<?php

namespace AOP\App\Database;

/**
 * Runs writes as one unit: all of them, or none. Inside a transaction that somebody else started (the tests of the
 * WordPress suite do) it uses a savepoint, so it never commits what is not its own.
 */
final class Transaction
{
    /**
     * @return \wpdb
     */
    private static function wpdb()
    {
        global $wpdb;

        return $wpdb;
    }

    /**
     * @param callable $work
     *
     * @return mixed What $work returns.
     *
     * @throws \Throwable What $work throws, after everything it wrote has been rolled back.
     */
    public static function run(callable $work)
    {
        $db = self::wpdb();
        $nested = (string) $db->get_var('SELECT @@autocommit') === '0';

        $db->query($nested ? 'SAVEPOINT aop_transaction' : 'START TRANSACTION');

        try {
            $result = $work();
        } catch (\Throwable $failure) {
            $db->query($nested ? 'ROLLBACK TO SAVEPOINT aop_transaction' : 'ROLLBACK');

            // What was cached while the rows were there is not true anymore.
            wp_cache_flush();

            throw $failure;
        }

        $db->query($nested ? 'RELEASE SAVEPOINT aop_transaction' : 'COMMIT');

        return $result;
    }

    /**
     * @return bool True when the tables that an import writes to can roll back (InnoDB).
     */
    public static function supported(): bool
    {
        $db = self::wpdb();

        foreach ([PageRepository::tableName(), $db->options] as $table) {
            $engine = $db->get_var($db->prepare(
                'SELECT ENGINE FROM information_schema.TABLES WHERE TABLE_SCHEMA = DATABASE() AND TABLE_NAME = %s',
                $table
            ));

            if (strtolower((string) $engine) !== 'innodb') {
                return false;
            }
        }

        return true;
    }
}