#include "src/compiler/cpp_generator.h"

#include <map>
#include <sstream>

#include "flatbuffers/util.h"

namespace grpc_cpp_generator {
namespace {

template <class T>
static grpc::string as_string(T x) {
  std::ostringstream out;
  out << x;
  return out.str();
}

static inline bool ClientOnlyStreaming(const grpc_generator::Method* method) {
  return method->ClientStreaming() && !method->ServerStreaming();
}

static inline bool ServerOnlyStreaming(const grpc_generator::Method* method) {
  return !method->ClientStreaming() && method->ServerStreaming();
}

static grpc::string FilenameIdentifier(const grpc::string& filename) {
  grpc::string result;
  for (unsigned i = 0; i < filename.size(); i++) {
    char c = filename[i];
    if (isalnum(c)) {
      result.push_back(c);
    } else {
      static char hex[] = "0123456789abcdef";
      result.push_back('_');
      result.push_back(hex[(c >> 4) & 0xf]);
      result.push_back(hex[c & 0xf]);
    }
  }
  return result;
}

template <class T, size_t N>
static T* array_end(T (&array)[N]) {
  return array + N;
}

static void PrintIncludes(grpc_generator::Printer* printer,
                          const std::vector<grpc::string>& headers,
                          const Parameters& params) {
  std::map<grpc::string, grpc::string> vars;

  vars["l"] = params.use_system_headers ? '<' : '"';
  vars["r"] = params.use_system_headers ? '>' : '"';

  auto& s = params.grpc_search_path;
  if (!s.empty()) {
    vars["l"] += s;
    if (s[s.size() - 1] != '/') {
      vars["l"] += '/';
    }
  }

  for (auto i = headers.begin(); i != headers.end(); i++) {
    vars["h"] = *i;
    printer->Print(vars, "#include $l$$h$$r$\n");
  }
  if (params.generate_callback_api) {
    // Callback API headers (guarded later by feature macro in emitted code).
    static const char* cb_headers[] = {
        "grpcpp/impl/codegen/callback_common.h",
        "grpcpp/impl/codegen/server_callback_handlers.h",
        "grpcpp/support/client_callback.h"};
    for (auto& h : cb_headers) {
      vars["h"] = h;
      printer->Print(vars, "#include $l$$h$$r$\n");
    }
  }
}

}  // namespace

grpc::string GetHeaderPrologue(grpc_generator::File* file,
                               const Parameters& params) {
  grpc::string output;
  {
    // Scope the output stream so it closes and finalizes output to the string.
    auto printer = file->CreatePrinter(&output);
    std::map<grpc::string, grpc::string> vars;

    vars["filename"] = file->filename();
    vars["filename_identifier"] = FilenameIdentifier(file->filename());
    vars["filename_base"] = file->filename_without_ext();
    vars["message_header_ext"] = params.message_header_extension;

    printer->Print(vars, "// Generated by the gRPC C++ plugin.\n");
    printer->Print(vars,
                   "// If you make any local change, they will be lost.\n");
    printer->Print(vars, "// source: $filename$\n");
    grpc::string leading_comments = file->GetLeadingComments("//");
    if (!leading_comments.empty()) {
      printer->Print(vars, "// Original file comments:\n");
      printer->Print(leading_comments.c_str());
    }
    printer->Print(vars, "#ifndef GRPC_$filename_identifier$__INCLUDED\n");
    printer->Print(vars, "#define GRPC_$filename_identifier$__INCLUDED\n");
    printer->Print(vars, "\n");
    printer->Print(vars, "#include \"$filename_base$$message_header_ext$\"\n");
    printer->Print(vars, file->additional_headers().c_str());
    printer->Print(vars, "\n");
  }
  return output;
}

grpc::string GetHeaderIncludes(grpc_generator::File* file,
                               const Parameters& params) {
  grpc::string output;
  {
    // Scope the output stream so it closes and finalizes output to the string.
    auto printer = file->CreatePrinter(&output);
    std::map<grpc::string, grpc::string> vars;

