/**
 * Stores notifications, pushes each new one to its user's sockets as
 * `notification_created`, and reads them back for `routes/notifications.ts`.
 * The services of follows, votes, likes, comments, dumps, playlists and the
 * chat call its `notify…` triggers. Every trigger passes a source key, so the
 * same event never notifies a user twice. What a notification names by id is
 * joined each time it is sent ({@link withCurrentRefs}), so its names and
 * links follow renames.
 *
 * @module
 */

import type {
  Notification,
  NotificationData,
  NotificationType,
  UserDumpPostedData,
} from "../../shared/notification.ts";
import { APIException } from "../lib/api-exception.ts";
import { db, transaction } from "../db/connection.ts";
import {
  isNotificationRow,
  notificationRowToApi,
} from "../model/notification.ts";
import { type Page, pageOf } from "../lib/pagination.ts";
import { sendToUser } from "./ws-service.ts";
import { mentionedUsernames } from "../../shared/mention.ts";

/** Each id of a user a notification names, beside the field of their name. */
const USER_FIELDS = [
  ["followerId", "followerUsername"],
  ["dumperId", "dumperUsername"],
  ["voterId", "voterUsername"],
  ["mentionerId", "mentionerUsername"],
  ["commenterId", "commenterUsername"],
  ["likerId", "likerUsername"],
] as const;

/**
 * Returns `data` with what may have changed since it was stored joined from
 * the database: each user's current name, and the slug and owner of its dump
 * and playlist, which the client builds their paths from. A user since deleted
 * keeps their stored name; a deleted dump or playlist gets no ref, and so no
 * link. Every notification the server sends goes through it, and so do the
 * digests.
 */
export function withCurrentRefs(data: NotificationData): NotificationData {
  const fields = data as unknown as Record<string, string | undefined>;
  const out: Record<string, string | undefined> = { ...fields };
  for (const [idField, nameField] of USER_FIELDS) {
    const id = fields[idField];
    if (!id) continue;
    const row = db.prepare(`SELECT username FROM users WHERE id = ?;`).get(
      id,
    ) as { username: string } | undefined;
    if (row) out[nameField] = row.username;
  }
  const context = fields.contextType;
  const dumpId = fields.dumpId ??
    (context === "dump" ? fields.contextId : undefined);
  const playlistId = fields.playlistId ??
    (context === "playlist" ? fields.contextId : undefined);
  const ref = (table: string, id: string) =>
    db.prepare(
      `SELECT t.slug, u.username FROM ${table} t JOIN users u ON u.id = t.user_id
        WHERE t.id = ?;`,
    ).get(id) as { slug: string; username: string } | undefined;
  if (dumpId) {
    const row = ref("dumps", dumpId);
    out.dumpSlug = row?.slug;
    out.dumpOwnerUsername = row?.username;
  }
  if (playlistId) {
    const row = ref("playlists", playlistId);
    out.playlistSlug = row?.slug;
    out.playlistOwnerUsername = row?.username;
  }
  return out as unknown as NotificationData;
}

/**
 * Stores a notification for `userId` and pushes it live. With a `sourceKey`,
 * a second one for the same `(userId, sourceKey)` is neither stored nor sent.
 */
function createNotification(
  userId: string,
  type: NotificationType,
  data: NotificationData,
  sourceKey: string | null = null,
): void {
  const id = crypto.randomUUID();
  const now = new Date();
  const createdAt = now.toISOString();
  const dataJson = JSON.stringify(data);

  let changes: number;

  if (sourceKey) {
    const result = db.prepare(
      `INSERT OR IGNORE INTO notifications (id, user_id, type, data, read, created_at, source_key)
       VALUES (?, ?, ?, ?, 0, ?, ?);`,
    ).run(id, userId, type, dataJson, createdAt, sourceKey);
    changes = result.changes as number;
  } else {
    const result = db.prepare(
      `INSERT INTO notifications (id, user_id, type, data, read, created_at, source_key)
       VALUES (?, ?, ?, ?, 0, ?, NULL);`,
    ).run(id, userId, type, dataJson, createdAt);
    changes = result.changes as number;
  }

  if (changes > 0) {
    sendToUser(userId, {
      type: "notification_created",
      notification: {
        id,
        userId,
        type,
        data: withCurrentRefs(data),
        read: false,
        createdAt: now,
      },
    });
  }
}

