// Copyright (C) 2009 The Android Open Source Project
//
// 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.google.gerrit.server.patch;

import static com.google.common.base.Preconditions.checkArgument;
import static java.nio.charset.StandardCharsets.UTF_8;
import static java.util.stream.Collectors.toSet;
import static org.eclipse.jgit.lib.Constants.OBJ_BLOB;

import com.google.common.base.Throwables;
import com.google.gerrit.extensions.client.DiffPreferencesInfo.Whitespace;
import com.google.gerrit.reviewdb.client.Patch;
import com.google.gerrit.reviewdb.client.Project;
import com.google.gerrit.server.config.ConfigUtil;
import com.google.gerrit.server.config.GerritServerConfig;
import com.google.gerrit.server.git.GitRepositoryManager;
import com.google.gerrit.server.git.InMemoryInserter;
import com.google.gerrit.server.git.MergeUtil;
import com.google.inject.assistedinject.Assisted;
import com.google.inject.assistedinject.AssistedInject;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Set;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.stream.Stream;
import org.eclipse.jgit.diff.DiffEntry;
import org.eclipse.jgit.diff.DiffFormatter;
import org.eclipse.jgit.diff.Edit;
import org.eclipse.jgit.diff.EditList;
import org.eclipse.jgit.diff.HistogramDiff;
import org.eclipse.jgit.diff.RawText;
import org.eclipse.jgit.diff.RawTextComparator;
import org.eclipse.jgit.lib.Config;
import org.eclipse.jgit.lib.Constants;
import org.eclipse.jgit.lib.FileMode;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.ObjectInserter;
import org.eclipse.jgit.lib.ObjectReader;
import org.eclipse.jgit.lib.Repository;
import org.eclipse.jgit.merge.ThreeWayMergeStrategy;
import org.eclipse.jgit.patch.FileHeader;
import org.eclipse.jgit.patch.FileHeader.PatchType;
import org.eclipse.jgit.revwalk.RevCommit;
import org.eclipse.jgit.revwalk.RevObject;
import org.eclipse.jgit.revwalk.RevTree;
import org.eclipse.jgit.revwalk.RevWalk;
import org.eclipse.jgit.treewalk.TreeWalk;
import org.eclipse.jgit.util.io.DisabledOutputStream;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class PatchListLoader implements Callable<PatchList> {
  static final Logger log = LoggerFactory.getLogger(PatchListLoader.class);

  public interface Factory {
    PatchListLoader create(PatchListKey key, Project.NameKey project);
  }

  private final GitRepositoryManager repoManager;
  private final PatchListCache patchListCache;
  private final ThreeWayMergeStrategy mergeStrategy;
  private final ExecutorService diffExecutor;
  private final AutoMerger autoMerger;
  private final PatchListKey key;
  private final Project.NameKey project;
  private final long timeoutMillis;
  private final boolean save;

  @AssistedInject
  PatchListLoader(
      GitRepositoryManager mgr,
      PatchListCache plc,
      @GerritServerConfig Config cfg,
      @DiffExecutor ExecutorService de,
      AutoMerger am,
      @Assisted PatchListKey k,
      @Assisted Project.NameKey p) {
    repoManager = mgr;
    patchListCache = plc;
    mergeStrategy = MergeUtil.getMergeStrategy(cfg);
    diffExecutor = de;
    autoMerger = am;
    key = k;
    project = p;
    timeoutMillis =
        ConfigUtil.getTimeUnit(
            cfg,
            "cache",
            PatchListCacheImpl.FILE_NAME,
            "timeout",
            TimeUnit.MILLISECONDS.convert(5, TimeUnit.SECONDS),
            TimeUnit.MILLISECONDS);
    save = AutoMerger.cacheAutomerge(cfg);
  }

  @Override
  public PatchList call() throws IOException, PatchListNotAvailableException {
    try (Repository repo = repoManager.openRepository(project);
        ObjectInserter ins = newInserter(repo);
        ObjectReader reader = ins.newReader();
        RevWalk rw = new RevWalk(reader)) {
      return readPatchList(repo, rw, ins);
    }
  }

  private static RawTextComparator comparatorFor(Whitespace ws) {
    switch (ws) {
      case IGNORE_ALL:
        return RawTextComparator.WS_IGNORE_ALL;

      case IGNORE_TRAILING:
        return RawTextComparator.WS_IGNORE_TRAILING;

      case IGNORE_LEADING_AND_TRAILING:
        return RawTextComparator.WS_IGNORE_CHANGE;

      case IGNORE_NONE:
      default:
        return RawTextComparator.DEFAULT;
    }
  }

  private ObjectInserter newInserter(Repository repo) {
    return save ? repo.newObjectInserter() : new InMemoryInserter(repo);
  }

