// Copyright (C) 2021 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.change;

import static java.util.stream.Collectors.toSet;

import com.google.common.collect.ImmutableMap;
import com.google.gerrit.entities.Project;
import com.google.gerrit.server.git.GitRepositoryManager;
import com.google.gerrit.server.permissions.PermissionBackend;
import com.google.gerrit.server.permissions.PermissionBackend.RefFilterOptions;
import com.google.gerrit.server.permissions.PermissionBackendException;
import com.google.inject.Inject;
import java.io.IOException;
import java.util.Collection;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import org.eclipse.jgit.errors.IncorrectObjectTypeException;
import org.eclipse.jgit.errors.MissingObjectException;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.Ref;
import org.eclipse.jgit.lib.RefDatabase;
import org.eclipse.jgit.lib.Repository;
import org.eclipse.jgit.revwalk.RevCommit;
import org.eclipse.jgit.revwalk.RevWalk;

public class IncludedInRefs {
  protected final GitRepositoryManager repoManager;
  protected final PermissionBackend permissionBackend;

  @Inject
  IncludedInRefs(GitRepositoryManager repoManager, PermissionBackend permissionBackend) {
    this.repoManager = repoManager;
    this.permissionBackend = permissionBackend;
  }

  public Map<String, Set<String>> apply(
      Project.NameKey project, Set<String> commits, Set<String> refNames)
      throws IOException, PermissionBackendException {
    try (Repository repo = repoManager.openRepository(project)) {
      Set<Ref> visibleRefs = getVisibleRefs(repo, refNames, project);

      if (!visibleRefs.isEmpty()) {
        try (RevWalk revWalk = new RevWalk(repo)) {
          revWalk.setRetainBody(false);
          Set<RevCommit> revCommits = getRevCommits(commits, revWalk);

          if (!revCommits.isEmpty()) {
            return commitsIncludedIn(
                revCommits, IncludedInUtil.getSortedRefs(visibleRefs, revWalk), revWalk);
          }
        }
      }
    }
    return ImmutableMap.of();
  }

  private Set<Ref> getVisibleRefs(Repository repo, Set<String> refNames, Project.NameKey project)
      throws PermissionBackendException {
    RefDatabase refDb = repo.getRefDatabase();
    Set<Ref> refs = new HashSet<>();
    for (String refName : refNames) {
      try {
        Ref ref = refDb.exactRef(refName);
        if (ref != null) {
          refs.add(ref);
        }
      } catch (IOException e) {
        // Ignore and continue to process rest of the refs so as to keep
        // the behavior similar to the ref not being visible to the user.
        // This will ensure that there is no information leak about the
        // ref when the ref is corrupted and is not visible to the user.
      }
    }
    return filterReadableRefs(project, refs, repo);
  }

  private Set<RevCommit> getRevCommits(Set<String> commits, RevWalk revWalk) throws IOException {
    Set<RevCommit> revCommits = new HashSet<>();
    for (String commit : commits) {
      try {
        revCommits.add(revWalk.parseCommit(ObjectId.fromString(commit)));
      } catch (MissingObjectException | IncorrectObjectTypeException | IllegalArgumentException e) {
        // Ignore and continue to process the rest of the commits so as to keep
        // the behavior similar to the commit not being included in any of the
        // visible specified refs. This will ensure that there is no information
        // leak about the commit when the commit is not visible to the user.
      }
    }
    return revCommits;
  }

  private Map<String, Set<String>> commitsIncludedIn(
      Collection<RevCommit> commits, Collection<Ref> refs, RevWalk revWalk) throws IOException {
    Map<String, Set<String>> refsByCommit = new HashMap<>();
    for (RevCommit commit : commits) {
      List<Ref> matchingRefs = revWalk.getMergedInto(commit, refs);
      if (matchingRefs.size() > 0) {
        refsByCommit.put(
            commit.getName(), matchingRefs.stream().map(Ref::getName).collect(toSet()));
      }
    }
    return refsByCommit;
  }

  /**
   * Filter readable refs according to the caller's refs visibility.
   *
   * @param project specific Gerrit project.
   * @param inputRefs a list of refs
   * @param repo repository opened for the Gerrit project.
   * @return set of visible refs to the caller
   */
  private Set<Ref> filterReadableRefs(Project.NameKey project, Set<Ref> inputRefs, Repository repo)
      throws PermissionBackendException {
    PermissionBackend.ForProject perm = permissionBackend.currentUser().project(project);
    return perm.filter(inputRefs, repo, RefFilterOptions.defaults()).stream().collect(toSet());
  }
}