    static const char* headers_strs[] = {
        "grpcpp/impl/codegen/async_stream.h",
        "grpcpp/impl/codegen/async_unary_call.h",
        "grpcpp/impl/codegen/method_handler.h",
        "grpcpp/impl/codegen/proto_utils.h",
        "grpcpp/impl/codegen/rpc_method.h",
        "grpcpp/impl/codegen/service_type.h",
        "grpcpp/impl/codegen/status.h",
        "grpcpp/impl/codegen/stub_options.h",
        "grpcpp/impl/codegen/sync_stream.h"};
    std::vector<grpc::string> headers(headers_strs, array_end(headers_strs));
    PrintIncludes(printer.get(), headers, params);
    printer->Print(vars, "\n");
    printer->Print(vars, "namespace grpc {\n");
    printer->Print(vars, "class CompletionQueue;\n");
    printer->Print(vars, "class Channel;\n");
    printer->Print(vars, "class ServerCompletionQueue;\n");
    printer->Print(vars, "class ServerContext;\n");
    printer->Print(vars, "}  // namespace grpc\n\n");

    if (!file->package().empty()) {
      std::vector<grpc::string> parts = file->package_parts();

      for (auto part = parts.begin(); part != parts.end(); part++) {
        vars["part"] = *part;
        printer->Print(vars, "namespace $part$ {\n");
      }
      printer->Print(vars, "\n");
    }
  }
  return output;
}

namespace {

static void PrintHeaderClientMethodInterfaces(
    grpc_generator::Printer* printer, const grpc_generator::Method* method,
    std::map<grpc::string, grpc::string>* vars, bool is_public) {
  (*vars)["Method"] = method->name();
  (*vars)["Request"] = method->input_type_name();
  (*vars)["Response"] = method->output_type_name();

  struct {
    grpc::string prefix;
    grpc::string method_params;  // extra arguments to method
    grpc::string raw_args;       // extra arguments to raw version of method
  } async_prefixes[] = {{"Async", ", void* tag", ", tag"},
                        {"PrepareAsync", "", ""}};

