// 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 internal_gengogrpc is internal to the protobuf module.
package internal_gengogrpc

import (
	"fmt"
	"strconv"
	"strings"

	descpb "github.com/golang/protobuf/protoc-gen-go/descriptor"
	"github.com/golang/protobuf/v2/protogen"
)

type fileInfo struct {
	*protogen.File
	locationMap map[string][]*descpb.SourceCodeInfo_Location
}

// GenerateFile generates a _grpc.pb.go file containing gRPC service definitions.
func GenerateFile(gen *protogen.Plugin, f *protogen.File) {
	if len(f.Services) == 0 {
		return
	}
	filename := f.GeneratedFilenamePrefix + "_grpc.pb.go"
	g := gen.NewGeneratedFile(filename, f.GoImportPath)
	g.P("// Code generated by protoc-gen-go-grpc. DO NOT EDIT.")
	g.P()
	g.P("package ", f.GoPackageName)
	g.P()
	GenerateFileContent(gen, f, g)
}

// GenerateFileContent generates the gRPC service definitions, excluding the package statement.
func GenerateFileContent(gen *protogen.Plugin, f *protogen.File, g *protogen.GeneratedFile) {
	if len(f.Services) == 0 {
		return
	}
	file := &fileInfo{
		File:        f,
		locationMap: make(map[string][]*descpb.SourceCodeInfo_Location),
	}
	for _, loc := range file.Proto.GetSourceCodeInfo().GetLocation() {
		key := pathKey(loc.Path)
		file.locationMap[key] = append(file.locationMap[key], loc)
	}

	// TODO: Remove this. We don't need to include these references any more.
	g.P("// Reference imports to suppress errors if they are not otherwise used.")
	g.P("var _ ", ident("context.Context"))
	g.P("var _ ", ident("grpc.ClientConn"))
	g.P()

	g.P("// This is a compile-time assertion to ensure that this generated file")
	g.P("// is compatible with the grpc package it is being compiled against.")
	g.P("const _ = ", ident("grpc.SupportPackageIsVersion4"))
	g.P()
	for _, service := range file.Services {
		genService(gen, file, g, service)
	}
}

func genService(gen *protogen.Plugin, file *fileInfo, g *protogen.GeneratedFile, service *protogen.Service) {
	clientName := service.GoName + "Client"

	g.P("// ", clientName, " is the client API for ", service.GoName, " service.")
	g.P("//")
	g.P("// For semantics around ctx use and closing/ending streaming RPCs, please refer to https://godoc.org/google.golang.org/grpc#ClientConn.NewStream.")

	// Client interface.
	if serviceOptions(gen, service).GetDeprecated() {
		g.P("//")
		g.P(deprecationComment)
	}
	g.P("type ", clientName, " interface {")
	for _, method := range service.Methods {
		genComment(g, file, method.Path)
		g.P(clientSignature(g, method))
	}
	g.P("}")
	g.P()

	// Client structure.
	g.P("type ", unexport(clientName), " struct {")
	g.P("cc *", ident("grpc.ClientConn"))
	g.P("}")
	g.P()

	// NewClient factory.
	if serviceOptions(gen, service).GetDeprecated() {
		g.P(deprecationComment)
	}
	g.P("func New", clientName, " (cc *", ident("grpc.ClientConn"), ") ", clientName, " {")
	g.P("return &", unexport(clientName), "{cc}")
	g.P("}")
	g.P()

	var methodIndex, streamIndex int
	// Client method implementations.
	for _, method := range service.Methods {
		if !method.Desc.IsStreamingServer() && !method.Desc.IsStreamingClient() {
			// Unary RPC method
			genClientMethod(gen, file, g, method, methodIndex)
			methodIndex++
		} else {
			// Streaming RPC method
			genClientMethod(gen, file, g, method, streamIndex)
			streamIndex++
		}
	}

	// Server interface.
	serverType := service.GoName + "Server"
	g.P("// ", serverType, " is the server API for ", service.GoName, " service.")
	if serviceOptions(gen, service).GetDeprecated() {
		g.P("//")
		g.P(deprecationComment)
	}
	g.P("type ", serverType, " interface {")
	for _, method := range service.Methods {
		genComment(g, file, method.Path)
		g.P(serverSignature(g, method))
	}
	g.P("}")
	g.P()

