/**
 * Adds indexes for the queries that scanned a whole table. The feeds page
 * dumps by `created_at`, and a user's dumps and upvotes by `(user_id,
 * created_at)`, which replace the indexes on `user_id` alone. Dumps and
 * playlists are looked up by slug. Each foreign key with ON DELETE gets an
 * index on its child column, which SQLite otherwise scans on every delete of
 * a parent row, and the followers of a user or playlist are read on every new
 * dump. Mentions look usernames up by `lower(username)`.
 *
 * @module
 */

import type { DatabaseSync } from "node:sqlite";

/**
 * Run once by `runMigrations`. A database made from schema.sql already has
 * these indexes.
 */
export function up(db: DatabaseSync): void {
  db.exec(`
    DROP INDEX IF EXISTS idx_dumps_user;
    DROP INDEX IF EXISTS idx_votes_user;
    CREATE INDEX IF NOT EXISTS idx_dumps_created        ON dumps(created_at);
    CREATE INDEX IF NOT EXISTS idx_dumps_user_created   ON dumps(user_id, created_at);
    CREATE INDEX IF NOT EXISTS idx_dumps_slug           ON dumps(slug);
    CREATE INDEX IF NOT EXISTS idx_votes_user_created   ON votes(user_id, created_at);
    CREATE INDEX IF NOT EXISTS idx_playlists_slug       ON playlists(slug);
    CREATE INDEX IF NOT EXISTS idx_comments_parent      ON comments(parent_id);
    CREATE INDEX IF NOT EXISTS idx_comments_user        ON comments(user_id);
    CREATE INDEX IF NOT EXISTS idx_follows_followed_user     ON follows(followed_user_id);
    CREATE INDEX IF NOT EXISTS idx_follows_followed_playlist ON follows(followed_playlist_id);
    CREATE INDEX IF NOT EXISTS idx_chat_messages_user   ON chat_messages(user_id);
    CREATE INDEX IF NOT EXISTS idx_invites_inviter      ON invites(inviter_id);
    CREATE INDEX IF NOT EXISTS idx_users_invited_by     ON users(invited_by);
    CREATE INDEX IF NOT EXISTS idx_password_reset_tokens_user ON password_reset_tokens(user_id);
    CREATE INDEX IF NOT EXISTS idx_users_username_lower ON users(lower(username));
  `);
}