// Copyright (C) 2020 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.googlesource.gerrit.plugins.replication.pull;

import static com.googlesource.gerrit.plugins.replication.pull.PullReplicationLogger.repLog;

import com.google.common.collect.Lists;
import com.google.gerrit.common.Nullable;
import com.google.gerrit.entities.Project;
import com.google.gerrit.server.git.GitRepositoryManager;
import com.google.inject.Inject;
import com.googlesource.gerrit.plugins.replication.ReplicationConfig;
import com.googlesource.gerrit.plugins.replication.pull.api.data.RevisionData;
import com.googlesource.gerrit.plugins.replication.pull.api.data.RevisionObjectData;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.Optional;
import org.eclipse.jgit.diff.DiffEntry;
import org.eclipse.jgit.diff.DiffEntry.ChangeType;
import org.eclipse.jgit.errors.CorruptObjectException;
import org.eclipse.jgit.errors.IncorrectObjectTypeException;
import org.eclipse.jgit.errors.LargeObjectException;
import org.eclipse.jgit.errors.MissingObjectException;
import org.eclipse.jgit.errors.RepositoryNotFoundException;
import org.eclipse.jgit.lib.Constants;
import org.eclipse.jgit.lib.FileMode;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.ObjectLoader;
import org.eclipse.jgit.lib.Ref;
import org.eclipse.jgit.lib.Repository;
import org.eclipse.jgit.revwalk.RevCommit;
import org.eclipse.jgit.revwalk.RevTree;
import org.eclipse.jgit.treewalk.TreeWalk;
import org.eclipse.jgit.treewalk.filter.TreeFilter;

public class RevisionReader {
  private static final String CONFIG_MAX_API_PAYLOAD_SIZE = "maxApiPayloadSize";
  private static final Long DEFAULT_MAX_PAYLOAD_SIZE_IN_BYTES = 10000L;
  static final String CONFIG_MAX_API_HISTORY_DEPTH = "maxApiHistoryDepth";
  private static final int DEFAULT_MAX_API_HISTORY_DEPTH = 128;
  private GitRepositoryManager gitRepositoryManager;
  private Long maxRefSize;
  private final int maxDepth;
  private ApplyObjectMetrics metrics;

  @Inject
  public RevisionReader(
      GitRepositoryManager gitRepositoryManager,
      ReplicationConfig cfg,
      ApplyObjectMetrics metrics) {
    this.gitRepositoryManager = gitRepositoryManager;
    this.maxRefSize =
        cfg.getConfig()
            .getLong("replication", CONFIG_MAX_API_PAYLOAD_SIZE, DEFAULT_MAX_PAYLOAD_SIZE_IN_BYTES);
    this.maxDepth =
        cfg.getConfig()
            .getInt("replication", CONFIG_MAX_API_HISTORY_DEPTH, DEFAULT_MAX_API_HISTORY_DEPTH);
    this.metrics = metrics;
  }

  public Optional<RevisionData> read(
      Project.NameKey project, String refName, int maxParentObjectIds)
      throws RepositoryNotFoundException, MissingObjectException, IncorrectObjectTypeException,
          CorruptObjectException, IOException {
    return read(project, null, refName, maxParentObjectIds);
  }

  public Optional<RevisionData> read(
      Project.NameKey project,
      @Nullable ObjectId refObjectId,
      String refName,
      int maxParentObjectIds)
      throws MissingObjectException, IncorrectObjectTypeException, CorruptObjectException,
          RepositoryNotFoundException, IOException {
    try (Repository git = gitRepositoryManager.openRepository(project)) {
      Long totalRefSize = 0l;

      Ref ref = git.exactRef(refName);
      if (ref == null) {
        return Optional.empty();
      }

      ObjectId objectId = refObjectId == null ? ref.getObjectId() : refObjectId;