	// Server registration.
	if serviceOptions(gen, service).GetDeprecated() {
		g.P(deprecationComment)
	}
	serviceDescVar := "_" + service.GoName + "_serviceDesc"
	g.P("func Register", service.GoName, "Server(s *", ident("grpc.Server"), ", srv ", serverType, ") {")
	g.P("s.RegisterService(&", serviceDescVar, `, srv)`)
	g.P("}")
	g.P()

	// Server handler implementations.
	var handlerNames []string
	for _, method := range service.Methods {
		hname := genServerMethod(gen, file, g, method)
		handlerNames = append(handlerNames, hname)
	}

	// Service descriptor.
	g.P("var ", serviceDescVar, " = ", ident("grpc.ServiceDesc"), " {")
	g.P("ServiceName: ", strconv.Quote(string(service.Desc.FullName())), ",")
	g.P("HandlerType: (*", serverType, ")(nil),")
	g.P("Methods: []", ident("grpc.MethodDesc"), "{")
	for i, method := range service.Methods {
		if method.Desc.IsStreamingClient() || method.Desc.IsStreamingServer() {
			continue
		}
		g.P("{")
		g.P("MethodName: ", strconv.Quote(method.GoName), ",")
		g.P("Handler: ", handlerNames[i], ",")
		g.P("},")
	}
	g.P("},")
	g.P("Streams: []", ident("grpc.StreamDesc"), "{")
	for i, method := range service.Methods {
		if !method.Desc.IsStreamingClient() && !method.Desc.IsStreamingServer() {
			continue
		}
		g.P("{")
		g.P("StreamName: ", strconv.Quote(method.GoName), ",")
		g.P("Handler: ", handlerNames[i], ",")
		if method.Desc.IsStreamingServer() {
			g.P("ServerStreams: true,")
		}
		if method.Desc.IsStreamingClient() {
			g.P("ClientStreams: true,")
		}
		g.P("},")
	}
	g.P("},")
	g.P("Metadata: \"", file.Desc.Path(), "\",")
	g.P("}")
	g.P()
}

func clientSignature(g *protogen.GeneratedFile, method *protogen.Method) string {
	s := method.GoName + "(ctx " + g.QualifiedGoIdent(ident("context.Context"))
	if !method.Desc.IsStreamingClient() {
		s += ", in *" + g.QualifiedGoIdent(method.InputType.GoIdent)
	}
	s += ", opts ..." + g.QualifiedGoIdent(ident("grpc.CallOption")) + ") ("
	if !method.Desc.IsStreamingClient() && !method.Desc.IsStreamingServer() {
		s += "*" + g.QualifiedGoIdent(method.OutputType.GoIdent)
	} else {
		s += method.ParentService.GoName + "_" + method.GoName + "Client"
	}
	s += ", error)"
	return s
}

func genClientMethod(gen *protogen.Plugin, file *fileInfo, g *protogen.GeneratedFile, method *protogen.Method, index int) {
	service := method.ParentService
	sname := fmt.Sprintf("/%s/%s", service.Desc.FullName(), method.Desc.Name())

	if methodOptions(gen, method).GetDeprecated() {
		g.P(deprecationComment)
	}
	g.P("func (c *", unexport(service.GoName), "Client) ", clientSignature(g, method), "{")
	if !method.Desc.IsStreamingServer() && !method.Desc.IsStreamingClient() {
		g.P("out := new(", method.OutputType.GoIdent, ")")
		g.P(`err := c.cc.Invoke(ctx, "`, sname, `", in, out, opts...)`)
		g.P("if err != nil { return nil, err }")
		g.P("return out, nil")
		g.P("}")
		g.P()
		return
	}
	streamType := unexport(service.GoName) + method.GoName + "Client"
	serviceDescVar := "_" + service.GoName + "_serviceDesc"
	g.P("stream, err := c.cc.NewStream(ctx, &", serviceDescVar, ".Streams[", index, `], "`, sname, `", opts...)`)
	g.P("if err != nil { return nil, err }")
	g.P("x := &", streamType, "{stream}")
	if !method.Desc.IsStreamingClient() {
		g.P("if err := x.ClientStream.SendMsg(in); err != nil { return nil, err }")
		g.P("if err := x.ClientStream.CloseSend(); err != nil { return nil, err }")
	}
	g.P("return x, nil")
	g.P("}")
	g.P()

	genSend := method.Desc.IsStreamingClient()
	genRecv := method.Desc.IsStreamingServer()
	genCloseAndRecv := !method.Desc.IsStreamingServer()

