/*
 * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org> 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 org.eclipse.jgit.errors.IncorrectObjectTypeException;
import org.eclipse.jgit.errors.MissingObjectException;

Replaces a RevCommit's parents until not colored with REWRITE.

Before a RevCommit is returned to the caller its parents are updated to
create a dense DAG. Instead of reporting the actual parents as recorded when
the commit was created the returned commit will reflect the next closest
commit that matched the revision walker's filters.
 This generator is the second phase of a path limited revision walk and assumes it is receiving RevCommits from TreeRevFilter, after they have been fully buffered by AbstractRevQueue. The full buffering is necessary to allow the simple loop used within our own rewrite(RevCommit) to pull completely through a strand of RevWalk.REWRITE colored commits and come up with a simplification that makes the DAG dense. Not fully buffering the commits first would cause this loop to abort early, due to commits not being parsed and colored correctly. 
See Also:
TreeRevFilter/**
 * Replaces a RevCommit's parents until not colored with REWRITE.
 * <p>
 * Before a RevCommit is returned to the caller its parents are updated to
 * create a dense DAG. Instead of reporting the actual parents as recorded when
 * the commit was created the returned commit will reflect the next closest
 * commit that matched the revision walker's filters.
 * <p>
 * This generator is the second phase of a path limited revision walk and
 * assumes it is receiving RevCommits from {@link TreeRevFilter},
 * after they have been fully buffered by {@link AbstractRevQueue}. The full
 * buffering is necessary to allow the simple loop used within our own
 * {@link #rewrite(RevCommit)} to pull completely through a strand of
 * {@link RevWalk#REWRITE} colored commits and come up with a simplification
 * that makes the DAG dense. Not fully buffering the commits first would cause
 * this loop to abort early, due to commits not being parsed and colored
 * correctly.
 *
 * @see TreeRevFilter
 */
class RewriteGenerator extends Generator {
	private static final int REWRITE = RevWalk.REWRITE;

	
For cleanup(RevCommit[]) to remove duplicate parents. /** For {@link #cleanup(RevCommit[])} to remove duplicate parents. */
	private static final int DUPLICATE = RevWalk.TEMP_MARK;

	private final Generator source;

	RewriteGenerator(Generator s) {
		super(s.firstParent);
		source = s;
	}

	@Override
	void shareFreeList(BlockRevQueue q) {
		source.shareFreeList(q);
	}

	@Override
	int outputType() {
		return source.outputType() & ~NEEDS_REWRITE;
	}

	@Override
	RevCommit next() throws MissingObjectException,
			IncorrectObjectTypeException, IOException {
		final RevCommit c = source.next();
		if (c == null) {
			return null;
		}
		boolean rewrote = false;
		final RevCommit[] pList = c.parents;
		final int nParents = pList.length;
		for (int i = 0; i < nParents; i++) {
			final RevCommit oldp = pList[i];
			final RevCommit newp = rewrite(oldp);
			if (firstParent) {
				if (newp == null) {
					c.parents = RevCommit.NO_PARENTS;
				} else {
					c.parents = new RevCommit[] { newp };
				}
				return c;
			}
			if (oldp != newp) {
				pList[i] = newp;
				rewrote = true;
			}
		}
		if (rewrote) {
			c.parents = cleanup(pList);
		}
		return c;
	}

	private RevCommit rewrite(RevCommit p) {
		for (;;) {
			final RevCommit[] pList = p.parents;
			if (pList.length > 1) {
				// This parent is a merge, so keep it.
				//
				return p;
			}

			if ((p.flags & RevWalk.UNINTERESTING) != 0) {
				// Retain uninteresting parents. They show where the
				// DAG was cut off because it wasn't interesting.
				//
				return p;
			}

			if ((p.flags & REWRITE) == 0) {
				// This parent was not eligible for rewriting. We
				// need to keep it in the DAG.
				//
				return p;
			}

			if (pList.length == 0) {
				// We can't go back any further, other than to
				// just delete the parent entirely.
				//
				return null;
			}

			p = pList[0];
		}
	}

	private RevCommit[] cleanup(RevCommit[] oldList) {
		// Remove any duplicate parents caused due to rewrites (e.g. a merge
		// with two sides that both simplified back into the merge base).
		// We also may have deleted a parent by marking it null.
		//
		int newCnt = 0;
		for (int o = 0; o < oldList.length; o++) {
			final RevCommit p = oldList[o];
			if (p == null)
				continue;
			if ((p.flags & DUPLICATE) != 0) {
				oldList[o] = null;
				continue;
			}
			p.flags |= DUPLICATE;
			newCnt++;
		}

		if (newCnt == oldList.length) {
			for (RevCommit p : oldList)
				p.flags &= ~DUPLICATE;
			return oldList;
		}

		final RevCommit[] newList = new RevCommit[newCnt];
		newCnt = 0;
		for (RevCommit p : oldList) {
			if (p != null) {
				newList[newCnt++] = p;
				p.flags &= ~DUPLICATE;
			}
		}

		return newList;
	}
}