Custom Sorting Associative Arrays by Multiple Keys in PHP

<?php

/**
 * Sorts an array of associative arrays by a specified key and order.
 * Can handle multiple sort criteria.
 *
 * @param array $data The array to sort.
 * @param array $sortFields An array of arrays, e.g., [['field' => 'name', 'order' => 'ASC'], ['field' => 'age', 'order' => 'DESC']]
 * @return array The sorted array.
 */
function sortAssociativeArray(array $data, array $sortFields): array
{
    usort($data, function ($a, $b) use ($sortFields) {
        foreach ($sortFields as $sortField) {
            $field = $sortField['field'];
            $order = strtoupper($sortField['order'] ?? 'ASC'); // Default to ASC

            if (!isset($a[$field]) || !isset($b[$field])) {
                // Handle cases where field might be missing (e.g., throw error, skip, or default comparison)
                continue; 
            }

            $cmp = ($a[$field] <=> $b[$field]); // Spaceship operator (PHP 7+)

            if ($cmp !== 0) {
                return ($order === 'DESC') ? -$cmp : $cmp;
            }
        }
        return 0; // Elements are equal based on all criteria
    });
    return $data;
}

// Example Usage:
$users = [
    ['name' => 'Alice', 'age' => 30, 'city' => 'New York'],
    ['name' => 'Bob', 'age' => 25, 'city' => 'London'],
    ['name' => 'Charlie', 'age' => 35, 'city' => 'Paris'],
    ['name' => 'Alice', 'age' => 28, 'city' => 'London'],
    ['name' => 'Bob', 'age' => 40, 'city' => 'New York'],
];

echo "Original Users:
";
foreach ($users as $user) {
    echo json_encode($user) . "
";
}

// Sort by name ASC, then by age DESC
$sortedUsers = sortAssociativeArray($users, [
    ['field' => 'name', 'order' => 'ASC'],
    ['field' => 'age', 'order' => 'DESC']
]);

echo "
Sorted Users (Name ASC, Age DESC):
";
foreach ($sortedUsers as $user) {
    echo json_encode($user) . "
";
}

// Sort by age ASC
$sortedByAge = sortAssociativeArray($users, [['field' => 'age', 'order' => 'ASC']]);

echo "
Sorted Users (Age ASC):
";
foreach ($sortedByAge as $user) {
    echo json_encode($user) . "
";
}
?>