  if (is_public) {
    if (method->NoStreaming()) {
      printer->Print(
          *vars,
          "virtual ::grpc::Status $Method$(::grpc::ClientContext* context, "
          "const $Request$& request, $Response$* response) = 0;\n");
      for (size_t i = 0; i < sizeof(async_prefixes) / sizeof(async_prefixes[0]);
           i++) {
        auto& async_prefix = async_prefixes[i];
        (*vars)["AsyncPrefix"] = async_prefix.prefix;
        printer->Print(
            *vars,
            "std::unique_ptr< "
            "::grpc::ClientAsyncResponseReaderInterface< $Response$>> "
            "$AsyncPrefix$$Method$(::grpc::ClientContext* context, "
            "const $Request$& request, "
            "::grpc::CompletionQueue* cq) {\n");
        printer->Indent();
        printer->Print(
            *vars,
            "return std::unique_ptr< "
            "::grpc::ClientAsyncResponseReaderInterface< $Response$>>("
            "$AsyncPrefix$$Method$Raw(context, request, cq));\n");
        printer->Outdent();
        printer->Print("}\n");
      }
    } else if (ClientOnlyStreaming(method)) {
      printer->Print(
          *vars,
          "std::unique_ptr< ::grpc::ClientWriterInterface< $Request$>>"
          " $Method$("
          "::grpc::ClientContext* context, $Response$* response) {\n");
      printer->Indent();
      printer->Print(
          *vars,
          "return std::unique_ptr< ::grpc::ClientWriterInterface< $Request$>>"
          "($Method$Raw(context, response));\n");
      printer->Outdent();
      printer->Print("}\n");
      for (size_t i = 0; i < sizeof(async_prefixes) / sizeof(async_prefixes[0]);
           i++) {
        auto& async_prefix = async_prefixes[i];
        (*vars)["AsyncPrefix"] = async_prefix.prefix;
        (*vars)["AsyncMethodParams"] = async_prefix.method_params;
        (*vars)["AsyncRawArgs"] = async_prefix.raw_args;
        printer->Print(
            *vars,
            "std::unique_ptr< ::grpc::ClientAsyncWriterInterface< $Request$>>"
            " $AsyncPrefix$$Method$(::grpc::ClientContext* context, "
            "$Response$* "
            "response, "
            "::grpc::CompletionQueue* cq$AsyncMethodParams$) {\n");
        printer->Indent();
        printer->Print(*vars,
                       "return std::unique_ptr< "
                       "::grpc::ClientAsyncWriterInterface< $Request$>>("
                       "$AsyncPrefix$$Method$Raw(context, response, "
                       "cq$AsyncRawArgs$));\n");
        printer->Outdent();
        printer->Print("}\n");
      }
    } else if (ServerOnlyStreaming(method)) {
      printer->Print(
          *vars,
          "std::unique_ptr< ::grpc::ClientReaderInterface< $Response$>>"
          " $Method$(::grpc::ClientContext* context, const $Request$& request)"
          " {\n");
      printer->Indent();
      printer->Print(
          *vars,
          "return std::unique_ptr< ::grpc::ClientReaderInterface< $Response$>>"
          "($Method$Raw(context, request));\n");
      printer->Outdent();
      printer->Print("}\n");
      for (size_t i = 0; i < sizeof(async_prefixes) / sizeof(async_prefixes[0]);
           i++) {
        auto& async_prefix = async_prefixes[i];
        (*vars)["AsyncPrefix"] = async_prefix.prefix;
        (*vars)["AsyncMethodParams"] = async_prefix.method_params;
        (*vars)["AsyncRawArgs"] = async_prefix.raw_args;
        printer->Print(
            *vars,
            "std::unique_ptr< ::grpc::ClientAsyncReaderInterface< $Response$>> "
            "$AsyncPrefix$$Method$("
            "::grpc::ClientContext* context, const $Request$& request, "
            "::grpc::CompletionQueue* cq$AsyncMethodParams$) {\n");
        printer->Indent();
        printer->Print(
            *vars,
            "return std::unique_ptr< "
            "::grpc::ClientAsyncReaderInterface< $Response$>>("
            "$AsyncPrefix$$Method$Raw(context, request, cq$AsyncRawArgs$));\n");
        printer->Outdent();
        printer->Print("}\n");
      }
    } else if (method->BidiStreaming()) {
      printer->Print(*vars,
                     "std::unique_ptr< ::grpc::ClientReaderWriterInterface< "
                     "$Request$, $Response$>> "
                     "$Method$(::grpc::ClientContext* context) {\n");
