/*
    * Copyright (C) 2012, 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 org.eclipse.jgit.lib.AnyObjectId;
  import org.eclipse.jgit.lib.ObjectIdOwnerMap;
  
  import com.googlecode.javaewah.EWAHCompressedBitmap;
  
  /**
   * Base implementation of the PackBitmapIndex.
   */
  abstract class BasePackBitmapIndex extends PackBitmapIndex {
  	private final ObjectIdOwnerMap<StoredBitmap> bitmaps;
  
  	BasePackBitmapIndex(ObjectIdOwnerMap<StoredBitmap> bitmaps) {
  		this.bitmaps = bitmaps;
  	}
  
  	/** {@inheritDoc} */
  	@Override
  	public EWAHCompressedBitmap getBitmap(AnyObjectId objectId) {
  		StoredBitmap sb = bitmaps.get(objectId);
  		return sb != null ? sb.getBitmap() : null;
  	}
  
  	ObjectIdOwnerMap<StoredBitmap> getBitmaps() {
  		return bitmaps;
  	}
  
  	/**
  	 * Data representation of the bitmap entry restored from a pack index. The
  	 * commit of the bitmap is the map key.
  	 */
  	static final class StoredBitmap extends ObjectIdOwnerMap.Entry {
  		private volatile Object bitmapContainer;
  		private final int flags;
  
  		StoredBitmap(AnyObjectId objectId, EWAHCompressedBitmap bitmap,
  				StoredBitmap xorBitmap, int flags) {
  			super(objectId);
  			this.bitmapContainer = xorBitmap == null
  					? bitmap
  					: new XorCompressedBitmap(bitmap, xorBitmap);
  			this.flags = flags;
  		}
  
  		/**
  		 * Computes and returns the full bitmap.
  		 *
  		 * @return the full bitmap
  		 */
  		EWAHCompressedBitmap getBitmap() {
  			// Fast path to immediately return the expanded result.
  			Object r = bitmapContainer;
  			if (r instanceof EWAHCompressedBitmap)
  				return (EWAHCompressedBitmap) r;
  
  			// Expand the bitmap and cache the result.
  			XorCompressedBitmap xb = (XorCompressedBitmap) r;
  			EWAHCompressedBitmap out = xb.bitmap;
  			for (;;) {
  				r = xb.xorBitmap.bitmapContainer;
  				if (r instanceof EWAHCompressedBitmap) {
  					out = out.xor((EWAHCompressedBitmap) r);
  					out.trim();
  					bitmapContainer = out;
  					return out;
  				}
  				xb = (XorCompressedBitmap) r;
  				out = out.xor(xb.bitmap);
  			}
  		}
  
  		/** @return the flags associated with the bitmap */
  		int getFlags() {
  			return flags;
  		}
  	}
  
  	private static final class XorCompressedBitmap {
  		final EWAHCompressedBitmap bitmap;
  		final StoredBitmap xorBitmap;
  
  		XorCompressedBitmap(EWAHCompressedBitmap b, StoredBitmap xb) {
  			bitmap = b;
  			xorBitmap = xb;
  		}
  	}
  }