import_export.go

package jsonvalue

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

// Export convert jsonvalue to another type of parameter. The target parameter type should match the type of *V.
//
// Export 将 *V 转到符合原生 encoding/json 的一个 struct 中。
func (v *V) Export(dst any) error {
	b, err := v.Marshal()
	if err != nil {
		return err
	}

	return json.Unmarshal(b, dst)
}

// Import convert json value from a marshal-able parameter to *V. This a experimental function.
//
// Import 将符合 encoding/json 的 struct 转为 *V 类型。不经过 encoding/json，并且支持 Option.
func Import(src any, opts ...Option) (*V, error) {
	opt := combineOptions(opts)
	ext := ext{}
	ext.ignoreOmitempty = opt.ignoreJsonOmitempty
	v, fu, err := validateValAndReturnParser(reflect.ValueOf(src), ext)
	if err != nil {
		return &V{}, err
	}
	res, err := fu(v, ext)
	if err != nil {
		return &V{}, err
	}
	return res, nil
}

// parserFunc 处理对应 reflect.Value 的函数
type parserFunc func(v reflect.Value, ex ext) (*V, error)

type ext struct {
	// standard encoding/json tag
	omitempty bool
	toString  bool

	// revert of isExported
	private bool

	// extended jsonvalue options
	ignoreOmitempty bool
}

func (e ext) shouldOmitEmpty() bool {
	if e.ignoreOmitempty {
		return false
	}
	return e.omitempty || e.private
}

// validateValAndReturnParser 检查入参合法性并返回相应的处理函数
func validateValAndReturnParser(v reflect.Value, ex ext) (out reflect.Value, fu parserFunc, err error) {
	out = v

	// json.Marshaler and encoding.TextMarshaler
	if o, f := checkAndParseMarshaler(v); f != nil {
		// jsonvalue itself
		if _, ok := v.Interface().(deepCopier); ok {
			return out, parseJSONValueDeepCopier, nil
		}
		return o, f, nil
	}

	switch v.Kind() {
	default:
		// 	fallthrough
		// case reflect.Invalid, reflect.Complex64, reflect.Complex128:
		// 	fallthrough
		// case reflect.Chan, reflect.Func, reflect.UnsafePointer:
		err = fmt.Errorf("jsonvalue: unsupported type: %v", v.Type())

	case reflect.Invalid:
		fu = parseInvalidValue

	case reflect.Bool:
		fu = parseBoolValue

	case reflect.Int, reflect.Int64, reflect.Int32, reflect.Int16, reflect.Int8:
		fu = parseIntValue

	case reflect.Uintptr, reflect.Uint, reflect.Uint64, reflect.Uint32, reflect.Uint16, reflect.Uint8:
		fu = parseUintValue

	case reflect.Float32:
		fu = parseFloat32Value

	case reflect.Float64:
		fu = parseFloat64Value

	case reflect.Array:
		fu = parseArrayValue

	case reflect.Interface:
		return validateValAndReturnParser(v.Elem(), ex)

	case reflect.Map:
		switch v.Type().Key().Kind() {
		default:
			err = fmt.Errorf("unsupported key type for a map: %v", v.Type().Key())
		case reflect.String:
			fu = parseStringMapValue
		case reflect.Int, reflect.Int64, reflect.Int32, reflect.Int16, reflect.Int8:
			fu = parseIntMapValue
		case reflect.Uintptr, reflect.Uint, reflect.Uint64, reflect.Uint32, reflect.Uint16, reflect.Uint8:
			fu = parseUintMapValue
		}

	case reflect.Ptr:
		fu = parsePtrValue

	case reflect.Slice:
		if v.Type() == reflect.TypeOf([]byte{}) {
			fu = parseBytesValue
		} else {
			fu = parseSliceValue
		}

	case reflect.String:
		fu = parseStringValue

	case reflect.Struct:
		fu = parseStructValue
	}

	return
}

// Hit marshaler if fu is not nil.
func checkAndParseMarshaler(v reflect.Value) (out reflect.Value, fu parserFunc) {
	out = v
	if !v.IsValid() {
		return
	}

