<?php

final class DifferentialTransactionEditor
  extends PhabricatorApplicationTransactionEditor {

  public function getTransactionTypes() {
    $types = parent::getTransactionTypes();

    $types[] = PhabricatorTransactions::TYPE_COMMENT;
    $types[] = PhabricatorTransactions::TYPE_EDGE;
    $types[] = PhabricatorTransactions::TYPE_VIEW_POLICY;
    $types[] = PhabricatorTransactions::TYPE_EDIT_POLICY;

    $types[] = DifferentialTransaction::TYPE_ACTION;
    $types[] = DifferentialTransaction::TYPE_INLINE;
    $types[] = DifferentialTransaction::TYPE_STATUS;
    $types[] = DifferentialTransaction::TYPE_UPDATE;

    return $types;
  }

  protected function getCustomTransactionOldValue(
    PhabricatorLiskDAO $object,
    PhabricatorApplicationTransaction $xaction) {

    switch ($xaction->getTransactionType()) {
      case PhabricatorTransactions::TYPE_VIEW_POLICY:
        return $object->getViewPolicy();
      case PhabricatorTransactions::TYPE_EDIT_POLICY:
        return $object->getEditPolicy();
      case DifferentialTransaction::TYPE_ACTION:
        return null;
      case DifferentialTransaction::TYPE_INLINE:
        return null;
      case DifferentialTransaction::TYPE_UPDATE:
        if ($this->getIsNewObject()) {
          return null;
        } else {
          return $object->getActiveDiff()->getPHID();
        }
    }

    return parent::getCustomTransactionOldValue($object, $xaction);
  }

  protected function getCustomTransactionNewValue(
    PhabricatorLiskDAO $object,
    PhabricatorApplicationTransaction $xaction) {

    switch ($xaction->getTransactionType()) {
      case PhabricatorTransactions::TYPE_VIEW_POLICY:
      case PhabricatorTransactions::TYPE_EDIT_POLICY:
      case DifferentialTransaction::TYPE_ACTION:
      case DifferentialTransaction::TYPE_UPDATE:
        return $xaction->getNewValue();
      case DifferentialTransaction::TYPE_INLINE:
        return null;
    }

    return parent::getCustomTransactionNewValue($object, $xaction);
  }

  protected function transactionHasEffect(
    PhabricatorLiskDAO $object,
    PhabricatorApplicationTransaction $xaction) {

    switch ($xaction->getTransactionType()) {
      case DifferentialTransaction::TYPE_INLINE:
        return $xaction->hasComment();
      case DifferentialTransaction::TYPE_ACTION:
        $status_closed = ArcanistDifferentialRevisionStatus::CLOSED;
        $status_abandoned = ArcanistDifferentialRevisionStatus::ABANDONED;
        $status_review = ArcanistDifferentialRevisionStatus::NEEDS_REVIEW;
        $status_revision = ArcanistDifferentialRevisionStatus::NEEDS_REVISION;

        $action_type = $xaction->getNewValue();
        switch ($action_type) {
          case DifferentialAction::ACTION_ACCEPT:
          case DifferentialAction::ACTION_REJECT:
            if ($action_type == DifferentialAction::ACTION_ACCEPT) {
              $new_status = DifferentialReviewerStatus::STATUS_ACCEPTED;
            } else {
              $new_status = DifferentialReviewerStatus::STATUS_REJECTED;
            }

            $actor = $this->getActor();
            $actor_phid = $actor->getPHID();

            // These transactions can cause effects in to ways: by altering the
            // status of an existing reviewer; or by adding the actor as a new
            // reviewer.

            $will_add_reviewer = true;
            foreach ($object->getReviewerStatus() as $reviewer) {
              if ($reviewer->hasAuthority($actor)) {
                if ($reviewer->getStatus() != $new_status) {
                  return true;
                }
              }
              if ($reviewer->getReviewerPHID() == $actor_phid) {
                $will_add_reviwer = false;
              }
            }

