Copyright (c) 2000, 2016 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) 2000, 2016 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.jdt.internal.corext.util;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.Map;

import org.eclipse.core.runtime.IProgressMonitor;

import org.eclipse.jdt.core.IType;
import org.eclipse.jdt.core.ITypeHierarchy;
import org.eclipse.jdt.core.ITypeHierarchyChangedListener;
import org.eclipse.jdt.core.JavaModelException;

A thread-safe cache for super type hierarchies.
/**
 * A thread-safe cache for super type hierarchies.
 */
// @see JDTUIHelperClasses
public class SuperTypeHierarchyCache {

	private static class HierarchyCacheEntry implements ITypeHierarchyChangedListener {

		private ITypeHierarchy fTypeHierarchy;
		private long fLastAccess;

		public HierarchyCacheEntry(ITypeHierarchy hierarchy) {
			fTypeHierarchy= hierarchy;
			fTypeHierarchy.addTypeHierarchyChangedListener(this);
			markAsAccessed();
		}

		@Override
		public void typeHierarchyChanged(ITypeHierarchy typeHierarchy) {
			removeHierarchyEntryFromCache(this);
		}

		public ITypeHierarchy getTypeHierarchy() {
			return fTypeHierarchy;
		}

		public void markAsAccessed() {
			fLastAccess= System.currentTimeMillis();
		}

		public long getLastAccess() {
			return fLastAccess;
		}

		public void dispose() {
			if (fTypeHierarchy != null) {
				fTypeHierarchy.removeTypeHierarchyChangedListener(this);
				fTypeHierarchy= null;
			}
		}

		@Override
		public String toString() {
			return "Super hierarchy of: " + fTypeHierarchy.getType().getElementName(); //$NON-NLS-1$
		}

	}


	private static final int CACHE_SIZE= 8;

	private static ArrayList<HierarchyCacheEntry> fgHierarchyCache= new ArrayList<>(CACHE_SIZE);
	private static Map<IType, MethodOverrideTester> fgMethodOverrideTesterCache= new LRUMap<>(CACHE_SIZE);

	private static int fgCacheHits= 0;
	private static int fgCacheMisses= 0;

	
Returns a super type hierarchy that contains the given type. The returned hierarchy may actually be based on a subtype of the requested type. Therefore, queries such as ITypeHierarchy.getAllClasses() or ITypeHierarchy.getRootInterfaces() may return more types than the same queries on a type hierarchy for just the given type. 
Params:
type – the focus type
Throws:
JavaModelException – if a problem occurs
Returns:
a supertype hierarchy that contains type/**
	 * Returns a super type hierarchy that contains the given type.
	 * The returned hierarchy may actually be based on a subtype of the
	 * requested type. Therefore, queries such as {@link ITypeHierarchy#getAllClasses()}
	 * or {@link ITypeHierarchy#getRootInterfaces()} may return more types than the same
	 * queries on a type hierarchy for just the given type.
	 *
	 * @param type the focus type
	 * @return a supertype hierarchy that contains <code>type</code>
	 * @throws JavaModelException if a problem occurs
	 */
	public static ITypeHierarchy getTypeHierarchy(IType type) throws JavaModelException {
		return getTypeHierarchy(type, null);
	}

	public static MethodOverrideTester getMethodOverrideTester(IType type) throws JavaModelException {
		MethodOverrideTester test= null;
		synchronized (fgMethodOverrideTesterCache) {
			test= fgMethodOverrideTesterCache.get(type);
		}
		if (test == null) {
			ITypeHierarchy hierarchy= getTypeHierarchy(type); // don't nest the locks
			synchronized (fgMethodOverrideTesterCache) {
				test= fgMethodOverrideTesterCache.get(type); // test again after waiting a long time for 'getTypeHierarchy'
				if (test == null) {
					test= new MethodOverrideTester(type, hierarchy);
					fgMethodOverrideTesterCache.put(type, test);
				}
			}
		}
		return test;
	}

	private static void removeMethodOverrideTester(ITypeHierarchy hierarchy) {
		synchronized (fgMethodOverrideTesterCache) {
			for (Iterator<MethodOverrideTester> iter= fgMethodOverrideTesterCache.values().iterator(); iter.hasNext();) {
				MethodOverrideTester curr= iter.next();
				if (curr.getTypeHierarchy().equals(hierarchy)) {
					iter.remove();
				}
			}
		}
	}