      ObjectLoader commitLoader = git.open(objectId);
      totalRefSize += commitLoader.getSize();
      verifySize(project, refName, objectId, totalRefSize, commitLoader);

      if (commitLoader.getType() == Constants.OBJ_BLOB) {
        return Optional.of(
            new RevisionData(
                Collections.emptyList(),
                null,
                null,
                Arrays.asList(
                    new RevisionObjectData(
                        objectId.name(), Constants.OBJ_BLOB, commitLoader.getCachedBytes()))));
      }

      if (commitLoader.getType() != Constants.OBJ_COMMIT) {
        repLog.trace(
            "Ref {} for project {} points to an object type {}",
            refName,
            project,
            commitLoader.getType());
        return Optional.empty();
      }

      RevCommit commit = RevCommit.parse(commitLoader.getCachedBytes());
      RevisionObjectData commitRev =
          new RevisionObjectData(objectId.name(), commit.getType(), commitLoader.getCachedBytes());

      RevTree tree = commit.getTree();
      ObjectId treeObjectId = commit.getTree().toObjectId();
      ObjectLoader treeLoader = git.open(treeObjectId);
      totalRefSize += treeLoader.getSize();
      verifySize(project, refName, treeObjectId, totalRefSize, treeLoader);

      RevisionObjectData treeRev =
          new RevisionObjectData(treeObjectId.name(), tree.getType(), treeLoader.getCachedBytes());

      List<RevisionObjectData> blobs = Lists.newLinkedList();
      try (TreeWalk walk = new TreeWalk(git)) {
        if (commit.getParentCount() > 0) {
          List<DiffEntry> diffEntries = readDiffs(git, commit, tree, walk);
          blobs = readBlobs(project, refName, git, totalRefSize, diffEntries);
        } else {
          walk.setRecursive(true);
          walk.setPostOrderTraversal(true);
          walk.addTree(tree);
          blobs = readBlobs(project, refName, git, totalRefSize, walk);
        }
      }

      List<ObjectId> parentObjectIds =
          getParentObjectIds(git, commit.getParents(), 0, Math.min(maxDepth, maxParentObjectIds));
      Collections.reverse(parentObjectIds);

      return Optional.of(new RevisionData(parentObjectIds, commitRev, treeRev, blobs));
    } catch (LargeObjectException e) {
      metrics.incrementMaxPayloadSizeReached();
      repLog.trace(
          "Ref {} size for project {} is greater than configured '{}'",
          refName,
          project,
          CONFIG_MAX_API_PAYLOAD_SIZE);
      return Optional.empty();
    }
  }

  private List<ObjectId> getParentObjectIds(
      Repository git, RevCommit[] commit, int parentsDepth, int maxParentObjectIds)
      throws MissingObjectException, IncorrectObjectTypeException, IOException {
    if (commit == null || commit.length == 0) {
      return Collections.emptyList();
    }

    ArrayList<ObjectId> parentObjectIds = new ArrayList<>();
    for (RevCommit revCommit : commit) {
      if (parentsDepth < maxParentObjectIds) {
        parentObjectIds.add(revCommit.getId());
        parentsDepth++;

        ObjectLoader ol = git.open(revCommit.getId(), Constants.OBJ_COMMIT);
        RevCommit[] commitParents = RevCommit.parse(ol.getCachedBytes()).getParents();

        List<ObjectId> nestedParentObjectIds =
            getParentObjectIds(git, commitParents, parentsDepth, maxParentObjectIds);
        parentObjectIds.addAll(nestedParentObjectIds);
        parentsDepth += nestedParentObjectIds.size();
      }
    }

    return parentObjectIds;
  }

  private List<DiffEntry> readDiffs(Repository git, RevCommit commit, RevTree tree, TreeWalk walk)
      throws MissingObjectException, IncorrectObjectTypeException, CorruptObjectException,
          IOException {
    walk.setFilter(TreeFilter.ANY_DIFF);
    walk.reset(getParentTree(git, commit), tree);
    return DiffEntry.scan(walk, true);
  }

  private List<RevisionObjectData> readBlobs(
      Project.NameKey projectName, String refName, Repository git, Long totalRefSize, TreeWalk walk)
      throws MissingObjectException, IncorrectObjectTypeException, CorruptObjectException,
          IOException {
    List<RevisionObjectData> blobs = Lists.newLinkedList();
    while (walk.next()) {
      ObjectId objectId = walk.getObjectId(0);
      ObjectLoader objectLoader = git.open(objectId);
      totalRefSize += objectLoader.getSize();
      verifySize(projectName, refName, objectId, totalRefSize, objectLoader);