	// Stream auxiliary types and methods.
	g.P("type ", service.GoName, "_", method.GoName, "Client interface {")
	if genSend {
		g.P("Send(*", method.InputType.GoIdent, ") error")
	}
	if genRecv {
		g.P("Recv() (*", method.OutputType.GoIdent, ", error)")
	}
	if genCloseAndRecv {
		g.P("CloseAndRecv() (*", method.OutputType.GoIdent, ", error)")
	}
	g.P(ident("grpc.ClientStream"))
	g.P("}")
	g.P()

	g.P("type ", streamType, " struct {")
	g.P(ident("grpc.ClientStream"))
	g.P("}")
	g.P()

	if genSend {
		g.P("func (x *", streamType, ") Send(m *", method.InputType.GoIdent, ") error {")
		g.P("return x.ClientStream.SendMsg(m)")
		g.P("}")
		g.P()
	}
	if genRecv {
		g.P("func (x *", streamType, ") Recv() (*", method.OutputType.GoIdent, ", error) {")
		g.P("m := new(", method.OutputType.GoIdent, ")")
		g.P("if err := x.ClientStream.RecvMsg(m); err != nil { return nil, err }")
		g.P("return m, nil")
		g.P("}")
		g.P()
	}
	if genCloseAndRecv {
		g.P("func (x *", streamType, ") CloseAndRecv() (*", method.OutputType.GoIdent, ", error) {")
		g.P("if err := x.ClientStream.CloseSend(); err != nil { return nil, err }")
		g.P("m := new(", method.OutputType.GoIdent, ")")
		g.P("if err := x.ClientStream.RecvMsg(m); err != nil { return nil, err }")
		g.P("return m, nil")
		g.P("}")
		g.P()
	}
}

func serverSignature(g *protogen.GeneratedFile, method *protogen.Method) string {
	var reqArgs []string
	ret := "error"
	if !method.Desc.IsStreamingClient() && !method.Desc.IsStreamingServer() {
		reqArgs = append(reqArgs, g.QualifiedGoIdent(ident("context.Context")))
		ret = "(*" + g.QualifiedGoIdent(method.OutputType.GoIdent) + ", error)"
	}
	if !method.Desc.IsStreamingClient() {
		reqArgs = append(reqArgs, "*"+g.QualifiedGoIdent(method.InputType.GoIdent))
	}
	if method.Desc.IsStreamingClient() || method.Desc.IsStreamingServer() {
		reqArgs = append(reqArgs, method.ParentService.GoName+"_"+method.GoName+"Server")
	}
	return method.GoName + "(" + strings.Join(reqArgs, ", ") + ") " + ret
}

func genServerMethod(gen *protogen.Plugin, file *fileInfo, g *protogen.GeneratedFile, method *protogen.Method) string {
	service := method.ParentService
	hname := fmt.Sprintf("_%s_%s_Handler", service.GoName, method.GoName)