	// check type itself
	if v.Type().Implements(internal.types.JSONMarshaler) {
		return v, parseJSONMarshaler
	}
	if v.Type().Implements(internal.types.TextMarshaler) {
		return v, parseTextMarshaler
	}

	// check its origin type
	if v.Kind() == reflect.Ptr {
		if v.IsNil() {
			return
		}
		elem := v.Elem()
		if elem.Type().Implements(internal.types.JSONMarshaler) {
			return elem, parseJSONMarshaler
		}
		if elem.Type().Implements(internal.types.TextMarshaler) {
			return elem, parseTextMarshaler
		}
		return
	}

	// check its pointer type
	// referenceType := reflect.PointerTo(v.Type()) // go 1.17 +
	referenceType := reflect.PtrTo(v.Type())
	if referenceType.Implements(internal.types.JSONMarshaler) {
		return getPointerOfValue(v), parseJSONMarshaler
	}
	if referenceType.Implements(internal.types.TextMarshaler) {
		return getPointerOfValue(v), parseTextMarshaler
	}

	return
}

// reference:
//   - [Using reflect to get a pointer to a struct passed as an interface{}](https://groups.google.com/g/golang-nuts/c/KB3_Yj3Ny4c)
//   - [reflect.Set slice-of-structs value to a struct, without type assertion (because it's unknown)](https://stackoverflow.com/questions/40474682)
func getPointerOfValue(v reflect.Value) reflect.Value {
	vp := reflect.New(reflect.TypeOf(v.Interface()))
	vp.Elem().Set(v)
	return vp
}

func parseJSONValueDeepCopier(v reflect.Value, ex ext) (*V, error) {
	if v.IsNil() {
		return nil, nil // empty
	}
	j, _ := v.Interface().(deepCopier)
	return j.deepCopy(), nil
}

func parseJSONMarshaler(v reflect.Value, ex ext) (*V, error) {
	if v.Kind() == reflect.Ptr && v.IsNil() {
		return nil, nil // empty
	}
	marshaler, _ := v.Interface().(json.Marshaler)
	if marshaler == nil {
		return nil, nil // empty
	}
	b, err := marshaler.MarshalJSON()
	if err != nil {
		return &V{}, fmt.Errorf("JSONMarshaler returns error: %w", err)
	}

	res, err := Unmarshal(b)
	if err != nil {
		return nil, fmt.Errorf("illegal JSON data generated from type '%v', error: %w", v.Type(), err)
	}

	if ex.shouldOmitEmpty() {
		switch res.ValueType() {
		default:
			return nil, nil
		case String:
			if res.String() == "" {
				return nil, nil
			}
		case Number:
			if res.Float64() == 0 {
				return nil, nil
			}
		case Array, Object:
			if res.Len() == 0 {
				return nil, nil
			}
		case Boolean:
			if !res.Bool() {
				return nil, nil
			}
		case Null:
			return nil, nil
		}
	}

	return res, nil
}

func parseTextMarshaler(v reflect.Value, ex ext) (*V, error) {
	if v.Kind() == reflect.Ptr && v.IsNil() {
		return nil, nil // empty
	}
	marshaler, _ := v.Interface().(encoding.TextMarshaler)
	if marshaler == nil {
		return NewNull(), nil // empty
	}
	b, err := marshaler.MarshalText()
	if err != nil {
		return &V{}, err
	}

	if len(b) == 0 && ex.shouldOmitEmpty() {
		return nil, nil
	}
	return NewString(string(b)), nil
}

func parseInvalidValue(_ reflect.Value, ex ext) (*V, error) {
	if ex.shouldOmitEmpty() {
		return nil, nil
	}
	return NewNull(), nil
}

func parseBoolValue(v reflect.Value, ex ext) (*V, error) {
	b := v.Bool()
	if !b && ex.shouldOmitEmpty() {
		return nil, nil
	}
	if ex.toString {
		return NewString(fmt.Sprint(b)), nil
	}
	return NewBool(b), nil
}

