package com.googlesource.gerrit.plugins.refprotection;

import static org.eclipse.jgit.lib.Constants.R_HEADS;
import static org.eclipse.jgit.lib.Constants.R_TAGS;

import com.google.gerrit.extensions.events.GitReferenceUpdatedListener;
import com.google.gerrit.extensions.restapi.AuthException;
import com.google.gerrit.extensions.restapi.BadRequestException;
import com.google.gerrit.extensions.restapi.ResourceConflictException;
import com.google.gerrit.reviewdb.client.Project;
import com.google.gerrit.server.CurrentUser;
import com.google.gerrit.server.git.GitRepositoryManager;
import com.google.gerrit.server.project.CreateBranch;
import com.google.gerrit.server.project.NoSuchProjectException;
import com.google.gerrit.server.project.ProjectControl;
import com.google.gerrit.server.project.ProjectResource;
import com.google.inject.Inject;

import org.eclipse.jgit.errors.RepositoryNotFoundException;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.Repository;
import org.eclipse.jgit.revwalk.RevCommit;
import org.eclipse.jgit.revwalk.RevWalk;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Date;

class RefUpdateListener implements GitReferenceUpdatedListener {

  private static final Logger log = LoggerFactory
      .getLogger(RefUpdateListener.class);
  private final CreateBranch.Factory createBranchFactory;
  private final ProjectControl.GenericFactory projectControl;
  private final CurrentUser user;
  private final GitRepositoryManager repoManager;

  @Inject
  RefUpdateListener(CreateBranch.Factory createBranchFactory,
      ProjectControl.GenericFactory p, CurrentUser user,
      GitRepositoryManager repoManager) {
    this.createBranchFactory = createBranchFactory;
    this.projectControl = p;
    this.user = user;
    this.repoManager = repoManager;
  }

  @Override
  public void onGitReferenceUpdated(final Event event) {
    if (isRelevantRef(event)) {
      Project.NameKey nameKey = new Project.NameKey(event.getProjectName());
      try {
        ProjectResource project =
            new ProjectResource(projectControl.controlFor(nameKey, user));
        if (isRefDeleted(event) || isNonFastForwardUpdate(event, project)) {
          createBackupBranch(event, project);
        }
      } catch (NoSuchProjectException | IOException e) {
        log.error(e.getMessage(), e);
      }
    }
  }

  /**
   * Create a backup branch for the given ref.
   *
   * @param event the Event
   */
  private void createBackupBranch(Event event, ProjectResource project) {
    String branchName = event.getRefName().replaceFirst(R_HEADS, "");
    try {
      String branchPrefix = "";
      int n = branchName.lastIndexOf("/");
      if (n != -1) {
        branchPrefix = branchName.substring(0, n + 1);
        branchName = branchName.substring(n + 1);
      }

      String ref =
          String.format("%sbackup-%s-%s", branchPrefix, branchName,
              new SimpleDateFormat("YYYYMMdd-HHmmss").format(new Date()));

      CreateBranch.Input input = new CreateBranch.Input();
      input.ref = ref;
      input.revision = event.getOldObjectId();

      createBranchFactory.create(ref).apply(project, input);
    } catch (BadRequestException | AuthException | ResourceConflictException
        | IOException e) {
      log.error(e.getMessage(), e);
    }
  }

  /**
   * Is the event on a relevant ref?
   *
   * @param event the Event
   * @return True if relevant, otherwise False.
   */
  private boolean isRelevantRef(Event event) {
    return (!isNewRef(event)) &&
           (event.getRefName().startsWith(R_HEADS)
            || event.getRefName().startsWith(R_TAGS));
  }

  /**
   * Is the event a new ref?
   *
   * @param event the Event
   * @return True if a new ref, otherwise False.
   */
  private boolean isNewRef(Event event) {
    return event.getOldObjectId().equals(ObjectId.zeroId().getName());
  }

  /**
   * Is the event a ref deletion?
   *
   * @param event the Event
   * @return True if a ref deletion, otherwise False.
   */
  private boolean isRefDeleted(Event event) {
    if (event.getNewObjectId().equals(ObjectId.zeroId().getName())) {
      log.info(String.format(
          "Ref Deleted: project [%s] refname [%s] old object id [%s]",
          event.getProjectName(), event.getRefName(), event.getOldObjectId()));
      return true;
    }
    return false;
  }

  /**
   * Is the event a non-fast-forward update?
   *
   * @param event the Event
   * @return True if a non-fast-forward update, otherwise False.
   */
  private boolean isNonFastForwardUpdate(Event event, ProjectResource project)
      throws RepositoryNotFoundException, IOException {
    Repository repo = null;
    RevWalk walk = null;
    try {
      repo = repoManager.openRepository(project.getNameKey());
      walk = new RevWalk(repo);
      RevCommit oldCommit =
          walk.parseCommit(repo.resolve(event.getOldObjectId()));
      RevCommit newCommit =
          walk.parseCommit(repo.resolve(event.getNewObjectId()));
      return !walk.isMergedInto(oldCommit, newCommit);
    } finally {
      if (walk != null) {
        walk.release();
      }
      if (repo != null) {
        repo.close();
      }
    }
  }
}