JSON form schema to validation rules

<?php

namespace App\Forms;

use Illuminate\Support\Facades\Validator;
use Illuminate\Validation\Rule;

/**
 * Field shape: {"key":"email","label":"Work email","type":"email","required":true,
 *               "options":["a","b"],"min":1,"max":5}
 */
final class SchemaRules
{
    /** @param  list<array<string,mixed>>  $fields */
    public static function rules(array $fields): array
    {
        $rules = [];

        foreach ($fields as $f) {
            $key = 'answers.'.$f['key'];
            $base = ($f['required'] ?? false) ? ['required'] : ['nullable'];

            $type = match ($f['type']) {
                'text' => ['string', 'max:'.($f['max'] ?? 255)],
                'textarea' => ['string', 'max:'.($f['max'] ?? 5000)],
                'email' => ['email:rfc', 'max:255'],
                'url' => ['url', 'max:2048'],
                'number' => ['numeric', ...self::bounds($f)],
                'date' => ['date'],
                'checkbox' => ['boolean'],
                'select', 'radio' => ['string', Rule::in($f['options'] ?? [])],
                'multiselect' => ['array', ...self::bounds($f)],
                default => ['prohibited'], // unknown types can never be submitted
            };

            $rules[$key] = [...$base, ...$type];

            if ($f['type'] === 'multiselect') {
                $rules[$key.'.*'] = ['string', Rule::in($f['options'] ?? [])];
            }
        }

        return $rules;
    }

    public static function attributes(array $fields): array
    {
        return collect($fields)->mapWithKeys(fn ($f) => ['answers.'.$f['key'] => $f['label'] ?? $f['key']])->all();
    }

    /** Validate a submission and return only the answers the schema knows about. */
    public static function validate(array $fields, array $input): array
    {
        $v = Validator::make($input, self::rules($fields), [], self::attributes($fields));

        return $v->validate()['answers'] ?? [];
    }

    private static function bounds(array $f): array
    {
        return array_filter([
            isset($f['min']) ? 'min:'.$f['min'] : null,
            isset($f['max']) ? 'max:'.$f['max'] : null,
        ]);
    }
}