	if !method.Desc.IsStreamingClient() && !method.Desc.IsStreamingServer() {
		g.P("func ", hname, "(srv interface{}, ctx ", ident("context.Context"), ", dec func(interface{}) error, interceptor ", ident("grpc.UnaryServerInterceptor"), ") (interface{}, error) {")
		g.P("in := new(", method.InputType.GoIdent, ")")
		g.P("if err := dec(in); err != nil { return nil, err }")
		g.P("if interceptor == nil { return srv.(", service.GoName, "Server).", method.GoName, "(ctx, in) }")
		g.P("info := &", ident("grpc.UnaryServerInfo"), "{")
		g.P("Server: srv,")
		g.P("FullMethod: ", strconv.Quote(fmt.Sprintf("/%s/%s", service.Desc.FullName(), method.Desc.Name())), ",")
		g.P("}")
		g.P("handler := func(ctx ", ident("context.Context"), ", req interface{}) (interface{}, error) {")
		g.P("return srv.(", service.GoName, "Server).", method.GoName, "(ctx, req.(*", method.InputType.GoIdent, "))")
		g.P("}")
		g.P("return interceptor(ctx, in, info, handler)")
		g.P("}")
		g.P()
		return hname
	}
	streamType := unexport(service.GoName) + method.GoName + "Server"
	g.P("func ", hname, "(srv interface{}, stream ", ident("grpc.ServerStream"), ") error {")
	if !method.Desc.IsStreamingClient() {
		g.P("m := new(", method.InputType.GoIdent, ")")
		g.P("if err := stream.RecvMsg(m); err != nil { return err }")
		g.P("return srv.(", service.GoName, "Server).", method.GoName, "(m, &", streamType, "{stream})")
	} else {
		g.P("return srv.(", service.GoName, "Server).", method.GoName, "(&", streamType, "{stream})")
	}
	g.P("}")
	g.P()

	genSend := method.Desc.IsStreamingServer()
	genSendAndClose := !method.Desc.IsStreamingServer()
	genRecv := method.Desc.IsStreamingClient()

	// Stream auxiliary types and methods.
	g.P("type ", service.GoName, "_", method.GoName, "Server interface {")
	if genSend {
		g.P("Send(*", method.OutputType.GoIdent, ") error")
	}
	if genSendAndClose {
		g.P("SendAndClose(*", method.OutputType.GoIdent, ") error")
	}
	if genRecv {
		g.P("Recv() (*", method.InputType.GoIdent, ", error)")
	}
	g.P(ident("grpc.ServerStream"))
	g.P("}")
	g.P()

	g.P("type ", streamType, " struct {")
	g.P(ident("grpc.ServerStream"))
	g.P("}")
	g.P()

	if genSend {
		g.P("func (x *", streamType, ") Send(m *", method.OutputType.GoIdent, ") error {")
		g.P("return x.ServerStream.SendMsg(m)")
		g.P("}")
		g.P()
	}
	if genSendAndClose {
		g.P("func (x *", streamType, ") SendAndClose(m *", method.OutputType.GoIdent, ") error {")
		g.P("return x.ServerStream.SendMsg(m)")
		g.P("}")
		g.P()
	}
	if genRecv {
		g.P("func (x *", streamType, ") Recv() (*", method.InputType.GoIdent, ", error) {")
		g.P("m := new(", method.InputType.GoIdent, ")")
		g.P("if err := x.ServerStream.RecvMsg(m); err != nil { return nil, err }")
		g.P("return m, nil")
		g.P("}")
		g.P()
	}

	return hname
}

var packages = map[string]protogen.GoImportPath{
	"context": "golang.org/x/net/context",
	"grpc":    "google.golang.org/grpc",
}

func ident(name string) protogen.GoIdent {
	idx := strings.LastIndex(name, ".")
	return protogen.GoIdent{
		GoImportPath: packages[name[:idx]],
		GoName:       name[idx+1:],
	}
}

func genComment(g *protogen.GeneratedFile, file *fileInfo, path []int32) (hasComment bool) {
	for _, loc := range file.locationMap[pathKey(path)] {
		if loc.LeadingComments == nil {
			continue
		}
		for _, line := range strings.Split(strings.TrimSuffix(loc.GetLeadingComments(), "\n"), "\n") {
			hasComment = true
			g.P("//", line)
		}
		break
	}
	return hasComment
}

const deprecationComment = "// Deprecated: Do not use."

// pathKey converts a location path to a string suitable for use as a map key.
func pathKey(path []int32) string {
	var buf []byte
	for i, x := range path {
		if i != 0 {
			buf = append(buf, ',')
		}
		buf = strconv.AppendInt(buf, int64(x), 10)
	}
	return string(buf)
}

func unexport(s string) string { return strings.ToLower(s[:1]) + s[1:] }