            return $will_add_reviewer;
          case DifferentialAction::ACTION_CLOSE:
            return ($object->getStatus() != $status_closed);
          case DifferentialAction::ACTION_ABANDON:
            return ($object->getStatus() != $status_abandoned);
          case DifferentialAction::ACTION_RECLAIM:
            return ($object->getStatus() == $status_abandoned);
          case DifferentialAction::ACTION_REOPEN:
            return ($object->getStatus() == $status_closed);
          case DifferentialAction::ACTION_RETHINK:
            return ($object->getStatus() != $status_revision);
          case DifferentialAction::ACTION_REQUEST:
            return ($object->getStatus() != $status_review);
          case DifferentialAction::ACTION_RESIGN:
            $actor_phid = $this->getActor()->getPHID();
            foreach ($object->getReviewerStatus() as $reviewer) {
              if ($reviewer->getReviewerPHID() == $actor_phid) {
                return true;
              }
            }
            return false;
          case DifferentialAction::ACTION_CLAIM:
            $actor_phid = $this->getActor()->getPHID();
            return ($actor_phid != $object->getAuthorPHID());
        }
    }

    return parent::transactionHasEffect($object, $xaction);
  }


  protected function applyCustomInternalTransaction(
    PhabricatorLiskDAO $object,
    PhabricatorApplicationTransaction $xaction) {

    $status_review = ArcanistDifferentialRevisionStatus::NEEDS_REVIEW;
    $status_revision = ArcanistDifferentialRevisionStatus::NEEDS_REVISION;

    switch ($xaction->getTransactionType()) {
      case PhabricatorTransactions::TYPE_VIEW_POLICY:
        $object->setViewPolicy($xaction->getNewValue());
        return;
      case PhabricatorTransactions::TYPE_EDIT_POLICY:
        $object->setEditPolicy($xaction->getNewValue());
        return;
      case PhabricatorTransactions::TYPE_SUBSCRIBERS:
      case PhabricatorTransactions::TYPE_COMMENT:
      case DifferentialTransaction::TYPE_INLINE:
        return;
      case PhabricatorTransactions::TYPE_EDGE:
        return;
      case DifferentialTransaction::TYPE_UPDATE:
        $object->setStatus($status_review);
        // TODO: Update the `diffPHID` once we add that.
        return;
      case DifferentialTransaction::TYPE_ACTION:
        switch ($xaction->getNewValue()) {
          case DifferentialAction::ACTION_RESIGN:
          case DifferentialAction::ACTION_ACCEPT:
          case DifferentialAction::ACTION_REJECT:
            // These have no direct effects, and affect review status only
            // indirectly by altering reviewers with TYPE_EDGE transactions.
            return;
          case DifferentialAction::ACTION_ABANDON:
            $object->setStatus(ArcanistDifferentialRevisionStatus::ABANDONED);
            return;
          case DifferentialAction::ACTION_RETHINK:
            $object->setStatus($status_revision);
            return;
          case DifferentialAction::ACTION_RECLAIM:
            $object->setStatus($status_review);
            return;
          case DifferentialAction::ACTION_REOPEN:
            $object->setStatus($status_review);
            return;
          case DifferentialAction::ACTION_REQUEST:
            $object->setStatus($status_review);
            return;
          case DifferentialAction::ACTION_CLOSE:
            $object->setStatus(ArcanistDifferentialRevisionStatus::CLOSED);
            return;
          case DifferentialAction::ACTION_CLAIM:
            $object->setAuthorPHID($this->getActor()->getPHID());
            return;
        }
        break;
    }

    return parent::applyCustomInternalTransaction($object, $xaction);
  }

  protected function expandTransaction(
    PhabricatorLiskDAO $object,
    PhabricatorApplicationTransaction $xaction) {

    $actor = $this->getActor();
    $actor_phid = $actor->getPHID();
    $type_edge = PhabricatorTransactions::TYPE_EDGE;
    $edge_reviewer = PhabricatorEdgeConfig::TYPE_DREV_HAS_REVIEWER;

    $results = parent::expandTransaction($object, $xaction);
    switch ($xaction->getTransactionType()) {
      case DifferentialTransaction::TYPE_UPDATE:
        $new_accept = DifferentialReviewerStatus::STATUS_ACCEPTED;
        $new_reject = DifferentialReviewerStatus::STATUS_REJECTED;
        $old_accept = DifferentialReviewerStatus::STATUS_ACCEPTED_OLDER;
        $old_reject = DifferentialReviewerStatus::STATUS_REJECTED_OLDER;

