	 * Returns the named attribute of this configuration element, or
	 * <code>null</code> if none.
	 * <p>
	 * The names of configuration element attributes are the same as the attribute
	 * names of the corresponding XML element. For example, the configuration markup
	 * </p>
	 * 
	 * <pre>
	 * &lt;bg pattern="stripes"/&gt;
	 * </pre>
	 * <p>
	 * corresponds to a configuration element named <code>"bg"</code> with an
	 * attribute named <code>"pattern"</code> with attribute value
	 * <code>"stripes"</code>.
	 * </p>
	 * <p>
	 * Note that any translation specified in the plug-in manifest file for this
	 * attribute is <b>not</b> automatically applied.
	 * </p>
	 *
	 * @param name the name of the attribute
	 * @return attribute value, or <code>null</code> if none
	 * @throws InvalidRegistryObjectException if this configuration element is no
	 *                                        longer valid
	 * @deprecated The method is equivalent to the {@link #getAttribute(String)}.
	 *             Contrary to its description, this method returns a translated
	 *             value. Use the {@link #getAttribute(String)} method instead.
	 */
	@Deprecated
	public String getAttributeAsIs(String name) throws InvalidRegistryObjectException;

	/**
	 * Returns the names of the attributes of this configuration element. Returns an
	 * empty array if this configuration element has no attributes.
	 * <p>
	 * The names of configuration element attributes are the same as the attribute
	 * names of the corresponding XML element. For example, the configuration markup
	 * </p>
	 * 
	 * <pre>
	 * &lt;bg color="blue" pattern="stripes"/&gt;
	 * </pre>
	 * <p>
	 * corresponds to a configuration element named <code>"bg"</code> with
	 * attributes named <code>"color"</code> and <code>"pattern"</code>.
	 * </p>
	 *
	 * @return the names of the attributes
	 * @throws InvalidRegistryObjectException if this configuration element is no
	 *                                        longer valid
	 */
	public String[] getAttributeNames() throws InvalidRegistryObjectException;

	/**
	 * Returns all configuration elements that are children of this configuration
	 * element. Returns an empty array if this configuration element has no
	 * children.
	 * <p>
	 * Each child corresponds to a nested XML element in the configuration markup.
	 * For example, the configuration markup
	 * </p>
	 * 
	 * <pre>
	 * &lt;view&gt;
	 * 	&lt;verticalHint&gt;top&lt;/verticalHint&gt;
	 * 	&lt;horizontalHint&gt;left&lt;/horizontalHint&gt;
	 * &lt;/view&gt;
	 * </pre>
	 * <p>
	 * corresponds to a configuration element, named <code>"view"</code>, with two
	 * children.
	 * </p>
	 *
	 * @return the child configuration elements
	 * @throws InvalidRegistryObjectException if this configuration element is no
	 *                                        longer valid
	 * @see #getChildren(String)
	 */
	public IConfigurationElement[] getChildren() throws InvalidRegistryObjectException;

	/**
	 * Returns all child configuration elements with the given name. Returns an
	 * empty array if this configuration element has no children with the given
	 * name.
	 *
	 * @param name the name of the child configuration element
	 * @return the child configuration elements with that name
	 * @throws InvalidRegistryObjectException if this configuration element is no
	 *                                        longer valid
	 * @see #getChildren()
	 */
	public IConfigurationElement[] getChildren(String name) throws InvalidRegistryObjectException;

	/**
	 * Returns the extension that declares this configuration element.
	 *
	 * @return the extension
	 * @throws InvalidRegistryObjectException if this configuration element is no
	 *                                        longer valid
	 */
	public IExtension getDeclaringExtension() throws InvalidRegistryObjectException;

	/**
	 * Returns the name of this configuration element. The name of a configuration
	 * element is the same as the XML tag of the corresponding XML element. For
	 * example, the configuration markup
	 * 
	 * <pre>
	 * &lt;wizard name="Create Project"/&gt;
	 * </pre>
	 * 
	 * corresponds to a configuration element named <code>"wizard"</code>.
	 *
	 * @return the name of this configuration element
	 * @throws InvalidRegistryObjectException if this configuration element is no
	 *                                        longer valid
	 */
	public String getName() throws InvalidRegistryObjectException;

