package json

import (
	"encoding"
	"reflect"
	"unsafe"
)

type interfaceDecoder struct {
	typ        *rtype
	structName string
	fieldName  string
	dec        *Decoder
}

func newInterfaceDecoder(dec *Decoder, typ *rtype, structName, fieldName string) *interfaceDecoder {
	return &interfaceDecoder{
		typ:        typ,
		structName: structName,
		fieldName:  fieldName,
		dec:        dec,
	}
}

func (d *interfaceDecoder) numDecoder(s *stream) decoder {
	if s.useNumber {
		return newNumberDecoder(d.structName, d.fieldName, func(p unsafe.Pointer, v Number) {
			*(*interface{})(p) = v
		})
	}
	return newFloatDecoder(d.structName, d.fieldName, func(p unsafe.Pointer, v float64) {
		*(*interface{})(p) = v
	})
}

var (
	interfaceMapType = type2rtype(
		reflect.TypeOf((*map[string]interface{})(nil)).Elem(),
	)
	stringType = type2rtype(
		reflect.TypeOf(""),
	)
)

func decodeStreamUnmarshaler(s *stream, unmarshaler Unmarshaler) error {
	start := s.cursor
	if err := s.skipValue(); err != nil {
		return err
	}
	src := s.buf[start:s.cursor]
	dst := make([]byte, len(src))
	copy(dst, src)

	if err := unmarshaler.UnmarshalJSON(dst); err != nil {
		return err
	}
	return nil
}

func decodeStreamTextUnmarshaler(s *stream, unmarshaler encoding.TextUnmarshaler) error {
	start := s.cursor
	if err := s.skipValue(); err != nil {
		return err
	}
	src := s.buf[start:s.cursor]
	dst := make([]byte, len(src))
	copy(dst, src)

	if err := unmarshaler.UnmarshalText(dst); err != nil {
		return err
	}
	return nil
}

func (d *interfaceDecoder) decodeStreamEmptyInterface(s *stream, p unsafe.Pointer) error {
	s.skipWhiteSpace()
	for {
		switch s.char() {
		case '{':
			var v map[string]interface{}
			ptr := unsafe.Pointer(&v)
			if err := newMapDecoder(
				interfaceMapType,
				stringType,
				newStringDecoder(d.structName, d.fieldName),
				interfaceMapType.Elem(),
				newInterfaceDecoder(d.dec, d.typ, d.structName, d.fieldName),
				d.structName,
				d.fieldName,
			).decodeStream(s, ptr); err != nil {
				return err
			}
			*(*interface{})(p) = v
			return nil
		case '[':
			var v []interface{}
			ptr := unsafe.Pointer(&v)
			if err := newSliceDecoder(
				newInterfaceDecoder(d.dec, d.typ, d.structName, d.fieldName),
				d.typ,
				d.typ.Size(),
				d.structName,
				d.fieldName,
			).decodeStream(s, ptr); err != nil {
				return err
			}
			*(*interface{})(p) = v
			return nil
		case '-', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
			return d.numDecoder(s).decodeStream(s, p)
		case '"':
			s.cursor++
			start := s.cursor
			for {
				switch s.char() {
				case '\\':
					if err := decodeEscapeString(s); err != nil {
						return err
					}
				case '"':
					literal := s.buf[start:s.cursor]
					s.cursor++
					*(*interface{})(p) = string(literal)
					return nil
				case nul:
					if s.read() {
						continue
					}
					return errUnexpectedEndOfJSON("string", s.totalOffset())
				}
				s.cursor++
			}
		case 't':
			if err := trueBytes(s); err != nil {
				return err
			}
			**(**interface{})(unsafe.Pointer(&p)) = true
			return nil
		case 'f':
			if err := falseBytes(s); err != nil {
				return err
			}
			**(**interface{})(unsafe.Pointer(&p)) = false
			return nil
		case 'n':
			if err := nullBytes(s); err != nil {
				return err
			}
			*(*interface{})(p) = nil
			return nil
		case nul:
			if s.read() {
				continue
			}
		}
		break
	}
	return errNotAtBeginningOfValue(s.totalOffset())
}

