// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package impl

import (
	"fmt"
	"reflect"

	"github.com/golang/protobuf/v2/internal/flags"
	pref "github.com/golang/protobuf/v2/reflect/protoreflect"
)

type fieldInfo struct {
	// TODO: specialize marshal and unmarshal functions?

	has     func(pointer) bool
	get     func(pointer) pref.Value
	set     func(pointer, pref.Value)
	clear   func(pointer)
	mutable func(pointer) pref.Mutable
}

func fieldInfoForWeak(fd pref.FieldDescriptor, fs reflect.StructField) fieldInfo {
	if !flags.Proto1Legacy {
		panic("weak fields not supported")
	}
	// TODO: support weak fields.
	panic(fmt.Sprintf("invalid field: %v", fd))
}

func fieldInfoForOneof(fd pref.FieldDescriptor, fs reflect.StructField, ot reflect.Type) fieldInfo {
	// TODO: support oneof fields.
	panic(fmt.Sprintf("invalid field: %v", fd))
}

func fieldInfoForMap(fd pref.FieldDescriptor, fs reflect.StructField) fieldInfo {
	// TODO: support map fields.
	panic(fmt.Sprintf("invalid field: %v", fd))
}

func fieldInfoForVector(fd pref.FieldDescriptor, fs reflect.StructField) fieldInfo {
	// TODO: support vector fields.
	panic(fmt.Sprintf("invalid field: %v", fd))
}

var emptyBytes = reflect.ValueOf([]byte{})

func fieldInfoForScalar(fd pref.FieldDescriptor, fs reflect.StructField) fieldInfo {
	ft := fs.Type
	nullable := fd.Syntax() == pref.Proto2
	if nullable {
		if ft.Kind() != reflect.Ptr && ft.Kind() != reflect.Slice {
			panic(fmt.Sprintf("invalid type: got %v, want pointer", ft))
		}
		if ft.Kind() == reflect.Ptr {
			ft = ft.Elem()
		}
	}
	conv := matchGoTypePBKind(ft, fd.Kind())
	fieldOffset := offsetOf(fs)
	// TODO: Implement unsafe fast path?
	return fieldInfo{
		has: func(p pointer) bool {
			rv := p.apply(fieldOffset).asType(fs.Type).Elem()
			if nullable {
				return !rv.IsNil()
			}
			switch rv.Kind() {
			case reflect.Bool:
				return rv.Bool()
			case reflect.Int32, reflect.Int64:
				return rv.Int() > 0
			case reflect.Uint32, reflect.Uint64:
				return rv.Uint() > 0
			case reflect.Float32, reflect.Float64:
				return rv.Float() > 0
			case reflect.String, reflect.Slice:
				return rv.Len() > 0
			default:
				panic(fmt.Sprintf("invalid type: %v", rv.Type())) // should never happen
			}
		},
		get: func(p pointer) pref.Value {
			rv := p.apply(fieldOffset).asType(fs.Type).Elem()
			if nullable {
				if rv.IsNil() {
					pv := fd.Default()
					if fd.Kind() == pref.BytesKind && len(pv.Bytes()) > 0 {
						return pref.ValueOf(append([]byte(nil), pv.Bytes()...)) // copy default bytes for safety
					}
					return pv
				}
				if rv.Kind() == reflect.Ptr {
					rv = rv.Elem()
				}
			}
			return conv.toPB(rv)
		},
		set: func(p pointer, v pref.Value) {
			rv := p.apply(fieldOffset).asType(fs.Type).Elem()
			if nullable && rv.Kind() == reflect.Ptr {
				if rv.IsNil() {
					rv.Set(reflect.New(ft))
				}
				rv = rv.Elem()
			}
			rv.Set(conv.toGo(v))
			if nullable && rv.Kind() == reflect.Slice && rv.IsNil() {
				rv.Set(emptyBytes)
			}
		},
		clear: func(p pointer) {
			rv := p.apply(fieldOffset).asType(fs.Type).Elem()
			rv.Set(reflect.Zero(rv.Type()))
		},
		mutable: func(p pointer) pref.Mutable {
			panic("invalid mutable call")
		},
	}
}

func fieldInfoForMessage(fd pref.FieldDescriptor, fs reflect.StructField) fieldInfo {
	// TODO: support vector fields.
	panic(fmt.Sprintf("invalid field: %v", fd))
}

