<?php
// File: detail_tagihan.php

// Aktifkan error log
error_reporting(E_ALL);
ini_set('display_errors', 0);

// === Konfigurasi lokasi log ===
$log_file = __DIR__ . '/flow_request.log';

// === Fungsi logging ===
function write_log($data, $file) {
    $log_entry = "[" . date('Y-m-d H:i:s') . "] " . $data . PHP_EOL;
    file_put_contents($file, $log_entry, FILE_APPEND);
}

// === Header default ===
header('Content-Type: application/json');

// === Verifikasi kode publik dari Meta ===
if (isset($_GET['public_code'])) {
    $public_code = $_GET['public_code'];
    // Kirim balik kode publik agar Meta bisa memverifikasi endpoint
    $response = [
        "status" => "ok",
        "public_code" => $public_code
    ];
    write_log("Public Code Verification: " . json_encode($response), $log_file);
    echo json_encode($response);
    exit;
}

// === Baca input JSON dari Meta ===
$raw_input = file_get_contents("php://input");
write_log("Raw Request: " . $raw_input, $log_file);

try {
    $body = json_decode($raw_input, true);
    if (!$body) {
        throw new Exception('Invalid JSON input');
    }

    // Ambil private key dari environment
    $privatePem = getenv('PRIVATE_KEY');
    if (!$privatePem) {
        throw new Exception('Private key not found in environment');
    }

    // Dekripsi request
    $decryptedData = decryptRequest($body, $privatePem);

    // Simulasi ambil data pelanggan (bisa dari DB nantinya)
    $requestData = $decryptedData['decryptedBody'];
    $id_pelanggan = $requestData['id_pelanggan'] ?? 'PLG001';
    $flow_token = $requestData['flow_token'] ?? 'UNKNOWN_TOKEN';

    // Misal data dari database
    $data_tagihan = [
        "id_pelanggan"     => $id_pelanggan,
        "nama_pelanggan"   => "Wian Darussalam",
        "paket_layanan"    => "Internet 20 Mbps",
        "harga_layanan"    => 200000,
        "jumlah_potongan"  => 0,
        "jumlah_tagihan"   => 200000,
        "jumlah_ppn"       => 20000,
        "jumlah_diskon"    => 0,
        "total_tagihan"    => 220000,
        "tanggal_limit"    => "2025-10-30"
    ];

    // === Format respon sesuai panduan Meta untuk DETAIL_TAGIHAN ===
    $screen = [
        "screen" => "DETAIL_TAGIHAN",
        "data" => [
            "extension_message_response" => [
                "params" => [
                    "flow_token" => $flow_token,
                    "id_pelanggan" => $data_tagihan['id_pelanggan'],
                    "nama_pelanggan" => $data_tagihan['nama_pelanggan'],
                    "paket_layanan" => $data_tagihan['paket_layanan'],
                    "harga_layanan" => $data_tagihan['harga_layanan'],
                    "jumlah_potongan" => $data_tagihan['jumlah_potongan'],
                    "jumlah_tagihan" => $data_tagihan['jumlah_tagihan'],
                    "jumlah_ppn" => $data_tagihan['jumlah_ppn'],
                    "jumlah_diskon" => $data_tagihan['jumlah_diskon'],
                    "total_tagihan" => $data_tagihan['total_tagihan'],
                    "tanggal_limit" => $data_tagihan['tanggal_limit']
                ]
            ]
        ]
    ];

    // Enkripsi response
    $resBody = encryptResponse($screen, $decryptedData['aesKeyBuffer'], $decryptedData['initialVectorBuffer']);

    // Tulis log response
    write_log("Response: " . json_encode($screen), $log_file);

    // === Kirim respon ke Meta ===
    echo $resBody;

} catch (Exception $e) {
    $error = ["error" => $e->getMessage()];
    write_log("Error: " . json_encode($error), $log_file);

    http_response_code(500);
    echo json_encode($error);
}

function decryptRequest($body, $privatePem)
{
    $encryptedAesKey = base64_decode($body['encrypted_aes_key']);
    $encryptedFlowData = base64_decode($body['encrypted_flow_data']);
    $initialVector = base64_decode($body['initial_vector']);

    // Load private key
    $privateKey = openssl_pkey_get_private($privatePem);
    if (!$privateKey) {
        throw new Exception('Failed to load private key');
    }

    // Decrypt the AES key
    $decryptedAesKey = '';
    if (!openssl_private_decrypt($encryptedAesKey, $decryptedAesKey, $privateKey, OPENSSL_PKCS1_OAEP_PADDING)) {
        throw new Exception('Decryption of AES key failed');
    }

    // Decrypt the Flow data using AES-GCM
    $tagLength = 16;
    $encryptedFlowDataBody = substr($encryptedFlowData, 0, -$tagLength);
    $tag = substr($encryptedFlowData, -$tagLength);

    $decrypted = openssl_decrypt($encryptedFlowDataBody, 'aes-128-gcm', $decryptedAesKey, OPENSSL_RAW_DATA, $initialVector, $tag);
    if ($decrypted === false) {
        throw new Exception('Decryption of flow data failed');
    }

    return [
        'decryptedBody' => json_decode($decrypted, true),
        'aesKeyBuffer' => $decryptedAesKey,
        'initialVectorBuffer' => $initialVector,
    ];
}

function encryptResponse($response, $aesKeyBuffer, $initialVectorBuffer)
{
    // Flip the initialization vector
    $flipped_iv = ~$initialVectorBuffer;

    // Encrypt the response data using AES-GCM
    $cipher = openssl_encrypt(json_encode($response), 'aes-128-gcm', $aesKeyBuffer, OPENSSL_RAW_DATA, $flipped_iv, $tag);
    if ($cipher === false) {
        throw new Exception('Encryption of response failed');
    }

    return base64_encode($cipher . $tag);
}
?>