/*
 * Copyright 2011 gitblit.com.
 *
 * Licensed 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 com.gitblit.utils;

import java.io.ByteArrayOutputStream;
import java.io.Serializable;
import java.text.MessageFormat;
import java.util.ArrayList;
import java.util.List;

import org.eclipse.jgit.api.BlameCommand;
import org.eclipse.jgit.blame.BlameResult;
import org.eclipse.jgit.diff.DiffEntry;
import org.eclipse.jgit.diff.DiffFormatter;
import org.eclipse.jgit.diff.RawText;
import org.eclipse.jgit.diff.RawTextComparator;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.Repository;
import org.eclipse.jgit.revwalk.RevCommit;
import org.eclipse.jgit.revwalk.RevTree;
import org.eclipse.jgit.revwalk.RevWalk;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.gitblit.models.AnnotatedLine;
import com.gitblit.models.PathModel.PathChangeModel;

/**
 * DiffUtils is a class of utility methods related to diff, patch, and blame.
 *
 * The diff methods support pluggable diff output types like Gitblit, Gitweb,
 * and Plain.
 *
 * @author James Moger
 *
 */
public class DiffUtils {

	private static final Logger LOGGER = LoggerFactory.getLogger(DiffUtils.class);

	/**
	 * Callback interface for binary diffs. All the getDiff methods here take an optional handler;
	 * if given and the {@link DiffOutputType} is {@link DiffOutputType#HTML HTML}, it is responsible
	 * for displaying a binary diff.
	 */
	public interface BinaryDiffHandler {

		/**
		 * Renders a binary diff. The result must be valid HTML, it will be inserted into an HTML table cell.
		 * May return {@code null} if the default behavior (which is typically just a textual note "Bnary
		 * files differ") is desired.
		 *
		 * @param diffEntry
		 *            current diff entry
		 *
		 * @return the rendered diff as HTML, or {@code null} if the default is desired.
		 */
		public String renderBinaryDiff(final DiffEntry diffEntry);

	}

	/**
	 * Enumeration for the diff output types.
	 */
	public static enum DiffOutputType {
		PLAIN, HTML;

		public static DiffOutputType forName(String name) {
			for (DiffOutputType type : values()) {
				if (type.name().equalsIgnoreCase(name)) {
					return type;
				}
			}
			return null;
		}
	}

	/**
	 * Encapsulates the output of a diff.
	 */
	public static class DiffOutput implements Serializable {
		private static final long serialVersionUID = 1L;

		public final DiffOutputType type;
		public final String content;
		public final DiffStat stat;

		DiffOutput(DiffOutputType type, String content, DiffStat stat) {
			this.type = type;
			this.content = content;
			this.stat = stat;
		}

		public PathChangeModel getPath(String path) {
			if (stat == null) {
				return null;
			}
			return stat.getPath(path);
		}
	}

	/**
	 * Class that represents the number of insertions and deletions from a
	 * chunk.
	 */
	public static class DiffStat implements Serializable {

		private static final long serialVersionUID = 1L;

		public final List<PathChangeModel> paths = new ArrayList<PathChangeModel>();

		private final String commitId;

		public DiffStat(String commitId) {
			this.commitId = commitId;
		}

		public PathChangeModel addPath(DiffEntry entry) {
			PathChangeModel pcm = PathChangeModel.from(entry, commitId);
			paths.add(pcm);
			return pcm;
		}

		public int getInsertions() {
			int val = 0;
			for (PathChangeModel entry : paths) {
				val += entry.insertions;
			}
			return val;
		}

		public int getDeletions() {
			int val = 0;
			for (PathChangeModel entry : paths) {
				val += entry.deletions;
			}
			return val;
		}

		public PathChangeModel getPath(String path) {
			PathChangeModel stat = null;
			for (PathChangeModel p : paths) {
				if (p.path.equals(path)) {
					stat = p;
					break;
				}
			}
			return stat;
		}

		@Override
		public String toString() {
			StringBuilder sb = new StringBuilder();
			for (PathChangeModel entry : paths) {
				sb.append(entry.toString()).append('\n');
			}
			sb.setLength(sb.length() - 1);
			return sb.toString();
		}
	}

	public static class NormalizedDiffStat implements Serializable {

		private static final long serialVersionUID = 1L;

		public final int insertions;
		public final int deletions;
		public final int blanks;

		NormalizedDiffStat(int insertions, int deletions, int blanks) {
			this.insertions = insertions;
			this.deletions = deletions;
			this.blanks = blanks;
		}
	}

