task-stream/libs/api/tracker/domain/src/lib/comment/comment.ts

import {
  BusinessRuleError,
  ForbiddenError,
  VersionedAggregateRoot,
  assertThat,
} from '@task-stream/api/shared/domain';
import { CommentAddedEvent } from '../events/comment-added.event';
import { CommentDeletedEvent } from '../events/comment-deleted.event';
import { CommentEditedEvent } from '../events/comment-edited.event';

/** Data of a comment (what CommentAddedEvent carries). */
export interface CommentProps {
  id: string;
  issueId: string;
  projectId: string;
  authorId: string;
  body: string;
  /**
   * The comment this one answers; always a top-level one (one level of
   * replies). Null for a top-level comment, and on comments made before
   * there were replies.
   */
  replyTo: string | null;
  deleted: boolean;
  createdAt: string;
  editedAt: string | null;
}

const MAX_BODY = 20_000;

/** Decisions and explanations inside a ticket, and the replies to them. */
export class Comment extends VersionedAggregateRoot implements CommentProps {
  public issueId!: string;
  public projectId!: string;
  public authorId!: string;
  public body!: string;
  public replyTo: string | null = null;
  public deleted = false;
  public createdAt!: string;
  public editedAt: string | null = null;

  constructor(id: string) {
    super();
    this.id = id;
  }

  edit(actorId: string, body: string): void {
    this.assertAlive();
    if (actorId !== this.authorId) {
      throw new ForbiddenError('Only the author can edit a comment');
    }
    const next = validCommentBody(body);
    if (next === this.body) return;
    this.apply(
      new CommentEditedEvent(
        actorId,
        this.id,
        this.projectId,
        this.issueId,
        next,
      ),
    );
  }

  /** @param canModerate whether the actor manages the project (may delete others' comments). */
  delete(actorId: string, canModerate: boolean): void {
    this.assertAlive();
    if (actorId !== this.authorId && !canModerate) {
      throw new ForbiddenError(
        'Only the author or a project admin can delete a comment',
      );
    }
    this.apply(
      new CommentDeletedEvent(actorId, this.id, this.projectId, this.issueId),
    );
  }

  /* ---- State transitions (also replayed by loadFromHistory) ---- */

  onCommentAddedEvent({ comment }: CommentAddedEvent): void {
    Object.assign(this, comment);
  }

  onCommentEditedEvent(event: CommentEditedEvent): void {
    this.body = event.body;
    this.editedAt = event.occurredAt;
  }

  onCommentDeletedEvent(): void {
    this.deleted = true;
  }

  private assertAlive(): void {
    if (this.deleted) throw new BusinessRuleError('Comment was deleted');
  }
}

export function validCommentBody(body: string): string {
  const trimmed = body.trim();
  assertThat(trimmed.length > 0, 'Comment cannot be empty');
  assertThat(
    trimmed.length <= MAX_BODY,
    `Comment cannot exceed ${MAX_BODY} characters`,
  );
  return trimmed;
}