/**
 * Returns a page of `userId`'s notifications, newest first, with their refs
 * joined, for `GET /api/me/notifications`.
 *
 * @throws {APIException} 500 when a row doesn't parse.
 */
export function getNotificationsForUser(
  userId: string,
  page: number,
  limit: number,
): Page<Notification> {
  const offset = (page - 1) * limit;
  const rawRows = db.prepare(
    `SELECT * FROM notifications WHERE user_id = ? ORDER BY created_at DESC LIMIT ? OFFSET ?;`,
  ).all(userId, limit + 1, offset);

  if (!rawRows.every(isNotificationRow)) {
    throw new APIException(500, "Malformed notification data");
  }
  return pageOf(
    rawRows.map(notificationRowToApi).map((n) => ({
      ...n,
      data: withCurrentRefs(n.data),
    })),
    limit,
  );
}

/**
 * Returns how many of `userId`'s notifications are unread. The WebSocket route
 * sends it in its `welcome` message, for the bell's count.
 */
export function getUnreadCount(userId: string): number {
  const row = db.prepare(
    `SELECT COUNT(*) as count FROM notifications WHERE user_id = ? AND read = 0;`,
  ).get(userId) as { count: number } | undefined;
  return row?.count ?? 0;
}

/**
 * Marks every notification of `userId` read, when they open the
 * `/notifications` page.
 */
export function markAllRead(userId: string): void {
  db.prepare(`UPDATE notifications SET read = 1 WHERE user_id = ?;`).run(
    userId,
  );
}

/**
 * Notifies `followedUserId` that `followerId` follows them, once however often
 * they unfollow and follow again. `followUser` calls it.
 */
export function notifyUserNewFollower(
  followerId: string,
  followedUserId: string,
): void {
  const followerRow = db.prepare(
    `SELECT username FROM users WHERE id = ?;`,
  ).get(followerId) as { username: string } | undefined;

  if (!followerRow) return;

  createNotification(
    followedUserId,
    "user_followed",
    { followerId, followerUsername: followerRow.username },
    `user-followed:${followedUserId}:${followerId}`,
  );
}

/**
 * Notifies a playlist's owner that `followerId` follows it, unless they are
 * the owner, and once however often they unfollow and follow again.
 * `followPlaylist` calls it.
 */
export function notifyPlaylistOwnerNewFollower(
  followerId: string,
  playlistId: string,
): void {
  const followerRow = db.prepare(
    `SELECT username FROM users WHERE id = ?;`,
  ).get(followerId) as { username: string } | undefined;

  const playlistRow = db.prepare(
    `SELECT title, user_id FROM playlists WHERE id = ?;`,
  ).get(playlistId) as { title: string; user_id: string } | undefined;

  if (!followerRow || !playlistRow) return;
  if (followerId === playlistRow.user_id) return;

  createNotification(
    playlistRow.user_id,
    "playlist_followed",
    {
      followerId,
      followerUsername: followerRow.username,
      playlistId,
      playlistTitle: playlistRow.title,
    },
    `followed:${playlistId}:${followerId}`,
  );
}

/**
 * Notifies everyone following `dumperId` that they posted a dump. The dump
 * service calls it for a public dump only, when it is created or goes public.
 * A follower is told of a dump once, however often it goes private and public
 * again.
 */
export function notifyUserFollowersNewDump(
  dumperId: string,
  dumpId: string,
  dumpTitle: string,
): void {
  const posterRow = db.prepare(
    `SELECT username FROM users WHERE id = ?;`,
  ).get(dumperId) as { username: string } | undefined;
  if (!posterRow) return;

  const followerRows = db.prepare(
    `SELECT follower_id FROM follows WHERE followed_user_id = ?;`,
  ).all(dumperId) as { follower_id: string }[];

  if (followerRows.length === 0) return;

  const data: UserDumpPostedData = {
    dumperId,
    dumperUsername: posterRow.username,
    dumpId,
    dumpTitle,
  };
  const dataJson = JSON.stringify(data);
  const sent = withCurrentRefs(data);
  const now = new Date();
  const createdAt = now.toISOString();
  const sourceKey = `dump:${dumpId}`;

