package ssob

import (
	"encoding/binary"
	"fmt"
	"math"
	"reflect"
)

func UnmarshalString(in []byte) (ret string, n int, err error) {
	if len(in) < 4 {
		return "", 0, fmt.Errorf("ssob: Decoding string: %w", ErrTypeInvalid)
	}
	l := int32(binary.BigEndian.Uint32(in))

	if len(in[4:]) < int(l) {
		return "", 0, fmt.Errorf("ssob: Invalid length of string: %w", ErrValueInvalid)
	}
	return string(in[4 : l+4]), int(l) + 4, nil
}

func UnmarshalBool(in []byte) (ret bool, n int, err error) {
	if len(in) < 1 {
		return false, 0, fmt.Errorf("ssob: Decoding bool: %w", ErrTypeInvalid)
	}

	if in[0] == byte(0) {
		return true, 1, nil
	}
	return false, 1, nil
}

func UnmarshalInt8(in []byte) (ret int8, n int, err error) {
	if len(in) < 1 {
		return 0, 0, fmt.Errorf("ssob: Decoding int8: %w", ErrTypeInvalid)
	}

	return int8(in[0]), 1, nil
}

func UnmarshalUint8(in []byte) (ret uint8, n int, err error) {
	if len(in) < 1 {
		return 0, 0, fmt.Errorf("ssob: Decoding uint8: %w", ErrTypeInvalid)
	}

	return uint8(in[0]), 1, nil
}

func UnmarshalInt16(in []byte) (ret int16, n int, err error) {
	if len(in) < 2 {
		return 0, 0, fmt.Errorf("ssob: Decoding int16: %w", ErrTypeInvalid)
	}

	return int16(binary.BigEndian.Uint16(in[0:2])), 2, nil
}

func UnmarshalUint16(in []byte) (ret uint16, n int, err error) {
	if len(in) < 2 {
		return 0, 0, fmt.Errorf("ssob: Decoding uint16: %w", ErrTypeInvalid)
	}

	return binary.BigEndian.Uint16(in[0:2]), 2, nil
}

func UnmarshalInt32(in []byte) (ret int32, n int, err error) {
	if len(in) < 4 {
		return 0, 0, fmt.Errorf("ssob: Decoding int32: %w", ErrTypeInvalid)
	}

	return int32(binary.BigEndian.Uint32(in[0:4])), 4, nil
}

func UnmarshalUint32(in []byte) (ret uint32, n int, err error) {
	if len(in) < 4 {
		return 0, 0, fmt.Errorf("ssob: Decoding uint32: %w", ErrTypeInvalid)
	}

	return binary.BigEndian.Uint32(in[0:4]), 4, nil
}

func UnmarshalFloat32(in []byte) (ret float32, n int, err error) {
	if len(in) < 4 {
		return 0, 0, fmt.Errorf("ssob: Decoding float32: %w", ErrTypeInvalid)
	}

	return float32(math.Float32frombits(binary.BigEndian.Uint32(in[0:4]))), 4, nil
}

func UnmarshalInt64(in []byte) (ret int64, n int, err error) {
	if len(in) < 8 {
		return 0, 0, fmt.Errorf("ssob: Decoding int64: %w", ErrTypeInvalid)
	}

	return int64(binary.BigEndian.Uint64(in[0:8])), 8, nil
}

func UnmarshalUint64(in []byte) (ret uint64, n int, err error) {
	if len(in) < 8 {
		return 0, 0, fmt.Errorf("ssob: Decoding uint64: %w", ErrTypeInvalid)
	}

	return binary.BigEndian.Uint64(in[0:8]), 8, nil
}

func UnmarshalFloat64(in []byte) (ret float64, n int, err error) {
	if len(in) < 8 {
		return 0, 0, fmt.Errorf("ssob: Decoding float64: %w", ErrTypeInvalid)
	}