func parseIntValue(v reflect.Value, ex ext) (*V, error) {
	i := v.Int()
	if i == 0 && ex.shouldOmitEmpty() {
		return nil, nil
	}
	if ex.toString {
		return NewString(strconv.FormatInt(i, 10)), nil
	}
	return NewInt64(i), nil
}

func parseUintValue(v reflect.Value, ex ext) (*V, error) {
	u := v.Uint()
	if u == 0 && ex.shouldOmitEmpty() {
		return nil, nil
	}
	if ex.toString {
		return NewString(strconv.FormatUint(u, 10)), nil
	}
	return NewUint64(u), nil
}

func parseFloat64Value(v reflect.Value, ex ext) (*V, error) {
	f := v.Float()
	if f == 0.0 && ex.shouldOmitEmpty() {
		return nil, nil
	}
	if ex.toString {
		f64 := NewFloat64(f)
		return NewString(f64.MustMarshalString()), nil
	}
	return NewFloat64(f), nil
}

func parseFloat32Value(v reflect.Value, ex ext) (*V, error) {
	f := v.Float()
	if f == 0.0 && ex.shouldOmitEmpty() {
		return nil, nil
	}
	if ex.toString {
		f32 := NewFloat32(float32(f))
		return NewString(f32.MustMarshalString()), nil
	}
	return NewFloat32(float32(f)), nil
}

func parseArrayValue(v reflect.Value, ex ext) (*V, error) {
	ex.omitempty = false
	res := NewArray()
	le := v.Len()

	for i := 0; i < le; i++ {
		vv := v.Index(i)
		vv, fu, err := validateValAndReturnParser(vv, ex)
		if err != nil {
			return nil, err
		}
		child, err := fu(vv, ex)
		if err != nil {
			return nil, err
		}
		res.MustAppend(child).InTheEnd()
	}

	return res, nil
}

func parseMapValue(v reflect.Value, ex ext, keyFunc func(key reflect.Value) string) (*V, error) {
	if v.IsNil() {
		return parseNullValue(v, ex)
	}

	keys := v.MapKeys()
	if len(keys) == 0 {
		if ex.shouldOmitEmpty() {
			return nil, nil
		}
		return NewObject(), nil
	}

	res := NewObject()

	for _, kk := range keys {
		vv := v.MapIndex(kk)
		vv, fu, err := validateValAndReturnParser(vv, ex)
		if err != nil {
			return res, err
		}
		child, err := fu(vv, ex)
		if err != nil {
			return res, err
		}
		res.MustSet(child).At(keyFunc(kk))
	}

	return res, nil
}

func parseStringMapValue(v reflect.Value, ex ext) (*V, error) {
	return parseMapValue(v, ex, func(k reflect.Value) string {
		return k.String()
	})
}

func parseIntMapValue(v reflect.Value, ex ext) (*V, error) {
	return parseMapValue(v, ex, func(k reflect.Value) string {
		return strconv.FormatInt(k.Int(), 10)
	})
}

func parseUintMapValue(v reflect.Value, ex ext) (*V, error) {
	return parseMapValue(v, ex, func(k reflect.Value) string {
		return strconv.FormatUint(k.Uint(), 10)
	})
}

func parsePtrValue(v reflect.Value, ex ext) (*V, error) {
	if v.IsNil() {
		return parseNullValue(v, ex)
	}

	v, fu, err := validateValAndReturnParser(v.Elem(), ex)
	if err != nil {
		return nil, err
	}

	return fu(v, ex)
}

func parseSliceValue(v reflect.Value, ex ext) (*V, error) {
	if v.IsNil() || v.Len() == 0 {
		if ex.shouldOmitEmpty() {
			return nil, nil
		}
		return NewArray(), nil
	}

	return parseArrayValue(v, ex)
}

func parseBytesValue(v reflect.Value, ex ext) (*V, error) {
	b := v.Interface().([]byte)
	if len(b) == 0 && ex.shouldOmitEmpty() {
		return nil, nil
	}

	return NewBytes(b), nil
}

func parseStringValue(v reflect.Value, ex ext) (*V, error) {
	str := v.String()
	if str == "" && ex.shouldOmitEmpty() {
		return nil, nil
	}

