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Currency Conversion and Localized Pricing - Implementation Summary

Issue #579: Implement currency conversion and localized pricing

Acceptance Criteria Status

✅ Currency detection by location - COMPLETED

  • Implemented CurrencyDetectionService that maps 50+ countries to their currencies
  • Supports country codes, country names, and timezone-based detection
  • Configurable confidence levels for detection methods
  • User model updated with location fields (country, countryCode, timezone, city)

✅ Currency conversion API - COMPLETED

  • Implemented CurrencyService with conversion capabilities
  • Implemented ExchangeRateService for managing exchange rates
  • Free/premium API integration support (exchangerate-api.com)
  • Automatic 24-hour rate refresh with fallback rates
  • /currency/convert and /currency/convert-multiple endpoints
  • Supports 50+ currencies with proper precision handling

✅ Localized pricing display - COMPLETED

  • Implemented PricingService for price calculations in local currency
  • Implemented LocalizedCourseService for course pricing
  • /pricing/localize endpoint for formatted price display
  • Multi-currency pricing support with locale-aware formatting
  • Currency symbol and name display
  • Support for pricing by region

✅ Payment processing in local currency - COMPLETED

  • Implemented LocalizedPaymentDto for payment creation with currency conversion
  • /pricing/for-payment endpoint for payment-ready pricing
  • Exchange rates stored in payment metadata for audit trail
  • Support for discount and tax calculations in local currency
  • Payment amounts rounded to currency precision (handling JPY, KRW, etc.)

Files Created

Currency Module

  • src/currency/currency.module.ts - Main module definition
  • src/currency/services/currency.service.ts - Core currency operations
  • src/currency/services/exchange-rate.service.ts - Exchange rate management
  • src/currency/services/currency-detection.service.ts - Location-based currency detection
  • src/currency/controllers/currency.controller.ts - REST API endpoints
  • src/currency/dtos/currency.dto.ts - Data transfer objects
  • src/currency/CURRENCY_IMPLEMENTATION.md - Detailed documentation

Payments Module Updates

  • src/payments/payments.module.ts - Updated with currency integration
  • src/payments/services/pricing.service.ts - Localized pricing calculations
  • src/payments/controllers/pricing.controller.ts - Pricing API endpoints
  • src/payments/dto/localized-payment.dto.ts - Localized payment DTOs

Courses Module Updates

  • src/courses/courses.module.ts - Created module with localized pricing
  • src/courses/services/localized-course.service.ts - Course pricing localization

User Module

  • src/users/users.module.ts - Created module

Migrations

  • src/migrations/1685000001000-add-currency-and-location-fields-to-users.ts
    • Adds: country, countryCode, timezone, city, preferredCurrency fields
  • src/migrations/1685000001001-add-currency-field-to-courses.ts
    • Adds: currency field to courses table

Entity Updates

  • Updated src/users/entities/user.entity.ts - Added location and currency fields
  • Updated src/courses/entities/course.entity.ts - Added currency field
  • Updated src/app.module.ts - Registered CurrencyModule and PaymentsModule

Key Features Implemented

1. Currency Conversion

  • Convert between any two currencies
  • Convert to multiple currencies in batch
  • Support for 50+ currencies with proper precision
  • Automatic handling of zero-decimal currencies (JPY, KRW, etc.)

2. Currency Detection

  • Detect currency from country code (high confidence)
  • Detect currency from country name (medium confidence)
  • Detect currency from timezone (low confidence)
  • Fallback to USD if location unknown

3. Exchange Rate Management

  • Automatic daily rate refresh from exchangerate-api.com
  • Fallback to cached rates if API unavailable
  • In-memory caching for performance
  • Manual refresh capability via API

4. Localized Pricing Display

  • Format prices with currency symbols
  • Locale-aware number formatting (e.g., 1.234,56 € vs $1,234.56)
  • Multi-currency pricing options
  • Regional pricing comparisons

5. Payment Processing

  • Automatic currency conversion before payment
  • Exchange rate tracking in payment records
  • Discount and tax calculations in local currency
  • Support for all payment methods in any currency

API Endpoints

Currency Endpoints

  • POST /currency/convert - Convert single currency
  • POST /currency/convert-multiple - Batch currency conversion
  • GET /currency/details/:currencyCode - Get currency details
  • POST /currency/detect - Detect currency from location
  • GET /currency/supported - List all supported countries/currencies
  • GET /currency/rates - Get current exchange rates
  • POST /currency/rates/refresh - Manually refresh rates
  • POST /currency/format-price - Format price for display

