// 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"
	"math"
	"reflect"
	"sync"

	descriptorV1 "github.com/golang/protobuf/protoc-gen-go/descriptor"
	pref "github.com/golang/protobuf/v2/reflect/protoreflect"
	ptype "github.com/golang/protobuf/v2/reflect/prototype"
)

var enumDescCache sync.Map // map[reflect.Type]protoreflect.EnumDescriptor

// loadEnumDesc returns an EnumDescriptor derived from the Go type,
// which must be an int32 kind and not implement the v2 API already.
func loadEnumDesc(t reflect.Type) pref.EnumDescriptor {
	// Fast-path: check if an EnumDescriptor is cached for this concrete type.
	if v, ok := enumDescCache.Load(t); ok {
		return v.(pref.EnumDescriptor)
	}

	// Slow-path: initialize EnumDescriptor from the proto descriptor.
	if t.Kind() != reflect.Int32 {
		panic(fmt.Sprintf("got %v, want int32 kind", t))
	}

	// Derive the enum descriptor from the raw descriptor proto.
	e := new(ptype.StandaloneEnum)
	ev := reflect.Zero(t).Interface()
	if _, ok := ev.(pref.ProtoEnum); ok {
		panic(fmt.Sprintf("%v already implements proto.Enum", t))
	}
	if ed, ok := ev.(legacyEnum); ok {
		b, idxs := ed.EnumDescriptor()
		fd := loadFileDesc(b)

		// Derive syntax.
		switch fd.GetSyntax() {
		case "proto2", "":
			e.Syntax = pref.Proto2
		case "proto3":
			e.Syntax = pref.Proto3
		}

		// Derive the full name and correct enum descriptor.
		var ed *descriptorV1.EnumDescriptorProto
		e.FullName = pref.FullName(fd.GetPackage())
		if len(idxs) == 1 {
			ed = fd.EnumType[idxs[0]]
			e.FullName = e.FullName.Append(pref.Name(ed.GetName()))
		} else {
			md := fd.MessageType[idxs[0]]
			e.FullName = e.FullName.Append(pref.Name(md.GetName()))
			for _, i := range idxs[1 : len(idxs)-1] {
				md = md.NestedType[i]
				e.FullName = e.FullName.Append(pref.Name(md.GetName()))
			}
			ed = md.EnumType[idxs[len(idxs)-1]]
			e.FullName = e.FullName.Append(pref.Name(ed.GetName()))
		}

		// Derive the enum values.
		for _, vd := range ed.GetValue() {
			e.Values = append(e.Values, ptype.EnumValue{
				Name:   pref.Name(vd.GetName()),
				Number: pref.EnumNumber(vd.GetNumber()),
			})
		}
	} else {
		// If the type does not implement legacyEnum, then there is no reliable
		// way to derive the original protobuf type information.
		// We are unable to use the global enum registry since it is
		// unfortunately keyed by the full name, which we do not know.
		// Furthermore, some generated enums register with a fork of
		// golang/protobuf so the enum may not even be found in the registry.
		//
		// Instead, create a bogus enum descriptor to ensure that
		// most operations continue to work. For example, textpb and jsonpb
		// will be unable to parse a message with an enum value by name.
		e.Syntax = pref.Proto2
		e.FullName = deriveFullName(t)
		e.Values = []ptype.EnumValue{{Name: "INVALID", Number: math.MinInt32}}
	}

	ed, err := ptype.NewEnum(e)
	if err != nil {
		panic(err)
	}
	enumDescCache.Store(t, ed)
	return ed
}