/**
 * Opens the database at {@link DB_PATH} when first imported, creating it from
 * schema.sql if the file doesn't exist, then applies the pending migrations
 * and runs the startup tasks before any importer runs. Only the services
 * import it.
 *
 * @module
 */

import { DatabaseSync } from "node:sqlite";
import { DB_PATH } from "../config.ts";
import { runMigrations } from "./migrate.ts";
import { runStartupTasks } from "./startup.ts";

const isNew = await Deno.stat(DB_PATH).then(() => false, () => true);

/**
 * Serves every query of the server, as its only connection. Its queries are
 * synchronous, so each one blocks the event loop while it runs.
 */
export const db: DatabaseSync = new DatabaseSync(DB_PATH);
// schema.sql holds every migration's change, so on a new database each
// migration below finds its work done and is only recorded.
if (isNew) {
  db.exec(
    await Deno.readTextFile(new URL("./schema.sql", import.meta.url)),
  );
}
// WAL lets readers run alongside a writer, and with synchronous = NORMAL a
// commit doesn't wait on an fsync: a power loss can lose the last commits but
// never corrupts the file. busy_timeout makes another connection to the file
// wait for the lock instead of failing. SQLite enforces foreign keys, and so
// the schema's ON DELETE cascades, only when each connection asks.
db.exec(`
  PRAGMA journal_mode = WAL;
  PRAGMA synchronous = NORMAL;
  PRAGMA busy_timeout = 5000;
  PRAGMA foreign_keys = ON;
`);
runMigrations(db);
await runStartupTasks(db);

/**
 * Runs `fn` in a transaction, so its writes commit together, in one commit
 * rather than one each, and a throw rolls them all back and rethrows. A call
 * inside another joins the outer transaction. `fn` must be synchronous: an
 * `await` would commit before the rest of it runs.
 */
export function transaction<T>(fn: () => T): T {
  if (db.isTransaction) return fn();
  db.exec("BEGIN;");
  try {
    const result = fn();
    db.exec("COMMIT;");
    return result;
  } catch (err) {
    db.exec("ROLLBACK;");
    throw err;
  }
}