/*

 * 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;

    }

}