      printer->Indent();
      printer->Print(
          *vars,
          "return std::unique_ptr< "
          "::grpc::ClientReaderWriterInterface< $Request$, $Response$>>("
          "$Method$Raw(context));\n");
      printer->Outdent();
      printer->Print("}\n");
      for (size_t i = 0; i < sizeof(async_prefixes) / sizeof(async_prefixes[0]);
           i++) {
        auto& async_prefix = async_prefixes[i];
        (*vars)["AsyncPrefix"] = async_prefix.prefix;
        (*vars)["AsyncMethodParams"] = async_prefix.method_params;
        (*vars)["AsyncRawArgs"] = async_prefix.raw_args;
        printer->Print(
            *vars,
            "std::unique_ptr< "
            "::grpc::ClientAsyncReaderWriterInterface< $Request$, $Response$>> "
            "$AsyncPrefix$$Method$(::grpc::ClientContext* context, "
            "::grpc::CompletionQueue* cq$AsyncMethodParams$) {\n");
        printer->Indent();
        printer->Print(
            *vars,
            "return std::unique_ptr< "
            "::grpc::ClientAsyncReaderWriterInterface< $Request$, $Response$>>("
            "$AsyncPrefix$$Method$Raw(context, cq$AsyncRawArgs$));\n");
        printer->Outdent();
        printer->Print("}\n");
      }
    }
  } else {
    if (method->NoStreaming()) {
      for (size_t i = 0; i < sizeof(async_prefixes) / sizeof(async_prefixes[0]);
           i++) {
        auto& async_prefix = async_prefixes[i];
        (*vars)["AsyncPrefix"] = async_prefix.prefix;
        printer->Print(
            *vars,
            "virtual ::grpc::ClientAsyncResponseReaderInterface< $Response$>* "
            "$AsyncPrefix$$Method$Raw(::grpc::ClientContext* context, "
            "const $Request$& request, "
            "::grpc::CompletionQueue* cq) = 0;\n");
      }
    } else if (ClientOnlyStreaming(method)) {
      printer->Print(
          *vars,
          "virtual ::grpc::ClientWriterInterface< $Request$>*"
          " $Method$Raw("
          "::grpc::ClientContext* context, $Response$* response) = 0;\n");
      for (size_t i = 0; i < sizeof(async_prefixes) / sizeof(async_prefixes[0]);
           i++) {
        auto& async_prefix = async_prefixes[i];
        (*vars)["AsyncPrefix"] = async_prefix.prefix;
        (*vars)["AsyncMethodParams"] = async_prefix.method_params;
        printer->Print(
            *vars,
            "virtual ::grpc::ClientAsyncWriterInterface< $Request$>*"
            " $AsyncPrefix$$Method$Raw(::grpc::ClientContext* context, "
            "$Response$* response, "
            "::grpc::CompletionQueue* cq$AsyncMethodParams$) = 0;\n");
      }
    } else if (ServerOnlyStreaming(method)) {
      printer->Print(
          *vars,
          "virtual ::grpc::ClientReaderInterface< $Response$>* "
          "$Method$Raw("
          "::grpc::ClientContext* context, const $Request$& request) = 0;\n");
      for (size_t i = 0; i < sizeof(async_prefixes) / sizeof(async_prefixes[0]);
           i++) {
        auto& async_prefix = async_prefixes[i];
        (*vars)["AsyncPrefix"] = async_prefix.prefix;
        (*vars)["AsyncMethodParams"] = async_prefix.method_params;
        printer->Print(
            *vars,
            "virtual ::grpc::ClientAsyncReaderInterface< $Response$>* "
            "$AsyncPrefix$$Method$Raw("
            "::grpc::ClientContext* context, const $Request$& request, "
            "::grpc::CompletionQueue* cq$AsyncMethodParams$) = 0;\n");
      }
    } else if (method->BidiStreaming()) {
      printer->Print(*vars,
                     "virtual ::grpc::ClientReaderWriterInterface< $Request$, "
                     "$Response$>* "
                     "$Method$Raw(::grpc::ClientContext* context) = 0;\n");
      for (size_t i = 0; i < sizeof(async_prefixes) / sizeof(async_prefixes[0]);
           i++) {
        auto& async_prefix = async_prefixes[i];
        (*vars)["AsyncPrefix"] = async_prefix.prefix;
        (*vars)["AsyncMethodParams"] = async_prefix.method_params;
        printer->Print(
            *vars,
            "virtual ::grpc::ClientAsyncReaderWriterInterface< "
            "$Request$, $Response$>* "
            "$AsyncPrefix$$Method$Raw(::grpc::ClientContext* context, "
            "::grpc::CompletionQueue* cq$AsyncMethodParams$) = 0;\n");
      }
    }
  }
}

