feat: find alpha2 by currency

query.go

@@ -16,6 +16,7 @@ type Query struct {
 	Alpha3ToAlpha2      map[string]string
 	NativeNameToAlpha2  map[string]string
 	CallingCodeToAlpha2 map[string]string
+	CurrencyToAlpha2    map[string][]Country
 }
 
 // FindCountryByName finds a country by given name
@@ -67,6 +68,20 @@ func (q *Query) FindCountryByCallingCode(callingCode string) (result Country, er
 	return q.Countries[alpha2], nil
 }
 
+// FindCountriesByCurrency finds a Country based on the given struct data
+func (q *Query) FindCountriesByCurrency(currency string) (results []Country, err error) {
+	if len(currency) != 3 {
+		return nil, makeError("Invalid currency format", currency)
+	}
+
+	alpha2, exists := q.CurrencyToAlpha2[currency]
+	if !exists {
+		return []Country{}, makeError("Could not find countries with currency name", currency)
+	}
+
+	return alpha2, nil
+}
+
 // FindAllCountries returns a list of all countries
 func (q *Query) FindAllCountries() (countries map[string]Country) {
 	return q.Countries

setup.go

@@ -30,6 +30,7 @@ func NewFromPath(dataPath string) *Query {
 		queryInstance.Alpha3ToAlpha2 = populateAlphaIndex(queryInstance.Countries)
 		queryInstance.NativeNameToAlpha2 = populateNativeNameIndex(queryInstance.Countries)
 		queryInstance.CallingCodeToAlpha2 = populateCallingCodeIndex(queryInstance.Countries)
+		queryInstance.CurrencyToAlpha2 = populateCallingCurrencyIndex(queryInstance.Countries)
 
 		subdivisions := populateSubdivisions(dataPath)
 		for k := range queryInstance.Countries {
@@ -220,3 +221,14 @@ func populateCallingCodeIndex(countries map[string]Country) map[string]string {
 	}
 	return index
 }
+
+func populateCallingCurrencyIndex(countries map[string]Country) map[string][]Country {
+	index := make(map[string][]Country)
+
+	for _, country := range countries {
+		for _, currency := range country.Currencies {
+			index[currency] = append(index[currency], country)
+		}
+	}
+	return index
+}