	/**
	 * Returns the element which contains this element. If this element is an
	 * immediate child of an extension, the returned value can be downcast to
	 * <code>IExtension</code>. Otherwise the returned value can be downcast to
	 * <code>IConfigurationElement</code>.
	 *
	 * @return the parent of this configuration element or <code>null</code>
	 * @throws InvalidRegistryObjectException if this configuration element is no
	 *                                        longer valid
	 * @since 3.0
	 */
	public Object getParent() throws InvalidRegistryObjectException;

	/**
	 * Returns the text value of this configuration element. For example, the
	 * configuration markup
	 * 
	 * <pre>
	 * &lt;script lang="javascript"&gt;.\scripts\cp.js&lt;/script&gt;
	 * </pre>
	 * 
	 * corresponds to a configuration element <code>"script"</code> with value
	 * <code>".\scripts\cp.js"</code>.
	 * <p>
	 * Values may span multiple lines (i.e., contain carriage returns and/or line
	 * feeds).
	 * <p>
	 * Note that any translation specified in the plug-in manifest file is
	 * automatically applied.
	 * </p>
	 *
	 * @return the text value of this configuration element or <code>null</code>
	 * @throws InvalidRegistryObjectException if this configuration element is no
	 *                                        longer valid
	 */
	public String getValue() throws InvalidRegistryObjectException;

	/**
	 * When multi-language support is enabled, this method returns the text value of
	 * this configuration element in the specified locale, or <code>null</code> if
	 * none.
	 * <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 #getValue()}.
	 * </p>
	 * 
	 * @param locale the requested locale
	 * @return the text value of this configuration element in the specified locale,
	 *         or <code>null</code>
	 * @throws InvalidRegistryObjectException if this configuration element is no
	 *                                        longer valid
	 * @see #getValue(String)
	 * @see IExtensionRegistry#isMultiLanguage()
	 * @since org.eclipse.equinox.registry 3.5
	 */
	public String getValue(String locale) throws InvalidRegistryObjectException;

	/**
	 * Returns the untranslated text value of this configuration element. For
	 * example, the configuration markup
	 * 
	 * <pre>
	 * &lt;script lang="javascript"&gt;.\scripts\cp.js&lt;/script&gt;
	 * </pre>
	 * 
	 * corresponds to a configuration element <code>"script"</code> with value
	 * <code>".\scripts\cp.js"</code>.
	 * <p>
	 * Values may span multiple lines (i.e., contain carriage returns and/or line
	 * feeds).
	 * <p>
	 * Note that translation specified in the plug-in manifest file is <b>not</b>
	 * automatically applied. For example, the configuration markup
	 * </p>
	 * 
	 * <pre>
	 * &lt;tooltip&gt;#hattip&lt;/tooltip&gt;
	 * </pre>
	 * <p>
	 * corresponds to a configuration element, named <code>"tooltip"</code>, with
	 * value <code>"#hattip"</code>.
	 * </p>
	 *
	 * @return the untranslated text value of this configuration element or
	 *         <code>null</code>
	 * @throws InvalidRegistryObjectException if this configuration element is no
	 *                                        longer valid
	 * @deprecated The method is equivalent to the {@link #getValue()}. Contrary to
	 *             its description, this method returns a translated value. Use the
	 *             {@link #getValue()} method instead.
	 */
	@Deprecated
	public String getValueAsIs() throws InvalidRegistryObjectException;

	/**
	 * Returns the namespace for this configuration element. This value can be used
	 * in various global facilities to discover this configuration element's
	 * contributor.
	 *
	 * @return the namespace for this configuration element
	 * @throws InvalidRegistryObjectException if this configuration element is no
	 *                                        longer valid
	 * @see IExtensionRegistry
	 * @since 3.1
	 * @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 configuration element.
	 *
	 * @return the namespace name for this configuration element
	 * @throws InvalidRegistryObjectException if this configuration element is no
	 *                                        longer valid
	 * @since org.eclipse.equinox.registry 3.2
	 */
	public String getNamespaceIdentifier() throws InvalidRegistryObjectException;

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

	/**
	 * {@inheritDoc}
	 * 
	 * @return true if the given element has same handle id
	 * @see #getHandleId()
	 */
	@Override
	public boolean equals(Object o);

	/**
	 * Returns whether this configuration element 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();

	/**
	 * Returns unique identifier of the registry object from which this element was
	 * created. Two configuration element instances are considered to be equal if
	 * their handle id's are same.
	 * 
	 * @return The handle id of the registry object from which this configuration
	 *         element was created.
	 * @see #equals(Object)
	 * @since 3.8
	 */
	public int getHandleId();
}