	return float64(math.Float64frombits(binary.BigEndian.Uint64(in[0:8]))), 8, nil
}

type unmarshalFunc func(e interface{}, in []byte) (n int, err error)

var decoderCache map[string]unmarshalFunc

func init() {
	decoderCache = make(map[string]unmarshalFunc)
	RegisterDecoder("bool", func(e interface{}, in []byte) (n int, err error) {
		if i, ok := e.(*bool); ok {
			*i, n, err = UnmarshalBool(in)
			return n, err
		}
		return 0, fmt.Errorf("ssob: Incompatible type - expected bool: %w", ErrTypeMismatch)
	})
	RegisterDecoder("int8", func(e interface{}, in []byte) (n int, err error) {
		if i, ok := e.(*int8); ok {
			*i, n, err = UnmarshalInt8(in)
			return n, err
		}
		return 0, fmt.Errorf("ssob: Incompatible type - expected int8: %w", ErrTypeMismatch)
	})
	RegisterDecoder("uint8", func(e interface{}, in []byte) (n int, err error) {
		if i, ok := e.(*uint8); ok {
			*i, n, err = UnmarshalUint8(in)
			return n, err
		}
		return 0, fmt.Errorf("ssob: Incompatible type - expected uint8: %w", ErrTypeMismatch)
	})
	RegisterDecoder("int16", func(e interface{}, in []byte) (n int, err error) {
		if i, ok := e.(*int16); ok {
			*i, n, err = UnmarshalInt16(in)
			return n, err
		}
		return 0, fmt.Errorf("ssob: Incompatible type - expected int16: %w", ErrTypeMismatch)
	})
	RegisterDecoder("uint16", func(e interface{}, in []byte) (n int, err error) {
		if i, ok := e.(*uint16); ok {
			*i, n, err = UnmarshalUint16(in)
			return n, err
		}
		return 0, fmt.Errorf("ssob: Incompatible type - expected uint16: %w", ErrTypeMismatch)
	})
	RegisterDecoder("int32", func(e interface{}, in []byte) (n int, err error) {
		if i, ok := e.(*int32); ok {
			*i, n, err = UnmarshalInt32(in)
			return n, err
		}
		return 0, fmt.Errorf("ssob: Incompatible type - expected int32: %w", ErrTypeMismatch)
	})
	RegisterDecoder("uint32", func(e interface{}, in []byte) (n int, err error) {
		if i, ok := e.(*uint32); ok {
			*i, n, err = UnmarshalUint32(in)
			return n, err
		}
		return 0, fmt.Errorf("ssob: Incompatible type - expected uint32: %w", ErrTypeMismatch)
	})
	RegisterDecoder("float32", func(e interface{}, in []byte) (n int, err error) {
		if i, ok := e.(*float32); ok {
			*i, n, err = UnmarshalFloat32(in)
			return n, err
		}
		return 0, fmt.Errorf("ssob: Incompatible type - expected float32: %w", ErrTypeMismatch)
	})
	RegisterDecoder("int64", func(e interface{}, in []byte) (n int, err error) {
		if i, ok := e.(*int64); ok {
			*i, n, err = UnmarshalInt64(in)
			return n, err
		}
		return 0, fmt.Errorf("ssob: Incompatible type - expected int64: %w", ErrTypeMismatch)
	})
	RegisterDecoder("uint64", func(e interface{}, in []byte) (n int, err error) {
		if i, ok := e.(*uint64); ok {
			*i, n, err = UnmarshalUint64(in)
			return n, err
		}
		return 0, fmt.Errorf("ssob: Incompatible type - expected uint64: %w", ErrTypeMismatch)
	})
	RegisterDecoder("float64", func(e interface{}, in []byte) (n int, err error) {
		if i, ok := e.(*float64); ok {
			*i, n, err = UnmarshalFloat64(in)
			return n, err
		}
		return 0, fmt.Errorf("ssob: Incompatible type - expected float64: %w", ErrTypeMismatch)
	})
	RegisterDecoder("string", func(e interface{}, in []byte) (n int, err error) {
		if i, ok := e.(*string); ok {
			*i, n, err = UnmarshalString(in)
			return n, err
		}
		return 0, fmt.Errorf("ssob: Incompatible type - expected string: %w", ErrTypeMismatch)
	})
}

