<?php

declare(strict_types=1);

// Example migration with a database.
//
// $context["pdo"] is the connection from MANAGE_BACKUP_DATABASE.
// Idempotent: checks first whether the index already exists. MySQL has no
// "ADD INDEX IF NOT EXISTS", hence the query against information_schema.

return function (array $context): void {
    if (!isset($context["pdo"])) {
        throw new RuntimeException(
            "This migration needs a database. MANAGE_BACKUP_DATABASE is not configured.",
        );
    }

    /** @var PDO $pdo */
    $pdo = $context["pdo"];

    $statement = $pdo->prepare(
        "SELECT COUNT(*) FROM information_schema.statistics
         WHERE table_schema = DATABASE()
           AND table_name = :table
           AND index_name = :index",
    );
    $statement->execute(["table" => "orders", "index" => "idx_orders_created"]);

    if ((int) $statement->fetchColumn() > 0) {
        return;
    }

    $pdo->exec("ALTER TABLE orders ADD INDEX idx_orders_created (created_at)");
};