<?php
class JWTHelper {
    private static function base64UrlEncode($data) {
        return str_replace(['+', '/', '='], ['-', '_', ''], base64_encode($data));
    }

    private static function base64UrlDecode($data) {
        $remainder = strlen($data) % 4;
        if ($remainder) {
            $padlen = 4 - $remainder;
            $data .= str_repeat('=', $padlen);
        }
        return base64_decode(str_replace(['-', '_'], ['+', '/'], $data));
    }

    /**
     * Encode payload into JWT
     */
    public static function encode($payload, $secret, $expiry = 86400) {
        $header = json_encode(['alg' => 'HS256', 'typ' => 'JWT']);
        
        $payload['exp'] = time() + $expiry;
        $payload['iat'] = time();
        
        $base64UrlHeader = self::base64UrlEncode($header);
        $base64UrlPayload = self::base64UrlEncode(json_encode($payload));
        
        $signature = hash_hmac('sha256', $base64UrlHeader . "." . $base64UrlPayload, $secret, true);
        $base64UrlSignature = self::base64UrlEncode($signature);
        
        return $base64UrlHeader . "." . $base64UrlPayload . "." . $base64UrlSignature;
    }

    /**
     * Decode and verify JWT
     */
    public static function decode($token, $secret) {
        $parts = explode('.', $token);
        if (count($parts) !== 3) {
            return false;
        }
        
        list($base64UrlHeader, $base64UrlPayload, $base64UrlSignature) = $parts;
        
        $signature = self::base64UrlDecode($base64UrlSignature);
        $expectedSignature = hash_hmac('sha256', $base64UrlHeader . "." . $base64UrlPayload, $secret, true);
        
        if (!hash_equals($signature, $expectedSignature)) {
            return false;
        }
        
        $payloadDecoded = self::base64UrlDecode($base64UrlPayload);
        $data = json_decode($payloadDecoded, true);
        
        if (!$data) {
            return false;
        }
        
        if (isset($data['exp']) && $data['exp'] < time()) {
            return false; // Token is expired
        }
        
        return $data;
    }
}