/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.maven.scm.provider.git.jgit.command.diff;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;

import org.apache.maven.scm.ScmException;
import org.apache.maven.scm.ScmFileSet;
import org.apache.maven.scm.ScmVersion;
import org.apache.maven.scm.command.diff.AbstractDiffCommand;
import org.apache.maven.scm.command.diff.DiffScmResult;
import org.apache.maven.scm.provider.ScmProviderRepository;
import org.apache.maven.scm.provider.git.command.GitCommand;
import org.apache.maven.scm.provider.git.command.diff.GitDiffConsumer;
import org.apache.maven.scm.provider.git.jgit.command.JGitUtils;
import org.eclipse.jgit.api.Git;
import org.eclipse.jgit.api.errors.GitAPIException;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.ObjectReader;
import org.eclipse.jgit.lib.Repository;
import org.eclipse.jgit.revwalk.RevWalk;
import org.eclipse.jgit.treewalk.AbstractTreeIterator;
import org.eclipse.jgit.treewalk.CanonicalTreeParser;

/**
 * @author Dominik Bartholdi (imod)
 * @since 1.9
 */
public class JGitDiffCommand extends AbstractDiffCommand implements GitCommand {

    @Override
    protected DiffScmResult executeDiffCommand(
            ScmProviderRepository repository, ScmFileSet fileSet, ScmVersion startRevision, ScmVersion endRevision)
            throws ScmException {

        Git git = null;
        try {
            git = JGitUtils.openRepo(fileSet.getBasedir());
            DiffScmResult diff = callDiff(git, startRevision, endRevision);
            git.getRepository().close();
            return diff;
        } catch (IOException | GitAPIException e) {
            throw new ScmException("JGit diff failure!", e);
        } finally {
            JGitUtils.closeRepo(git);
        }
    }

    public DiffScmResult callDiff(Git git, ScmVersion startRevision, ScmVersion endRevision)
            throws IOException, GitAPIException, ScmException {

        AbstractTreeIterator oldTree = null;
        if (startRevision != null && !startRevision.getName().trim().isEmpty()) {
            String startRev = startRevision.getName().trim();
            oldTree = getTreeIterator(git.getRepository(), startRev);
        }

        AbstractTreeIterator newTree = null;
        if (endRevision != null && !endRevision.getName().trim().isEmpty()) {
            String endRev = endRevision.getName().trim();
            newTree = getTreeIterator(git.getRepository(), endRev);
        }

        OutputStream out = new ByteArrayOutputStream();

        git.diff()
                .setOutputStream(out)
                .setOldTree(oldTree)
                .setNewTree(newTree)
                .setCached(false)
                .call();
        git.diff()
                .setOutputStream(out)
                .setOldTree(oldTree)
                .setNewTree(newTree)
                .setCached(true)
                .call();

        out.flush();

        GitDiffConsumer consumer = new GitDiffConsumer(null);
        String fullDiff = out.toString();
        out.close();

        String[] lines = fullDiff.split("\n");
        for (String aLine : lines) {
            consumer.consumeLine(aLine);
        }

        return new DiffScmResult(
                "JGit diff", consumer.getChangedFiles(), consumer.getDifferences(), consumer.getPatch());
    }

    private AbstractTreeIterator getTreeIterator(Repository repo, String name) throws IOException {
        final ObjectId id = repo.resolve(name);
        if (id == null) {
            throw new IllegalArgumentException(name);
        }
        final CanonicalTreeParser p = new CanonicalTreeParser();

        try (ObjectReader or = repo.newObjectReader();
                RevWalk revWalk = new RevWalk(repo)) {
            p.reset(or, revWalk.parseTree(id));
            return p;
        }
    }
}
