/*
    * Copyright (C) 2012, Google Inc.
    * 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
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   *   disclaimer in the documentation and/or other materials provided
   *   with the distribution.
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   * - 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
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  package org.eclipse.jgit.internal.storage.pack;
  
  import java.io.IOException;
  import java.util.Arrays;
  
  import org.eclipse.jgit.errors.IncorrectObjectTypeException;
  import org.eclipse.jgit.errors.MissingObjectException;
  import org.eclipse.jgit.lib.BitmapIndex;
  import org.eclipse.jgit.lib.BitmapIndex.Bitmap;
  import org.eclipse.jgit.lib.BitmapIndex.BitmapBuilder;
  import org.eclipse.jgit.lib.Constants;
  import org.eclipse.jgit.lib.NullProgressMonitor;
  import org.eclipse.jgit.lib.ObjectId;
  import org.eclipse.jgit.lib.ProgressMonitor;
  import org.eclipse.jgit.revwalk.ObjectWalk;
  import org.eclipse.jgit.revwalk.RevCommit;
  import org.eclipse.jgit.revwalk.RevFlag;
  import org.eclipse.jgit.revwalk.RevObject;
  import org.eclipse.jgit.revwalk.RevWalk;
  import org.eclipse.jgit.revwalk.filter.RevFilter;
  
  /** Helper class for PackWriter to do ObjectWalks with pack index bitmaps. */
  final class PackWriterBitmapWalker {
  
  	private final ObjectWalk walker;
  
  	private final BitmapIndex bitmapIndex;
  
  	private final ProgressMonitor pm;
  
  	private long countOfBitmapIndexMisses;
  
  	PackWriterBitmapWalker(
  			ObjectWalk walker, BitmapIndex bitmapIndex, ProgressMonitor pm) {
  		this.walker = walker;
  		this.bitmapIndex = bitmapIndex;
  		this.pm = (pm == null) ? NullProgressMonitor.INSTANCE : pm;
  	}
  
  	long getCountOfBitmapIndexMisses() {
  		return countOfBitmapIndexMisses;
  	}
  
  	BitmapBuilder findObjects(Iterable<? extends ObjectId> start, BitmapBuilder seen,
  			boolean ignoreMissing)
  			throws MissingObjectException, IncorrectObjectTypeException,
  				   IOException {
  		if (!ignoreMissing) {
  			return findObjectsWalk(start, seen, false);
  		}
  
  		try {
  			return findObjectsWalk(start, seen, true);
  		} catch (MissingObjectException ignore) {
  			// An object reachable from one of the "start"s is missing.
  			// Walk from the "start"s one at a time so it can be excluded.
 		}
 
 		final BitmapBuilder result = bitmapIndex.newBitmapBuilder();
 		for (ObjectId obj : start) {
 			Bitmap bitmap = bitmapIndex.getBitmap(obj);
 			if (bitmap != null) {
 				result.or(bitmap);
 			}
 		}
 
 		for (ObjectId obj : start) {
 			if (result.contains(obj)) {
 				continue;
 			}
 			try {
 				result.or(findObjectsWalk(Arrays.asList(obj), result, false));
 			} catch (MissingObjectException ignore) {
 				// An object reachable from this "start" is missing.
 				//
 				// This can happen when the client specified a "have" line
 				// pointing to an object that is present but unreachable:
 				// "git prune" and "git fsck" only guarantee that the object
 				// database will continue to contain all objects reachable
 				// from a ref and does not guarantee connectivity for other
 				// objects in the object database.
 				//
 				// In this situation, skip the relevant "start" and move on
 				// to the next one.
 				//
 				// TODO(czhen): Make findObjectsWalk resume the walk instead
 				// once RevWalk and ObjectWalk support that.
 			}
 		}
 		return result;
 	}
 
 	private BitmapBuilder findObjectsWalk(Iterable<? extends ObjectId> start, BitmapBuilder seen,
 			boolean ignoreMissingStart)
 			throws MissingObjectException, IncorrectObjectTypeException,
 			IOException {
 		walker.reset();
 		final BitmapBuilder bitmapResult = bitmapIndex.newBitmapBuilder();
 
 		for (ObjectId obj : start) {
 			Bitmap bitmap = bitmapIndex.getBitmap(obj);
 			if (bitmap != null)
 				bitmapResult.or(bitmap);
 		}
 
 		boolean marked = false;
 		for (ObjectId obj : start) {
 			try {
 				if (!bitmapResult.contains(obj)) {
 					walker.markStart(walker.parseAny(obj));
 					marked = true;
 				}
 			} catch (MissingObjectException e) {
 				if (ignoreMissingStart)
 					continue;
 				throw e;
 			}
 		}
 
