basic currency service for loading at runtime

backend/internal/core/currencies/currencies.go

@@ -0,0 +1,87 @@
+// Package currencies provides a shared definition of currencies. This uses a global
+// variable to hold the currencies.
+package currencies
+
+import (
+	"bytes"
+	_ "embed"
+	"encoding/json"
+	"io"
+	"sync"
+)
+
+//go:embed currencies.json
+var defaults []byte
+
+type CollectorFunc func() ([]Currency, error)
+
+func CollectJSON(reader io.Reader) CollectorFunc {
+	return func() ([]Currency, error) {
+		var currencies []Currency
+		err := json.NewDecoder(reader).Decode(&currencies)
+		if err != nil {
+			return nil, err
+		}
+
+		return currencies, nil
+	}
+}
+
+func CollectDefaults() CollectorFunc {
+	return CollectJSON(bytes.NewReader(defaults))
+}
+
+func CollectionCurrencies(collectors ...CollectorFunc) ([]Currency, error) {
+	out := make([]Currency, 0, len(collectors))
+	for i := range collectors {
+		c, err := collectors[i]()
+		if err != nil {
+			return nil, err
+		}
+
+		out = append(out, c...)
+	}
+
+	return out, nil
+}
+
+type Currency struct {
+	Name   string `json:"name"`
+	Code   string `json:"code"`
+	Local  string `json:"local"`
+	Symbol string `json:"symbol"`
+}
+
+type CurrencyRegistry struct {
+	mu       sync.RWMutex
+	registry map[string]Currency
+}
+
+func NewCurrencyService(currencies []Currency) *CurrencyRegistry {
+	registry := make(map[string]Currency, len(currencies))
+	for i := range currencies {
+		registry[currencies[i].Code] = currencies[i]
+	}
+
+	return &CurrencyRegistry{
+		registry: registry,
+	}
+}
+
+func (cs *CurrencyRegistry) GetCurrencies() []Currency {
+	cs.mu.RLock()
+	defer cs.mu.RUnlock()
+	out := make([]Currency, 0, len(cs.registry))
+	for key := range cs.registry {
+		out = append(out, cs.registry[key])
+	}
+
+	return out
+}
+
+func (cs *CurrencyRegistry) IsSupported(code string) bool {
+	cs.mu.RLock()
+	defer cs.mu.RUnlock()
+	_, ok := cs.registry[code]
+	return ok
+}

backend/internal/core/currencies/currencies.json

@@ -0,0 +1 @@
+[]