Currency Exchange Best Practices

Multi-Layer Validation Architecture

Implementation Code Example

// Production-ready currency exchange implementation
class CurrencyValidator {
  constructor(apiKey) {
    this.apiKey = apiKey;
    this.cache = new Map();
    this.rateLimit = new RateLimit(100, 60000); // 100 requests per minute
  }

  async convertCurrency(from, to, amount, options = {}) {
    try {
      // Step 1: Validate currency codes (ISO 4217)
      if (!this.isValidCurrencyCode(from) || !this.isValidCurrencyCode(to)) {
        return { valid: false, reason: 'Invalid currency code', confidence: 1.0 };
      }

      // Step 2: Check cache for recent rate
      const cacheKey = `${from}-${to}`;
      const cached = this.cache.get(cacheKey);
      if (cached && !this.isCacheExpired(cached)) {
        return this.applyRate(cached.rate, amount, to);
      }

      // Step 3: Rate limiting
      if (!this.rateLimit.check()) {
        throw new Error('Rate limit exceeded');
      }

      // Step 4: API conversion with retry logic
      const result = await this.apiConversion(from, to, amount, options);

      // Step 5: Cache result with TTL
      this.cache.set(cacheKey, {
        rate: result.rate,
        timestamp: Date.now(),
        ttl: options.cacheTTL || 300000 // 5 minute default
      });

      return result;

    } catch (error) {
      return this.handleError(error, from, to, amount);
    }
  }

  async apiConversion(fromCurrency, toCurrency, amount, options) {
    const response = await fetch(`https://currency-exchange.app/api/v1-convert-currency?from=${fromCurrency}&to=${toCurrency}&amount=${amount}`, {
      method: 'GET',
      headers: {
        'accept': 'application/json',
        'x-api-key': this.apiKey
      }
    });

    if (!response.ok) {
      throw new Error(`API error: ${response.status}`);
    }

    return await response.json();
  }

  handleError(error, from, to, amount) {
    console.error('Currency conversion error:', error);

    // Graceful degradation - return stale cached rate if available
    const cacheKey = `${from}-${to}`;
    const stale = this.cache.get(cacheKey);
    if (stale) {
      return {
        ...this.applyRate(stale.rate, amount, to),
        warning: 'Using cached rate - API unavailable',
        freshness: Date.now() - stale.timestamp
      };
    }

    return {
      valid: false,
      reason: 'API unavailable - no cached rate available',
      error: error.message
    };
  }
}