/**
 * Stores likes on comments and keeps each comment's `like_count` in step with
 * them. Likes have no HTTP endpoint to cast or remove. The WebSocket route
 * (`routes/ws.ts`) calls this module on `comment_like_cast` and
 * `comment_like_remove` messages, then broadcasts the new count. The comment
 * routes use it only to list a comment's likers.
 *
 * @module
 */

import { APIException } from "../lib/api-exception.ts";
import { isUserRow, type User, userRowToApi } from "../model/user.ts";
import { db, transaction } from "../db/connection.ts";
import { type Page, pageOf } from "../lib/pagination.ts";
import { notifyCommentOwnerLike } from "./notification-service.ts";

/**
 * Returned to the WebSocket route by {@link castCommentLike} and
 * {@link removeCommentLike}. The route acks the liker with `likeCount`, then
 * broadcasts it to every client, or to the liker's alone when the comment's
 * dump `isPrivate`.
 */
export interface LikeResult {
  likeCount: number;
  isPrivate: boolean;
}

/**
 * Returns whether the comment's dump is private, or throws a 404 when `userId`
 * can't see it.
 */
function commentVisibility(commentId: string, userId: string): boolean {
  const row = db.prepare(
    `SELECT d.is_private, d.user_id FROM comments c JOIN dumps d ON d.id = c.dump_id
     WHERE c.id = ?;`,
  ).get(commentId) as { is_private: number; user_id: string } | undefined;
  if (!row || (row.is_private && row.user_id !== userId)) {
    throw new APIException(404, "Comment not found");
  }
  return Boolean(row.is_private);
}

/**
 * Records `userId`'s like on a comment and notifies the comment's author. The
 * notification is best-effort: if it fails, the like still counts.
 *
 * @throws {APIException} 404 when the comment doesn't exist or sits on someone
 * else's private dump, 409 when the user already likes it.
 */
export function castCommentLike(
  commentId: string,
  userId: string,
): LikeResult {
  const isPrivate = commentVisibility(commentId, userId);
  let likeCount: number;
  try {
    likeCount = transaction(() => {
      db.prepare(
        `INSERT INTO comment_likes (comment_id, user_id, created_at) VALUES (?, ?, ?);`,
      ).run(commentId, userId, new Date().toISOString());
      db.prepare(
        `UPDATE comments SET like_count = like_count + 1 WHERE id = ?;`,
      ).run(commentId);
      const row = db.prepare(
        `SELECT like_count FROM comments WHERE id = ?;`,
      ).get(commentId) as { like_count: number };
      return row.like_count;
    });
  } catch (err) {
    if (err instanceof Error && err.message.includes("UNIQUE constraint")) {
      throw new APIException(409, "Already liked");
    }
    throw err;
  }
  // The like is committed: a failed notification must not report it as failed.
  try {
    notifyCommentOwnerLike(userId, commentId);
  } catch { /* ignore */ }
  return { likeCount, isPrivate };
}

/**
 * Takes back `userId`'s like on a comment. It doesn't check that the user can
 * still see the comment, since a like on a dump that has gone private is still
 * theirs to take back.
 *
 * @throws {APIException} 404 when the user doesn't like the comment.
 */
export function removeCommentLike(
  commentId: string,
  userId: string,
): LikeResult {
  const dumpRow = db.prepare(
    `SELECT d.is_private FROM comments c JOIN dumps d ON d.id = c.dump_id
     WHERE c.id = ?;`,
  ).get(commentId) as { is_private: number } | undefined;
  const isPrivate = Boolean(dumpRow?.is_private);
  return transaction(() => {
    const result = db.prepare(
      `DELETE FROM comment_likes WHERE comment_id = ? AND user_id = ?;`,
    ).run(commentId, userId);
    if (result.changes === 0) {
      throw new APIException(404, "Like not found");
    }
    db.prepare(
      `UPDATE comments SET like_count = like_count - 1 WHERE id = ?;`,
    ).run(commentId);
    const row = db.prepare(
      `SELECT like_count FROM comments WHERE id = ?;`,
    ).get(commentId) as { like_count: number };
    return { likeCount: row.like_count, isPrivate };
  });
}

/**
 * Returns the ids of the comments `userId` likes. The WebSocket route sends
 * them in its `welcome` message, and the client shows those like buttons
 * pressed.
 */
export function getUserCommentLikes(userId: string): string[] {
  const rows = db.prepare(
    `SELECT comment_id FROM comment_likes WHERE user_id = ?;`,
  ).all(userId) as { comment_id: string }[];
  return rows.map((r) => r.comment_id);
}

/**
 * Returns a page of the users who like a comment, latest like first, for
 * `GET /api/comments/:commentId/likers`. It doesn't check that the caller may
 * see the comment: the route does that first, with `getDump`.
 *
 * @throws {APIException} 500 when a row doesn't parse as a user.
 */
export function getCommentLikers(
  commentId: string,
  page: number,
  limit: number,
): Page<User> {
  const offset = (page - 1) * limit;

  const rawRows = db.prepare(
    `SELECT u.id, u.username, u.password_hash, u.role, u.created_at, u.updated_at,
            u.avatar_mime, u.description, u.invited_by, u.email,
            i.username as invited_by_username
     FROM users u
     LEFT JOIN users i ON i.id = u.invited_by
     INNER JOIN comment_likes cl ON cl.comment_id = ? AND cl.user_id = u.id
     ORDER BY cl.created_at DESC
     LIMIT ? OFFSET ?;`,
  ).all(commentId, limit + 1, offset);

  if (!rawRows.every(isUserRow)) {
    throw new APIException(500, "Malformed user data");
  }

  return pageOf(rawRows.map(userRowToApi), limit);
}