      RevisionObjectData rev =
          new RevisionObjectData(
              objectId.name(), objectLoader.getType(), objectLoader.getCachedBytes());
      blobs.add(rev);
    }
    return blobs;
  }

  /**
   * Reads and evaluates the git objects in this revision. The following are filtered out:
   * <li>DELETE changes
   * <li>git submodule commits, because the git commit hash is not present in this repo.
   *
   *     <p>The method keeps track of the total size of all objects it has processed, and verifies
   *     it is below the acceptable threshold.
   *
   * @param projectName - the name of the project, used to check total object size threshold
   * @param refName - the ref name, used to check total object size threshold
   * @param git - this git repo, used to load the objects
   * @param totalRefSize - tracks the total size of objects processed
   * @param diffEntries - a list of the diff entries for this revision
   * @return a List of `RevisionObjectData`, an object that includes the git object SHA, the git
   *     object change type and the object contents.
   * @throws MissingObjectException - if the object can't be found
   * @throws IOException - if processing failed for another reason
   */
  private List<RevisionObjectData> readBlobs(
      Project.NameKey projectName,
      String refName,
      Repository git,
      Long totalRefSize,
      List<DiffEntry> diffEntries)
      throws MissingObjectException, IOException {
    List<RevisionObjectData> blobs = Lists.newLinkedList();
    for (DiffEntry diffEntry : diffEntries) {
      if (!(ChangeType.DELETE.equals(diffEntry.getChangeType()) || gitSubmoduleCommit(diffEntry))) {
        ObjectId diffObjectId = diffEntry.getNewId().toObjectId();
        ObjectLoader objectLoader = git.open(diffObjectId);
        totalRefSize += objectLoader.getSize();
        verifySize(projectName, refName, diffObjectId, totalRefSize, objectLoader);
        RevisionObjectData rev =
            new RevisionObjectData(
                diffObjectId.name(), objectLoader.getType(), objectLoader.getCachedBytes());
        blobs.add(rev);
      }
    }
    return blobs;
  }

  private boolean gitSubmoduleCommit(DiffEntry diffEntry) {
    return diffEntry.getNewMode().equals(FileMode.GITLINK);
  }

  private RevTree getParentTree(Repository git, RevCommit commit)
      throws MissingObjectException, IOException {
    RevCommit parent = commit.getParent(0);
    ObjectLoader parentLoader = git.open(parent.getId());
    RevCommit parentCommit = RevCommit.parse(parentLoader.getCachedBytes());
    return parentCommit.getTree();
  }

  private void verifySize(
      Project.NameKey projectName,
      String refName,
      ObjectId objectId,
      Long totalRefSize,
      ObjectLoader loader)
      throws LargeObjectException {
    if (loader.isLarge()) {
      repLog.warn(
          "Objects associated with {}:{} ({}) are too big to fit into the object loader's memory",
          projectName,
          refName,
          objectTypeToString(loader.getType()));
      throw new LargeObjectException(objectId);
    }

    if (totalRefSize > maxRefSize) {
      repLog.warn(
          "Objects associated with {}:{} ({}) use {} bytes, over the maximum limit of {} bytes",
          projectName,
          refName,
          objectTypeToString(loader.getType()),
          totalRefSize,
          maxRefSize);
      throw new LargeObjectException(objectId);
    }
  }

  private static String objectTypeToString(int type) {
    switch (type) {
      case Constants.OBJ_BLOB:
        return "BLOB";
      case Constants.OBJ_COMMIT:
        return "COMMIT";
      case Constants.OBJ_TREE:
        return "TREE";
      default:
        return "type:" + type;
    }
  }
}