  // One insert per follower, so that only the rows actually stored are sent,
  // each with its stored id: the client dedupes a refetch against it.
  const insert = db.prepare(
    `INSERT OR IGNORE INTO notifications (id, user_id, type, data, read, created_at, source_key)
     VALUES (?, ?, ?, ?, 0, ?, ?);`,
  );

  // One transaction for the whole fan-out: a commit per follower is what made
  // a popular user's dump slow to post. The live events go out inside it, but
  // the commit follows in the same tick, before any client can ask back.
  transaction(() => {
    for (const row of followerRows) {
      const id = crypto.randomUUID();
      const result = insert.run(
        id,
        row.follower_id,
        "user_dump_posted",
        dataJson,
        createdAt,
        sourceKey,
      );
      if ((result.changes as number) > 0) {
        sendToUser(row.follower_id, {
          type: "notification_created",
          notification: {
            id,
            userId: row.follower_id,
            type: "user_dump_posted",
            data: sent,
            read: false,
            createdAt: now,
          },
        });
      }
    }
  });
}

/**
 * Notifies a dump's poster that `voterId` upvoted it, unless they are the
 * poster, and once however often the vote is withdrawn and cast again.
 * `castVote` calls it.
 */
export function notifyDumpOwnerUpvote(
  voterId: string,
  dumpId: string,
): void {
  const voterRow = db.prepare(
    `SELECT username FROM users WHERE id = ?;`,
  ).get(voterId) as { username: string } | undefined;

  const dumpRow = db.prepare(
    `SELECT title, user_id FROM dumps WHERE id = ?;`,
  ).get(dumpId) as { title: string; user_id: string } | undefined;

  if (!voterRow || !dumpRow) return;
  if (voterId === dumpRow.user_id) return;

  createNotification(
    dumpRow.user_id,
    "dump_upvoted",
    {
      voterId,
      voterUsername: voterRow.username,
      dumpId,
      dumpTitle: dumpRow.title,
    },
    `upvote:${dumpId}:${voterId}`,
  );
}

/**
 * Notifies every user @mentioned in `body`, except its author, that they were
 * mentioned in the comment, dump, playlist or chat message `contextId`. Call
 * it again after each edit: a user already notified for this context isn't
 * notified twice. `skipUserId` spares a mentioned user; the chat uses it for
 * those who have it open.
 */
export function notifyMentions(
  mentionerUserId: string,
  body: string,
  contextType: "comment" | "dump" | "playlist" | "chat",
  contextId: string,
  contextTitle: string,
  dumpId?: string,
  skipUserId?: (userId: string) => boolean,
): void {
  const mentionerRow = db.prepare(
    `SELECT username FROM users WHERE id = ?;`,
  ).get(mentionerUserId) as { username: string } | undefined;
  if (!mentionerRow) return;

  const usernames = mentionedUsernames(body);

  for (const username of usernames) {
    const mentionedRow = db.prepare(
      `SELECT id FROM users WHERE lower(username) = ?;`,
    ).get(username) as { id: string } | undefined;
    if (!mentionedRow || mentionedRow.id === mentionerUserId) continue;
    if (skipUserId?.(mentionedRow.id)) continue;

    createNotification(
      mentionedRow.id,
      "user_mentioned",
      {
        mentionerId: mentionerUserId,
        mentionerUsername: mentionerRow.username,
        contextType,
        contextId,
        contextTitle,
        dumpId,
      },
      `mention:${contextType}:${contextId}:${mentionedRow.id}`,
    );
  }
}