static void PrintHeaderClientMethod(grpc_generator::Printer* printer,
                                    const grpc_generator::Method* method,
                                    std::map<grpc::string, grpc::string>* vars,
                                    bool is_public) {
  (*vars)["Method"] = method->name();
  (*vars)["Request"] = method->input_type_name();
  (*vars)["Response"] = method->output_type_name();
  struct {
    grpc::string prefix;
    grpc::string method_params;  // extra arguments to method
    grpc::string raw_args;       // extra arguments to raw version of method
  } async_prefixes[] = {{"Async", ", void* tag", ", tag"},
                        {"PrepareAsync", "", ""}};

  if (is_public) {
    if (method->NoStreaming()) {
      printer->Print(
          *vars,
          "::grpc::Status $Method$(::grpc::ClientContext* context, "
          "const $Request$& request, $Response$* response) override;\n");
      if ((*vars)["generate_callback_api"] == "1") {
        // Native gRPC callback unary wrappers (function callback & reactor
        // variants).
        printer->Print(*vars,
                       "// Callback unary (function form). Request/response "
                       "must outlive callback.\n");
        printer->Print(*vars,
                       "void async_$Method$(::grpc::ClientContext* context, "
                       "const $Request$& request, $Response$* response, "
                       "std::function<void(::grpc::Status)> on_done);\n");
        printer->Print(*vars, "// Callback unary (reactor form).\n");
        printer->Print(*vars,
                       "void async_$Method$(::grpc::ClientContext* context, "
                       "const $Request$& request, $Response$* response, "
                       "::grpc::ClientUnaryReactor* reactor);\n");
      }
      for (size_t i = 0; i < sizeof(async_prefixes) / sizeof(async_prefixes[0]);
           i++) {
        auto& async_prefix = async_prefixes[i];
        (*vars)["AsyncPrefix"] = async_prefix.prefix;
        printer->Print(
            *vars,
            "std::unique_ptr< ::grpc::ClientAsyncResponseReader< $Response$>> "
            "$AsyncPrefix$$Method$(::grpc::ClientContext* context, "
            "const $Request$& request, "
            "::grpc::CompletionQueue* cq) {\n");
        printer->Indent();
        printer->Print(*vars,
                       "return std::unique_ptr< "
                       "::grpc::ClientAsyncResponseReader< $Response$>>("
                       "$AsyncPrefix$$Method$Raw(context, request, cq));\n");
        printer->Outdent();
        printer->Print("}\n");
      }
    } else if (ClientOnlyStreaming(method)) {
      printer->Print(
          *vars,
          "std::unique_ptr< ::grpc::ClientWriter< $Request$>>"
          " $Method$("
          "::grpc::ClientContext* context, $Response$* response) {\n");
      printer->Indent();
      printer->Print(*vars,
                     "return std::unique_ptr< ::grpc::ClientWriter< $Request$>>"
                     "($Method$Raw(context, response));\n");
      printer->Outdent();
      printer->Print("}\n");
      if ((*vars)["generate_callback_api"] == "1") {
        printer->Print(*vars, "// Client streaming callback reactor entry.\n");
        printer->Print(
            *vars,
            "void async_$Method$(::grpc::ClientContext* context, $Response$* "
            "response, ::grpc::ClientWriteReactor< $Request$ >* reactor);\n");
      }
      for (size_t i = 0; i < sizeof(async_prefixes) / sizeof(async_prefixes[0]);
           i++) {
        auto& async_prefix = async_prefixes[i];
        (*vars)["AsyncPrefix"] = async_prefix.prefix;
        (*vars)["AsyncMethodParams"] = async_prefix.method_params;
        (*vars)["AsyncRawArgs"] = async_prefix.raw_args;
        printer->Print(*vars,
                       "std::unique_ptr< ::grpc::ClientAsyncWriter< $Request$>>"
                       " $AsyncPrefix$$Method$(::grpc::ClientContext* context, "
                       "$Response$* response, "
                       "::grpc::CompletionQueue* cq$AsyncMethodParams$) {\n");
        printer->Indent();
        printer->Print(
            *vars,
            "return std::unique_ptr< ::grpc::ClientAsyncWriter< $Request$>>("
            "$AsyncPrefix$$Method$Raw(context, response, "
            "cq$AsyncRawArgs$));\n");
        printer->Outdent();
        printer->Print("}\n");
      }
    } else if (ServerOnlyStreaming(method)) {
      printer->Print(
          *vars,
          "std::unique_ptr< ::grpc::ClientReader< $Response$>>"
          " $Method$(::grpc::ClientContext* context, const $Request$& request)"
          " {\n");
      printer->Indent();
      printer->Print(
          *vars,
          "return std::unique_ptr< ::grpc::ClientReader< $Response$>>"
          "($Method$Raw(context, request));\n");
      printer->Outdent();
      printer->Print("}\n");
      if ((*vars)["generate_callback_api"] == "1") {
        printer->Print(*vars, "// Server streaming callback reactor entry.\n");
        printer->Print(*vars,
                       "void async_$Method$(::grpc::ClientContext* context, "
                       "const $Request$& request, ::grpc::ClientReadReactor< "
                       "$Response$ >* reactor);\n");
      }
      for (size_t i = 0; i < sizeof(async_prefixes) / sizeof(async_prefixes[0]);
           i++) {
        auto& async_prefix = async_prefixes[i];
        (*vars)["AsyncPrefix"] = async_prefix.prefix;
        (*vars)["AsyncMethodParams"] = async_prefix.method_params;
        (*vars)["AsyncRawArgs"] = async_prefix.raw_args;
        printer->Print(
