// Copyright (C) 2013 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.restapi.project;

import com.google.gerrit.extensions.restapi.AuthException;
import com.google.gerrit.extensions.restapi.ResourceConflictException;
import com.google.gerrit.extensions.restapi.ResourceNotFoundException;
import com.google.gerrit.extensions.restapi.Response;
import com.google.gerrit.extensions.restapi.RestReadView;
import com.google.gerrit.server.git.GitRepositoryManager;
import com.google.gerrit.server.permissions.PermissionBackend;
import com.google.gerrit.server.permissions.PermissionBackendException;
import com.google.gerrit.server.permissions.ProjectPermission;
import com.google.gerrit.server.permissions.RefPermission;
import com.google.gerrit.server.project.ProjectResource;
import com.google.inject.Inject;
import com.google.inject.Singleton;
import java.io.IOException;
import org.eclipse.jgit.errors.IncorrectObjectTypeException;
import org.eclipse.jgit.errors.MissingObjectException;
import org.eclipse.jgit.errors.RepositoryNotFoundException;
import org.eclipse.jgit.lib.Constants;
import org.eclipse.jgit.lib.Ref;
import org.eclipse.jgit.lib.Repository;
import org.eclipse.jgit.revwalk.RevCommit;
import org.eclipse.jgit.revwalk.RevWalk;

@Singleton
public class GetHead implements RestReadView<ProjectResource> {
  private final GitRepositoryManager repoManager;
  private final CommitsCollection commits;
  private final PermissionBackend permissionBackend;

  @Inject
  GetHead(
      GitRepositoryManager repoManager,
      CommitsCollection commits,
      PermissionBackend permissionBackend) {
    this.repoManager = repoManager;
    this.commits = commits;
    this.permissionBackend = permissionBackend;
  }

  @Override
  public Response<String> apply(ProjectResource rsrc)
      throws AuthException, ResourceNotFoundException, IOException, PermissionBackendException,
          ResourceConflictException {
    rsrc.getProjectState().checkStatePermitsRead();
    try (Repository repo = repoManager.openRepository(rsrc.getNameKey())) {
      Ref head = repo.getRefDatabase().exactRef(Constants.HEAD);
      if (head == null) {
        throw new ResourceNotFoundException(Constants.HEAD);
      } else if (head.isSymbolic()) {
        String n = head.getTarget().getName();
        permissionBackend
            .user(rsrc.getUser())
            .project(rsrc.getNameKey())
            .ref(n)
            .check(RefPermission.READ);
        return Response.ok(n);
      } else if (head.getObjectId() != null) {
        try (RevWalk rw = new RevWalk(repo)) {
          RevCommit commit = rw.parseCommit(head.getObjectId());
          if (commits.canRead(rsrc.getProjectState(), repo, commit)) {
            return Response.ok(head.getObjectId().name());
          }
          throw new AuthException("not allowed to see HEAD");
        } catch (MissingObjectException | IncorrectObjectTypeException e) {
          try {
            permissionBackend
                .user(rsrc.getUser())
                .project(rsrc.getNameKey())
                .check(ProjectPermission.WRITE_CONFIG);
          } catch (AuthException ae) {
            throw new AuthException("not allowed to see HEAD", ae);
          }
        }
      }
      throw new ResourceNotFoundException(Constants.HEAD);
    } catch (RepositoryNotFoundException e) {
      throw new ResourceNotFoundException(rsrc.getName(), e);
    }
  }
}