Caching External API Responses in PHP with TTL

<?php

class ApiCache {
    private $cacheDir;
    private $defaultTtl;

    public function __construct($cacheDir = __DIR__ . '/cache', $defaultTtl = 3600) {
        $this->cacheDir = $cacheDir;
        $this->defaultTtl = $defaultTtl;
        if (!is_dir($this->cacheDir)) {
            mkdir($this->cacheDir, 0777, true);
        }
    }

    private function getCacheFilePath($key) {
        return $this->cacheDir . '/' . md5($key) . '.cache';
    }

    public function get($key) {
        $filePath = $this->getCacheFilePath($key);
        if (file_exists($filePath)) {
            $content = file_get_contents($filePath);
            $data = json_decode($content, true);

            if ($data && isset($data['expiry']) && $data['expiry'] > time()) {
                return $data['value'];
            } else {
                // Cache expired, delete it
                unlink($filePath);
            }
        }
        return null;
    }

    public function set($key, $value, $ttl = null) {
        $ttl = $ttl ?? $this->defaultTtl;
        $filePath = $this->getCacheFilePath($key);
        $data = [
            'expiry' => time() + $ttl,
            'value' => $value
        ];
        file_put_contents($filePath, json_encode($data));
    }

    public function remember($key, callable $callback, $ttl = null) {
        $cachedValue = $this->get($key);
        if ($cachedValue !== null) {
            return $cachedValue;
        }

        $liveValue = $callback();
        $this->set($key, $liveValue, $ttl);
        return $liveValue;
    }
}

// Example Usage:
// $apiCache = new ApiCache();

// function fetch_user_data_from_api($userId) {
//     echo "Fetching user {$userId} from API...
";
//     // Simulate API call delay
//     sleep(1);
//     return ['id' => $userId, 'name' => 'User ' . $userId, 'email' => "user{$userId}@example.com"];
// }

// // First call - fetches from API and caches for 60 seconds
// $user1 = $apiCache->remember('user_1_data', function() {
//     return fetch_user_data_from_api(1);
// }, 60);
// var_dump($user1);

// // Second call (within 60 seconds) - fetches from cache
// $user1_cached = $apiCache->remember('user_1_data', function() {
//     return fetch_user_data_from_api(1);
// }); // Uses default TTL if not specified
// var_dump($user1_cached);
?>