        // When a revision is updated, change all "reject" to "rejected older
        // revision". This means we won't immediately push the update back into
        // "needs review", but outstanding rejects will still block it from
        // moving to "accepted".
        $edits = array();
        foreach ($object->getReviewerStatus() as $reviewer) {
          if ($reviewer->getStatus() == $new_reject) {
            $edits[$reviewer->getReviewerPHID()] = array(
              'data' => array(
                'status' => $old_reject,
              ),
            );
          }

          // TODO: If sticky accept is off, do a similar update for accepts.
        }

        if ($edits) {
          $results[] = id(new DifferentialTransaction())
            ->setTransactionType($type_edge)
            ->setMetadataValue('edge:type', $edge_reviewer)
            ->setIgnoreOnNoEffect(true)
            ->setNewValue(array('+' => $edits));
        }
        break;

      case PhabricatorTransactions::TYPE_COMMENT:
        // When a user leaves a comment, upgrade their reviewer status from
        // "added" to "commented" if they're also a reviewer. We may further
        // upgrade this based on other actions in the transaction group.

        $status_added = DifferentialReviewerStatus::STATUS_ADDED;
        $status_commented = DifferentialReviewerStatus::STATUS_COMMENTED;

        $data = array(
          'status' => $status_commented,
        );

        $edits = array();
        foreach ($object->getReviewerStatus() as $reviewer) {
          if ($reviewer->getReviewerPHID() == $actor_phid) {
            if ($reviewer->getStatus() == $status_added) {
              $edits[$actor_phid] = array(
                'data' => $data,
              );
            }
          }
        }

        if ($edits) {
          $results[] = id(new DifferentialTransaction())
            ->setTransactionType($type_edge)
            ->setMetadataValue('edge:type', $edge_reviewer)
            ->setIgnoreOnNoEffect(true)
            ->setNewValue(array('+' => $edits));
        }
        break;

      case DifferentialTransaction::TYPE_ACTION:
        $action_type = $xaction->getNewValue();

        switch ($action_type) {
          case DifferentialAction::ACTION_ACCEPT:
          case DifferentialAction::ACTION_REJECT:
            if ($action_type == DifferentialAction::ACTION_ACCEPT) {
              $data = array(
                'status' => DifferentialReviewerStatus::STATUS_ACCEPTED,
              );
            } else {
              $data = array(
                'status' => DifferentialReviewerStatus::STATUS_REJECTED,
              );
            }

            $edits = array();

            foreach ($object->getReviewerStatus() as $reviewer) {
              if ($reviewer->hasAuthority($actor)) {
                $edits[$reviewer->getReviewerPHID()] = array(
                  'data' => $data,
                );
              }
            }

            // Also either update or add the actor themselves as a reviewer.
            $edits[$actor_phid] = array(
              'data' => $data,
            );

            $results[] = id(new DifferentialTransaction())
              ->setTransactionType($type_edge)
              ->setMetadataValue('edge:type', $edge_reviewer)
              ->setIgnoreOnNoEffect(true)
              ->setNewValue(array('+' => $edits));
            break;

          case DifferentialAction::ACTION_CLAIM:
            // If the user is commandeering, add the previous owner as a
            // reviewer and remove the actor.

            $edits = array(
              '-' => array(
                $actor_phid => $actor_phid,
              ),
            );

            $owner_phid = $object->getAuthorPHID();
            if ($owner_phid) {
              $reviewer = new DifferentialReviewer(
                $owner_phid,
                array(
                  'status' => DifferentialReviewerStatus::STATUS_ADDED,
                ));

              $edits['+'] = array(
                $owner_phid => array(
                  'data' => $reviewer->getEdgeData(),
                ),
              );
            }

            $results[] = id(new DifferentialTransaction())
              ->setTransactionType($type_edge)
              ->setMetadataValue('edge:type', $edge_reviewer)
              ->setIgnoreOnNoEffect(true)
              ->setNewValue($edits);

            break;
          case DifferentialAction::ACTION_RESIGN:
            // If the user is resigning, add a separate reviewer edit
            // transaction which removes them as a reviewer.