func (d *interfaceDecoder) decodeStream(s *stream, p unsafe.Pointer) error {
	runtimeInterfaceValue := *(*interface{})(unsafe.Pointer(&interfaceHeader{
		typ: d.typ,
		ptr: p,
	}))
	rv := reflect.ValueOf(runtimeInterfaceValue)
	if rv.NumMethod() > 0 && rv.CanInterface() {
		if u, ok := rv.Interface().(Unmarshaler); ok {
			return decodeStreamUnmarshaler(s, u)
		}
		if u, ok := rv.Interface().(encoding.TextUnmarshaler); ok {
			return decodeStreamTextUnmarshaler(s, u)
		}
		return nil
	}
	iface := rv.Interface()
	ifaceHeader := (*interfaceHeader)(unsafe.Pointer(&iface))
	typ := ifaceHeader.typ
	if d.typ == typ || typ == nil {
		// concrete type is empty interface
		return d.decodeStreamEmptyInterface(s, p)
	}
	if typ.Kind() == reflect.Ptr && typ.Elem() == d.typ || typ.Kind() != reflect.Ptr {
		return d.decodeStreamEmptyInterface(s, p)
	}
	if s.char() == 'n' {
		if err := nullBytes(s); err != nil {
			return err
		}
		*(*interface{})(p) = nil
		return nil
	}
	decoder, err := d.dec.compileToGetDecoder(uintptr(unsafe.Pointer(typ)), typ)
	if err != nil {
		return err
	}
	return decoder.decodeStream(s, ifaceHeader.ptr)
}

func (d *interfaceDecoder) decode(buf []byte, cursor int64, p unsafe.Pointer) (int64, error) {
	runtimeInterfaceValue := *(*interface{})(unsafe.Pointer(&interfaceHeader{
		typ: d.typ,
		ptr: p,
	}))
	rv := reflect.ValueOf(runtimeInterfaceValue)
	iface := rv.Interface()
	ifaceHeader := (*interfaceHeader)(unsafe.Pointer(&iface))
	typ := ifaceHeader.typ
	if d.typ == typ || typ == nil {
		// concrete type is empty interface
		return d.decodeEmptyInterface(buf, cursor, p)
	}
	if typ.Kind() == reflect.Ptr && typ.Elem() == d.typ || typ.Kind() != reflect.Ptr {
		return d.decodeEmptyInterface(buf, cursor, p)
	}
	if buf[cursor] == 'n' {
		if cursor+3 >= int64(len(buf)) {
			return 0, errUnexpectedEndOfJSON("null", cursor)
		}
		if buf[cursor+1] != 'u' {
			return 0, errInvalidCharacter(buf[cursor+1], "null", cursor)
		}
		if buf[cursor+2] != 'l' {
			return 0, errInvalidCharacter(buf[cursor+2], "null", cursor)
		}
		if buf[cursor+3] != 'l' {
			return 0, errInvalidCharacter(buf[cursor+3], "null", cursor)
		}
		cursor += 4
		**(**interface{})(unsafe.Pointer(&p)) = nil
		return cursor, nil
	}
	decoder, err := d.dec.compileToGetDecoder(uintptr(unsafe.Pointer(typ)), typ)
	if err != nil {
		return 0, err
	}
	return decoder.decode(buf, cursor, ifaceHeader.ptr)
}

