app is now using historical exchange rates for transactions

README.md

@@ -12,8 +12,9 @@ A comprehensive portfolio management application built with Go that allows users
 
 ### Currency Conversion
 - **Automatic Currency Detection**: Automatically detects stock currencies from Yahoo Finance
-- **Real-time Exchange Rates**: Fetches current exchange rates from `exchangerate-api.com`
-- **Smart Caching**: 1-hour cache for exchange rates to optimize performance
+- **Historical Exchange Rates**: Fetches historical exchange rates from the actual transaction date for accurate conversion
+- **Smart Caching**: 24-hour cache for historical rates, 1-hour cache for current rates to optimize performance
+- **Fallback System**: Uses current rates when historical rates are unavailable (marked with *)
 - **160+ Currencies Supported**: Including major currencies like USD, EUR, GBP, JPY, CHF
 
 ### User Experience
@@ -110,9 +111,10 @@ portfolio-tracker/
 
 The application automatically:
 - Detects the currency of stocks from Yahoo Finance
-- Converts transaction amounts to your portfolio's base currency
+- Converts transaction amounts using historical exchange rates from the transaction date
 - Displays both original and converted amounts for transparency
-- Updates exchange rates hourly for accuracy
+- Falls back to current rates when historical rates are unavailable (marked with *)
+- Provides accurate historical portfolio valuation
 
 ### Stock Data
 
@@ -177,9 +179,9 @@ The application uses SQLite and automatically creates the database file at `data
 
 ### Multi-Currency Portfolio Management
 - Create portfolios in different base currencies
-- Automatic currency conversion for cross-currency transactions
-- Real-time exchange rate fetching and caching
-- Clear indication of converted vs. original amounts
+- Automatic historical currency conversion using transaction-date exchange rates
+- Historical and real-time exchange rate fetching with smart caching
+- Clear indication of converted vs. original amounts with fallback indicators
 
 ### Transaction Management
 - Support for Buy, Sell, and Dividend transactions
@@ -209,7 +211,8 @@ This project is licensed under the MIT License - see the LICENSE file for detail
 ## 🔗 External APIs
 
 - **Yahoo Finance**: Stock data, prices, and company information
-- **ExchangeRate API**: Currency exchange rates (free tier, no API key required)
+- **ExchangeRate API**: Historical and current currency exchange rates (free tier, no API key required)
+- **Frankfurter API**: Fallback for historical exchange rates when primary API is unavailable
 
 ## ⚠️ Disclaimer