/*
    * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org>
    * and other copyright owners as documented in the project's IP log.
    *
    * This program and the accompanying materials are made available
    * under the terms of the Eclipse Distribution License v1.0 which
    * accompanies this distribution, is reproduced below, and is
    * available at http://www.eclipse.org/org/documents/edl-v10.php
    *
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or
   * without modification, are permitted provided that the following
   * conditions are met:
   *
   * - Redistributions of source code must retain the above copyright
   *   notice, this list of conditions and the following disclaimer.
   *
   * - Redistributions in binary form must reproduce the above
   *   copyright notice, this list of conditions and the following
   *   disclaimer in the documentation and/or other materials provided
   *   with the distribution.
   *
   * - Neither the name of the Eclipse Foundation, Inc. nor the
   *   names of its contributors may be used to endorse or promote
   *   products derived from this software without specific prior
   *   written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
   * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
   * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
   * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
   * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
   * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
   * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
   * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   */
  
  package org.eclipse.jgit.internal.storage.file;
  
  import java.lang.ref.SoftReference;
  
  import org.eclipse.jgit.storage.file.WindowCacheConfig;
  
  class DeltaBaseCache {
  	private static final int CACHE_SZ = 1024;
  
  	static final SoftReference<Entry> DEAD;
  
  	private static int hash(long position) {
  		return (((int) position) << 22) >>> 22;
  	}
  
  	private static volatile int defaultMaxByteCount;
  
  	private final int maxByteCount;
  
  	private final Slot[] cache;
  
  	private Slot lruHead;
  
  	private Slot lruTail;
  
  	private int openByteCount;
  
  	static {
  		DEAD = new SoftReference<>(null);
  		reconfigure(new WindowCacheConfig());
  	}
  
  	static void reconfigure(WindowCacheConfig cfg) {
  		defaultMaxByteCount = cfg.getDeltaBaseCacheLimit();
  	}
  
  	DeltaBaseCache() {
  		maxByteCount = defaultMaxByteCount;
  		cache = new Slot[CACHE_SZ];
  	}
  
  	Entry get(PackFile pack, long position) {
  		Slot e = cache[hash(position)];
  		if (e == null)
  			return null;
  		if (e.provider == pack && e.position == position) {
  			final Entry buf = e.data.get();
  			if (buf != null) {
  				moveToHead(e);
  				return buf;
  			}
  		}
  		return null;
  	}
  
  	void store(final PackFile pack, final long position,
 			final byte[] data, final int objectType) {
 		if (data.length > maxByteCount)
 			return; // Too large to cache.
 
 		Slot e = cache[hash(position)];
 		if (e == null) {
 			e = new Slot();
 			cache[hash(position)] = e;
 		} else {
 			clearEntry(e);
 		}
 
 		openByteCount += data.length;
 		releaseMemory();
 
 		e.provider = pack;
 		e.position = position;
 		e.sz = data.length;
 		e.data = new SoftReference<>(new Entry(data, objectType));
 		moveToHead(e);
 	}
 
 	private void releaseMemory() {
 		while (openByteCount > maxByteCount && lruTail != null) {
 			final Slot currOldest = lruTail;
 			final Slot nextOldest = currOldest.lruPrev;
 
 			clearEntry(currOldest);
 			currOldest.lruPrev = null;
 			currOldest.lruNext = null;
 
 			if (nextOldest == null)
 				lruHead = null;
 			else
 				nextOldest.lruNext = null;
 			lruTail = nextOldest;
 		}
 	}
 
 	private void moveToHead(Slot e) {
 		unlink(e);
 		e.lruPrev = null;
 		e.lruNext = lruHead;
 		if (lruHead != null)
 			lruHead.lruPrev = e;
 		else
 			lruTail = e;
 		lruHead = e;
 	}
 
 	private void unlink(Slot e) {
 		final Slot prev = e.lruPrev;
 		final Slot next = e.lruNext;
 		if (prev != null)
 			prev.lruNext = next;
 		if (next != null)
 			next.lruPrev = prev;
 	}
 
 	private void clearEntry(Slot e) {
 		openByteCount -= e.sz;
 		e.provider = null;
 		e.data = DEAD;
 		e.sz = 0;
 	}
 
 	static class Entry {
 		final byte[] data;
 
 		final int type;
 
 		Entry(byte[] aData, int aType) {
 			data = aData;
 			type = aType;
 		}
 	}
 
 	private static class Slot {
 		Slot lruPrev;
 
 		Slot lruNext;
 
 		PackFile provider;
 
 		long position;
 
 		int sz;
 
 		SoftReference<Entry> data = DEAD;
 	}
 }