  public PatchList readPatchList(Repository repo, RevWalk rw, ObjectInserter ins)
      throws IOException, PatchListNotAvailableException {
    ObjectReader reader = rw.getObjectReader();
    checkArgument(reader.getCreatedFromInserter() == ins);
    RawTextComparator cmp = comparatorFor(key.getWhitespace());
    try (DiffFormatter df = new DiffFormatter(DisabledOutputStream.INSTANCE)) {
      RevCommit b = rw.parseCommit(key.getNewId());
      RevObject a = aFor(key, repo, rw, ins, b);

      if (a == null) {
        // TODO(sop) Remove this case.
        // This is an octopus merge commit which should be compared against the
        // auto-merge. However since we don't support computing the auto-merge
        // for octopus merge commits, we fall back to diffing against the first
        // parent, even though this wasn't what was requested.
        //
        ComparisonType comparisonType = ComparisonType.againstParent(1);
        PatchListEntry[] entries = new PatchListEntry[2];
        entries[0] = newCommitMessage(cmp, reader, null, b);
        entries[1] = newMergeList(cmp, reader, null, b, comparisonType);
        return new PatchList(a, b, true, comparisonType, entries);
      }

      ComparisonType comparisonType = getComparisonType(a, b);

      RevCommit aCommit = a instanceof RevCommit ? (RevCommit) a : null;
      RevTree aTree = rw.parseTree(a);
      RevTree bTree = b.getTree();

      df.setReader(reader, repo.getConfig());
      df.setDiffComparator(cmp);
      df.setDetectRenames(true);
      List<DiffEntry> diffEntries = df.scan(aTree, bTree);

      Set<String> paths = null;
      if (key.getOldId() != null && b.getParentCount() == 1) {
        PatchListKey newKey = PatchListKey.againstDefaultBase(key.getNewId(), key.getWhitespace());
        PatchListKey oldKey = PatchListKey.againstDefaultBase(key.getOldId(), key.getWhitespace());
        paths =
            Stream.concat(
                    patchListCache.get(newKey, project).getPatches().stream(),
                    patchListCache.get(oldKey, project).getPatches().stream())
                .map(PatchListEntry::getNewName)
                .collect(toSet());
      }

      int cnt = diffEntries.size();
      List<PatchListEntry> entries = new ArrayList<>();
      entries.add(
          newCommitMessage(
              cmp, reader, comparisonType.isAgainstParentOrAutoMerge() ? null : aCommit, b));
      boolean isMerge = b.getParentCount() > 1;
      if (isMerge) {
        entries.add(
            newMergeList(
                cmp,
                reader,
                comparisonType.isAgainstParentOrAutoMerge() ? null : aCommit,
                b,
                comparisonType));
      }
      for (int i = 0; i < cnt; i++) {
        DiffEntry e = diffEntries.get(i);
        if (paths == null || paths.contains(e.getNewPath()) || paths.contains(e.getOldPath())) {

          FileHeader fh = toFileHeader(key, df, e);
          long oldSize = getFileSize(reader, e.getOldMode(), e.getOldPath(), aTree);
          long newSize = getFileSize(reader, e.getNewMode(), e.getNewPath(), bTree);
          entries.add(newEntry(aTree, fh, newSize, newSize - oldSize));
        }
      }
      return new PatchList(
          a, b, isMerge, comparisonType, entries.toArray(new PatchListEntry[entries.size()]));
    }
  }

  private ComparisonType getComparisonType(RevObject a, RevCommit b) {
    for (int i = 0; i < b.getParentCount(); i++) {
      if (b.getParent(i).equals(a)) {
        return ComparisonType.againstParent(i + 1);
      }
    }

    if (key.getOldId() == null && b.getParentCount() > 0) {
      return ComparisonType.againstAutoMerge();
    }

    return ComparisonType.againstOtherPatchSet();
  }

  private static long getFileSize(ObjectReader reader, FileMode mode, String path, RevTree t)
      throws IOException {
    if (!isBlob(mode)) {
      return 0;
    }
    try (TreeWalk tw = TreeWalk.forPath(reader, path, t)) {
      return tw != null ? reader.open(tw.getObjectId(0), OBJ_BLOB).getSize() : 0;
    }
  }

  private static boolean isBlob(FileMode mode) {
    int t = mode.getBits() & FileMode.TYPE_MASK;
    return t == FileMode.TYPE_FILE || t == FileMode.TYPE_SYMLINK;
  }

  private FileHeader toFileHeader(
      PatchListKey key, final DiffFormatter diffFormatter, final DiffEntry diffEntry)
      throws IOException {

