/**
 * Indexes for the queries that ran as full scans.
 *
 * - feeds page by created_at (newest first), a user's dumps and upvotes by
 *   (user_id, created_at) — these replace the bare user_id indexes;
 * - dump and playlist pages are looked up by slug;
 * - the child side of every ON DELETE CASCADE / SET NULL foreign key, which
 *   SQLite otherwise scans on each parent delete (a comment's replies, a user's
 *   comments, follows, chat messages, invites, reset tokens), and the
 *   followers of a user or playlist, read on every new dump;
 * - @mentions resolve usernames case-insensitively, by lower(username).
 *
 * Idempotent: also runs against fresh databases created from schema.sql, where
 * these indexes already exist.
 *
 * @module
 */

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

/** Applies this migration to `db`. */
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));
  `);
}