 		if (marked) {
 			if (seen == null) {
 				walker.setRevFilter(new AddToBitmapFilter(bitmapResult));
 			} else {
 				walker.setRevFilter(
 						new AddUnseenToBitmapFilter(seen, bitmapResult));
 			}
 
 			while (walker.next() != null) {
 				// Iterate through all of the commits. The BitmapRevFilter does
 				// the work.
 				//
 				// filter.include returns true for commits that do not have
 				// a bitmap in bitmapIndex and are not reachable from a
 				// bitmap in bitmapIndex encountered earlier in the walk.
 				// Thus the number of commits returned by next() measures how
 				// much history was traversed without being able to make use
 				// of bitmaps.
 				pm.update(1);
 				countOfBitmapIndexMisses++;
 			}
 
 			RevObject ro;
 			while ((ro = walker.nextObject()) != null) {
 				bitmapResult.addObject(ro, ro.getType());
 				pm.update(1);
 			}
 		}
 
 		return bitmapResult;
 	}
 
 	/**
 	 * A RevFilter that adds the visited commits to {@code bitmap} as a side
 	 * effect.
 	 * <p>
 	 * When the walk hits a commit that is part of {@code bitmap}'s
 	 * BitmapIndex, that entire bitmap is ORed into {@code bitmap} and the
 	 * commit and its parents are marked as SEEN so that the walk does not
 	 * have to visit its ancestors.  This ensures the walk is very short if
 	 * there is good bitmap coverage.
 	 */
 	static class AddToBitmapFilter extends RevFilter {
 		private final BitmapBuilder bitmap;
 
 		AddToBitmapFilter(BitmapBuilder bitmap) {
 			this.bitmap = bitmap;
 		}
 
 		@Override
 		public final boolean include(RevWalk walker, RevCommit cmit) {
 			Bitmap visitedBitmap;
 
 			if (bitmap.contains(cmit)) {
 				// already included
 			} else if ((visitedBitmap = bitmap.getBitmapIndex()
 					.getBitmap(cmit)) != null) {
 				bitmap.or(visitedBitmap);
 			} else {
 				bitmap.addObject(cmit, Constants.OBJ_COMMIT);
 				return true;
 			}
 
 			for (RevCommit p : cmit.getParents()) {
 				p.add(RevFlag.SEEN);
 			}
 			return false;
 		}
 
 		@Override
 		public final RevFilter clone() {
 			throw new UnsupportedOperationException();
 		}
 
 		@Override
 		public final boolean requiresCommitBody() {
 			return false;
 		}
 	}
 
 	/**
 	 * A RevFilter that adds the visited commits to {@code bitmap} as a side
 	 * effect.
 	 * <p>
 	 * When the walk hits a commit that is part of {@code bitmap}'s
 	 * BitmapIndex, that entire bitmap is ORed into {@code bitmap} and the
 	 * commit and its parents are marked as SEEN so that the walk does not
 	 * have to visit its ancestors.  This ensures the walk is very short if
 	 * there is good bitmap coverage.
 	 * <p>
 	 * Commits named in {@code seen} are considered already seen.  If one is
 	 * encountered, that commit and its parents will be marked with the SEEN
 	 * flag to prevent the walk from visiting its ancestors.
 	 */
 	static class AddUnseenToBitmapFilter extends RevFilter {
 		private final BitmapBuilder seen;
 		private final BitmapBuilder bitmap;
 
 		AddUnseenToBitmapFilter(BitmapBuilder seen, BitmapBuilder bitmapResult) {
 			this.seen = seen;
 			this.bitmap = bitmapResult;
 		}
 
 		@Override
 		public final boolean include(RevWalk walker, RevCommit cmit) {
 			Bitmap visitedBitmap;
 
 			if (seen.contains(cmit) || bitmap.contains(cmit)) {
 				// already seen or included
 			} else if ((visitedBitmap = bitmap.getBitmapIndex()
 					.getBitmap(cmit)) != null) {
 				bitmap.or(visitedBitmap);
 			} else {
 				bitmap.addObject(cmit, Constants.OBJ_COMMIT);
 				return true;
 			}
 
 			for (RevCommit p : cmit.getParents()) {
 				p.add(RevFlag.SEEN);
 			}
 			return false;
 		}
 
 		@Override
 		public final RevFilter clone() {
 			throw new UnsupportedOperationException();
 		}
 
 		@Override
 		public final boolean requiresCommitBody() {
 			return false;
 		}
 	}
 }