orderedjson.go

package orderedjson

import (
	"encoding/json"
	"slices"
	"strings"
)

type OrderedJSON struct {
	keys   []string
	values map[string]any
}

func New() *OrderedJSON {
	return &OrderedJSON{
		keys:   make([]string, 0),
		values: make(map[string]any),
	}
}

func (ojson *OrderedJSON) UnmarshalJSON(data []byte) error {
	dec := json.NewDecoder(strings.NewReader(string(data)))

	for dec.More() {
		t, err := dec.Token()
		if err != nil {
			return err
		}
		var name string
		var ok bool
		if name, ok = t.(string); !ok {
			continue
		}
		t, err = dec.Token()
		if err != nil {
			return err
		}
		ojson.keys = append(ojson.keys, name)
		ojson.values[name] = t
	}

	return nil
}

func (oj *OrderedJSON) MarshalJSON() ([]byte, error) {
	if len(oj.keys) == 0 {
		return []byte("{}"), nil
	}

	var buf strings.Builder
	buf.WriteString("{")

	for i, key := range oj.keys {
		if i > 0 {
			buf.WriteString(",")
		}

		keyBytes, err := json.Marshal(key)
		if err != nil {
			return nil, err
		}
		buf.Write(keyBytes)
		buf.WriteString(":")

		valueBytes, err := json.Marshal(oj.values[key])
		if err != nil {
			return nil, err
		}
		buf.Write(valueBytes)
	}

	buf.WriteString("}")
	return []byte(buf.String()), nil
}

func (oj *OrderedJSON) Delete(key string) {
	if _, exists := oj.values[key]; exists {
		delete(oj.values, key)
		for i, k := range oj.keys {
			if k == key {
				oj.keys = slices.Delete(oj.keys, i, i+1)
				break
			}
		}
	}
}