Multi-Currency Payment Platform

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// Card Vault - Token generation
async tokenize(cardData) {
  // Validate card format
  if (!luhnCheck(cardData.number)) {
    throw new ValidationError('Invalid card number');
  }
  
  // Encrypt with hardware security module
  const encrypted = await hsm.encrypt(cardData);
  
  // Store encrypted data
  const token = generateToken();
  await cardStore.save(token, encrypted);
  
  // Return token (never the card)
  return { token, last4: cardData.number.slice(-4) };
}

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class CurrencyService {
  async getRate(from, to, amount) {
    // Check cache first
    const cached = await redis.get(`rate:${from}:${to}`);
    if (cached && !this.isStale(cached)) {
      return this.applyMargin(cached);
    }
    
    // Fetch from providers with failover
    const rate = await this.fetchWithFailover([
      () => xe.getRate(from, to),
      () => fixer.getRate(from, to),
      () => bankFeed.getRate(from, to)
    ]);
    
    // Cache for 60 seconds
    await redis.setex(`rate:${from}:${to}`, 60, rate);
    
    return this.applyMargin(rate);
  }
}