func (d *interfaceDecoder) decodeEmptyInterface(buf []byte, cursor int64, p unsafe.Pointer) (int64, error) {
	cursor = skipWhiteSpace(buf, cursor)
	switch buf[cursor] {
	case '{':
		var v map[string]interface{}
		ptr := unsafe.Pointer(&v)
		dec := newMapDecoder(
			interfaceMapType,
			stringType,
			newStringDecoder(d.structName, d.fieldName),
			interfaceMapType.Elem(),
			newInterfaceDecoder(d.dec, d.typ, d.structName, d.fieldName),
			d.structName, d.fieldName,
		)
		cursor, err := dec.decode(buf, cursor, ptr)
		if err != nil {
			return 0, err
		}
		**(**interface{})(unsafe.Pointer(&p)) = v
		return cursor, nil
	case '[':
		var v []interface{}
		ptr := unsafe.Pointer(&v)
		dec := newSliceDecoder(
			newInterfaceDecoder(d.dec, d.typ, d.structName, d.fieldName),
			d.typ,
			d.typ.Size(),
			d.structName, d.fieldName,
		)
		cursor, err := dec.decode(buf, cursor, ptr)
		if err != nil {
			return 0, err
		}
		**(**interface{})(unsafe.Pointer(&p)) = v
		return cursor, nil
	case '-', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
		return newFloatDecoder(d.structName, d.fieldName, func(p unsafe.Pointer, v float64) {
			*(*interface{})(p) = v
		}).decode(buf, cursor, p)
	case '"':
		cursor++
		start := cursor
		for {
			switch buf[cursor] {
			case '\\':
				cursor++
				continue
			case '"':
				literal := buf[start:cursor]
				cursor++
				**(**interface{})(unsafe.Pointer(&p)) = *(*string)(unsafe.Pointer(&literal))
				return cursor, nil
			case nul:
				return 0, errUnexpectedEndOfJSON("string", cursor)
			}
			cursor++
		}
	case 't':
		if cursor+3 >= int64(len(buf)) {
			return 0, errUnexpectedEndOfJSON("bool(true)", cursor)
		}
		if buf[cursor+1] != 'r' {
			return 0, errInvalidCharacter(buf[cursor+1], "bool(true)", cursor)
		}
		if buf[cursor+2] != 'u' {
			return 0, errInvalidCharacter(buf[cursor+2], "bool(true)", cursor)
		}
		if buf[cursor+3] != 'e' {
			return 0, errInvalidCharacter(buf[cursor+3], "bool(true)", cursor)
		}
		cursor += 4
		**(**interface{})(unsafe.Pointer(&p)) = true
		return cursor, nil
	case 'f':
		if cursor+4 >= int64(len(buf)) {
			return 0, errUnexpectedEndOfJSON("bool(false)", cursor)
		}
		if buf[cursor+1] != 'a' {
			return 0, errInvalidCharacter(buf[cursor+1], "bool(false)", cursor)
		}
		if buf[cursor+2] != 'l' {
			return 0, errInvalidCharacter(buf[cursor+2], "bool(false)", cursor)
		}
		if buf[cursor+3] != 's' {
			return 0, errInvalidCharacter(buf[cursor+3], "bool(false)", cursor)
		}
		if buf[cursor+4] != 'e' {
			return 0, errInvalidCharacter(buf[cursor+4], "bool(false)", cursor)
		}
		cursor += 5
		**(**interface{})(unsafe.Pointer(&p)) = false
		return cursor, nil
	case 'n':
		if cursor+3 >= int64(len(buf)) {
			return 0, errUnexpectedEndOfJSON("null", cursor)
		}
		if buf[cursor+1] != 'u' {
			return 0, errInvalidCharacter(buf[cursor+1], "null", cursor)
		}
		if buf[cursor+2] != 'l' {
			return 0, errInvalidCharacter(buf[cursor+2], "null", cursor)
		}
		if buf[cursor+3] != 'l' {
			return 0, errInvalidCharacter(buf[cursor+3], "null", cursor)
		}
		cursor += 4
		**(**interface{})(unsafe.Pointer(&p)) = nil
		return cursor, nil
	}
	return cursor, errNotAtBeginningOfValue(cursor)
}