            $results[] = id(new DifferentialTransaction())
              ->setTransactionType($type_edge)
              ->setMetadataValue('edge:type', $edge_reviewer)
              ->setIgnoreOnNoEffect(true)
              ->setNewValue(
                array(
                  '-' => array(
                    $actor_phid => $actor_phid,
                  ),
                ));

            break;
        }
      break;
    }

    return $results;
  }

  protected function applyCustomExternalTransaction(
    PhabricatorLiskDAO $object,
    PhabricatorApplicationTransaction $xaction) {

    switch ($xaction->getTransactionType()) {
      case PhabricatorTransactions::TYPE_VIEW_POLICY:
      case PhabricatorTransactions::TYPE_EDIT_POLICY:
        return;
      case PhabricatorTransactions::TYPE_SUBSCRIBERS:
      case PhabricatorTransactions::TYPE_EDGE:
      case PhabricatorTransactions::TYPE_COMMENT:
      case DifferentialTransaction::TYPE_ACTION:
      case DifferentialTransaction::TYPE_INLINE:
        return;
      case DifferentialTransaction::TYPE_UPDATE:
        // Now that we're inside the transaction, do a final check.
        $diff = $this->loadDiff($xaction->getNewValue());

        // TODO: It would be slightly cleaner to just revalidate this
        // transaction somehow using the same validation code, but that's
        // not easy to do at the moment.

        if (!$diff) {
          throw new Exception(pht('Diff does not exist!'));
        } else {
          $revision_id = $diff->getRevisionID();
          if ($revision_id && ($revision_id != $object->getID())) {
            throw new Exception(
              pht(
                'Diff is already attached to another revision. You lost '.
                'a race?'));
          }
        }

        $diff->setRevisionID($object->getID());
        $diff->save();

        $object->setLineCount($diff->getLineCount());
        $object->setRepositoryPHID($diff->getRepositoryPHID());

        return;
    }

    return parent::applyCustomExternalTransaction($object, $xaction);
  }

  protected function mergeEdgeData($type, array $u, array $v) {
    $result = parent::mergeEdgeData($type, $u, $v);

    switch ($type) {
      case PhabricatorEdgeConfig::TYPE_DREV_HAS_REVIEWER:
        // When the same reviewer has their status updated by multiple
        // transactions, we want the strongest status to win. An example of
        // this is when a user adds a comment and also accepts a revision which
        // they are a reviewer on. The comment creates a "commented" status,
        // while the accept creates an "accepted" status. Since accept is
        // stronger, it should win and persist.

        $u_status = idx($u, 'status');
        $v_status = idx($v, 'status');
        $u_str = DifferentialReviewerStatus::getStatusStrength($u_status);
        $v_str = DifferentialReviewerStatus::getStatusStrength($v_status);
        if ($u_str > $v_str) {
          $result['status'] = $u_status;
        } else {
          $result['status'] = $v_status;
        }
        break;
    }

    return $result;
  }


  protected function applyFinalEffects(
    PhabricatorLiskDAO $object,
    array $xactions) {

    $status_accepted = ArcanistDifferentialRevisionStatus::ACCEPTED;
    $status_revision = ArcanistDifferentialRevisionStatus::NEEDS_REVISION;
    $status_review = ArcanistDifferentialRevisionStatus::NEEDS_REVIEW;

    $old_status = $object->getStatus();
    switch ($old_status) {
      case $status_accepted:
      case $status_revision:
      case $status_review:
        // Load the most up-to-date version of the revision and its reviewers,
        // so we don't need to try to deduce the state of reviewers by examining
        // all the changes made by the transactions.
        $new_revision = id(new DifferentialRevisionQuery())
          ->setViewer($this->getActor())
          ->needReviewerStatus(true)
          ->withIDs(array($object->getID()))
          ->executeOne();
        if (!$new_revision) {
          throw new Exception(
            pht('Failed to load revision from transaction finalization.'));
        }

        // Try to move a revision to "accepted". We look for:
        //
        //   - at least one accepting reviewer who is a user; and
        //   - no rejects; and
        //   - no rejects of older diffs; and
        //   - no blocking reviewers.

