package utils

import (
	"encoding/json"
	"errors"
	"os"
	"reflect"
	"runtime/debug"
	"strconv"
	"strings"
	"time"
	"unicode"

	"github.com/go-playground/validator/v10"
	E "github.com/yusing/go-proxy/internal/error"
	"github.com/yusing/go-proxy/internal/utils/functional"
	"github.com/yusing/go-proxy/internal/utils/strutils"
	"gopkg.in/yaml.v3"
)

type SerializedObject = map[string]any

var (
	ErrInvalidType           = E.New("invalid type")
	ErrNilValue              = E.New("nil")
	ErrUnsettable            = E.New("unsettable")
	ErrUnsupportedConversion = E.New("unsupported conversion")
	ErrUnknownField          = E.New("unknown field")
)

var defaultValues = functional.NewMapOf[reflect.Type, func() any]()

func RegisterDefaultValueFactory[T any](factory func() *T) {
	t := reflect.TypeFor[T]()
	if t.Kind() == reflect.Ptr {
		panic("pointer of pointer")
	}
	if defaultValues.Has(t) {
		panic("default value for " + t.String() + " already registered")
	}
	defaultValues.Store(t, func() any { return factory() })
}

func New(t reflect.Type) reflect.Value {
	if dv, ok := defaultValues.Load(t); ok {
		return reflect.ValueOf(dv())
	}
	return reflect.New(t)
}

func extractFields(t reflect.Type) []reflect.StructField {
	for t.Kind() == reflect.Ptr {
		t = t.Elem()
	}
	if t.Kind() != reflect.Struct {
		return nil
	}
	var fields []reflect.StructField
	for i := range t.NumField() {
		field := t.Field(i)
		if !field.IsExported() {
			continue
		}
		if field.Anonymous {
			fields = append(fields, extractFields(field.Type)...)
		} else {
			fields = append(fields, field)
		}
	}
	return fields
}

// Deserialize takes a SerializedObject and a target value, and assigns the values in the SerializedObject to the target value.
// Deserialize ignores case differences between the field names in the SerializedObject and the target.
//
// The target value must be a struct or a map[string]any.
// If the target value is a struct, the SerializedObject will be deserialized into the struct fields and validate if needed.
// If the target value is a map[string]any, the SerializedObject will be deserialized into the map.
//
// The function returns an error if the target value is not a struct or a map[string]any, or if there is an error during deserialization.
func Deserialize(src SerializedObject, dst any) E.Error {
	if src == nil {
		return E.Errorf("deserialize: src is %w", ErrNilValue)
	}
	if dst == nil {
		return E.Errorf("deserialize: dst is %w\n%s", ErrNilValue, debug.Stack())
	}

	dstV := reflect.ValueOf(dst)
	dstT := dstV.Type()

	for dstT.Kind() == reflect.Ptr {
		if dstV.IsNil() {
			if dstV.CanSet() {
				dstV.Set(New(dstT.Elem()))
			} else {
				return E.Errorf("deserialize: dst is %w\n%s", ErrNilValue, debug.Stack())
			}
		}
		dstV = dstV.Elem()
		dstT = dstV.Type()
	}

	// convert data fields to lower no-snake
	// convert target fields to lower no-snake
	// then check if the field of data is in the target

	errs := E.NewBuilder("deserialize error")

	switch dstV.Kind() {
	case reflect.Struct:
		needValidate := false
		mapping := make(map[string]reflect.Value)
		fieldName := make(map[string]string)
		fields := extractFields(dstT)
		for _, field := range fields {
			var key string
			if jsonTag, ok := field.Tag.Lookup("json"); ok {
				if jsonTag == "-" {
					continue
				}
				key = strutils.CommaSeperatedList(jsonTag)[0]
			} else {
				key = field.Name
			}
			key = strutils.ToLowerNoSnake(key)
			mapping[key] = dstV.FieldByName(field.Name)
			fieldName[field.Name] = key

