/*
    * Copyright (C) 2013, Google Inc. and others
    *
    * This program and the accompanying materials are made available under the
    * terms of the Eclipse Distribution License v. 1.0 which is available at
    * https://www.eclipse.org/org/documents/edl-v10.php.
    *
    * SPDX-License-Identifier: BSD-3-Clause
    */
  
  package org.eclipse.jgit.internal.storage.file;
  
  import java.util.Collections;
  import java.util.Iterator;
  import java.util.NoSuchElementException;
  
  import org.eclipse.jgit.internal.storage.file.BasePackBitmapIndex.StoredBitmap;
  import org.eclipse.jgit.lib.AnyObjectId;
  import org.eclipse.jgit.lib.BitmapIndex;
  import org.eclipse.jgit.lib.ObjectId;
  
  import com.googlecode.javaewah.EWAHCompressedBitmap;
  import com.googlecode.javaewah.IntIterator;
  
  /**
   * A PackBitmapIndex that remaps the bitmaps in the previous index to the
   * positions in the new pack index. Note, unlike typical PackBitmapIndex
   * implementations this implementation is not thread safe, as it is intended to
   * be used with a PackBitmapIndexBuilder, which is also not thread safe.
   */
  public class PackBitmapIndexRemapper extends PackBitmapIndex
  		implements Iterable<PackBitmapIndexRemapper.Entry> {
  
  	private final BasePackBitmapIndex oldPackIndex;
  	final PackBitmapIndex newPackIndex;
  	private final BitSet inflated;
  	private final int[] prevToNewMapping;
  
  	/**
  	 * A PackBitmapIndex that maps the positions in the prevBitmapIndex to the
  	 * ones in the newIndex.
  	 *
  	 * @param prevBitmapIndex
  	 *            the bitmap index with the old mapping.
  	 * @param newIndex
  	 *            the bitmap index with the new mapping.
  	 * @return a bitmap index that attempts to do the mapping between the two.
  	 */
  	public static PackBitmapIndexRemapper newPackBitmapIndex(
  			BitmapIndex prevBitmapIndex, PackBitmapIndex newIndex) {
  		if (!(prevBitmapIndex instanceof BitmapIndexImpl))
  			return new PackBitmapIndexRemapper(newIndex);
  
  		PackBitmapIndex prevIndex = ((BitmapIndexImpl) prevBitmapIndex)
  				.getPackBitmapIndex();
  		if (!(prevIndex instanceof BasePackBitmapIndex))
  			return new PackBitmapIndexRemapper(newIndex);
  
  		return new PackBitmapIndexRemapper(
  				(BasePackBitmapIndex) prevIndex, newIndex);
  	}
  
  	private PackBitmapIndexRemapper(PackBitmapIndex newPackIndex) {
  		this.oldPackIndex = null;
  		this.newPackIndex = newPackIndex;
  		this.inflated = null;
  		this.prevToNewMapping = null;
  	}
  
  	private PackBitmapIndexRemapper(
  			BasePackBitmapIndex oldPackIndex, PackBitmapIndex newPackIndex) {
  		this.oldPackIndex = oldPackIndex;
  		this.newPackIndex = newPackIndex;
  		inflated = new BitSet(newPackIndex.getObjectCount());
  
  		prevToNewMapping = new int[oldPackIndex.getObjectCount()];
  		for (int pos = 0; pos < prevToNewMapping.length; pos++)
  			prevToNewMapping[pos] = newPackIndex.findPosition(
  					oldPackIndex.getObject(pos));
  	}
  
  	/** {@inheritDoc} */
  	@Override
  	public int findPosition(AnyObjectId objectId) {
  		return newPackIndex.findPosition(objectId);
  	}
  
  	/** {@inheritDoc} */
  	@Override
  	public ObjectId getObject(int position) throws IllegalArgumentException {
  		return newPackIndex.getObject(position);
  	}
  
  	/** {@inheritDoc} */
  	@Override
  	public int getObjectCount() {
  		return newPackIndex.getObjectCount();
  	}
  
 	/** {@inheritDoc} */
 	@Override
 	public EWAHCompressedBitmap ofObjectType(
 			EWAHCompressedBitmap bitmap, int type) {
 		return newPackIndex.ofObjectType(bitmap, type);
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public Iterator<Entry> iterator() {
 		if (oldPackIndex == null)
 			return Collections.<Entry> emptyList().iterator();
 
 		final Iterator<StoredBitmap> it = oldPackIndex.getBitmaps().iterator();
 		return new Iterator<Entry>() {
 			private Entry entry;
 
 			@Override
 			public boolean hasNext() {
 				while (entry == null && it.hasNext()) {
 					StoredBitmap sb = it.next();
 					if (newPackIndex.findPosition(sb) != -1)
 						entry = new Entry(sb, sb.getFlags());
 				}
 				return entry != null;
 			}
 
 			@Override
 			public Entry next() {
 				if (!hasNext())
 					throw new NoSuchElementException();
 
 				Entry res = entry;
 				entry = null;
 				return res;
 			}
 
 			@Override
 			public void remove() {
 				throw new UnsupportedOperationException();
 			}
 		};
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public EWAHCompressedBitmap getBitmap(AnyObjectId objectId) {
 		EWAHCompressedBitmap bitmap = newPackIndex.getBitmap(objectId);
 		if (bitmap != null || oldPackIndex == null)
 			return bitmap;
 
 		StoredBitmap oldBitmap = oldPackIndex.getBitmaps().get(objectId);
 		if (oldBitmap == null)
 			return null;
 
 		if (newPackIndex.findPosition(objectId) == -1)
 			return null;
 
 		inflated.clear();
 		for (IntIterator i = oldBitmap.getBitmap().intIterator(); i.hasNext();)
 			inflated.set(prevToNewMapping[i.next()]);
 		bitmap = inflated.toEWAHCompressedBitmap();
 		bitmap.trim();
 		return bitmap;
 	}
 
 	/** An entry in the old PackBitmapIndex. */
 	public static final class Entry extends ObjectId {
 		private final int flags;
 
 		Entry(AnyObjectId src, int flags) {
 			super(src);
 			this.flags = flags;
 		}
 
 		/** @return the flags associated with the bitmap. */
 		public int getFlags() {
 			return flags;
 		}
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public int getBitmapCount() {
 		// The count is only useful for the end index, not the remapper.
 		return 0;
 	}
 }