Add codec wrapper modifier (#905)

* Add codec wrapper modifier

* Fix WrapperModifierConfig description comment

* Improve comments for wrapper modifier

pkg/codec/config.go

@@ -23,6 +23,7 @@ import (
 // - extract element -> [ElementExtractorModifierConfig]
 // - epoch to time -> [EpochToTimeModifierConfig]
 // - address to string -> [AddressBytesToStringModifierConfig]
+// - field wrapper -> [WrapperModifierConfig]
 type ModifiersConfig []ModifierConfig
 
 func (m *ModifiersConfig) UnmarshalJSON(data []byte) error {
@@ -55,6 +56,8 @@ func (m *ModifiersConfig) UnmarshalJSON(data []byte) error {
 			(*m)[i] = &PropertyExtractorConfig{}
 		case ModifierAddressToString:
 			(*m)[i] = &AddressBytesToStringModifierConfig{}
+		case ModifierWrapper:
+			(*m)[i] = &ModifiersConfig{}
 		default:
 			return fmt.Errorf("%w: unknown modifier type: %s", types.ErrInvalidConfig, mType)
 		}
@@ -88,6 +91,7 @@ const (
 	ModifierEpochToTime     ModifierType = "epoch to time"
 	ModifierExtractProperty ModifierType = "extract property"
 	ModifierAddressToString ModifierType = "address to string"
+	ModifierWrapper         ModifierType = "wrapper"
 )
 
 type ModifierConfig interface {
@@ -248,6 +252,80 @@ func (c *AddressBytesToStringModifierConfig) MarshalJSON() ([]byte, error) {
 	})
 }
 
+// WrapperModifierConfig replaces each field based on cfg map keys with a struct containing one field with the value of the original field which has is named based on map values.
+// Wrapper modifier does not maintain the original pointers.
+// Wrapper modifier config shouldn't edit fields that affect each other since the results are not deterministic.
+//
+//		Example #1:
+//
+//		Based on this input struct:
+//			type example struct {
+//				A string
+//			}
+//
+//		And the wrapper config defined as:
+//	 		{"D": "W"}
+//
+//		Result:
+//			type example struct {
+//				D
+//			}
+//
+//		where D is a struct that contains the original value of D under the name W:
+//			type D struct {
+//				W string
+//			}
+//
+//
+//		Example #2:
+//		Wrapper modifier works on any type of field, including nested fields or nested fields in slices etc.!
+//
+//		Based on this input struct:
+//			type example struct {
+//				A []B
+//			}
+//
+//			type B struct {
+//				C string
+//				D string
+//			}
+//
+//		And the wrapper config defined as:
+//	 		{"A.C": "E", "A.D": "F"}
+//
+//		Result:
+//			type example struct {
+//				A []B
+//			}
+//
+//			type B struct {
+//				C type struct { E string }
+//				D type struct { F string }
+//			}
+//
+//		Where each element of slice A under fields C.E and D.F retains the values of their respective input slice elements A.C and A.D .
+type WrapperModifierConfig struct {
+	// Fields key defines the fields to be wrapped and the name of the wrapper struct.
+	// The field becomes a subfield of the wrapper struct where the name of the subfield is map value.
+	Fields map[string]string
+}
+
+func (r *WrapperModifierConfig) ToModifier(_ ...mapstructure.DecodeHookFunc) (Modifier, error) {
+	fields := map[string]string{}
+	for i, f := range r.Fields {
+		// using a private variable will make the field not serialize, essentially dropping the field
+		fields[upperFirstCharacter(f)] = fmt.Sprintf("dropFieldPrivateName-%s", i)
+	}
+	return NewWrapperModifier(r.Fields), nil
+}
+
+func (r *WrapperModifierConfig) MarshalJSON() ([]byte, error) {
+	return json.Marshal(&modifierMarshaller[WrapperModifierConfig]{
+		Type: ModifierWrapper,
+		T:    r,
+	})
+}
+
 type typer struct {
 	Type string
 }

pkg/codec/wrapper.go

@@ -0,0 +1,62 @@
+package codec
+
+import (
+	"fmt"
+	"reflect"
+)
+
+func NewWrapperModifier(fields map[string]string) Modifier {
+	m := &wrapperModifier{
+		modifierBase: modifierBase[string]{
+			fields:           fields,
+			onToOffChainType: map[reflect.Type]reflect.Type{},
+			offToOnChainType: map[reflect.Type]reflect.Type{},
+		},
+	}
+
+	m.modifyFieldForInput = func(_ string, field *reflect.StructField, _ string, fieldName string) error {
+		field.Type = reflect.StructOf([]reflect.StructField{{
+			Name: fieldName,
+			Type: field.Type,
+		}})
+		return nil
+	}
+
+	return m
+}
+
+type wrapperModifier struct {
+	modifierBase[string]
+}
+
+func (t *wrapperModifier) TransformToOnChain(offChainValue any, _ string) (any, error) {
+	return transformWithMaps(offChainValue, t.offToOnChainType, t.fields, unwrapFieldMapAction)
+}
+
+func (t *wrapperModifier) TransformToOffChain(onChainValue any, _ string) (any, error) {
+	return transformWithMaps(onChainValue, t.onToOffChainType, t.fields, wrapFieldMapAction)
+}
+
+func wrapFieldMapAction(typesMap map[string]any, fieldName string, wrappedFieldName string) error {
+	field, exists := typesMap[fieldName]
+	if !exists {
+		return fmt.Errorf("field %s does not exist", fieldName)
+	}
+
+	typesMap[fieldName] = map[string]any{wrappedFieldName: field}
+	return nil
+}
+
+func unwrapFieldMapAction(typesMap map[string]any, fieldName string, wrappedFieldName string) error {
+	_, exists := typesMap[fieldName]
+	if !exists {
+		return fmt.Errorf("field %s does not exist", fieldName)
+	}
+	val, isOk := typesMap[fieldName].(map[string]any)[wrappedFieldName]
+	if !isOk {
+		return fmt.Errorf("field %s.%s does not exist", fieldName, wrappedFieldName)
+	}
+
+	typesMap[fieldName] = val
+	return nil
+}