        $has_accepting_user = false;
        $has_rejecting_reviewer = false;
        $has_rejecting_older_reviewer = false;
        $has_blocking_reviewer = false;
        foreach ($new_revision->getReviewerStatus() as $reviewer) {
          $reviewer_status = $reviewer->getStatus();
          switch ($reviewer_status) {
            case DifferentialReviewerStatus::STATUS_REJECTED:
              $has_rejecting_reviewer = true;
              break;
            case DifferentialReviewerStatus::STATUS_REJECTED_OLDER:
              $has_rejecting_older_reviewer = true;
              break;
            case DifferentialReviewerStatus::STATUS_BLOCKING:
              $has_blocking_reviewer = true;
              break;
            case DifferentialReviewerStatus::STATUS_ACCEPTED:
              if ($reviewer->isUser()) {
                $has_accepting_user = true;
              }
              break;
          }
        }

        $new_status = null;
        if ($has_accepting_user &&
            !$has_rejecting_reviewer &&
            !$has_rejecting_older_reviewer &&
            !$has_blocking_reviewer) {
          $new_status = $status_accepted;
        } else if ($has_rejecting_reviewer) {
          // This isn't accepted, and there's at least one rejecting reviewer,
          // so the revision needs changes. This usually happens after a
          // "reject".
          $new_status = $status_revision;
        } else if ($old_status == $status_accepted) {
          // This revision was accepted, but it no longer satisfies the
          // conditions for acceptance. This usually happens after an accepting
          // reviewer resigns or is removed.
          $new_status = $status_review;
        }

        if ($new_status !== null && $new_status != $old_status) {
          $xaction = id(new DifferentialTransaction())
            ->setTransactionType(DifferentialTransaction::TYPE_STATUS)
            ->setOldValue($old_status)
            ->setNewValue($new_status);

          $xaction = $this->populateTransaction($object, $xaction)->save();

          $xactions[] = $xaction;

          $object->setStatus($new_status)->save();
        }
        break;
      default:
        // Revisions can't transition out of other statuses (like closed or
        // abandoned) as a side effect of reviewer status changes.
        break;
    }

    return $xactions;
  }


  protected function validateTransaction(
    PhabricatorLiskDAO $object,
    $type,
    array $xactions) {

    $errors = parent::validateTransaction($object, $type, $xactions);

    foreach ($xactions as $xaction) {
      switch ($type) {
        case DifferentialTransaction::TYPE_UPDATE:
          $diff = $this->loadDiff($xaction->getNewValue());
          if (!$diff) {
            $errors[] = new PhabricatorApplicationTransactionValidationError(
              $type,
              pht('Invalid'),
              pht('The specified diff does not exist.'),
              $xaction);
          } else if (($diff->getRevisionID()) &&
            ($diff->getRevisionID() != $object->getID())) {
            $errors[] = new PhabricatorApplicationTransactionValidationError(
              $type,
              pht('Invalid'),
              pht(
                'You can not update this revision to the specified diff, '.
                'because the diff is already attached to another revision.'),
              $xaction);
          }
          break;
        case DifferentialTransaction::TYPE_ACTION:
          $error = $this->validateDifferentialAction(
            $object,
            $type,
            $xaction,
            $xaction->getNewValue());
          if ($error) {
            $errors[] = new PhabricatorApplicationTransactionValidationError(
              $type,
              pht('Invalid'),
              $error,
              $xaction);
          }
          break;
      }
    }

    return $errors;
  }

  private function validateDifferentialAction(
    DifferentialRevision $revision,
    $type,
    DifferentialTransaction $xaction,
    $action) {

    $author_phid = $revision->getAuthorPHID();
    $actor_phid = $this->getActor()->getPHID();
    $actor_is_author = ($author_phid == $actor_phid);

    $config_close_key = 'differential.always-allow-close';
    $always_allow_close = PhabricatorEnv::getEnvConfig($config_close_key);

    $config_reopen_key = 'differential.allow-reopen';
    $allow_reopen = PhabricatorEnv::getEnvConfig($config_reopen_key);

    $config_self_accept_key = 'differential.allow-self-accept';
    $allow_self_accept = PhabricatorEnv::getEnvConfig($config_self_accept_key);

    $revision_status = $revision->getStatus();

