<?php

declare(strict_types=1);

// Example migration for a project with JSON files: adds a new field to
// every existing record.
//
// Idempotent: already-updated records stay unchanged, so the migration can
// safely run again after a partial failure.

return function (array $context): void {
    $file = $context["app_root"] . "/data/products.json";
    if (!is_file($file)) {
        return;
    }

    $data = json_decode((string) file_get_contents($file), true);
    if (!is_array($data)) {
        throw new RuntimeException("products.json is not readable or not valid JSON.");
    }

    $changed = false;
    foreach ($data as $index => $product) {
        if (is_array($product) && !array_key_exists("category_id", $product)) {
            $data[$index]["category_id"] = null;
            $changed = true;
        }
    }

    if (!$changed) {
        return;
    }

    $json = json_encode(
        $data,
        JSON_PRETTY_PRINT | JSON_UNESCAPED_UNICODE | JSON_UNESCAPED_SLASHES,
    );
    if ($json === false) {
        throw new RuntimeException("products.json could not be encoded.");
    }

    // Write atomically, so an interruption never leaves a half-written file.
    $tmpFile = $file . ".tmp";
    if (file_put_contents($tmpFile, $json, LOCK_EX) === false || !rename($tmpFile, $file)) {
        @unlink($tmpFile);
        throw new RuntimeException("products.json could not be written.");
    }
};