package org.apache.solr.util;

import java.util.concurrent.ConcurrentHashMap;

/**
 * @author Noble Paul (Noble.Paul@corp.aol.com)
 *         Date: Jul 29, 2008
 *         Time: 10:40:07 AM
 */
public class ConcurrentFIFOCache {
  private ConcurrentHashMap<Object,Entry> map ;
  private int size;
  final Entry header ;
  final Entry tail ;


  public ConcurrentFIFOCache(int size ) {
    if(size < 1) throw new IllegalArgumentException("Size must be > 0");
    this.size = size;
    this.map = new ConcurrentHashMap<Object, Entry>(size);
    header = new Entry(null,null);
    tail = new Entry(null, null);
    tail.after =  header;
    header.before = tail;
  }

  public Object get(Object key){
    return map.get(key).value;
  }
  public synchronized void put(Object key, Object value){
    Entry e = new Entry(key, value);
    map.put(key, e);
    e.before =  header.before;
    e.after = header;
    if(map.size()> size ){
      map.remove(tail.after.key);
      tail.after.remove();
    }
  }

  public synchronized Object remove(Object key){
    Entry e =  map.remove(key);
    e.remove();
    return e.value;
  }



  class Entry {
    final Object key,value;
    volatile Entry after,before;

    public Entry(Object key,Object value) {
      this.key = key;
      this.value = value;
    }

    void remove() {
      if(before !=null) before.after =  after;
      if(after !=null) after.before =  before;
    }

    public int hashCode() {
      return key.hashCode();
    }
  }


}