new internal enum package

internal/enum/valueof.go

@@ -1,6 +1,16 @@
 package enum
 
-import "fmt"
+import (
+	"encoding/json"
+	"flag"
+	"fmt"
+)
+
+// Enum is an interface for enum types that support [flag.Value].
+type Enum interface {
+	flag.Value
+	~int
+}
 
 // ValueOf returns the index of the value v in the name/index slice.
 func ValueOf(v string, name string, index []uint8) int {
@@ -13,13 +23,29 @@ func ValueOf(v string, name string, index []uint8) int {
 	return -1
 }
 
-// Set sets the target to the value represented by v (using [ValueOf]).
-func Set[T ~int](target *T, v string, name string, index []uint8) error {
+// Set sets the target enum to the value represented by v (using [ValueOf]).
+func Set[T Enum](enum *T, v string, name string, index []uint8) error {
 	i := ValueOf(v, name, index)
 	if i == -1 {
 		return fmt.Errorf("unknown value: %s", v)
 	} else {
-		*target = T(i)
+		*enum = T(i)
 		return nil
 	}
 }
+
+// MarshalJSON marshals the enum to JSON using the string representation.
+func MarshalJSON[T Enum](enum T) ([]byte, error) {
+	return []byte(fmt.Sprintf(`"%s"`, enum.String())), nil
+}
+
+// UnmarshalJSON unmarshals the enum from JSON. It expects a string
+// representation.
+func UnmarshalJSON[T Enum](enum T, data []byte) error {
+	var s string
+	if err := json.Unmarshal(data, &s); err != nil {
+		return err
+	}
+
+	return enum.Set(s)
+}

portfolio/accounts/type.go

@@ -1,9 +1,6 @@
 package accounts
 
 import (
-	"encoding/json"
-	"fmt"
-
 	"github.com/oxisto/money-gopher/internal/enum"
 )
 
@@ -27,23 +24,18 @@ func (t *AccountType) Get() any {
 }
 
 // Set implements [flag.Value].
-func (t *AccountType) Set(v string) error {
-	return enum.Set(t, v, _AccountType_name, _AccountType_index[:])
+func (t AccountType) Set(v string) error {
+	return enum.Set(&t, v, _AccountType_name, _AccountType_index[:])
 }
 
 // MarshalJSON marshals the account type to JSON using the string
 // representation.
 func (t AccountType) MarshalJSON() ([]byte, error) {
-	return []byte(fmt.Sprintf(`"%s"`, t.String())), nil
+	return enum.MarshalJSON(t)
 }
 
 // UnmarshalJSON unmarshals the account type from JSON. It expects a string
 // representation.
-func (t *AccountType) UnmarshalJSON(data []byte) error {
-	var s string
-	if err := json.Unmarshal(data, &s); err != nil {
-		return err
-	}
-
-	return t.Set(s)
+func (t AccountType) UnmarshalJSON(data []byte) error {
+	return enum.UnmarshalJSON(t, data)
 }