func decRegister(e interface{}) (err error) {
	t := reflect.TypeOf(e)
	if t == nil {
		return fmt.Errorf("ssob: nil type: %w", ErrTypeInvalid)
	}

	switch t.Kind() {
	case reflect.Invalid:
		return fmt.Errorf("ssob: invalid type: %w", ErrTypeInvalid)
	case reflect.Array:
		f := func(e interface{}, in []byte) (n int, err error) {
			t := reflect.TypeOf(e)
			v := reflect.ValueOf(e)
			pos := 0

			if t.Kind() != reflect.Ptr || v.IsNil() {
				return 0, fmt.Errorf("ssob: Cannot unmarshal to nil pointer: %w", ErrValueInvalid)
			}

			l, r, err := UnmarshalInt32(in)
			pos += r
			if err != nil {
				return pos, err
			}

			ti := v.Elem()
			if int(l) != ti.Len() {
				return pos, fmt.Errorf("ssob: Invalid array length. Expected %s got %s: %w", string(l), string(ti.Len()), ErrValueInvalid)
			}
			for i := 0; i < int(l); i++ {
				e := reflect.New(reflect.TypeOf(ti.Interface()).Elem())
				r, err := unmarshal(e.Interface(), in[pos:])
				pos += r
				if err != nil {
					return pos, err
				}
				ti.Index(i).Set(reflect.Indirect(e))
			}
			return pos, nil
		}
		decoderCache[string(t.Kind())] = f
	case reflect.Slice:
		f := func(e interface{}, in []byte) (n int, err error) {
			t := reflect.TypeOf(e)
			v := reflect.ValueOf(e)
			pos := 0

			if t.Kind() != reflect.Ptr || v.IsNil() {
				return 0, fmt.Errorf("ssob: Cannot unmarshal to nil pointer: %w", ErrValueInvalid)
			}

			l, r, err := UnmarshalInt32(in)
			pos += r
			if err != nil {
				return pos, err
			}

			ti := v.Elem()
			ti.Set(reflect.MakeSlice(reflect.TypeOf(ti.Interface()), 0, ti.Cap()))
			for i := 0; i < int(l); i++ {
				e := reflect.New(reflect.TypeOf(ti.Interface()).Elem())
				r, err := unmarshal(e.Interface(), in[pos:])
				pos += r
				if err != nil {
					return pos, err
				}
				ti.Set(reflect.Append(ti, reflect.Indirect(e)))
			}
			return pos, nil
		}
		decoderCache[string(t.Kind())] = f
	case reflect.Struct:
		zt := reflect.New(t)
		n := zt.Elem().NumField()
		mfields := []int{}
		for i := 0; i < n; i++ {
			if zt.Elem().Field(i).CanSet() {
				mfields = append(mfields, i)
			}
		}
		if len(mfields) == 0 {
			return fmt.Errorf("ssob: No exported fields for %s: %w", string(t.Name()), ErrParseFailed)
		}

		f := func(e interface{}, in []byte) (n int, err error) {
			t := reflect.TypeOf(e)
			v := reflect.ValueOf(e)
			pos := 0

			if t.Kind() != reflect.Ptr || v.IsNil() {
				return 0, fmt.Errorf("ssob: Cannot unmarshal to nil pointer: %w", ErrValueInvalid)
			}

			vi := reflect.Indirect(v)
			for _, i := range mfields {
				ni, err := unmarshal(vi.Field(i).Addr().Interface(), in[pos:])
				pos += ni
				if err != nil {
					return pos, err
				}
			}

			return pos, nil
		}
		decoderCache[t.Name()] = f
	case reflect.Map:
		f := func(e interface{}, in []byte) (n int, err error) {
			t := reflect.TypeOf(e)
			v := reflect.ValueOf(e)
			pos := 0