    Future<FileHeader> result =
        diffExecutor.submit(
            new Callable<FileHeader>() {
              @Override
              public FileHeader call() throws IOException {
                synchronized (diffEntry) {
                  return diffFormatter.toFileHeader(diffEntry);
                }
              }
            });

    try {
      return result.get(timeoutMillis, TimeUnit.MILLISECONDS);
    } catch (InterruptedException | TimeoutException e) {
      log.warn(
          timeoutMillis
              + " ms timeout reached for Diff loader"
              + " in project "
              + project
              + " on commit "
              + key.getNewId().name()
              + " on path "
              + diffEntry.getNewPath()
              + " comparing "
              + diffEntry.getOldId().name()
              + ".."
              + diffEntry.getNewId().name());
      result.cancel(true);
      synchronized (diffEntry) {
        return toFileHeaderWithoutMyersDiff(diffFormatter, diffEntry);
      }
    } catch (ExecutionException e) {
      // If there was an error computing the result, carry it
      // up to the caller so the cache knows this key is invalid.
      Throwables.throwIfInstanceOf(e.getCause(), IOException.class);
      throw new IOException(e.getMessage(), e.getCause());
    }
  }

  private FileHeader toFileHeaderWithoutMyersDiff(DiffFormatter diffFormatter, DiffEntry diffEntry)
      throws IOException {
    HistogramDiff histogramDiff = new HistogramDiff();
    histogramDiff.setFallbackAlgorithm(null);
    diffFormatter.setDiffAlgorithm(histogramDiff);
    return diffFormatter.toFileHeader(diffEntry);
  }

  private PatchListEntry newCommitMessage(
      RawTextComparator cmp, ObjectReader reader, RevCommit aCommit, RevCommit bCommit)
      throws IOException {
    Text aText = aCommit != null ? Text.forCommit(reader, aCommit) : Text.EMPTY;
    Text bText = Text.forCommit(reader, bCommit);
    return createPatchListEntry(cmp, aCommit, aText, bText, Patch.COMMIT_MSG);
  }

  private PatchListEntry newMergeList(
      RawTextComparator cmp,
      ObjectReader reader,
      RevCommit aCommit,
      RevCommit bCommit,
      ComparisonType comparisonType)
      throws IOException {
    Text aText = aCommit != null ? Text.forMergeList(comparisonType, reader, aCommit) : Text.EMPTY;
    Text bText = Text.forMergeList(comparisonType, reader, bCommit);
    return createPatchListEntry(cmp, aCommit, aText, bText, Patch.MERGE_LIST);
  }

  private static PatchListEntry createPatchListEntry(
      RawTextComparator cmp, RevCommit aCommit, Text aText, Text bText, String fileName) {
    byte[] rawHdr = getRawHeader(aCommit != null, fileName);
    byte[] aContent = aText.getContent();
    byte[] bContent = bText.getContent();
    long size = bContent.length;
    long sizeDelta = bContent.length - aContent.length;
    RawText aRawText = new RawText(aContent);
    RawText bRawText = new RawText(bContent);
    EditList edits = new HistogramDiff().diff(cmp, aRawText, bRawText);
    FileHeader fh = new FileHeader(rawHdr, edits, PatchType.UNIFIED);
    return new PatchListEntry(fh, edits, size, sizeDelta);
  }

  private static byte[] getRawHeader(boolean hasA, String fileName) {
    StringBuilder hdr = new StringBuilder();
    hdr.append("diff --git");
    if (hasA) {
      hdr.append(" a/").append(fileName);
    } else {
      hdr.append(" ").append(FileHeader.DEV_NULL);
    }
    hdr.append(" b/").append(fileName);
    hdr.append("\n");

    if (hasA) {
      hdr.append("--- a/").append(fileName).append("\n");
    } else {
      hdr.append("--- ").append(FileHeader.DEV_NULL).append("\n");
    }
    hdr.append("+++ b/").append(fileName).append("\n");
    return hdr.toString().getBytes(UTF_8);
  }

  private PatchListEntry newEntry(RevTree aTree, FileHeader fileHeader, long size, long sizeDelta) {
    if (aTree == null // want combined diff
        || fileHeader.getPatchType() != PatchType.UNIFIED
        || fileHeader.getHunks().isEmpty()) {
      return new PatchListEntry(fileHeader, Collections.<Edit>emptyList(), size, sizeDelta);
    }

    List<Edit> edits = fileHeader.toEditList();
    if (edits.isEmpty()) {
      return new PatchListEntry(fileHeader, Collections.<Edit>emptyList(), size, sizeDelta);
    }
    return new PatchListEntry(fileHeader, edits, size, sizeDelta);
  }

  private RevObject aFor(
      PatchListKey key, Repository repo, RevWalk rw, ObjectInserter ins, RevCommit b)
      throws IOException {
    if (key.getOldId() != null) {
      return rw.parseAny(key.getOldId());
    }

    switch (b.getParentCount()) {
      case 0:
        return rw.parseAny(emptyTree(ins));
      case 1:
        {
          RevCommit r = b.getParent(0);
          rw.parseBody(r);
          return r;
        }
      case 2:
        if (key.getParentNum() != null) {
          RevCommit r = b.getParent(key.getParentNum() - 1);
          rw.parseBody(r);
          return r;
        }
        return autoMerger.merge(repo, rw, ins, b, mergeStrategy);
      default:
        // TODO(sop) handle an octopus merge.
        return null;
    }
  }

  private static ObjectId emptyTree(ObjectInserter ins) throws IOException {
    ObjectId id = ins.insert(Constants.OBJ_TREE, new byte[] {});
    ins.flush();
    return id;
  }
}