Cache API Responses with TTL in PHP

<?php

/**
 * Fetches data from an API, with a caching mechanism.
 * Caches responses to a local file with a Time-To-Live (TTL).
 *
 * @param string $apiUrl The URL of the API endpoint.
 * @param int $ttlSeconds Time-to-Live for the cache in seconds.
 * @param string $cacheDir Directory to store cache files.
 * @return array|null Decoded API response data or null on failure.
 */
function fetchApiWithCache(string $apiUrl, int $ttlSeconds = 3600, string $cacheDir = 'cache/api_cache'): ?array
{
    if (!is_dir($cacheDir)) {
        mkdir($cacheDir, 0777, true);
    }

    $cacheKey = md5($apiUrl);
    $cacheFile = $cacheDir . '/' . $cacheKey . '.json';

    // Check if cache exists and is still valid
    if (file_exists($cacheFile) && (time() - filemtime($cacheFile) < $ttlSeconds)) {
        $cachedData = file_get_contents($cacheFile);
        if ($cachedData !== false) {
            error_log("Serving from cache: " . $apiUrl);
            return json_decode($cachedData, true);
        }
    }

    // Cache is expired or doesn't exist, fetch from API
    error_log("Fetching from API: " . $apiUrl);
    $response = @file_get_contents($apiUrl); // Using @ to suppress warnings for failed fetches

    if ($response === false) {
        error_log("Failed to fetch data from API: " . $apiUrl);
        return null;
    }

    $data = json_decode($response, true);

    if (json_last_error() === JSON_ERROR_NONE) {
        // Store valid response in cache
        file_put_contents($cacheFile, $response);
        return $data;
    } else {
        error_log("Failed to decode JSON from API: " . $apiUrl . " - " . json_last_error_msg());
        return null;
    }
}

// Example usage:
// $data = fetchApiWithCache('https://jsonplaceholder.typicode.com/posts/1', 60); // Cache for 60 seconds
//
// if ($data) {
//     echo "API Data (cached or fresh):
";
//     print_r($data);
// } else {
//     echo "Could not retrieve API data.
";
// }
//
// // Subsequent calls within 60 seconds will use the cache
// $data2 = fetchApiWithCache('https://jsonplaceholder.typicode.com/posts/1', 60);
//
// $data_different = fetchApiWithCache('https://jsonplaceholder.typicode.com/posts/2', 300); // Different endpoint, different cache
?>