// Copyright (C) 2016 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.account;

import static org.eclipse.jgit.lib.Constants.OBJ_BLOB;

import com.google.gerrit.common.Nullable;
import com.google.gerrit.reviewdb.client.RefNames;
import com.google.gerrit.server.config.AllUsersName;
import com.google.gerrit.server.git.GitRepositoryManager;
import com.google.inject.Inject;
import com.google.inject.Singleton;
import java.io.IOException;
import org.eclipse.jgit.errors.ConfigInvalidException;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.Ref;
import org.eclipse.jgit.lib.Repository;
import org.eclipse.jgit.notes.NoteMap;
import org.eclipse.jgit.revwalk.RevWalk;

/**
 * Class to read external IDs from NoteDb.
 *
 * <p>In NoteDb external IDs are stored in the All-Users repository in a Git Notes branch called
 * refs/meta/external-ids where the sha1 of the external ID is used as note name. Each note content
 * is a git config file that contains an external ID. It has exactly one externalId subsection with
 * an accountId and optionally email and password:
 *
 * <pre>
 * [externalId "username:jdoe"]
 *   accountId = 1003407
 *   email = jdoe@example.com
 *   password = bcrypt:4:LCbmSBDivK/hhGVQMfkDpA==:XcWn0pKYSVU/UJgOvhidkEtmqCp6oKB7
 * </pre>
 */
@Singleton
public class ExternalIds {
  public static final int MAX_NOTE_SZ = 1 << 19;

  public static ObjectId readRevision(Repository repo) throws IOException {
    Ref ref = repo.exactRef(RefNames.REFS_EXTERNAL_IDS);
    return ref != null ? ref.getObjectId() : ObjectId.zeroId();
  }

  public static NoteMap readNoteMap(RevWalk rw, ObjectId rev) throws IOException {
    if (!rev.equals(ObjectId.zeroId())) {
      return NoteMap.read(rw.getObjectReader(), rw.parseCommit(rev));
    }
    return NoteMap.newEmptyMap();
  }

  private final GitRepositoryManager repoManager;
  private final AllUsersName allUsersName;

  @Inject
  public ExternalIds(GitRepositoryManager repoManager, AllUsersName allUsersName) {
    this.repoManager = repoManager;
    this.allUsersName = allUsersName;
  }

  public ObjectId readRevision() throws IOException {
    try (Repository repo = repoManager.openRepository(allUsersName)) {
      return readRevision(repo);
    }
  }

  /** Reads and returns the specified external ID. */
  @Nullable
  public ExternalId get(ExternalId.Key key) throws IOException, ConfigInvalidException {
    try (Repository repo = repoManager.openRepository(allUsersName);
        RevWalk rw = new RevWalk(repo)) {
      ObjectId rev = readRevision(repo);
      if (rev.equals(ObjectId.zeroId())) {
        return null;
      }

      return parse(key, rw, rev);
    }
  }

  private ExternalId parse(ExternalId.Key key, RevWalk rw, ObjectId rev)
      throws IOException, ConfigInvalidException {
    NoteMap noteMap = readNoteMap(rw, rev);
    ObjectId noteId = key.sha1();
    if (!noteMap.contains(noteId)) {
      return null;
    }

    byte[] raw =
        rw.getObjectReader().open(noteMap.get(noteId), OBJ_BLOB).getCachedBytes(MAX_NOTE_SZ);
    return ExternalId.parse(noteId.name(), raw);
  }
}