Pricing Endpoints

  • POST /pricing/localize - Get localized price
  • POST /pricing/for-payment - Get payment-ready pricing
  • POST /pricing/multi-currency - Get multi-currency pricing
  • POST /pricing/apply-discount - Apply discount
  • POST /pricing/apply-tax - Apply tax

Database Schema

User Entity - New Fields

- country (varchar) - Country name
- countryCode (varchar(2), indexed) - ISO 3166-1 code
- timezone (varchar) - IANA timezone
- city (varchar) - City name
- preferredCurrency (varchar(3), default: USD, indexed) - Currency preference

Course Entity - New Fields

- currency (varchar(3), default: USD, indexed) - Base currency

Configuration

Environment Variables

# Exchange Rate API (optional, defaults to exchangerate-api.com)
EXCHANGE_RATE_API_URL=https://api.exchangerate-api.com/v4/latest/USD
EXCHANGE_RATE_API_KEY=your_api_key

Supported Currencies & Countries

50+ supported country/currency pairs including:

  • North America: USD (US), CAD (CA), MXN (MX)
  • Europe: EUR (multiple countries), GBP (GB), SEK (SE), NOK (NO), CHF (CH)
  • Asia: JPY (JP), CNY (CN), INR (IN), SGD (SG), HKD (HK), THB (TH)
  • Australia/Oceania: AUD (AU), NZD (NZ)
  • South America: BRL (BR), ARS (AR), CLP (CL)
  • Africa: ZAR (ZA), EGP (EG), NGN (NG), KES (KE)
  • Middle East: AED (AE), SAR (SA), ILS (IL), TRY (TR)

Usage Examples

Detect User Currency

// From user profile
const userCurrency = currencyDetectionService.detectCurrency({
  countryCode: 'IN',
});
// Returns: 'INR'

Convert Course Price to User Currency

const localizedPrice = await pricingService.getLocalizedPrice(
  99.99, // Base price
  'USD', // Base currency
  'INR', // User currency
  'en-IN', // User locale
);
// Returns: { baseAmount: 99.99, convertedAmount: 8312.91, formattedPrice: '₹8,312.91', ... }

Get Course with Localized Pricing

const course = await courseService.findOne(courseId);
const localizedCourse = await localizedCourseService.getLocalizedCoursePrice(
  course,
  'INR', // User's currency
  'en-IN', // User's locale
);

Process Payment in Local Currency

const pricing = await pricingService.getPricingForPayment(
  99.99, // USD price
  'USD',
  'INR', // User's currency
);
// Payment is processed in INR with correct rounding

Testing Recommendations

  1. Currency Detection

    • Test with various country codes
    • Test with timezone-based detection fallback
    • Verify confidence levels

  2. Currency Conversion

    • Test USD to major currencies (EUR, GBP, JPY, INR, etc.)
    • Test zero-decimal currencies (JPY, KRW)
    • Test exchange rate updates

  3. Localized Pricing

    • Test price formatting with different locales
    • Verify currency symbols display correctly
    • Test discount/tax calculations in different currencies

  4. Payment Processing

    • Create payments in different currencies
    • Verify exchange rates are stored
    • Test rounding for zero-decimal currencies

Future Enhancements

  1. Multi-currency pricing per course (instructor setting)
  2. Geo-IP based automatic currency detection
  3. Historical exchange rate tracking
  4. Tax calculation by region
  5. Premium exchange rate service integration
  6. Payment method localization (PayPal, cards by country)
  7. Blockchain/crypto payment support with live rates

Rollback Instructions

If needed, rollback migrations:

npm run migrate:rollback

The feature is fully backward compatible with USD as default.

Testing The Implementation

Manual Test Steps

  1. Start the application

    npm run start:dev

  2. Test Currency Detection

    curl -X POST http://localhost:3000/currency/detect \
  -H "Content-Type: application/json" \
  -d '{"countryCode":"IN"}'

  3. Test Currency Conversion

    curl -X POST http://localhost:3000/currency/convert \
  -H "Content-Type: application/json" \
  -d '{"amount":99.99,"fromCurrency":"USD","toCurrency":"INR"}'

  4. Test Localized Pricing

    curl -X POST http://localhost:3000/pricing/localize \
  -H "Content-Type: application/json" \
  -d '{"basePrice":99.99,"baseCurrency":"USD","userCurrency":"INR","userLocale":"en-IN"}'

Deployment Checklist

  • Code reviewed and tested
  • Migrations created for database schema
  • Environment variables documented
  • API endpoints documented
  • DTOs and services properly structured
  • Module dependencies properly configured
  • Error handling implemented
  • Logging added for debugging
  • Swagger documentation ready
  • Backward compatibility maintained

Implementation Status: ✅ COMPLETE

All acceptance criteria have been met and the feature is ready for deployment.