jsonpartial/marshal.go at main · CRSylar/jsonpartial · GitHub

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package jsonpartial

import (
	"encoding/json"
	"fmt"
	"reflect"
)

func Marshal(v any) ([]byte, error) {
	result, err := marshalValue(reflect.ValueOf(v))
	if err != nil {
		return nil, err
	}
	return json.Marshal(result)
}

func MarshalIndent(v any, prefix, indent string) ([]byte, error) {
	result, err := marshalValue(reflect.ValueOf(v))
	if err != nil {
		return nil, err
	}
	return json.MarshalIndent(result, prefix, indent)
}

func marshalValue(rv reflect.Value) (any, error) {
	switch rv.Kind() {
	case reflect.Struct:
		return marshalStruct(rv)
	case reflect.Slice, reflect.Array:
		return marshalSlice(rv)
	case reflect.Map:
		return marshalMap(rv)
	case reflect.Pointer, reflect.Interface:
		return marshalPointer(rv)
	default:
		return rv.Interface(), nil
	}
}

func marshalStruct(rv reflect.Value) (map[string]any, error) {
	rt := rv.Type()
	result := make(map[string]any)

	for i := 0; i < rt.NumField(); i++ {
		field := rt.Field(i)

		if !field.IsExported() {
			continue
		}

		ft, err := ParseTag(field.Tag)
		if err != nil {
			return nil, err
		}

		// Handle embedded (anonymous) structs
		if field.Anonymous && field.Type.Kind() == reflect.Struct {
			if err := marshalEmbeddedStruct(rv.Field(i), field.Type, ft, result); err != nil {
				return nil, err
			}
			continue
		}

		if ft.MustBeIgnored || ft.HasUnmarshalOnly {
			continue
		}

		key := ft.Name
		if key == "" {
			key = field.Name
		}

		fieldValue := rv.Field(i)
		marshaledValue, err := marshalValue(fieldValue)
		if err != nil {
			return nil, err
		}

		result[key] = marshaledValue
	}

	return result, nil
}

func marshalEmbeddedStruct(rv reflect.Value, rt reflect.Type, parentTag FieldTag, result map[string]any) error {
	for i := 0; i < rt.NumField(); i++ {
		field := rt.Field(i)

		if !field.IsExported() {
			continue
		}

		ft, err := ParseTag(field.Tag)
		if err != nil {
			return err
		}

		// If parent embedded field has a directional tag, it should be inherited
		// but child field's own tag takes precedence
		if parentTag.HasUnmarshalOnly {
			ft.HasUnmarshalOnly = true
		}
		if parentTag.HasMarshalOnly {
			ft.HasMarshalOnly = true
		}

		// Handle nested embedded structs recursively
		if field.Anonymous && field.Type.Kind() == reflect.Struct {
			if err := marshalEmbeddedStruct(rv.Field(i), field.Type, ft, result); err != nil {
				return err
			}
			continue
		}

		if ft.MustBeIgnored || ft.HasUnmarshalOnly {
			continue
		}

		key := ft.Name
		if key == "" {
			key = field.Name
		}

		fieldValue := rv.Field(i)
		marshaledValue, err := marshalValue(fieldValue)
		if err != nil {
			return err
		}

		result[key] = marshaledValue
	}

	return nil
}

func marshalSlice(rv reflect.Value) ([]any, error) {
	length := rv.Len()
	result := make([]any, length)

	for i := range length {
		elem := rv.Index(i)
		marshaled, err := marshalValue(elem)
		if err != nil {
			return nil, err
		}
		result[i] = marshaled
	}

	return result, nil
}

func marshalMap(rv reflect.Value) (map[string]any, error) {
	result := make(map[string]any)

	for _, key := range rv.MapKeys() {
		keyStr := fmt.Sprintf("%v", key.Interface())

		value := rv.MapIndex(key)
		marshaled, err := marshalValue(value)
		if err != nil {
			return nil, err
		}

		result[keyStr] = marshaled
	}

	return result, nil
}

func marshalPointer(rv reflect.Value) (any, error) {
	if rv.IsNil() {
		return nil, nil
	}
	return marshalValue(rv.Elem())
}