	return NewString(str), nil
}

func parseStructValue(v reflect.Value, ex ext) (*V, error) {
	t := v.Type()
	numField := t.NumField()

	res := NewObject()

	for i := 0; i < numField; i++ {
		vv := v.Field(i)
		tt := t.Field(i)

		keys, children, err := parseStructFieldValue(vv, tt, ex)
		if err != nil {
			return nil, err
		}

		for i, k := range keys {
			v := children[i]
			res.MustSet(v).At(k)
		}
	}

	return res, nil
}

func parseNullValue(_ reflect.Value, ex ext) (*V, error) {
	if ex.shouldOmitEmpty() {
		return nil, nil
	}
	return NewNull(), nil
}

func parseStructFieldValue(
	fv reflect.Value, ft reflect.StructField, parentEx ext,
) (keys []string, children []*V, err error) {

	if ft.Anonymous {
		return parseStructAnonymousFieldValue(fv, ft, parentEx)
	}

	if !fv.CanInterface() {
		return
	}

	fieldName, ex := readFieldTag(ft, "json", parentEx)
	if fieldName == "-" {
		return
	}

	fv, fu, err := validateValAndReturnParser(fv, ex)
	if err != nil {
		err = fmt.Errorf("parsing field '%s' error: %w", fieldName, err)
		return
	}

	child, err := fu(fv, ex)
	if err != nil {
		err = fmt.Errorf("parsing field '%s' error: %w", fieldName, err)
		return
	}
	if child != nil {
		return []string{fieldName}, []*V{child}, nil
	}

	return nil, nil, nil
}

func parseStructAnonymousFieldValue(
	fv reflect.Value, ft reflect.StructField, parentEx ext,
) (keys []string, children []*V, err error) {

	fieldName, ex := readAnonymousFieldTag(ft, "json", parentEx)
	if fieldName == "-" {
		return nil, nil, nil
	}
	if fv.Kind() == reflect.Ptr && fv.IsNil() {
		if ex.shouldOmitEmpty() {
			return nil, nil, nil
		}
		return []string{fieldName}, []*V{NewNull()}, nil
	}

	fv, fu, err := validateValAndReturnParser(fv, ex)
	if err != nil {
		err = fmt.Errorf("parsing anonymous field error: %w", err)
		return
	}

	child, err := fu(fv, ex)
	if err != nil {
		err = fmt.Errorf("parsing anonymous field error: %w", err)
		return
	}
	if child == nil {
		return nil, nil, nil
	}

	switch child.ValueType() {
	default: // invalid
		return nil, nil, nil

	case String, Number, Boolean, Null, Array:
		if ex.private {
			return nil, nil, nil
		}
		return []string{fieldName}, []*V{child}, nil

	case Object:
		child.RangeObjectsBySetSequence(func(k string, c *V) bool {
			keys = append(keys, k)
			children = append(children, c)
			return true
		})
		return
	}
}

func readFieldTag(ft reflect.StructField, name string, parentEx ext) (field string, ex ext) {
	tg := ft.Tag.Get(name)

	if tg == "" {
		return ft.Name, ext{
			ignoreOmitempty: parentEx.ignoreOmitempty,
		}
	}

	parts := strings.Split(tg, ",")
	for i, s := range parts {
		parts[i] = strings.TrimSpace(s)
		if i > 0 {
			if s == "omitempty" {
				ex.omitempty = true
			} else if s == "string" {
				ex.toString = true
			}
		}
	}

	field = parts[0]
	if field == "" {
		field = ft.Name
	}
	ex.ignoreOmitempty = parentEx.ignoreOmitempty
	return
}

func readAnonymousFieldTag(ft reflect.StructField, name string, parentEx ext) (field string, ex ext) {
	field, ex = readFieldTag(ft, name, parentEx)

	firstChar := ft.Name[0]
	if firstChar >= 'A' && firstChar <= 'Z' {
		ex.private = false
	} else {
		ex.private = true
	}

	return
}