Copyright (c) 2007, 2008 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
/*******************************************************************************
 * Copyright (c) 2007, 2008 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.internal.expressions;

import java.util.HashMap;
import java.util.Map;

import org.eclipse.core.expressions.Expression;
import org.eclipse.core.expressions.ExpressionConverter;

import org.eclipse.core.runtime.CoreException;
import org.eclipse.core.runtime.IConfigurationElement;
import org.eclipse.core.runtime.IExtensionDelta;
import org.eclipse.core.runtime.IExtensionRegistry;
import org.eclipse.core.runtime.IRegistryChangeEvent;
import org.eclipse.core.runtime.IRegistryChangeListener;
import org.eclipse.core.runtime.InvalidRegistryObjectException;
import org.eclipse.core.runtime.Platform;

This manages the extension point that allows core expression reuse.
Since:
3.3/**
 * This manages the extension point that allows core expression reuse.
 *
 * @since 3.3
 */
public class DefinitionRegistry implements IRegistryChangeListener {
	private Map<String, Expression> cache= null;

	private Map<String, Expression> getCache() {
		if (cache == null) {
			cache= new HashMap<>();
		}
		return cache;
	}

	public DefinitionRegistry() {
		Platform.getExtensionRegistry().addRegistryChangeListener(this, "org.eclipse.core.expressions"); //$NON-NLS-1$
	}

	
Get the expression with the id defined by an extension. This class will
cache the expressions when appropriate, so it's OK to always ask the
registry.
Params:
id – The unique ID of the expression definition
Throws:
CoreException – If the expression cannot be found.
Returns:
the expression/**
	 * Get the expression with the id defined by an extension. This class will
	 * cache the expressions when appropriate, so it's OK to always ask the
	 * registry.
	 *
	 * @param id The unique ID of the expression definition
	 * @return the expression
	 * @throws CoreException If the expression cannot be found.
	 */
	public Expression getExpression(String id) throws CoreException {
		Expression cachedExpression= getCache().get(id);
		if (cachedExpression != null) {
			return cachedExpression;
		}

		IExtensionRegistry registry= Platform.getExtensionRegistry();
		IConfigurationElement[] ces= registry.getConfigurationElementsFor("org.eclipse.core.expressions", "definitions"); //$NON-NLS-1$ //$NON-NLS-2$

		Expression foundExpression= null;
		for (IConfigurationElement ce : ces) {
			String cid= ce.getAttribute("id"); //$NON-NLS-1$
			if (cid != null && cid.equals(id)) {
				try {
					foundExpression= getExpression(id, ce);
					break;
				} catch (InvalidRegistryObjectException e) {
					throw new CoreException(new ExpressionStatus(ExpressionStatus.MISSING_EXPRESSION, Messages.format(
						ExpressionMessages.Missing_Expression, id)));
				}
			}
		}
		if (foundExpression == null) {
			throw new CoreException(new ExpressionStatus(ExpressionStatus.MISSING_EXPRESSION, Messages.format(
				ExpressionMessages.Missing_Expression, id)));
		}
		return foundExpression;
	}

	private Expression getExpression(String id, IConfigurationElement element) throws InvalidRegistryObjectException,
		CoreException {
		Expression expr= ExpressionConverter.getDefault().perform(element.getChildren()[0]);
		if (expr != null) {
			getCache().put(id, expr);
		}
		return expr;
	}

	@Override
	public void registryChanged(IRegistryChangeEvent event) {
		IExtensionDelta[] extensionDeltas= event.getExtensionDeltas("org.eclipse.core.expressions", "definitions"); //$NON-NLS-1$//$NON-NLS-2$
		for (IExtensionDelta extensionDelta : extensionDeltas) {
			if (extensionDelta.getKind() == IExtensionDelta.REMOVED) {
				IConfigurationElement[] ces= extensionDelta.getExtension().getConfigurationElements();
				for (IConfigurationElement ce : ces) {
					String id= ce.getAttribute("id"); //$NON-NLS-1$
					if (id != null) {
						getCache().remove(id);
					}
				}
			}
		}
	}
}