            *vars,
            "std::unique_ptr< ::grpc::ClientAsyncReader< $Response$>> "
            "$AsyncPrefix$$Method$("
            "::grpc::ClientContext* context, const $Request$& request, "
            "::grpc::CompletionQueue* cq$AsyncMethodParams$) {\n");
        printer->Indent();
        printer->Print(
            *vars,
            "return std::unique_ptr< ::grpc::ClientAsyncReader< $Response$>>("
            "$AsyncPrefix$$Method$Raw(context, request, cq$AsyncRawArgs$));\n");
        printer->Outdent();
        printer->Print("}\n");
      }
    } else if (method->BidiStreaming()) {
      printer->Print(
          *vars,
          "std::unique_ptr< ::grpc::ClientReaderWriter< $Request$, $Response$>>"
          " $Method$(::grpc::ClientContext* context) {\n");
      printer->Indent();
      printer->Print(*vars,
                     "return std::unique_ptr< "
                     "::grpc::ClientReaderWriter< $Request$, $Response$>>("
                     "$Method$Raw(context));\n");
      printer->Outdent();
      printer->Print("}\n");
      if ((*vars)["generate_callback_api"] == "1") {
        printer->Print(*vars,
                       "// Bidirectional streaming callback reactor entry.\n");
        printer->Print(
            *vars,
            "void async_$Method$(::grpc::ClientContext* context, "
            "::grpc::ClientBidiReactor< $Request$, $Response$ >* reactor);\n");
      }
      for (size_t i = 0; i < sizeof(async_prefixes) / sizeof(async_prefixes[0]);
           i++) {
        auto& async_prefix = async_prefixes[i];
        (*vars)["AsyncPrefix"] = async_prefix.prefix;
        (*vars)["AsyncMethodParams"] = async_prefix.method_params;
        (*vars)["AsyncRawArgs"] = async_prefix.raw_args;
        printer->Print(*vars,
                       "std::unique_ptr<  ::grpc::ClientAsyncReaderWriter< "
                       "$Request$, $Response$>> "
                       "$AsyncPrefix$$Method$(::grpc::ClientContext* context, "
                       "::grpc::CompletionQueue* cq$AsyncMethodParams$) {\n");
        printer->Indent();
        printer->Print(
            *vars,
            "return std::unique_ptr< "
            "::grpc::ClientAsyncReaderWriter< $Request$, $Response$>>("
            "$AsyncPrefix$$Method$Raw(context, cq$AsyncRawArgs$));\n");
        printer->Outdent();
        printer->Print("}\n");
      }
    }
  } else {
    if (method->NoStreaming()) {
      for (size_t i = 0; i < sizeof(async_prefixes) / sizeof(async_prefixes[0]);
           i++) {
        auto& async_prefix = async_prefixes[i];
        (*vars)["AsyncPrefix"] = async_prefix.prefix;
        printer->Print(
            *vars,
            "::grpc::ClientAsyncResponseReader< $Response$>* "
            "$AsyncPrefix$$Method$Raw(::grpc::ClientContext* context, "
            "const $Request$& request, "
            "::grpc::CompletionQueue* cq) override;\n");
      }
      if ((*vars)["generate_callback_api"] == "1") {
        // Native callback unary forms declared earlier (no private sync helper
        // needed).
      }
    } else if (ClientOnlyStreaming(method)) {
      printer->Print(*vars,
                     "::grpc::ClientWriter< $Request$>* $Method$Raw("
                     "::grpc::ClientContext* context, $Response$* response) "
                     "override;\n");
      for (size_t i = 0; i < sizeof(async_prefixes) / sizeof(async_prefixes[0]);
           i++) {
        auto& async_prefix = async_prefixes[i];
        (*vars)["AsyncPrefix"] = async_prefix.prefix;
        (*vars)["AsyncMethodParams"] = async_prefix.method_params;
        (*vars)["AsyncRawArgs"] = async_prefix.raw_args;
        printer->Print(
            *vars,
            "::grpc::ClientAsyncWriter< $Request$>* $AsyncPrefix$$Method$Raw("
            "::grpc::ClientContext* context, $Response$* response, "
            "::grpc::CompletionQueue* cq$AsyncMethodParams$) override;\n");
      }
    } else if (ServerOnlyStreaming(method)) {
      printer->Print(*vars,
                     "::grpc::ClientReader< $Response$>* $Method$Raw("
                     "::grpc::ClientContext* context, const $Request$& request)"
                     " override;\n");
      for (size_t i = 0; i < sizeof(async_prefixes) / sizeof(async_prefixes[0]);
           i++) {
        auto& async_prefix = async_prefixes[i];
        (*vars)["AsyncPrefix"] = async_prefix.prefix;
        (*vars)["AsyncMethodParams"] = async_prefix.method_params;
        (*vars)["AsyncRawArgs"] = async_prefix.raw_args;
        printer->Print(
            *vars,
            "::grpc::ClientAsyncReader< $Response$>* $AsyncPrefix$$Method$Raw("
            "::grpc::ClientContext* context, const $Request$& request, "
            "::grpc::CompletionQueue* cq$AsyncMethodParams$) override;\n");
      }
    } else if (method->BidiStreaming()) {
      printer->Print(*vars,
                     "::grpc::ClientReaderWriter< $Request$, $Response$>* "
                     "$Method$Raw(::grpc::ClientContext* context) override;\n");
      for (size_t i = 0; i < sizeof(async_prefixes) / sizeof(async_prefixes[0]);
           i++) {
        auto& async_prefix = async_prefixes[i];
        (*vars)["AsyncPrefix"] = async_prefix.prefix;
        (*vars)["AsyncMethodParams"] = async_prefix.method_params;
        (*vars)["AsyncRawArgs"] = async_prefix.raw_args;
        printer->Print(
            *vars,
            "::grpc::ClientAsyncReaderWriter< $Request$, $Response$>* "
            "$AsyncPrefix$$Method$Raw(::grpc::ClientContext* context, "
            "::grpc::CompletionQueue* cq$AsyncMethodParams$) override;\n");
      }
    }
  }
}