			_, needValidate = field.Tag.Lookup("validate")

			aliases, ok := field.Tag.Lookup("aliases")
			if ok {
				for _, alias := range strutils.CommaSeperatedList(aliases) {
					mapping[alias] = dstV.FieldByName(field.Name)
					fieldName[field.Name] = alias
				}
			}
		}
		for k, v := range src {
			if field, ok := mapping[strutils.ToLowerNoSnake(k)]; ok {
				err := Convert(reflect.ValueOf(v), field)
				if err != nil {
					errs.Add(err.Subject(k))
				}
			} else {
				errs.Add(ErrUnknownField.Subject(k).Withf(strutils.DoYouMean(NearestField(k, mapping))))
			}
		}
		if needValidate {
			err := validate.Struct(dstV.Interface())
			var valErrs validator.ValidationErrors
			if errors.As(err, &valErrs) {
				for _, e := range valErrs {
					detail := e.ActualTag()
					if e.Param() != "" {
						detail += ":" + e.Param()
					}
					errs.Add(ErrValidationError.
						Subject(e.StructNamespace()).
						Withf("require %q", detail))
				}
			}
		}
		return errs.Error()
	case reflect.Map:
		if dstV.IsNil() {
			dstV.Set(reflect.MakeMap(dstT))
		}
		for k := range src {
			mapVT := dstT.Elem()
			tmp := New(mapVT).Elem()
			err := Convert(reflect.ValueOf(src[k]), tmp)
			if err == nil {
				dstV.SetMapIndex(reflect.ValueOf(k), tmp)
			} else {
				errs.Add(err.Subject(k))
			}
		}
		return errs.Error()
	default:
		return ErrUnsupportedConversion.Subject("deserialize to " + dstT.String())
	}
}

func isIntFloat(t reflect.Kind) bool {
	return t >= reflect.Bool && t <= reflect.Float64
}

// Convert attempts to convert the src to dst.
//
// If src is a map, it is deserialized into dst.
// If src is a slice, each of its elements are converted and stored in dst.
// For any other type, it is converted using the reflect.Value.Convert function (if possible).
//
// If dst is not settable, an error is returned.
// If src cannot be converted to dst, an error is returned.
// If any error occurs during conversion (e.g. deserialization), it is returned.
//
// Returns:
//   - error: the error occurred during conversion, or nil if no error occurred.
func Convert(src reflect.Value, dst reflect.Value) E.Error {
	if !dst.IsValid() {
		return E.Errorf("convert: dst is %w", ErrNilValue)
	}

	if !src.IsValid() {
		if dst.CanSet() {
			dst.Set(reflect.Zero(dst.Type()))
			return nil
		}
		return E.Errorf("convert: src is %w", ErrNilValue)
	}

	srcT := src.Type()
	dstT := dst.Type()

	if src.Kind() == reflect.Interface {
		src = src.Elem()
		srcT = src.Type()
	}

	if !dst.CanSet() {
		return ErrUnsettable.Subject(dstT.String())
	}

	if dst.Kind() == reflect.Pointer {
		if dst.IsNil() {
			dst.Set(New(dstT.Elem()))
		}
		dst = dst.Elem()
		dstT = dst.Type()
	}

	srcKind := srcT.Kind()

	switch {
	case srcT.AssignableTo(dstT):
		dst.Set(src)
		return nil
	// case srcT.ConvertibleTo(dstT):
	// 	dst.Set(src.Convert(dstT))
	// 	return nil
	case srcKind == reflect.String:
		if convertible, err := ConvertString(src.String(), dst); convertible {
			return err
		}
	case isIntFloat(srcKind):
		var strV string
		switch {
		case src.CanInt():
			strV = strconv.FormatInt(src.Int(), 10)
		case srcKind == reflect.Bool:
			strV = strconv.FormatBool(src.Bool())
		case src.CanUint():
			strV = strconv.FormatUint(src.Uint(), 10)
		case src.CanFloat():
			strV = strconv.FormatFloat(src.Float(), 'f', -1, 64)
		}
		if convertible, err := ConvertString(strV, dst); convertible {
			return err
		}
	case srcKind == reflect.Map:
		if src.Len() == 0 {
			return nil
		}
		obj, ok := src.Interface().(SerializedObject)
		if !ok {
			return ErrUnsupportedConversion.Subject(dstT.String() + " to " + srcT.String())
		}
		return Deserialize(obj, dst.Addr().Interface())
	case srcKind == reflect.Slice:
		if src.Len() == 0 {
			return nil
		}
		if dstT.Kind() != reflect.Slice {
			return ErrUnsupportedConversion.Subject(dstT.String() + " to " + srcT.String())
		}
		newSlice := reflect.MakeSlice(dstT, 0, src.Len())
		i := 0
		for _, v := range src.Seq2() {
			tmp := New(dstT.Elem()).Elem()
			err := Convert(v, tmp)
			if err != nil {
				return err.Subjectf("[%d]", i)
			}
			newSlice = reflect.Append(newSlice, tmp)
			i++
		}
		dst.Set(newSlice)
		return nil
	}
	return ErrUnsupportedConversion.Subjectf("%s to %s", srcT, dstT)
}

