package ssob

import (
	"encoding/binary"
	"errors"
	"reflect"
)

func UnmarshalString(in []byte) (ret string, n int, err error) {
	if len(in) < 4 {
		return "", 0, errors.New("ssob: Invalid input to decode string")
	}
	l := int32(binary.BigEndian.Uint32(in))

	if len(in[4:]) < int(l) {
		return "", 0, errors.New("ssob: Invalid length of string")
	}
	return string(in[4 : l+4]), int(l) + 4, nil
}

func UnmarshalInt8(in []byte) (ret int8, n int, err error) {
	if len(in) < 1 {
		return 0, 0, errors.New("ssob: Invalid input to decode int8")
	}

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

func UnmarshalUint8(in []byte) (ret uint8, n int, err error) {
	if len(in) < 1 {
		return 0, 0, errors.New("ssob: Invalid input to decode uint8")
	}

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

func UnmarshalInt16(in []byte) (ret int16, n int, err error) {
	if len(in) < 2 {
		return 0, 0, errors.New("ssob: Invalid input to decode int16")
	}

	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, errors.New("ssob: Invalid input to decode uint16")
	}

	return binary.BigEndian.Uint16(in[0:1]), 2, nil
}

func UnmarshalInt32(in []byte) (ret int32, n int, err error) {
	if len(in) < 4 {
		return 0, 0, errors.New("ssob: Invalid input to decode int32")
	}

	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, errors.New("ssob: Invalid input to decode uint32")
	}

	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, errors.New("ssob: Invalid input to decode float32")
	}

	return float32(binary.BigEndian.Uint64(in[0:4])), 4, nil
}

func UnmarshalInt64(in []byte) (ret int64, n int, err error) {
	if len(in) < 8 {
		return 0, 0, errors.New("ssob: Invalid input to decode int64")
	}

	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, errors.New("ssob: Invalid input to decode uint64")
	}

	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, errors.New("ssob: Invalid input to decode float64")
	}

	return float64(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("int8", func(e interface{}, in []byte) (n int, err error) {
		if i, ok := e.(*int8); ok {
			*i, n, err = UnmarshalInt8(in)
			return n, nil
		}
		return 0, errors.New("ssob: Incompatible type - expected int8")
	})
	RegisterDecoder("uint8", func(e interface{}, in []byte) (n int, err error) {
		if i, ok := e.(*uint8); ok {
			*i, n, err = UnmarshalUint8(in)
			return n, nil
		}
		return 0, errors.New("ssob: Incompatible type - expected uint8")
	})
	RegisterDecoder("int16", func(e interface{}, in []byte) (n int, err error) {
		if i, ok := e.(*int16); ok {
			*i, n, err = UnmarshalInt16(in)
			return n, nil
		}
		return 0, errors.New("ssob: Incompatible type - expected int16")
	})
	RegisterDecoder("uint16", func(e interface{}, in []byte) (n int, err error) {
		if i, ok := e.(*uint16); ok {
			*i, n, err = UnmarshalUint16(in)
			return n, nil
		}
		return 0, errors.New("ssob: Incompatible type - expected uint16")
	})
	RegisterDecoder("int32", func(e interface{}, in []byte) (n int, err error) {
		if i, ok := e.(*int32); ok {
			*i, n, err = UnmarshalInt32(in)
			return n, nil
		}
		return 0, errors.New("ssob: Incompatible type - expected int32")
	})
	RegisterDecoder("uint32", func(e interface{}, in []byte) (n int, err error) {
		if i, ok := e.(*uint32); ok {
			*i, n, err = UnmarshalUint32(in)
			return n, nil
		}
		return 0, errors.New("ssob: Incompatible type - expected uint32")
	})
	RegisterDecoder("float32", func(e interface{}, in []byte) (n int, err error) {
		if i, ok := e.(*float32); ok {
			*i, n, err = UnmarshalFloat32(in)
			return n, nil
		}
		return 0, errors.New("ssob: Incompatible type - expected float32")
	})
	RegisterDecoder("int64", func(e interface{}, in []byte) (n int, err error) {
		if i, ok := e.(*int64); ok {
			*i, n, err = UnmarshalInt64(in)
			return n, nil
		}
		return 0, errors.New("ssob: Incompatible type - expected int64")
	})
	RegisterDecoder("uint64", func(e interface{}, in []byte) (n int, err error) {
		if i, ok := e.(*uint64); ok {
			*i, n, err = UnmarshalUint64(in)
			return n, nil
		}
		return 0, errors.New("ssob: Incompatible type - expected uint64")
	})
	RegisterDecoder("float64", func(e interface{}, in []byte) (n int, err error) {
		if i, ok := e.(*float64); ok {
			*i, n, err = UnmarshalFloat64(in)
			return n, nil
		}
		return 0, errors.New("ssob: Incompatible type - expected float64")
	})
	RegisterDecoder("string", func(e interface{}, in []byte) (n int, err error) {
		if i, ok := e.(*string); ok {
			*i, n, err = UnmarshalString(in)
			return n, nil
		}
		return 0, errors.New("ssob: Incompatible type - expected string")
	})
}

func decRegister(e interface{}) (err error) {
	t := reflect.TypeOf(e)
	v := reflect.ValueOf(e)
	switch t.Kind() {
	case reflect.Invalid:
		return errors.New("ssob: Invalid type")
	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, errors.New("ssob: Cannot unmarshal to nil pointer")
			}

			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:
		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, errors.New("ssob: Cannot unmarshal to nil pointer")
			}

			vi := reflect.Indirect(v)
			l := vi.NumField()
			for i := 0; i < l; i++ {
				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, errors.New("ssob: Cannot unmarshal to nil pointer")
			}

			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
	default:
		return errors.New("ssob: Unknown type " + string(v.Kind()))
	}

	return nil
}

func unmarshalBaseType(e interface{}, in []byte) (n int, err error) {
	switch t := e.(type) {
	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, errors.New("ssob: No base type")
	}
}

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 t.Kind() != reflect.Ptr || v.IsNil() {
		return 0, errors.New("ssob: Need a pointer that is fully allocated for unmarshalling")
	}

	p := reflect.Indirect(v)
	if p.Kind() != reflect.Ptr {
		if p.Kind() == reflect.Struct {
			key = reflect.TypeOf(p.Interface()).Name()
		} else {
			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)
}

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