static void PrintHeaderClientMethodData(
    grpc_generator::Printer* printer, const grpc_generator::Method* method,
    std::map<grpc::string, grpc::string>* vars) {
  (*vars)["Method"] = method->name();
  printer->Print(*vars,
                 "const ::grpc::internal::RpcMethod rpcmethod_$Method$_;\n");
}

static void PrintHeaderServerMethodSync(
    grpc_generator::Printer* printer, const grpc_generator::Method* method,
    std::map<grpc::string, grpc::string>* vars) {
  (*vars)["Method"] = method->name();
  (*vars)["Request"] = method->input_type_name();
  (*vars)["Response"] = method->output_type_name();
  printer->Print(method->GetLeadingComments("//").c_str());
  if (method->NoStreaming()) {
    printer->Print(*vars,
                   "virtual ::grpc::Status $Method$("
                   "::grpc::ServerContext* context, const $Request$* request, "
                   "$Response$* response);\n");
  } else if (ClientOnlyStreaming(method)) {
    printer->Print(*vars,
                   "virtual ::grpc::Status $Method$("
                   "::grpc::ServerContext* context, "
                   "::grpc::ServerReader< $Request$>* reader, "
                   "$Response$* response);\n");
  } else if (ServerOnlyStreaming(method)) {
    printer->Print(*vars,
                   "virtual ::grpc::Status $Method$("
                   "::grpc::ServerContext* context, const $Request$* request, "
                   "::grpc::ServerWriter< $Response$>* writer);\n");
  } else if (method->BidiStreaming()) {
    printer->Print(
        *vars,
        "virtual ::grpc::Status $Method$("
        "::grpc::ServerContext* context, "
        "::grpc::ServerReaderWriter< $Response$, $Request$>* stream);"
        "\n");
  }
  printer->Print(method->GetTrailingComments("//").c_str());
}

