Premium Rate Number Detection: Stop SMS Toll Fraud Before It Costs $127K

// Premium Rate Number Detection API
async function detectPremiumRate(phoneNumber) {
  const response = await fetch(
    'https://api.phone-check.app/v1/validate',
    {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
        'Authorization': 'Bearer YOUR_API_KEY'
      },
      body: JSON.stringify({
        phone: phoneNumber,
        check_premium_rate: true,
        check_risk_score: true
      })
    }
  );

  const data = await response.json();

  // Block premium rate numbers
  if (data.is_premium_rate) {
    console.log('Premium rate detected:', {
      country: data.country,
      rate_type: data.rate_type,
      estimated_cost: data.estimated_cost_per_sms
    });
    return { allowed: false, reason: 'premium_rate' };
  }

  // Block high-risk numbers
  if (data.risk_score > 0.7) {
    return { allowed: false, reason: 'high_risk' };
  }

  return { allowed: true };
}

// Usage in verification flow
const result = await detectPremiumRate('+447098123456');
if (!result.allowed) {
  // Block verification attempt
  return;
}

// Premium rate number ranges database
const premiumRateRanges = {
  GB: ['+4470', '+4471', '+4472', '+4473', '+4476', '+4477'], // UK
  LV: ['+37180', '+37181', '+37182', '+37190', '+37191'], // Latvia
  EE: ['+37280', '+37281', '+37282', '+37290'], // Estonia
  BE: ['+3270', '+3278', '+3290'], // Belgium
  ES: ['+3480', '+3490', '+3491'], // Spain
  LT: ['+37080', '+37090'], // Lithuania
  RO: ['+40900', '+40901', '+40902'], // Romania
  CZ: ['+420900', '+420901', '+420902', '+420903'], // Czech Republic
};

function isPremiumRateNumber(phoneNumber) {
  // Normalize to E.164 format
  const normalized = normalizeToE164(phoneNumber);

  // Extract country code and prefix
  const countryCode = normalized.substring(1, 3);
  const prefix = normalized.substring(0, 5);

  // Check against premium rate ranges
  if (premiumRateRanges[countryCode]) {
    for (const range of premiumRateRanges[countryCode]) {
      if (prefix.startsWith(range.substring(0, 4))) {
        return {
          is_premium: true,
          country: countryCode,
          range: range
        };
      }
    }
  }

  return { is_premium: false };
}

// Intelligent rate limiting by country
class PremiumRateLimiter {
  constructor() {
    this.attempts = new Map();
    this.thresholds = {
      // Stricter limits for high-risk countries
      GB: { requests: 5, window: 3600 }, // UK: 5 per hour
      LV: { requests: 3, window: 3600 }, // Latvia: 3 per hour
      EE: { requests: 3, window: 3600 }, // Estonia: 3 per hour
      // Normal limits for low-risk countries
      US: { requests: 20, window: 3600 }, // US: 20 per hour
      CA: { requests: 20, window: 3600 }, // Canada: 20 per hour
    };
  }

  checkLimit(phoneNumber) {
    const country = this.extractCountry(phoneNumber);
    const threshold = this.thresholds[country] || { requests: 10, window: 3600 };

    const key = phoneNumber.substring(0, 7); // Country + area code
    const now = Date.now();
    const history = this.attempts.get(key) || [];

    // Clean old attempts
    const recent = history.filter(t => now - t < threshold.window * 1000);

    if (recent.length >= threshold.requests) {
      return { allowed: false, reason: 'rate_limit_exceeded' };
    }

    recent.push(now);
    this.attempts.set(key, recent);
    return { allowed: true };
  }

  extractCountry(phone) {
    return phone.substring(1, 3); // Extract country code
  }
}

// VoIP detection for premium rate fraud prevention
async function validatePhoneNumber(phoneNumber) {
  const response = await fetch(
    'https://api.phone-check.app/v1/phone-details',
    {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
        'Authorization': 'Bearer YOUR_API_KEY'
      },
      body: JSON.stringify({ phone: phoneNumber })
    }
  );

  const data = await response.json();

  // Comprehensive fraud checks
  const checks = {
    isPremiumRate: data.line_type === 'premium_rate',
    isVoIP: data.line_type === 'voip',
    isDisposable: data.disposable || false,
    isHighRiskCountry: data.risk_country || false,
    riskScore: data.risk_score || 0
  };

  // Block if any risk indicators present
  if (checks.isPremiumRate) {
    return { allowed: false, reason: 'premium_rate_detected' };
  }

  if (checks.isVoIP && checks.isDisposable) {
    return { allowed: false, reason: 'disposable_voip' };
  }

  if (checks.riskScore > 0.7) {
    return { allowed: false, reason: 'high_risk_score' };
  }

  return { allowed: true, checks };
}