// messageV1 is the protoV1.Message interface.
type messageV1 interface {
	Reset()
	String() string
	ProtoMessage()
}

var (
	boolType    = reflect.TypeOf(bool(false))
	int32Type   = reflect.TypeOf(int32(0))
	int64Type   = reflect.TypeOf(int64(0))
	uint32Type  = reflect.TypeOf(uint32(0))
	uint64Type  = reflect.TypeOf(uint64(0))
	float32Type = reflect.TypeOf(float32(0))
	float64Type = reflect.TypeOf(float64(0))
	stringType  = reflect.TypeOf(string(""))
	bytesType   = reflect.TypeOf([]byte(nil))

	enumIfaceV2    = reflect.TypeOf((*pref.ProtoEnum)(nil)).Elem()
	messageIfaceV1 = reflect.TypeOf((*messageV1)(nil)).Elem()
	messageIfaceV2 = reflect.TypeOf((*pref.ProtoMessage)(nil)).Elem()

	byteType = reflect.TypeOf(byte(0))
)

// matchGoTypePBKind matches a Go type with the protobuf kind.
//
// This matcher deliberately supports a wider range of Go types than what
// protoc-gen-go historically generated to be able to automatically wrap some
// v1 messages generated by other forks of protoc-gen-go.
func matchGoTypePBKind(t reflect.Type, k pref.Kind) converter {
	switch k {
	case pref.BoolKind:
		if t.Kind() == reflect.Bool {
			return makeScalarConverter(t, boolType)
		}
	case pref.Int32Kind, pref.Sint32Kind, pref.Sfixed32Kind:
		if t.Kind() == reflect.Int32 {
			return makeScalarConverter(t, int32Type)
		}
	case pref.Int64Kind, pref.Sint64Kind, pref.Sfixed64Kind:
		if t.Kind() == reflect.Int64 {
			return makeScalarConverter(t, int64Type)
		}
	case pref.Uint32Kind, pref.Fixed32Kind:
		if t.Kind() == reflect.Uint32 {
			return makeScalarConverter(t, uint32Type)
		}
	case pref.Uint64Kind, pref.Fixed64Kind:
		if t.Kind() == reflect.Uint64 {
			return makeScalarConverter(t, uint64Type)
		}
	case pref.FloatKind:
		if t.Kind() == reflect.Float32 {
			return makeScalarConverter(t, float32Type)
		}
	case pref.DoubleKind:
		if t.Kind() == reflect.Float64 {
			return makeScalarConverter(t, float64Type)
		}
	case pref.StringKind:
		if t.Kind() == reflect.String || (t.Kind() == reflect.Slice && t.Elem() == byteType) {
			return makeScalarConverter(t, stringType)
		}
	case pref.BytesKind:
		if t.Kind() == reflect.String || (t.Kind() == reflect.Slice && t.Elem() == byteType) {
			return makeScalarConverter(t, bytesType)
		}
	case pref.EnumKind:
		// Handle v2 enums, which must satisfy the proto.Enum interface.
		if t.Kind() != reflect.Ptr && t.Implements(enumIfaceV2) {
			// TODO: implement this.
		}

		// Handle v1 enums, which we identify as simply a named int32 type.
		if t.Kind() == reflect.Int32 && t.PkgPath() != "" {
			// TODO: need logic to wrap a legacy enum to implement this.
		}
	case pref.MessageKind, pref.GroupKind:
		// Handle v2 messages, which must satisfy the proto.Message interface.
		if t.Kind() == reflect.Ptr && t.Implements(messageIfaceV2) {
			// TODO: implement this.
		}

		// Handle v1 messages, which we need to wrap as a v2 message.
		if t.Kind() == reflect.Ptr && t.Implements(messageIfaceV1) {
			// TODO: need logic to wrap a legacy message.
		}
	}
	panic(fmt.Sprintf("invalid Go type %v for protobuf kind %v", t, k))
}

// converter provides functions for converting to/from Go reflect.Value types
// and protobuf protoreflect.Value types.
type converter struct {
	toPB func(reflect.Value) pref.Value
	toGo func(pref.Value) reflect.Value
}

func makeScalarConverter(goType, pbType reflect.Type) converter {
	return converter{
		toPB: func(v reflect.Value) pref.Value {
			if v.Type() != goType {
				panic(fmt.Sprintf("invalid type: got %v, want %v", v.Type(), goType))
			}
			if goType.Kind() == reflect.String && pbType.Kind() == reflect.Slice && v.Len() == 0 {
				return pref.ValueOf([]byte(nil)) // ensure empty string is []byte(nil)
			}
			return pref.ValueOf(v.Convert(pbType).Interface())
		},
		toGo: func(v pref.Value) reflect.Value {
			rv := reflect.ValueOf(v.Interface())
			if rv.Type() != pbType {
				panic(fmt.Sprintf("invalid type: got %v, want %v", rv.Type(), pbType))
			}
			if pbType.Kind() == reflect.String && goType.Kind() == reflect.Slice && rv.Len() == 0 {
				return reflect.Zero(goType) // ensure empty string is []byte(nil)
			}
			return rv.Convert(goType)
		},
	}
}