	/**
	 * Returns the complete diff of the specified commit compared to its primary
	 * parent.
	 *
	 * @param repository
	 * @param commit
	 * @param outputType
	 * @return the diff
	 */
	public static DiffOutput getCommitDiff(Repository repository, RevCommit commit,
			DiffOutputType outputType) {
		return getDiff(repository, null, commit, null, outputType);
	}

	/**
	 * Returns the complete diff of the specified commit compared to its primary parent.
	 *
	 * @param repository
	 * @param commit
	 * @param outputType
	 * @param handler
	 *            to use for rendering binary diffs if {@code outputType} is {@link DiffOutputType#HTML HTML}.
	 *            May be {@code null}, resulting in the default behavior.
	 * @return the diff
	 */
	public static DiffOutput getCommitDiff(Repository repository, RevCommit commit,
			DiffOutputType outputType, BinaryDiffHandler handler) {
		return getDiff(repository, null, commit, null, outputType, handler);
	}


	/**
	 * Returns the diff for the specified file or folder from the specified
	 * commit compared to its primary parent.
	 *
	 * @param repository
	 * @param commit
	 * @param path
	 * @param outputType
	 * @return the diff
	 */
	public static DiffOutput getDiff(Repository repository, RevCommit commit, String path,
			DiffOutputType outputType) {
		return getDiff(repository, null, commit, path, outputType);
	}

	/**
	 * Returns the diff for the specified file or folder from the specified
	 * commit compared to its primary parent.
	 *
	 * @param repository
	 * @param commit
	 * @param path
	 * @param outputType
	 * @param handler
	 *            to use for rendering binary diffs if {@code outputType} is {@link DiffOutputType#HTML HTML}.
	 *            May be {@code null}, resulting in the default behavior.
	 * @return the diff
	 */
	public static DiffOutput getDiff(Repository repository, RevCommit commit, String path,
			DiffOutputType outputType, BinaryDiffHandler handler) {
		return getDiff(repository, null, commit, path, outputType, handler);
	}

	/**
	 * Returns the complete diff between the two specified commits.
	 *
	 * @param repository
	 * @param baseCommit
	 * @param commit
	 * @param outputType
	 * @return the diff
	 */
	public static DiffOutput getDiff(Repository repository, RevCommit baseCommit, RevCommit commit,
			DiffOutputType outputType) {
		return getDiff(repository, baseCommit, commit, null, outputType);
	}

	/**
	 * Returns the complete diff between the two specified commits.
	 *
	 * @param repository
	 * @param baseCommit
	 * @param commit
	 * @param outputType
	 * @param handler
	 *            to use for rendering binary diffs if {@code outputType} is {@link DiffOutputType#HTML HTML}.
	 *            May be {@code null}, resulting in the default behavior.
	 * @return the diff
	 */
	public static DiffOutput getDiff(Repository repository, RevCommit baseCommit, RevCommit commit,
			DiffOutputType outputType, BinaryDiffHandler handler) {
		return getDiff(repository, baseCommit, commit, null, outputType, handler);
	}

	/**
	 * Returns the diff between two commits for the specified file.
	 *
	 * @param repository
	 * @param baseCommit
	 *            if base commit is null the diff is to the primary parent of
	 *            the commit.
	 * @param commit
	 * @param path
	 *            if the path is specified, the diff is restricted to that file
	 *            or folder. if unspecified, the diff is for the entire commit.
	 * @param outputType
	 * @return the diff
	 */
	public static DiffOutput getDiff(Repository repository, RevCommit baseCommit, RevCommit commit,
			String path, DiffOutputType outputType) {
		return getDiff(repository, baseCommit, commit, path, outputType, null);
	}

	/**
	 * Returns the diff between two commits for the specified file.
	 *
	 * @param repository
	 * @param baseCommit
	 *            if base commit is null the diff is to the primary parent of
	 *            the commit.
	 * @param commit
	 * @param path
	 *            if the path is specified, the diff is restricted to that file
	 *            or folder. if unspecified, the diff is for the entire commit.
	 * @param outputType
	 * @param handler
	 *            to use for rendering binary diffs if {@code outputType} is {@link DiffOutputType#HTML HTML}.
	 *            May be {@code null}, resulting in the default behavior.
	 * @return the diff
	 */
	public static DiffOutput getDiff(Repository repository, RevCommit baseCommit, RevCommit commit, String path, DiffOutputType outputType,
			final BinaryDiffHandler handler) {
		DiffStat stat = null;
		String diff = null;
		try {
			ByteArrayOutputStream os = null;
			RawTextComparator cmp = RawTextComparator.DEFAULT;
			DiffFormatter df;
			switch (outputType) {
			case HTML:
				df = new GitBlitDiffFormatter(commit.getName(), path, handler);
				break;
			case PLAIN:
			default:
				os = new ByteArrayOutputStream();
				df = new DiffFormatter(os);
				break;
			}
			df.setRepository(repository);
			df.setDiffComparator(cmp);
			df.setDetectRenames(true);

