initial commit [141.14.140.180,mike]

currency.go

@@ -0,0 +1,95 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"os"
+	"path/filepath"
+	"time"
+
+	"github.com/shopspring/decimal"
+)
+
+var baseCurrency = "EUR"
+var ratesAPIURL = "https://open.er-api.com/v6/latest/EUR"
+
+type RatesCache struct {
+	Timestamp time.Time          `json:"timestamp"`
+	Rates     map[string]float64 `json:"rates"`
+}
+
+// fetchRates downloads exchange rates from the API or loads them from a local cache
+// if they are less than 24 hours old.
+func fetchRates() error {
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return fmt.Errorf("could not find user home dir for cache: %w", err)
+	}
+	cacheFile := filepath.Join(home, ".goca_rates.json")
+
+	var data RatesCache
+	useCache := false
+
+	// Try loading from cache
+	file, err := os.Open(cacheFile)
+	if err == nil {
+		if err := json.NewDecoder(file).Decode(&data); err == nil {
+			if time.Since(data.Timestamp) < 24*time.Hour && len(data.Rates) > 0 {
+				useCache = true
+			}
+		}
+		file.Close()
+	}
+
+	if !useCache {
+		// Fetch from API
+		client := &http.Client{Timeout: 5 * time.Second}
+		resp, err := client.Get(ratesAPIURL)
+		if err != nil {
+			return fmt.Errorf("failed to fetch rates from API: %w", err)
+		}
+		defer resp.Body.Close()
+
+		var apiResp struct {
+			Rates map[string]float64 `json:"rates"`
+		}
+		if err := json.NewDecoder(resp.Body).Decode(&apiResp); err != nil {
+			return fmt.Errorf("failed to decode rates API response: %w", err)
+		}
+
+		data = RatesCache{
+			Timestamp: time.Now(),
+			Rates:     apiResp.Rates,
+		}
+
+		// Save to cache asynchronously
+		go func() {
+			file, err := os.Create(cacheFile)
+			if err == nil {
+				json.NewEncoder(file).Encode(data)
+				file.Close()
+			}
+		}()
+	}
+
+	// Populate unit registry with rates
+	for code, rate := range data.Rates {
+		// Avoid division by zero
+		if rate > 0 {
+			factor := decimal.NewFromFloat(1.0).Div(decimal.NewFromFloat(rate))
+			unitRegistry[code] = UnitInfo{factor, DimCurrency, code}
+		}
+	}
+	unitRegistry["EUR"] = UnitInfo{decimal.NewFromFloat(1.0), DimCurrency, "EUR"}
+
+	return nil
+}
+
+// eurRatesLookup returns the conversion factor of the currency to EUR.
+func eurRatesLookup(code string) decimal.Decimal {
+	if u, ok := unitRegistry[code]; ok && u.Dimension == DimCurrency {
+		return u.Factor
+	}
+	return decimal.NewFromFloat(1.0)
+}