	
Returns a super type hierarchy that contains the given type. The returned hierarchy may actually be based on a subtype of the requested type. Therefore, queries such as ITypeHierarchy.getAllClasses() or ITypeHierarchy.getRootInterfaces() may return more types than the same queries on a type hierarchy for just the given type. 
Params:
type – the focus type
progressMonitor – progress monitor
Throws:
JavaModelException – if a problem occurs
Returns:
a supertype hierarchy that contains type/**
	 * Returns a super type hierarchy that contains the given type.
	 * The returned hierarchy may actually be based on a subtype of the
	 * requested type. Therefore, queries such as {@link ITypeHierarchy#getAllClasses()}
	 * or {@link ITypeHierarchy#getRootInterfaces()} may return more types than the same
	 * queries on a type hierarchy for just the given type.
	 *
	 * @param type the focus type
	 * @param progressMonitor progress monitor
	 * @return a supertype hierarchy that contains <code>type</code>
	 * @throws JavaModelException if a problem occurs
	 */
	public static ITypeHierarchy getTypeHierarchy(IType type, IProgressMonitor progressMonitor) throws JavaModelException {
		ITypeHierarchy hierarchy= findTypeHierarchyInCache(type);
		if (hierarchy == null) {
			fgCacheMisses++;
			hierarchy= type.newSupertypeHierarchy(progressMonitor);
			addTypeHierarchyToCache(hierarchy);
		} else {
			fgCacheHits++;
		}
		return hierarchy;
	}

	private static void addTypeHierarchyToCache(ITypeHierarchy hierarchy) {
		synchronized (fgHierarchyCache) {
			int nEntries= fgHierarchyCache.size();
			if (nEntries >= CACHE_SIZE) {
				// find obsolete entries or remove entry that was least recently accessed
				HierarchyCacheEntry oldest= null;
				ArrayList<HierarchyCacheEntry> obsoleteHierarchies= new ArrayList<>(CACHE_SIZE);
				for (int i= 0; i < nEntries; i++) {
					HierarchyCacheEntry entry= fgHierarchyCache.get(i);
					ITypeHierarchy curr= entry.getTypeHierarchy();
					if (!curr.exists() || hierarchy.contains(curr.getType())) {
						obsoleteHierarchies.add(entry);
					} else {
						if (oldest == null || entry.getLastAccess() < oldest.getLastAccess()) {
							oldest= entry;
						}
					}
				}
				if (!obsoleteHierarchies.isEmpty()) {
					for (int i= 0; i < obsoleteHierarchies.size(); i++) {
						removeHierarchyEntryFromCache(obsoleteHierarchies.get(i));
					}
				} else if (oldest != null) {
					removeHierarchyEntryFromCache(oldest);
				}
			}
			HierarchyCacheEntry newEntry= new HierarchyCacheEntry(hierarchy);
			fgHierarchyCache.add(newEntry);
		}
	}


	
Check if the given type is in the hierarchy cache.
Params:
type – a type
Returns:
true if a hierarchy for the given type is cached/**
	 * Check if the given type is in the hierarchy cache.
	 * @param type a type
	 * @return <code>true</code> if a hierarchy for the given type is cached
	 */
	public static boolean hasInCache(IType type) {
		return findTypeHierarchyInCache(type) != null;
	}


	private static ITypeHierarchy findTypeHierarchyInCache(IType type) {
		synchronized (fgHierarchyCache) {
			for (int i= fgHierarchyCache.size() - 1; i>= 0; i--) {
				HierarchyCacheEntry curr= fgHierarchyCache.get(i);
				ITypeHierarchy hierarchy= curr.getTypeHierarchy();
				if (!hierarchy.exists()) {
					removeHierarchyEntryFromCache(curr);
				} else {
					if (hierarchy.contains(type)) {
						curr.markAsAccessed();
						return hierarchy;
					}
				}
			}
		}
		return null;
	}

	private static void removeHierarchyEntryFromCache(HierarchyCacheEntry entry) {
		synchronized (fgHierarchyCache) {
			removeMethodOverrideTester(entry.getTypeHierarchy());
			entry.dispose();
			fgHierarchyCache.remove(entry);
		}
	}


	
Gets the number of times the hierarchy could be taken from the hierarchy.
Returns:
Returns a int/**
	 * Gets the number of times the hierarchy could be taken from the hierarchy.
	 * @return Returns a int
	 */
	public static int getCacheHits() {
		return fgCacheHits;
	}

	
Gets the number of times the hierarchy was build. Used for testing.
Returns:
Returns a int/**
	 * Gets the number of times the hierarchy was build. Used for testing.
	 * @return Returns a int
	 */
	public static int getCacheMisses() {
		return fgCacheMisses;
	}
}