			RevTree commitTree = commit.getTree();
			RevTree baseTree;
			if (baseCommit == null) {
				if (commit.getParentCount() > 0) {
					final RevWalk rw = new RevWalk(repository);
					RevCommit parent = rw.parseCommit(commit.getParent(0).getId());
					rw.dispose();
					baseTree = parent.getTree();
				} else {
					// FIXME initial commit. no parent?!
					baseTree = commitTree;
				}
			} else {
				baseTree = baseCommit.getTree();
			}

			List<DiffEntry> diffEntries = df.scan(baseTree, commitTree);
			if (path != null && path.length() > 0) {
				for (DiffEntry diffEntry : diffEntries) {
					if (diffEntry.getNewPath().equalsIgnoreCase(path)) {
						df.format(diffEntry);
						break;
					}
				}
			} else {
				df.format(diffEntries);
			}
			df.flush();
			if (df instanceof GitBlitDiffFormatter) {
				// workaround for complex private methods in DiffFormatter
				diff = ((GitBlitDiffFormatter) df).getHtml();
				stat = ((GitBlitDiffFormatter) df).getDiffStat();
			} else {
				diff = os.toString();
			}
		} catch (Throwable t) {
			LOGGER.error("failed to generate commit diff!", t);
		}

		return new DiffOutput(outputType, diff, stat);
	}

	/**
	 * Returns the diff between the two commits for the specified file or folder
	 * formatted as a patch.
	 *
	 * @param repository
	 * @param baseCommit
	 *            if base commit is unspecified, the patch is generated against
	 *            the primary parent of the specified commit.
	 * @param commit
	 * @param path
	 *            if path is specified, the patch is generated only for the
	 *            specified file or folder. if unspecified, the patch is
	 *            generated for the entire diff between the two commits.
	 * @return patch as a string
	 */
	public static String getCommitPatch(Repository repository, RevCommit baseCommit,
			RevCommit commit, String path) {
		String diff = null;
		try {
			final ByteArrayOutputStream os = new ByteArrayOutputStream();
			RawTextComparator cmp = RawTextComparator.DEFAULT;
			PatchFormatter df = new PatchFormatter(os);
			df.setRepository(repository);
			df.setDiffComparator(cmp);
			df.setDetectRenames(true);

			RevTree commitTree = commit.getTree();
			RevTree baseTree;
			if (baseCommit == null) {
				if (commit.getParentCount() > 0) {
					final RevWalk rw = new RevWalk(repository);
					RevCommit parent = rw.parseCommit(commit.getParent(0).getId());
					baseTree = parent.getTree();
				} else {
					// FIXME initial commit. no parent?!
					baseTree = commitTree;
				}
			} else {
				baseTree = baseCommit.getTree();
			}

			List<DiffEntry> diffEntries = df.scan(baseTree, commitTree);
			if (path != null && path.length() > 0) {
				for (DiffEntry diffEntry : diffEntries) {
					if (diffEntry.getNewPath().equalsIgnoreCase(path)) {
						df.format(diffEntry);
						break;
					}
				}
			} else {
				df.format(diffEntries);
			}
			diff = df.getPatch(commit);
			df.flush();
		} catch (Throwable t) {
			LOGGER.error("failed to generate commit diff!", t);
		}
		return diff;
	}

	/**
	 * Returns the diffstat between the two commits for the specified file or folder.
	 *
	 * @param repository
	 * @param base
	 *            if base commit is unspecified, the diffstat is generated against
	 *            the primary parent of the specified tip.
	 * @param tip
	 * @param path
	 *            if path is specified, the diffstat is generated only for the
	 *            specified file or folder. if unspecified, the diffstat is
	 *            generated for the entire diff between the two commits.
	 * @return patch as a string
	 */
	public static DiffStat getDiffStat(Repository repository, String base, String tip) {
		RevCommit baseCommit = null;
		RevCommit tipCommit = null;
		RevWalk revWalk = new RevWalk(repository);
		try {
			tipCommit = revWalk.parseCommit(repository.resolve(tip));
			if (!StringUtils.isEmpty(base)) {
				baseCommit = revWalk.parseCommit(repository.resolve(base));
			}
			return getDiffStat(repository, baseCommit, tipCommit, null);
		} catch (Exception e) {
			LOGGER.error("failed to generate diffstat!", e);
		} finally {
			revWalk.dispose();
		}
		return null;
	}

	public static DiffStat getDiffStat(Repository repository, RevCommit commit) {
		return getDiffStat(repository, null, commit, null);
	}