    $status_accepted = ArcanistDifferentialRevisionStatus::ACCEPTED;
    $status_abandoned = ArcanistDifferentialRevisionStatus::ABANDONED;
    $status_closed = ArcanistDifferentialRevisionStatus::CLOSED;

    switch ($action) {
      case DifferentialAction::ACTION_ACCEPT:
        if ($actor_is_author && !$allow_self_accept) {
          return pht(
            'You can not accept this revision because you are the owner.');
        }

        if ($revision_status == $status_abandoned) {
          return pht(
            'You can not accept this revision because it has been '.
            'abandoned.');
        }

        if ($revision_status == $status_closed) {
          return pht(
            'You can not accept this revision because it has already been '.
            'closed.');
        }
        break;

      case DifferentialAction::ACTION_REJECT:
        if ($actor_is_author) {
          return pht(
            'You can not request changes to your own revision.');
        }

        if ($revision_status == $status_abandoned) {
          return pht(
            'You can not request changes to this revision because it has been '.
            'abandoned.');
        }

        if ($revision_status == $status_closed) {
          return pht(
            'You can not request changes to this revision because it has '.
            'already been closed.');
        }
        break;

      case DifferentialAction::ACTION_RESIGN:
        // You can always resign from a revision if you're a reviewer. If you
        // aren't, this is a no-op rather than invalid.
        break;

      case DifferentialAction::ACTION_CLAIM:
        // You can claim a revision if you're not the owner. If you are, this
        // is a no-op rather than invalid.

        if ($revision_status == $status_closed) {
          return pht(
            "You can not commandeer this revision because it has already been ".
            "closed.");
        }
        break;

      case DifferentialAction::ACTION_ABANDON:
        if (!$actor_is_author) {
          return pht(
            "You can not abandon this revision because you do not own it. ".
            "You can only abandon revisions you own.");
        }

        if ($revision_status == $status_closed) {
          return pht(
            "You can not abandon this revision because it has already been ".
            "closed.");
        }

        // NOTE: Abandons of already-abandoned revisions are treated as no-op
        // instead of invalid. Other abandons are OK.

        break;

      case DifferentialAction::ACTION_RECLAIM:
        if (!$actor_is_author) {
          return pht(
            "You can not reclaim this revision because you do not own ".
            "it. You can only reclaim revisions you own.");
        }

        if ($revision_status == $status_closed) {
          return pht(
            "You can not reclaim this revision because it has already been ".
            "closed.");
        }

        // NOTE: Reclaims of other non-abandoned revisions are treated as no-op
        // instead of invalid.

        break;

      case DifferentialAction::ACTION_REOPEN:
        if (!$allow_reopen) {
          return pht(
            'The reopen action is not enabled on this Phabricator install. '.
            'Adjust your configuration to enable it.');
        }

        // NOTE: If the revision is not closed, this is caught as a no-op
        // instead of an invalid transaction.

        break;

      case DifferentialAction::ACTION_RETHINK:
        if (!$actor_is_author) {
          return pht(
            "You can not plan changes to this revision because you do not ".
            "own it. To plan chagnes to a revision, you must be its owner.");
        }

        switch ($revision_status) {
          case ArcanistDifferentialRevisionStatus::ACCEPTED:
          case ArcanistDifferentialRevisionStatus::NEEDS_REVISION:
          case ArcanistDifferentialRevisionStatus::NEEDS_REVIEW:
            // These are OK.
            break;
          case ArcanistDifferentialRevisionStatus::ABANDONED:
            return pht(
              "You can not plan changes to this revision because it has ".
              "been abandoned.");
          case ArcanistDifferentialRevisionStatus::CLOSED:
            return pht(
              "You can not plan changes to this revision because it has ".
              "already been closed.");
          default:
            throw new Exception(
              pht(
                'Encountered unexpected revision status ("%s") when '.
                'validating "%s" action.',
                $revision_status,
                $action));
        }
        break;

      case DifferentialAction::ACTION_REQUEST:
        if (!$actor_is_author) {
          return pht(
            "You can not request review of this revision because you do ".
            "not own it. To request review of a revision, you must be its ".
            "owner.");
        }

        switch ($revision_status) {
          case ArcanistDifferentialRevisionStatus::ACCEPTED:
          case ArcanistDifferentialRevisionStatus::NEEDS_REVISION:
            // These are OK.
            break;
          case ArcanistDifferentialRevisionStatus::NEEDS_REVIEW:
            // This will be caught as "no effect" later on.
            break;
          case ArcanistDifferentialRevisionStatus::ABANDONED:
            return pht(
              "You can not request review of this revision because it has ".
              "been abandoned. Instead, reclaim it.");
          case ArcanistDifferentialRevisionStatus::CLOSED:
            return pht(
              "You can not request review of this revision because it has ".
              "already been closed.");
          default:
            throw new Exception(
              pht(
                'Encountered unexpected revision status ("%s") when '.
                'validating "%s" action.',
                $revision_status,
                $action));
        }
        break;

      case DifferentialAction::ACTION_CLOSE:

