/*
 * Copyright (c) 2002, 2011, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation. Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

/*
 */

package java.io;

import java.util.Iterator;
import java.util.Map;
import java.util.LinkedHashMap;
import java.util.Set;

class ExpiringCache {
 private long millisUntilExpiration;
 private Map<String,Entry> map;
 // Clear out old entries every few queries
 private int queryCount;
 private int queryOverflow = 300;
 private int MAX_ENTRIES = 200;

 static class Entry {
 private long timestamp;
 private String val;

 Entry(long timestamp, String val) {
 this.timestamp = timestamp;
 this.val = val;
 }

 long timestamp() { return timestamp; }
 void setTimestamp(long timestamp) { this.timestamp = timestamp; }

 String val() { return val; }
 void setVal(String val) { this.val = val; }
 }

 ExpiringCache() {
 this(30000);
 }

 @SuppressWarnings("serial")
 ExpiringCache(long millisUntilExpiration) {
 this.millisUntilExpiration = millisUntilExpiration;
 map = new LinkedHashMap<>() {
 protected boolean removeEldestEntry(Map.Entry<String,Entry> eldest) {
 return size() > MAX_ENTRIES;
 }
 };
 }

 synchronized String get(String key) {
 if (++queryCount >= queryOverflow) {
 cleanup();
 }
 Entry entry = entryFor(key);
 if (entry != null) {
 return entry.val();
 }
 return null;
 }

 synchronized void put(String key, String val) {
 if (++queryCount >= queryOverflow) {
 cleanup();
 }
 Entry entry = entryFor(key);
 if (entry != null) {
 entry.setTimestamp(System.currentTimeMillis());
 entry.setVal(val);
 } else {
 map.put(key, new Entry(System.currentTimeMillis(), val));
 }
 }

 synchronized void clear() {
 map.clear();
 }

 private Entry entryFor(String key) {
 Entry entry = map.get(key);
 if (entry != null) {
 long delta = System.currentTimeMillis() - entry.timestamp();
 if (delta < 0 || delta >= millisUntilExpiration) {
 map.remove(key);
 entry = null;
 }
 }
 return entry;
 }

 private void cleanup() {
 Set<String> keySet = map.keySet();
 // Avoid ConcurrentModificationExceptions
 String[] keys = new String[keySet.size()];
 int i = 0;
 for (String key: keySet) {
 keys[i++] = key;
 }
 for (int j = 0; j < keys.length; j++) {
 entryFor(keys[j]);
 }
 queryCount = 0;
 }
}