package csvutil

import (
	"encoding"
	"encoding/base64"
	"reflect"
	"strconv"
)

var (
	textUnmarshaler = reflect.TypeOf((*encoding.TextUnmarshaler)(nil)).Elem()
	csvUnmarshaler  = reflect.TypeOf((*Unmarshaler)(nil)).Elem()
)

var intDecoders = map[int]decodeFunc{
	8:  decodeIntN(8),
	16: decodeIntN(16),
	32: decodeIntN(32),
	64: decodeIntN(64),
}

var uintDecoders = map[int]decodeFunc{
	8:  decodeUintN(8),
	16: decodeUintN(16),
	32: decodeUintN(32),
	64: decodeUintN(64),
}

var (
	decodeFloat32 = decodeFloatN(32)
	decodeFloat64 = decodeFloatN(64)
)

type decodeFunc func(s string, v reflect.Value) error

func decodeFuncValue(f func([]byte, any) error) decodeFunc {
	return func(s string, v reflect.Value) error {
		return f([]byte(s), v.Interface())
	}
}

func decodeFuncValuePtr(f func([]byte, any) error) decodeFunc {
	return func(s string, v reflect.Value) error {
		v = v.Addr()
		return f([]byte(s), v.Interface())
	}
}

func decodeString(s string, v reflect.Value) error {
	v.SetString(s)
	return nil
}

func decodeIntN(bits int) decodeFunc {
	return func(s string, v reflect.Value) error {
		n, err := strconv.ParseInt(s, 10, bits)
		if err != nil {
			return &UnmarshalTypeError{Value: s, Type: v.Type()}
		}
		v.SetInt(n)
		return nil
	}
}

func decodeUintN(bits int) decodeFunc {
	return func(s string, v reflect.Value) error {
		n, err := strconv.ParseUint(s, 10, bits)
		if err != nil {
			return &UnmarshalTypeError{Value: s, Type: v.Type()}
		}
		v.SetUint(n)
		return nil
	}
}

func decodeFloatN(bits int) decodeFunc {
	return func(s string, v reflect.Value) error {
		n, err := strconv.ParseFloat(s, bits)
		if err != nil {
			return &UnmarshalTypeError{Value: s, Type: v.Type()}
		}
		v.SetFloat(n)
		return nil
	}
}

func decodeBool(s string, v reflect.Value) error {
	b, err := strconv.ParseBool(s)
	if err != nil {
		return &UnmarshalTypeError{Value: s, Type: v.Type()}
	}
	v.SetBool(b)
	return nil
}

func decodePtrTextUnmarshaler(s string, v reflect.Value) error {
	return decodeTextUnmarshaler(s, v.Addr())
}

func decodeTextUnmarshaler(s string, v reflect.Value) error {
	return v.Interface().(encoding.TextUnmarshaler).UnmarshalText([]byte(s))
}

func decodePtrFieldUnmarshaler(s string, v reflect.Value) error {
	return decodeFieldUnmarshaler(s, v.Addr())
}

func decodeFieldUnmarshaler(s string, v reflect.Value) error {
	return v.Interface().(Unmarshaler).UnmarshalCSV([]byte(s))
}

func decodePtr(typ reflect.Type, funcMap map[reflect.Type]func([]byte, any) error, ifaceFuncs []ifaceDecodeFunc) (decodeFunc, error) {
	next, err := decodeFn(typ.Elem(), funcMap, ifaceFuncs)
	if err != nil {
		return nil, err
	}

	return func(s string, v reflect.Value) error {
		if v.IsNil() {
			v.Set(reflect.New(v.Type().Elem()))
		}
		return next(s, v.Elem())
	}, nil
}

func decodeInterface(funcMap map[reflect.Type]func([]byte, any) error, ifaceFuncs []ifaceDecodeFunc) decodeFunc {
	return func(s string, v reflect.Value) error {
		if v.NumMethod() != 0 {
			return &UnmarshalTypeError{
				Value: s,
				Type:  v.Type(),
			}
		}

		if v.IsNil() {
			v.Set(reflect.ValueOf(s))
			return nil
		}

		el := walkValue(v)
		if !el.CanSet() {
			if el.IsValid() {
				// we may get a value receiver unmarshalers or registered funcs
				// underneath the interface in which case we should call
				// Unmarshal/Registered func.
				typ := el.Type()
				if f, ok := funcMap[typ]; ok {
					return decodeFuncValue(f)(s, el)
				}
				for _, f := range ifaceFuncs {
					if typ.AssignableTo(f.argType) {
						return decodeFuncValue(f.f)(s, el)
					}
				}
				if typ.Implements(csvUnmarshaler) {
					return decodeFieldUnmarshaler(s, el)
				}
				if typ.Implements(textUnmarshaler) {
					return decodeTextUnmarshaler(s, el)
				}
			}
			v.Set(reflect.ValueOf(s))
			return nil
		}

		fn, err := decodeFn(el.Type(), funcMap, ifaceFuncs)
		if err != nil {
			return err
		}
		return fn(s, el)
	}
}

func decodeBytes(s string, v reflect.Value) error {
	b, err := base64.StdEncoding.DecodeString(s)
	if err != nil {
		return err
	}
	v.SetBytes(b)
	return nil
}

func decodeFn(typ reflect.Type, funcMap map[reflect.Type]func([]byte, any) error, ifaceFuncs []ifaceDecodeFunc) (decodeFunc, error) {
	if f, ok := funcMap[typ]; ok {
		return decodeFuncValue(f), nil
	}
	if f, ok := funcMap[reflect.PtrTo(typ)]; ok {
		return decodeFuncValuePtr(f), nil
	}

	for _, f := range ifaceFuncs {
		if typ.AssignableTo(f.argType) {
			return decodeFuncValue(f.f), nil
		}
		if reflect.PtrTo(typ).AssignableTo(f.argType) {
			return decodeFuncValuePtr(f.f), nil
		}
	}

	if reflect.PtrTo(typ).Implements(csvUnmarshaler) {
		return decodePtrFieldUnmarshaler, nil
	}
	if reflect.PtrTo(typ).Implements(textUnmarshaler) {
		return decodePtrTextUnmarshaler, nil
	}

	switch typ.Kind() {
	case reflect.Ptr:
		return decodePtr(typ, funcMap, ifaceFuncs)
	case reflect.Interface:
		return decodeInterface(funcMap, ifaceFuncs), nil
	case reflect.String:
		return decodeString, nil
	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		return intDecoders[typ.Bits()], nil
	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
		return uintDecoders[typ.Bits()], nil
	case reflect.Float32:
		return decodeFloat32, nil
	case reflect.Float64:
		return decodeFloat64, nil
	case reflect.Bool:
		return decodeBool, nil
	case reflect.Slice:
		if typ.Elem().Kind() == reflect.Uint8 {
			return decodeBytes, nil
		}
	}

	return nil, &UnsupportedTypeError{Type: typ}
}