package main

import (
	"encoding/json"
	"errors"
	"fmt"
	"unsafe"
)

type JSONString []byte

const _leadOfJSONString = '^'
const _leadOfJSONStringLen = 1

var _emptyJSONString = []byte{'"', '"'}

func (s JSONString) MarshalJSON() ([]byte, error) {
	if !s.IsSet() {
		b := make([]byte, len(_emptyJSONString))
		copy(b, _emptyJSONString)
		return b, nil
	}

	b := make([]byte, 0, len(s)-_leadOfJSONStringLen+len(_emptyJSONString))
	b = append(b, _emptyJSONString[0]) //"
	b = s.AppentString(b)              //aaaaa
	b = append(b, _emptyJSONString[1]) //"
	return b, nil
}

func (s *JSONString) UnmarshalJSON(b []byte) error {
	if len(b) < len(_emptyJSONString) || b[0] != _emptyJSONString[0] || b[len(b)-1] != _emptyJSONString[len(_emptyJSONString)-1] {
		return errors.New("missing quotation mark")
	}

	if len(b) == len(_emptyJSONString) { //empty string
		*s = make([]byte, _leadOfJSONStringLen)
		(*s)[0] = _leadOfJSONString
		return nil
	}

	b = b[1 : len(b)-1]
	bs := *(*string)(unsafe.Pointer(&b))
	s.Set(bs)
	return nil
}

func (s *JSONString) String() string {
	if !s.IsSet() {
		return ""
	}

	return string((*s)[1:])
}

func (s *JSONString) AppentString(buf []byte) []byte {
	if !s.IsSet() {
		return buf
	}

	return append(buf, (*s)[1:]...)
}

func (s *JSONString) Set(v string) {
	if len(*s) == 0 || len(*s)-len(v) > 128 {
		*s = make([]byte, 0, _leadOfJSONStringLen+len(v))
	} else {
		*s = (*s)[:0]
	}

	*s = append([]byte{_leadOfJSONString}, v...)
}

func (s *JSONString) IsSet() bool {
	return len(*s) > 0 && ((*s)[0] == _leadOfJSONString)
}

func (s *JSONString) Clear() {
	*s = nil
}

type StringTestMessage struct {
	ID   int        `json:"id"`
	Name JSONString `json:"name,omitempty"`
}

func StringUnmarshalTest() {
	{
		msg := &StringTestMessage{}
		err := json.Unmarshal([]byte(`{"id":0}`), msg)
		if err != nil {
			panic(err)
		}
		fmt.Printf("%t|%+v\n", msg.Name.IsSet(), msg) //false|&{ID:0 Name:[]}
	}

	{
		msg := &StringTestMessage{}
		err := json.Unmarshal([]byte(`{"id":111}`), msg) //false|&{ID:111 Name:[]}
		if err != nil {
			panic(err)
		}
		fmt.Printf("%t|%+v\n", msg.Name.IsSet(), msg)
	}

	{
		msg := &StringTestMessage{}
		err := json.Unmarshal([]byte(`{"id":111,"name":""}`), msg) //true|&{ID:111 Name:[94]}
		if err != nil {
			panic(err)
		}
		fmt.Printf("%t|%+v\n", msg.Name.IsSet(), msg)
	}

	{
		msg := &StringTestMessage{}
		err := json.Unmarshal([]byte(`{"id":111,"name":"123"}`), msg) //true|&{ID:111 Name:[94 49 50 51]}
		if err != nil {
			panic(err)
		}
		fmt.Printf("%t|%+v\n", msg.Name.IsSet(), msg)
	}
}

func StringMarshalTest() {
	msg := &StringTestMessage{}
	b, err := json.Marshal(msg)
	if err != nil {
		panic(err)
	}
	fmt.Printf("%t|%s\n", msg.Name.IsSet(), b) //false|{"id":0}

	msg.ID = 111
	b, err = json.Marshal(msg)
	if err != nil {
		panic(err)
	}
	fmt.Printf("%t|%s\n", msg.Name.IsSet(), b) //false|{"id":111}

	msg.Name.Set("")
	b, err = json.Marshal(msg)
	if err != nil {
		panic(err)
	}
	fmt.Printf("%t|%s\n", msg.Name.IsSet(), b) //true|{"id":111,"name":""}

	msg.Name.Clear()
	b, err = json.Marshal(msg)
	if err != nil {
		panic(err)
	}
	fmt.Printf("%t|%s\n", msg.Name.IsSet(), b) //false|{"id":111}

	msg.Name.Set("")
	b, err = json.Marshal(msg)
	if err != nil {
		panic(err)
	}
	fmt.Printf("%t|%s\n", msg.Name.IsSet(), b) //true|{"id":111,"name":""}

	msg.Name.Clear()
	b, err = json.Marshal(msg)
	if err != nil {
		panic(err)
	}
	fmt.Printf("%t|%s\n", msg.Name.IsSet(), b) //false|{"id":111}

	msg.Name.Set("")
	b, err = json.Marshal(msg)
	if err != nil {
		panic(err)
	}
	fmt.Printf("%t|%s\n", msg.Name.IsSet(), b) //true|{"id":111,"name":""}

	msg.Name.Set("123")
	b, err = json.Marshal(msg)
	if err != nil {
		panic(err)
	}
	fmt.Printf("%t|%s\n", msg.Name.IsSet(), b) //true|{"id":111,"name":"123"}
}