func ConvertString(src string, dst reflect.Value) (convertible bool, convErr E.Error) {
	convertible = true
	dstT := dst.Type()
	if dst.Kind() == reflect.Ptr {
		if dst.IsNil() {
			dst.Set(New(dstT.Elem()))
		}
		dst = dst.Elem()
		dstT = dst.Type()
	}
	if dst.Kind() == reflect.String {
		dst.SetString(src)
		return
	}
	switch dstT {
	case reflect.TypeFor[time.Duration]():
		if src == "" {
			dst.Set(reflect.Zero(dstT))
			return
		}
		d, err := time.ParseDuration(src)
		if err != nil {
			return true, E.From(err)
		}
		dst.Set(reflect.ValueOf(d))
		return
	default:
	}
	if dstKind := dst.Kind(); isIntFloat(dstKind) {
		var i any
		var err error
		switch {
		case dstKind == reflect.Bool:
			i, err = strconv.ParseBool(src)
		case dst.CanInt():
			i, err = strconv.ParseInt(src, 10, dstT.Bits())
		case dst.CanUint():
			i, err = strconv.ParseUint(src, 10, dstT.Bits())
		case dst.CanFloat():
			i, err = strconv.ParseFloat(src, dstT.Bits())
		}
		if err != nil {
			return true, E.From(err)
		}
		dst.Set(reflect.ValueOf(i).Convert(dstT))
		return
	}
	// check if (*T).Convertor is implemented
	if parser, ok := dst.Addr().Interface().(strutils.Parser); ok {
		return true, E.From(parser.Parse(src))
	}
	// yaml like
	isMultiline := strings.ContainsRune(src, '\n')
	var tmp any
	switch dst.Kind() {
	case reflect.Slice:
		// one liner is comma separated list
		if !isMultiline {
			values := strutils.CommaSeperatedList(src)
			dst.Set(reflect.MakeSlice(dst.Type(), len(values), len(values)))
			errs := E.NewBuilder("invalid slice values")
			for i, v := range values {
				err := Convert(reflect.ValueOf(v), dst.Index(i))
				if err != nil {
					errs.Add(err.Subjectf("[%d]", i))
				}
			}
			if errs.HasError() {
				return true, errs.Error()
			}
			return
		}
		lines := strutils.SplitLine(src)
		sl := make([]string, 0, len(lines))
		for _, line := range lines {
			line = strings.TrimLeftFunc(line, func(r rune) bool {
				return r == '-' || unicode.IsSpace(r)
			})
			if line == "" || line[0] == '#' {
				continue
			}
			sl = append(sl, line)
		}
		tmp = sl
	case reflect.Map, reflect.Struct:
		rawMap := make(SerializedObject)
		err := yaml.Unmarshal([]byte(src), &rawMap)
		if err != nil {
			return true, E.From(err)
		}
		tmp = rawMap
	default:
		return false, nil
	}
	return true, Convert(reflect.ValueOf(tmp), dst)
}

func DeserializeYAML[T any](data []byte, target T) E.Error {
	m := make(map[string]any)
	if err := yaml.Unmarshal(data, m); err != nil {
		return E.From(err)
	}
	return Deserialize(m, target)
}

func DeserializeYAMLMap[V any](data []byte) (_ functional.Map[string, V], err E.Error) {
	m := make(map[string]any)
	if err = E.From(yaml.Unmarshal(data, m)); err != nil {
		return
	}
	m2 := make(map[string]V, len(m))
	if err = Deserialize(m, m2); err != nil {
		return
	}
	return functional.NewMapFrom(m2), nil
}

func LoadJSON[T any](path string, dst *T) error {
	data, err := os.ReadFile(path)
	if err != nil {
		return err
	}
	return json.Unmarshal(data, dst)
}

func SaveJSON[T any](path string, src *T, perm os.FileMode) error {
	data, err := json.Marshal(src)
	if err != nil {
		return err
	}
	return os.WriteFile(path, data, perm)
}