<?php
/**
 * POST /api/verify-otp
 *
 * Verify an OTP code submitted by the user (Flutter app).
 *
 * Request body:
 *   {
 *     "phone": "+9627XXXXXXXX",
 *     "otp": "4829",
 *     "app_key": "SECRET_APP_KEY"
 *   }
 */

header('Content-Type: application/json; charset=utf-8');
header('Access-Control-Allow-Origin: *');
header('Access-Control-Allow-Methods: POST, OPTIONS');
header('Access-Control-Allow-Headers: Content-Type, X-App-Key');

if ($_SERVER['REQUEST_METHOD'] === 'OPTIONS') {
    http_response_code(204);
    exit;
}

if ($_SERVER['REQUEST_METHOD'] !== 'POST') {
    http_response_code(405);
    echo json_encode(['success' => false, 'message' => 'method_not_allowed']);
    exit;
}

require_once __DIR__ . '/../includes/Database.php';
require_once __DIR__ . '/../includes/Redis.php';
require_once __DIR__ . '/../includes/RateLimit.php';
require_once __DIR__ . '/../includes/Auth.php';
require_once __DIR__ . '/../includes/Logger.php';

// Authenticate — requires app key
Auth::requireAuth('app');

$input = json_decode(file_get_contents('php://input'), true);

if (!$input || !isset($input['phone']) || !isset($input['otp'])) {
    http_response_code(400);
    echo json_encode(['success' => false, 'message' => 'missing_phone_or_otp']);
    RequestLogger::log('verify-otp', 'POST', $input, 400, 'missing_fields');
    exit;
}

$phone = trim($input['phone']);
$otp = trim($input['otp']);

// Validate phone format
if (!preg_match('/^\+[1-9]\d{6,14}$/', $phone)) {
    http_response_code(400);
    echo json_encode(['success' => false, 'message' => 'invalid_phone_format']);
    RequestLogger::log('verify-otp', 'POST', $input, 400, 'invalid_phone');
    exit;
}

// Validate OTP format (3 or 4 digits)
if (!preg_match('/^\d{3,4}$/', $otp)) {
    http_response_code(400);
    echo json_encode(['success' => false, 'message' => 'invalid_otp_format']);
    RequestLogger::log('verify-otp', 'POST', $input, 400, 'invalid_otp_format');
    exit;
}

$redis = RedisClient::getInstance();
$db = Database::getInstance();
$redisKey = "otp:{$phone}";

// Check if OTP exists in Redis
$stored = $redis->get($redisKey);

if ($stored === false || $stored === null) {
    // OTP expired or never existed
    echo json_encode([
        'success' => false,
        'message' => 'expired',
    ]);
    RequestLogger::log('verify-otp', 'POST', $input, 200, 'expired');
    exit;
}

// Decode stored data
if (is_string($stored)) {
    $otpData = json_decode($stored, true);
} else {
    $otpData = $stored;
}

if (!is_array($otpData) || !isset($otpData['otp'])) {
    // Corrupted data — clean up
    $redis->del($redisKey);
    echo json_encode(['success' => false, 'message' => 'expired']);
    RequestLogger::log('verify-otp', 'POST', $input, 200, 'corrupted_data');
    exit;
}

// Check max attempts
if (isset($otpData['attempts']) && (int) $otpData['attempts'] >= MAX_OTP_ATTEMPTS) {
    $redis->del($redisKey);
    echo json_encode([
        'success' => false,
        'message' => 'max_attempts',
    ]);
    RequestLogger::log('verify-otp', 'POST', $input, 200, 'max_attempts');
    exit;
}

// Increment attempt counter
$otpData['attempts'] = (int) ($otpData['attempts'] ?? 0) + 1;
$ttl = $redis->ttl($redisKey);
if ($ttl > 0) {
    $redis->setex($redisKey, $ttl, json_encode($otpData));
}

// Timing-safe comparison
if (hash_equals($otpData['otp'], $otp)) {
    // Success — clean up Redis
    $redis->del($redisKey);

    // Update database
    try {
        $stmt = $db->prepare(
            "UPDATE otp_requests
             SET verified_at = NOW(), status = 'verified'
             WHERE phone = ? AND otp_code = ? AND verified_at IS NULL
             ORDER BY created_at DESC
             LIMIT 1"
        );
        $stmt->execute([$phone, $otp]);
    } catch (\Throwable $e) {
        // Non-critical — OTP is already verified via Redis
        error_log('verify-otp DB update error: ' . $e->getMessage());
    }

    echo json_encode([
        'success' => true,
        'message' => 'verified',
    ]);
    RequestLogger::log('verify-otp', 'POST', $input, 200);

} else {
    // Wrong OTP
    $remainingAttempts = MAX_OTP_ATTEMPTS - (int) $otpData['attempts'];

    echo json_encode([
        'success'            => false,
        'message'            => 'invalid_otp',
        'remaining_attempts' => max(0, $remainingAttempts),
    ]);
    RequestLogger::log('verify-otp', 'POST', $input, 200, 'invalid_otp');
}