			if t.Kind() != reflect.Ptr || v.IsNil() {
				return 0, fmt.Errorf("ssob: Cannot unmarshal to nil pointer: %w", ErrValueInvalid)
			}

			l, r, err := UnmarshalInt32(in)
			pos += r
			if err != nil {
				return pos, err
			}

			vi := reflect.Indirect(v)
			vt := reflect.TypeOf(vi.Interface())
			tk := vt.Key()
			tv := vt.Elem()
			for i := int32(0); i < l; i++ {
				ek := reflect.New(tk)
				ev := reflect.New(tv)
				r, err := unmarshal(ek.Interface(), in[pos:])
				pos += r
				if err != nil {
					return pos, err
				}
				r, err = unmarshal(ev.Interface(), in[pos:])
				pos += r
				if err != nil {
					return pos, err
				}
				vi.SetMapIndex(reflect.Indirect(ek), reflect.Indirect(ev))
			}

			return pos, nil
		}
		decoderCache[string(t.Kind())] = f
	case reflect.Bool:
		f := func(e interface{}, in []byte) (n int, err error) {
			v := reflect.ValueOf(e)
			i := bool(false)
			pos := 0

			r, err := unmarshalBaseType(&i, in[pos:])
			pos += r
			if err != nil {
				return pos, err
			}
			v.Elem().SetBool(bool(i))

			return pos, nil
		}
		decoderCache[t.Name()] = f
	case reflect.Uint8:
		f := func(e interface{}, in []byte) (n int, err error) {
			v := reflect.ValueOf(e)
			i := uint8(0)
			pos := 0

			r, err := unmarshalBaseType(&i, in[pos:])
			pos += r
			if err != nil {
				return pos, err
			}
			v.Elem().SetUint(uint64(i))

			return pos, nil
		}
		decoderCache[t.Name()] = f
	case reflect.Uint16:
		f := func(e interface{}, in []byte) (n int, err error) {
			v := reflect.ValueOf(e)
			i := uint16(0)
			pos := 0

			r, err := unmarshalBaseType(&i, in[pos:])
			pos += r
			if err != nil {
				return pos, err
			}
			v.Elem().SetUint(uint64(i))

			return pos, nil
		}
		decoderCache[t.Name()] = f
	case reflect.Uint32:
		f := func(e interface{}, in []byte) (n int, err error) {
			v := reflect.ValueOf(e)
			i := uint32(0)
			pos := 0

			r, err := unmarshalBaseType(&i, in[pos:])
			pos += r
			if err != nil {
				return pos, err
			}
			v.Elem().SetUint(uint64(i))

			return pos, nil
		}
		decoderCache[t.Name()] = f
	case reflect.Uint64:
		f := func(e interface{}, in []byte) (n int, err error) {
			v := reflect.ValueOf(e)
			i := uint64(0)
			pos := 0

			r, err := unmarshalBaseType(&i, in[pos:])
			pos += r
			if err != nil {
				return pos, err
			}
			v.Elem().SetUint(uint64(i))

			return pos, nil
		}
		decoderCache[t.Name()] = f
	case reflect.Int8:
		f := func(e interface{}, in []byte) (n int, err error) {
			v := reflect.ValueOf(e)
			i := int8(0)
			pos := 0

			r, err := unmarshalBaseType(&i, in[pos:])
			pos += r
			if err != nil {
				return pos, err
			}
			v.Elem().SetInt(int64(i))

			return pos, nil
		}
		decoderCache[t.Name()] = f
	case reflect.Int16:
		f := func(e interface{}, in []byte) (n int, err error) {
			v := reflect.ValueOf(e)
			i := int16(0)
			pos := 0

			r, err := unmarshalBaseType(&i, in[pos:])
			pos += r
			if err != nil {
				return pos, err
			}
			v.Elem().SetInt(int64(i))