/**
 * Notifies a dump's poster that `commenterId` commented on it, unless they are
 * the poster. `createComment` calls it for replies too, but not on an edit.
 */
export function notifyDumpOwnerNewComment(
  commenterId: string,
  commentId: string,
  dumpId: string,
): void {
  const commenterRow = db.prepare(
    `SELECT username FROM users WHERE id = ?;`,
  ).get(commenterId) as { username: string } | undefined;

  const dumpRow = db.prepare(
    `SELECT title, user_id FROM dumps WHERE id = ?;`,
  ).get(dumpId) as { title: string; user_id: string } | undefined;

  if (!commenterRow || !dumpRow) return;
  if (commenterId === dumpRow.user_id) return;

  createNotification(
    dumpRow.user_id,
    "dump_commented",
    {
      commenterId,
      commenterUsername: commenterRow.username,
      commentId,
      dumpId,
      dumpTitle: dumpRow.title,
    },
    `comment:${commentId}`,
  );
}

/**
 * Notifies a comment's author that `likerId` likes it, unless they are the
 * author, and once however often the like is withdrawn and given again.
 */
export function notifyCommentOwnerLike(
  likerId: string,
  commentId: string,
): void {
  const likerRow = db.prepare(
    `SELECT username FROM users WHERE id = ?;`,
  ).get(likerId) as { username: string } | undefined;

  const commentRow = db.prepare(
    `SELECT c.user_id, c.dump_id, d.title as dump_title
     FROM comments c JOIN dumps d ON c.dump_id = d.id WHERE c.id = ?;`,
  ).get(commentId) as
    | { user_id: string; dump_id: string; dump_title: string }
    | undefined;

  if (!likerRow || !commentRow) return;
  if (likerId === commentRow.user_id) return;

  createNotification(
    commentRow.user_id,
    "comment_liked",
    {
      likerId,
      likerUsername: likerRow.username,
      commentId,
      dumpId: commentRow.dump_id,
      dumpTitle: commentRow.dump_title,
    },
    `like:${commentId}:${likerId}`,
  );
}

/**
 * Notifies everyone following a playlist that a dump was added to it. The
 * playlist service calls it only when both are public, since a follower can't
 * open a private one.
 */
export function notifyPlaylistFollowersNewDump(
  playlistId: string,
  playlistTitle: string,
  dumpId: string,
  dumpTitle: string,
): void {
  const followerRows = db.prepare(
    `SELECT follower_id FROM follows WHERE followed_playlist_id = ?;`,
  ).all(playlistId) as { follower_id: string }[];

  transaction(() => {
    for (const row of followerRows) {
      createNotification(
        row.follower_id,
        "playlist_dump_added",
        { dumpId, dumpTitle, playlistId, playlistTitle },
        `pdump:${playlistId}:${dumpId}`,
      );
    }
  });
}

/**
 * Notifies the followers of each playlist of the dumps in it that became
 * visible to them: a playlist's followers are told of a dump once both are
 * public. The dump service calls it with `dumpId` when a dump goes public, for
 * each public playlist holding it; the playlist service with `playlistId`
 * when a playlist goes public, for each public dump in it, from the bottom of
 * the playlist up. A dump the followers were told of before either went
 * private isn't notified again. Adding a dump to a public playlist calls
 * {@link notifyPlaylistFollowersNewDump} directly.
 */
export function notifyPlaylistFollowersNowPublic(
  of: { dumpId: string } | { playlistId: string },
): void {
  const [column, id] = "dumpId" in of
    ? ["pd.dump_id", of.dumpId]
    : ["pd.playlist_id", of.playlistId];
  const rows = db.prepare(
    `SELECT p.id AS playlist_id, p.title AS playlist_title,
            d.id AS dump_id, d.title AS dump_title
       FROM playlist_dumps pd
       JOIN playlists p ON p.id = pd.playlist_id
       JOIN dumps d ON d.id = pd.dump_id
      WHERE ${column} = ? AND p.is_public = 1 AND d.is_private = 0
      ORDER BY pd.position DESC;`,
  ).all(id) as {
    playlist_id: string;
    playlist_title: string;
    dump_id: string;
    dump_title: string;
  }[];

  transaction(() => {
    for (const row of rows) {
      notifyPlaylistFollowersNewDump(
        row.playlist_id,
        row.playlist_title,
        row.dump_id,
        row.dump_title,
      );
    }
  });
}