/*
 * 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.revwalk;

import java.io.IOException;

import org.eclipse.jgit.errors.IncorrectObjectTypeException;
import org.eclipse.jgit.errors.MissingObjectException;
import org.eclipse.jgit.errors.StopWalkException;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.revwalk.filter.RevFilter;
import org.eclipse.jgit.treewalk.TreeWalk;
import org.eclipse.jgit.treewalk.filter.TreeFilter;

/**
 * First phase of a path limited revision walk.
 * <p>
 * This filter is ANDed to evaluate after all other filters and ties the
 * configured {@link TreeFilter} into the revision walking process.
 * <p>
 * Each commit is differenced concurrently against all of its parents to look
 * for tree entries that are interesting to the TreeFilter. If none are found
 * the commit is colored with {@link RevWalk#REWRITE}, allowing a later pass
 * implemented by {@link RewriteGenerator} to remove those colored commits from
 * the DAG.
 *
 * @see RewriteGenerator
 */
class RewriteTreeFilter extends RevFilter {
	private static final int PARSED = RevWalk.PARSED;

	private static final int UNINTERESTING = RevWalk.UNINTERESTING;

	private static final int REWRITE = RevWalk.REWRITE;

	private final TreeWalk pathFilter;

	RewriteTreeFilter(final RevWalk walker, final TreeFilter t) {
		pathFilter = new TreeWalk(walker.db);
		pathFilter.setFilter(t);
		pathFilter.setRecursive(t.shouldBeRecursive());
	}

	@Override
	public RevFilter clone() {
		throw new UnsupportedOperationException();
	}

	@Override
	public boolean include(final RevWalk walker, final RevCommit c)
			throws StopWalkException, MissingObjectException,
			IncorrectObjectTypeException, IOException {
		// Reset the tree filter to scan this commit and parents.
		//
		final RevCommit[] pList = c.parents;
		final int nParents = pList.length;
		final TreeWalk tw = pathFilter;
		final ObjectId[] trees = new ObjectId[nParents + 1];
		for (int i = 0; i < nParents; i++) {
			final RevCommit p = c.parents[i];
			if ((p.flags & PARSED) == 0)
				p.parseHeaders(walker);
			trees[i] = p.getTree();
		}
		trees[nParents] = c.getTree();
		tw.reset(trees);

		if (nParents == 1) {
			// We have exactly one parent. This is a very common case.
			//
			int chgs = 0, adds = 0;
			while (tw.next()) {
				chgs++;
				if (tw.getRawMode(0) == 0 && tw.getRawMode(1) != 0)
					adds++;
				else
					break; // no point in looking at this further.
			}

			if (chgs == 0) {
				// No changes, so our tree is effectively the same as
				// our parent tree. We pass the buck to our parent.
				//
				c.flags |= REWRITE;
				return false;
			} else {
				// We have interesting items, but neither of the special
				// cases denoted above.
				//
				return true;
			}
		} else if (nParents == 0) {
			// We have no parents to compare against. Consider us to be
			// REWRITE only if we have no paths matching our filter.
			//
			if (tw.next())
				return true;
			c.flags |= REWRITE;
			return false;
		}

		// We are a merge commit. We can only be REWRITE if we are same
		// to _all_ parents. We may also be able to eliminate a parent if
		// it does not contribute changes to us. Such a parent may be an
		// uninteresting side branch.
		//
		final int[] chgs = new int[nParents];
		final int[] adds = new int[nParents];
		while (tw.next()) {
			final int myMode = tw.getRawMode(nParents);
			for (int i = 0; i < nParents; i++) {
				final int pMode = tw.getRawMode(i);
				if (myMode == pMode && tw.idEqual(i, nParents))
					continue;

				chgs[i]++;
				if (pMode == 0 && myMode != 0)
					adds[i]++;
			}
		}

		boolean same = false;
		boolean diff = false;
		for (int i = 0; i < nParents; i++) {
			if (chgs[i] == 0) {
				// No changes, so our tree is effectively the same as
				// this parent tree. We pass the buck to only this one
				// parent commit.
				//

				final RevCommit p = pList[i];
				if ((p.flags & UNINTERESTING) != 0) {
					// This parent was marked as not interesting by the
					// application. We should look for another parent
					// that is interesting.
					//
					same = true;
					continue;
				}

				c.flags |= REWRITE;
				c.parents = new RevCommit[] { p };
				return false;
			}

			if (chgs[i] == adds[i]) {
				// All of the differences from this parent were because we
				// added files that they did not have. This parent is our
				// "empty tree root" and thus their history is not relevant.
				// Cut our grandparents to be an empty list.
				//
				pList[i].parents = RevCommit.NO_PARENTS;
			}

			// We have an interesting difference relative to this parent.
			//
			diff = true;
		}

		if (diff && !same) {
			// We did not abort above, so we are different in at least one
			// way from all of our parents. We have to take the blame for
			// that difference.
			//
			return true;
		}

		// We are the same as all of our parents. We must keep them
		// as they are and allow those parents to flow into pending
		// for further scanning.
		//
		c.flags |= REWRITE;
		return false;
	}
}