@RequiresCapability(WorkInProgressCapability.WORK_IN_PROGRESS)
class WorkInProgressAction implements UiAction<ChangeResource>,
    RestModifyView<ChangeResource, WorkInProgressAction.Input> {
  private static final Logger log = LoggerFactory
      .getLogger(WorkInProgressAction.class);

  static class Input {
    String message;
  }

  private final Provider<ReviewDb> dbProvider;

  @Inject
  WorkInProgressAction(Provider<ReviewDb> dbProvider) {
    this.dbProvider = dbProvider;
  }

  @Override
  public String apply(ChangeResource rsrc, Input input)
      throws ResourceConflictException {
    ChangeControl control = rsrc.getControl();
    if (!control.getCurrentUser().isIdentifiedUser()) {
      throw new AuthException("not permitted to modify change status");
    }
    IdentifiedUser caller = (IdentifiedUser) control.getCurrentUser();
    Change change = rsrc.getChange();
    if (change.getStatus() != Status.NEW) {
      throw new ResourceConflictException("change is " + status(change));
    }
    ChangeMessage message;
    ReviewDb db = dbProvider.get();
    db.changes().beginTransaction(change.getId());
    try {
      change = db.changes().atomicUpdate(
        change.getId(),
        new AtomicUpdate<Change>() {
          @Override
          public Change update(Change change) {
            if (change.getStatus() == Status.NEW) {
              change.setStatus(Status.WORKINPROGRESS);
              ChangeUtil.updated(change);
              return change;
            }
            return null;
          }
        });
      if (change == null) {
        throw new ResourceConflictException("change is "
            + status(db.changes().get(rsrc.getChange().getId())));
      }
      // TODO(davido): Do we need to reindex that change?
      //indexer.index(change);
      message = newMessage(input, caller, change);
      db.changeMessages().insert(Collections.singleton(message));
      new ApprovalsUtil(db).syncChangeStatus(change);
      db.commit();
    } finally {
      db.rollback();
    }

    try {
      ReplyToChangeSender cm = restoredSenderFactory.create(change);
      cm.setFrom(caller.getAccountId());
      cm.setChangeMessage(message);
      cm.send();
    } catch (Exception e) {
      log.error("Cannot email update for change " + change.getChangeId(), e);
    }
    return String.format("changed");
  }

  @Override
  public Description getDescription(ChangeResource resource) {
    return new Description()
        .setLabel("Work In Progress")
        .setTitle("Set Work In Progress");
  }

  private ChangeMessage newMessage(Input input, IdentifiedUser caller,
      Change change) throws OrmException {
    StringBuilder msg = new StringBuilder(
        "Change "
        + change.getId().get()
        + ": Work In Progress");
    if (!Strings.nullToEmpty(input.message).trim().isEmpty()) {
      msg.append("\n\n");
      msg.append(input.message.trim());
    }

    ChangeMessage message = new ChangeMessage(
        new ChangeMessage.Key(
            change.getId(),
            ChangeUtil.messageUUID(dbProvider.get())),
        caller.getAccountId(),
        change.getLastUpdatedOn(),
        change.currentPatchSetId());
    message.setMessage(msg.toString());
    return message;
  }

  private static String status(Change change) {
    return change != null
        ? change.getStatus().name().toLowerCase()
        : "deleted";
  }
}