			return pos, nil
		}
		decoderCache[t.Name()] = f
	case reflect.Int32:
		f := func(e interface{}, in []byte) (n int, err error) {
			v := reflect.ValueOf(e)
			i := int32(0)
			pos := 0

			r, err := unmarshalBaseType(&i, in[pos:])
			pos += r
			if err != nil {
				return pos, err
			}
			v.Elem().SetInt(int64(i))

			return pos, nil
		}
		decoderCache[t.Name()] = f
	case reflect.Int64:
		f := func(e interface{}, in []byte) (n int, err error) {
			v := reflect.ValueOf(e)
			i := int64(0)
			pos := 0

			r, err := unmarshalBaseType(&i, in[pos:])
			pos += r
			if err != nil {
				return pos, err
			}
			v.Elem().SetInt(int64(i))

			return pos, nil
		}
		decoderCache[t.Name()] = f
	case reflect.String:
		f := func(e interface{}, in []byte) (n int, err error) {
			v := reflect.ValueOf(e)
			i := string("")
			pos := 0

			r, err := unmarshalBaseType(&i, in[pos:])
			pos += r
			if err != nil {
				return pos, err
			}
			v.Elem().SetString(i)

			return pos, nil
		}
		decoderCache[t.Name()] = f
	default:
		return fmt.Errorf("ssob: %s: %w", string(t.Name()), ErrTypeUnknown)
	}

	return nil
}

func unmarshalBaseType(e interface{}, in []byte) (n int, err error) {
	switch t := e.(type) {
	case *bool:
		return decoderCache["bool"](t, in)
	case *int8:
		return decoderCache["int8"](t, in)
	case *uint8:
		return decoderCache["uint8"](t, in)
	case *int16:
		return decoderCache["int16"](t, in)
	case *uint16:
		return decoderCache["uint16"](t, in)
	case *int32:
		return decoderCache["int32"](t, in)
	case *uint32:
		return decoderCache["uint32"](t, in)
	case *int64:
		return decoderCache["int64"](t, in)
	case *uint64:
		return decoderCache["uint64"](t, in)
	case *float32:
		return decoderCache["float32"](t, in)
	case *float64:
		return decoderCache["float64"](t, in)
	case *string:
		return decoderCache["string"](t, in)
	default:
		return 0, fmt.Errorf("ssob: No base type: %w", ErrTypeUnknown)
	}
}

func unmarshal(e interface{}, in []byte) (n int, err error) {
	n, err = unmarshalBaseType(e, in)
	if err == nil {
		return n, err
	}

	var key string
	t := reflect.TypeOf(e)
	v := reflect.ValueOf(e)
	if !v.IsValid() || t.Kind() != reflect.Ptr || v.IsNil() {
		return 0, fmt.Errorf("ssob: Need a pointer that is fully allocated for unmarshalling: %w", ErrValueInvalid)
	}

	p := reflect.Indirect(v)
	if p.Kind() != reflect.Ptr && p.Kind() != reflect.Interface {
		switch p.Kind() {
		case reflect.Bool, reflect.Int8, reflect.Int16, reflect.Int32,
			reflect.Int64, reflect.Uint8, reflect.Uint16, reflect.Uint32,
			reflect.Uint64, reflect.String, reflect.Struct:
			key = reflect.TypeOf(p.Interface()).Name()
		default:
			key = string(p.Kind())
		}

		if f, ok := decoderCache[key]; ok {
			return f(v.Interface(), in)
		} else {
			err = decRegister(p.Interface())
			if err != nil {
				return 0, err
			}
			return unmarshal(e, in)
		}
	}
	if !p.Elem().IsValid() {
		err = allocType(v)
		if err != nil {
			return 0, err
		}
		p = reflect.Indirect(v)
	}

	return unmarshal(p.Interface(), in)
}

func RegisterDecoder(name string, f func(e interface{}, in []byte) (n int, err error)) {
	decoderCache[name] = f
}