        // TODO: Permit the daemons to take this action in all cases.

        if (!$actor_is_author && !$always_allow_close) {
          return pht(
            "You can not close this revision because you do not own it. To ".
            "close a revision, you must be its owner.");
        }

        if ($revision_status != $status_accepted) {
          return pht(
            "You can not close this revision because it has not been ".
            "accepted. You can only close accepted revisions.");
        }
        break;
    }

    return null;
  }

  protected function sortTransactions(array $xactions) {
    $xactions = parent::sortTransactions($xactions);

    $head = array();
    $tail = array();

    foreach ($xactions as $xaction) {
      $type = $xaction->getTransactionType();
      if ($type == DifferentialTransaction::TYPE_INLINE) {
        $tail[] = $xaction;
      } else {
        $head[] = $xaction;
      }
    }

    return array_values(array_merge($head, $tail));
  }

  protected function requireCapabilities(
    PhabricatorLiskDAO $object,
    PhabricatorApplicationTransaction $xaction) {

    switch ($xaction->getTransactionType()) {
    }

    return parent::requireCapabilities($object, $xaction);
  }

  protected function shouldPublishFeedStory(
    PhabricatorLiskDAO $object,
    array $xactions) {
    return true;
  }

  protected function shouldSendMail(
    PhabricatorLiskDAO $object,
    array $xactions) {
    return true;
  }

  protected function getMailTo(PhabricatorLiskDAO $object) {
    $phids = array();
    $phids[] = $object->getAuthorPHID();
    foreach ($object->getReviewerStatus() as $reviewer) {
      $phids[] = $reviewer->getReviewerPHID();
    }
    return $phids;
  }

  protected function getMailSubjectPrefix() {
    return PhabricatorEnv::getEnvConfig('metamta.differential.subject-prefix');
  }

  protected function getMailThreadID(PhabricatorLiskDAO $object) {
    // This is nonstandard, but retains threading with older messages.
    $phid = $object->getPHID();
    return "differential-rev-{$phid}-req";
  }

  protected function buildReplyHandler(PhabricatorLiskDAO $object) {
    return id(new DifferentialReplyHandler())
      ->setMailReceiver($object);
  }

  protected function buildMailTemplate(PhabricatorLiskDAO $object) {
    $id = $object->getID();
    $title = $object->getTitle();

    $original_title = $object->getOriginalTitle();

    $subject = "D{$id}: {$title}";
    $thread_topic = "D{$id}: {$original_title}";

    return id(new PhabricatorMetaMTAMail())
      ->setSubject($subject)
      ->addHeader('Thread-Topic', $thread_topic);
  }

  protected function buildMailBody(
    PhabricatorLiskDAO $object,
    array $xactions) {

    $body = parent::buildMailBody($object, $xactions);

    $type_inline = DifferentialTransaction::TYPE_INLINE;

    $inlines = array();
    foreach ($xactions as $xaction) {
      if ($xaction->getTransactionType() == $type_inline) {
        $inlines[] = $xaction;
      }
    }

    if ($inlines) {
      $body->addTextSection(
        pht('INLINE COMMENTS'),
        $this->renderInlineCommentsForMail($object, $inlines));
    }

    $body->addTextSection(
      pht('REVISION DETAIL'),
      PhabricatorEnv::getProductionURI('/D'.$object->getID()));


    return $body;
  }

  protected function supportsSearch() {
    return true;
  }

  protected function extractFilePHIDsFromCustomTransaction(
    PhabricatorLiskDAO $object,
    PhabricatorApplicationTransaction $xaction) {

    switch ($xaction->getTransactionType()) {
    }

    return parent::extractFilePHIDsFromCustomTransaction($object, $xaction);
  }

  protected function expandCustomRemarkupBlockTransactions(
    PhabricatorLiskDAO $object,
    array $xactions,
    $blocks,
    PhutilMarkupEngine $engine) {


    $flat_blocks = array_mergev($blocks);
    $huge_block = implode("\n\n", $flat_blocks);

