/*
    * 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.revwalk;
  
  import java.io.IOException;
  import java.util.Arrays;
  
  import org.eclipse.jgit.errors.IncorrectObjectTypeException;
  import org.eclipse.jgit.errors.MissingObjectException;
  import org.eclipse.jgit.internal.revwalk.AddToBitmapFilter;
  import org.eclipse.jgit.internal.revwalk.AddUnseenToBitmapFilter;
  import org.eclipse.jgit.lib.AnyObjectId;
  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.NullProgressMonitor;
  import org.eclipse.jgit.lib.ObjectId;
  import org.eclipse.jgit.lib.ProgressMonitor;
  import org.eclipse.jgit.revwalk.filter.ObjectFilter;
  
  /**
   * Helper class to do ObjectWalks with pack index bitmaps.
   *
   * @since 4.10
   */
  public final class BitmapWalker {
  
  	private final ObjectWalk walker;
  
  	private final BitmapIndex bitmapIndex;
  
  	private final ProgressMonitor pm;
  
  	private long countOfBitmapIndexMisses;
  
  	/**
  	 * Create a BitmapWalker.
  	 *
  	 * @param walker walker to use when traversing the object graph.
  	 * @param bitmapIndex index to obtain bitmaps from.
  	 * @param pm progress monitor to report progress on.
  	 */
  	public BitmapWalker(
  			ObjectWalk walker, BitmapIndex bitmapIndex, ProgressMonitor pm) {
  		this.walker = walker;
  		this.bitmapIndex = bitmapIndex;
  		this.pm = (pm == null) ? NullProgressMonitor.INSTANCE : pm;
  	}
  
  	/**
  	 * Return the number of objects that had to be walked because they were not covered by a
  	 * bitmap.
  	 *
  	 * @return the number of objects that had to be walked because they were not covered by a
  	 *     bitmap.
  	 */
  	public long getCountOfBitmapIndexMisses() {
  		return countOfBitmapIndexMisses;
  	}
  
  	/**
  	 * Return, as a bitmap, the objects reachable from the objects in start.
  	 *
  	 * @param start
  	 *            the objects to start the object traversal from.
  	 * @param seen
  	 *            the objects to skip if encountered during traversal.
  	 * @param ignoreMissing
  	 *            true to ignore missing objects, false otherwise.
  	 * @return as a bitmap, the objects reachable from the objects in start.
  	 * @throws org.eclipse.jgit.errors.MissingObjectException
  	 *             the object supplied is not available from the object
  	 *             database. This usually indicates the supplied object is
  	 *             invalid, but the reference was constructed during an earlier
  	 *             invocation to
  	 *             {@link org.eclipse.jgit.revwalk.RevWalk#lookupAny(AnyObjectId, int)}.
  	 * @throws org.eclipse.jgit.errors.IncorrectObjectTypeException
  	 *             the object was not parsed yet and it was discovered during
  	 *             parsing that it is not actually the type of the instance
  	 *             passed in. This usually indicates the caller used the wrong
  	 *             type in a
  	 *             {@link org.eclipse.jgit.revwalk.RevWalk#lookupAny(AnyObjectId, int)}
  	 *             call.
  	 * @throws java.io.IOException
  	 *             a pack file or loose object could not be read.
  	 */
  	public 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));
 			}
 			walker.setObjectFilter(new BitmapObjectFilter(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;
 	}
 
 	/**
 	 * Filter that excludes objects already in the given bitmap.
 	 */
 	static class BitmapObjectFilter extends ObjectFilter {
 		private final BitmapBuilder bitmap;
 
 		BitmapObjectFilter(BitmapBuilder bitmap) {
 			this.bitmap = bitmap;
 		}
 
 		@Override
 		public final boolean include(ObjectWalk walker, AnyObjectId objid)
 			throws MissingObjectException, IncorrectObjectTypeException,
 			       IOException {
 			return !bitmap.contains(objid);
 		}
 	}
 }