	/**
	 * Returns the diffstat between the two commits for the specified file or folder.
	 *
	 * @param repository
	 * @param baseCommit
	 *            if base commit is unspecified, the diffstat is generated against
	 *            the primary parent of the specified commit.
	 * @param commit
	 * @param path
	 *            if path is specified, the diffstat is generated only for the
	 *            specified file or folder. if unspecified, the diffstat is
	 *            generated for the entire diff between the two commits.
	 * @return patch as a string
	 */
	public static DiffStat getDiffStat(Repository repository, RevCommit baseCommit,
			RevCommit commit, String path) {
		DiffStat stat = null;
		try {
			RawTextComparator cmp = RawTextComparator.DEFAULT;
			DiffStatFormatter df = new DiffStatFormatter(commit.getName());
			df.setRepository(repository);
			df.setDiffComparator(cmp);
			df.setDetectRenames(true);

			RevTree commitTree = commit.getTree();
			RevTree baseTree;
			if (baseCommit == null) {
				if (commit.getParentCount() > 0) {
					final RevWalk rw = new RevWalk(repository);
					RevCommit parent = rw.parseCommit(commit.getParent(0).getId());
					baseTree = parent.getTree();
				} else {
					// FIXME initial commit. no parent?!
					baseTree = commitTree;
				}
			} else {
				baseTree = baseCommit.getTree();
			}

			List<DiffEntry> diffEntries = df.scan(baseTree, commitTree);
			if (path != null && path.length() > 0) {
				for (DiffEntry diffEntry : diffEntries) {
					if (diffEntry.getNewPath().equalsIgnoreCase(path)) {
						df.format(diffEntry);
						break;
					}
				}
			} else {
				df.format(diffEntries);
			}
			stat = df.getDiffStat();
			df.flush();
		} catch (Throwable t) {
			LOGGER.error("failed to generate commit diff!", t);
		}
		return stat;
	}

	/**
	 * Returns the list of lines in the specified source file annotated with the
	 * source commit metadata.
	 *
	 * @param repository
	 * @param blobPath
	 * @param objectId
	 * @return list of annotated lines
	 */
	public static List<AnnotatedLine> blame(Repository repository, String blobPath, String objectId) {
		List<AnnotatedLine> lines = new ArrayList<AnnotatedLine>();
		try {
			ObjectId object;
			if (StringUtils.isEmpty(objectId)) {
				object = JGitUtils.getDefaultBranch(repository);
			} else {
				object = repository.resolve(objectId);
			}
			BlameCommand blameCommand = new BlameCommand(repository);
			blameCommand.setFilePath(blobPath);
			blameCommand.setStartCommit(object);
			BlameResult blameResult = blameCommand.call();
			RawText rawText = blameResult.getResultContents();
			int length = rawText.size();
			for (int i = 0; i < length; i++) {
				RevCommit commit = blameResult.getSourceCommit(i);
				AnnotatedLine line = new AnnotatedLine(commit, i + 1, rawText.getString(i));
				lines.add(line);
			}
		} catch (Throwable t) {
			LOGGER.error(MessageFormat.format("failed to generate blame for {0} {1}!", blobPath, objectId), t);
		}
		return lines;
	}

	/**
	 * Normalizes a diffstat to an N-segment display.
	 *
	 * @params segments
	 * @param insertions
	 * @param deletions
	 * @return a normalized diffstat
	 */
	public static NormalizedDiffStat normalizeDiffStat(final int segments, final int insertions, final int deletions) {
		final int total = insertions + deletions;
		final float fi = ((float) insertions) / total;
		int si;
		int sd;
		int sb;
		if (deletions == 0) {
			// only addition
			si = Math.min(insertions, segments);
			sd = 0;
			sb = si < segments ? (segments - si) : 0;
		} else if (insertions == 0) {
			// only deletion
			si = 0;
			sd = Math.min(deletions, segments);
			sb = sd < segments ? (segments - sd) : 0;
		} else if (total <= segments) {
			// total churn fits in segment display
			si = insertions;
			sd = deletions;
			sb = segments - total;
		} else if ((segments % 2) > 0 && fi > 0.45f && fi < 0.55f) {
			// odd segment display, fairly even +/-, use even number of segments
			si = Math.round(((float) insertions)/total * (segments - 1));
			sd = segments - 1 - si;
			sb = 1;
		} else {
			si = Math.round(((float) insertions)/total * segments);
			sd = segments - si;
			sb = 0;
		}

		return new NormalizedDiffStat(si, sd, sb);
	}
}