    $task_map = array();
    $task_refs = id(new ManiphestCustomFieldStatusParser())
      ->parseCorpus($huge_block);
    foreach ($task_refs as $match) {
      foreach ($match['monograms'] as $monogram) {
        $task_id = (int)trim($monogram, 'tT');
        $task_map[$task_id] = true;
      }
    }

    $rev_map = array();
    $rev_refs = id(new DifferentialCustomFieldDependsOnParser())
      ->parseCorpus($huge_block);
    foreach ($rev_refs as $match) {
      foreach ($match['monograms'] as $monogram) {
        $rev_id = (int)trim($monogram, 'dD');
        $rev_map[$rev_id] = true;
      }
    }

    $edges = array();

    if ($task_map) {
      $tasks = id(new ManiphestTaskQuery())
        ->setViewer($this->getActor())
        ->withIDs(array_keys($task_map))
        ->execute();

      if ($tasks) {
        $edge_related = PhabricatorEdgeConfig::TYPE_DREV_HAS_RELATED_TASK;
        $edges[$edge_related] = mpull($tasks, 'getPHID', 'getPHID');
      }
    }

    if ($rev_map) {
      $revs = id(new DifferentialRevisionQuery())
        ->setViewer($this->getActor())
        ->withIDs(array_keys($rev_map))
        ->execute();
      $rev_phids = mpull($revs, 'getPHID', 'getPHID');

      // NOTE: Skip any write attempts if a user cleverly implies a revision
      // depends upon itself.
      unset($rev_phids[$object->getPHID()]);

      if ($revs) {
        $edge_depends = PhabricatorEdgeConfig::TYPE_DREV_DEPENDS_ON_DREV;
        $edges[$edge_depends] = $rev_phids;
      }
    }

    $result = array();
    foreach ($edges as $type => $specs) {
      $result[] = id(new DifferentialTransaction())
        ->setTransactionType(PhabricatorTransactions::TYPE_EDGE)
        ->setMetadataValue('edge:type', $type)
        ->setNewValue(array('+' => $specs));
    }

    return $result;
  }

  private function renderInlineCommentsForMail(
    PhabricatorLiskDAO $object,
    array $inlines) {

    $context_key = 'metamta.differential.unified-comment-context';
    $show_context = PhabricatorEnv::getEnvConfig($context_key);

    $changeset_ids = array();
    foreach ($inlines as $inline) {
      $id = $inline->getComment()->getChangesetID();
      $changeset_ids[$id] = $id;
    }

    // TODO: We should write a proper Query class for this eventually.
    $changesets = id(new DifferentialChangeset())->loadAllWhere(
      'id IN (%Ld)',
      $changeset_ids);
    if ($show_context) {
      $hunk_parser = new DifferentialHunkParser();
      foreach ($changesets as $changeset) {
        $changeset->attachHunks($changeset->loadHunks());
      }
    }

    $inline_groups = DifferentialTransactionComment::sortAndGroupInlines(
      $inlines,
      $changesets);

    $result = array();
    foreach ($inline_groups as $changeset_id => $group) {
      $changeset = idx($changesets, $changeset_id);
      if (!$changeset) {
        continue;
      }

      foreach ($group as $inline) {
        $comment = $inline->getComment();
        $file = $changeset->getFilename();
        $start = $comment->getLineNumber();
        $len = $comment->getLineLength();
        if ($len) {
          $range = $start.'-'.($start + $len);
        } else {
          $range = $start;
        }

        $inline_content = $comment->getContent();

        if (!$show_context) {
          $result[] = "{$file}:{$range} {$inline_content}";
        } else {
          $result[] = "================";
          $result[] = "Comment at: " . $file . ":" . $range;
          $result[] = $hunk_parser->makeContextDiff(
            $changeset->getHunks(),
            $comment->getIsNewFile(),
            $comment->getLineNumber(),
            $comment->getLineLength(),
            1);
          $result[] = "----------------";

          $result[] = $inline_content;
          $result[] = null;
        }
      }
    }

    return implode("\n", $result);
  }

  private function loadDiff($phid) {
    return id(new DifferentialDiffQuery())
      ->withPHIDs(array($phid))
      ->setViewer($this->getActor())
      ->executeOne();
  }


}