static void PrintHeaderServerMethodAsync(
    grpc_generator::Printer* printer, const grpc_generator::Method* method,
    std::map<grpc::string, grpc::string>* vars) {
  (*vars)["Method"] = method->name();
  (*vars)["Request"] = method->input_type_name();
  (*vars)["Response"] = method->output_type_name();
  printer->Print(*vars, "template <class BaseClass>\n");
  printer->Print(*vars,
                 "class WithAsyncMethod_$Method$ : public BaseClass {\n");
  printer->Print(
      " private:\n"
      "  void BaseClassMustBeDerivedFromService(const Service */*service*/) "
      "{}\n");
  printer->Print(" public:\n");
  printer->Indent();
  printer->Print(*vars,
                 "WithAsyncMethod_$Method$() {\n"
                 "  ::grpc::Service::MarkMethodAsync($Idx$);\n"
                 "}\n");
  printer->Print(*vars,
                 "~WithAsyncMethod_$Method$() override {\n"
                 "  BaseClassMustBeDerivedFromService(this);\n"
                 "}\n");
  if (method->NoStreaming()) {
    printer->Print(
        *vars,
        "// disable synchronous version of this method\n"
        "::grpc::Status $Method$("
        "::grpc::ServerContext* /*context*/, const $Request$* /*request*/, "
        "$Response$* /*response*/) final override {\n"
        "  abort();\n"
        "  return ::grpc::Status(::grpc::StatusCode::UNIMPLEMENTED, \"\");\n"
        "}\n");
    printer->Print(
        *vars,
        "void Request$Method$("
        "::grpc::ServerContext* context, $Request$* request, "
        "::grpc::ServerAsyncResponseWriter< $Response$>* response, "
        "::grpc::CompletionQueue* new_call_cq, "
        "::grpc::ServerCompletionQueue* notification_cq, void *tag) {\n");
    printer->Print(*vars,
                   "  ::grpc::Service::RequestAsyncUnary($Idx$, context, "
                   "request, response, new_call_cq, notification_cq, tag);\n");
    printer->Print("}\n");
  } else if (ClientOnlyStreaming(method)) {
    printer->Print(
        *vars,
        "// disable synchronous version of this method\n"
        "::grpc::Status $Method$("
        "::grpc::ServerContext* /*context*/, "
        "::grpc::ServerReader< $Request$>* /*reader*/, "
        "$Response$* /*response*/) final override {\n"
        "  abort();\n"
        "  return ::grpc::Status(::grpc::StatusCode::UNIMPLEMENTED, \"\");\n"
        "}\n");
    printer->Print(
        *vars,
        "void Request$Method$("
        "::grpc::ServerContext* context, "
        "::grpc::ServerAsyncReader< $Response$, $Request$>* reader, "
        "::grpc::CompletionQueue* new_call_cq, "
        "::grpc::ServerCompletionQueue* notification_cq, void *tag) {\n");
    printer->Print(*vars,
                   "  ::grpc::Service::RequestAsyncClientStreaming($Idx$, "
                   "context, reader, new_call_cq, notification_cq, tag);\n");
    printer->Print("}\n");
  } else if (ServerOnlyStreaming(method)) {
    printer->Print(
        *vars,
        "// disable synchronous version of this method\n"
        "::grpc::Status $Method$("
        "::grpc::ServerContext* /*context*/, const $Request$* /*request*/, "
        "::grpc::ServerWriter< $Response$>* /*writer*/) final override "
        "{\n"
        "  abort();\n"
        "  return ::grpc::Status(::grpc::StatusCode::UNIMPLEMENTED, \"\");\n"
        "}\n");
    printer->Print(
        *vars,
        "void Request$Method$("
        "::grpc::ServerContext* context, $Request$* request, "
        "::grpc::ServerAsyncWriter< $Response$>* writer, "
        "::grpc::CompletionQueue* new_call_cq, "
        "::grpc::ServerCompletionQueue* notification_cq, void *tag) {\n");
    printer->Print(
        *vars,
        "  ::grpc::Service::RequestAsyncServerStreaming($Idx$, "
        "context, request, writer, new_call_cq, notification_cq, tag);\n");
    printer->Print("}\n");
  } else if (method->BidiStreaming()) {
    printer->Print(
        *vars,
        "// disable synchronous version of this method\n"
        "::grpc::Status $Method$("
        "::grpc::ServerContext* /*context*/, "
        "::grpc::ServerReaderWriter< $Response$, $Request$>* /*stream*/) "
        "final override {\n"
        "  abort();\n"
        "  return ::grpc::Status(::grpc::StatusCode::UNIMPLEMENTED, \"\");\n"
        "}\n");
    printer->Print(
        *vars,
        "void Request$Method$("
        "::grpc::ServerContext* context, "
        "::grpc::ServerAsyncReaderWriter< $Response$, $Request$>* stream, "
        "::grpc::CompletionQueue* new_call_cq, "
        "::grpc::ServerCompletionQueue* notification_cq, void *tag) {\n");
    printer->Print(*vars,
                   "  ::grpc::Service::RequestAsyncBidiStreaming($Idx$, "
                   "context, stream, new_call_cq, notification_cq, tag);\n");
    printer->Print("}\n");
  }
  printer->Outdent();
  printer->Print(*vars, "};\n");
}

static void PrintHeaderServerMethodStreamedUnary(
    grpc_generator::Printer* printer, const grpc_generator::Method* method,
    std::map<grpc::string, grpc::string>* vars) {
  (*vars)["Method"] = method->name();
  (*vars)["Request"] = method->input_type_name();
  (*vars)["Response"] = method->output_type_name();
  if (method->NoStreaming()) {
    printer->Print(*vars, "template <class BaseClass>\n");
    printer->Print(*vars,
                   "class WithStreamedUnaryMethod_$Method$ : "
                   "public BaseClass {\n");
    printer->Print(
        " private:\n"
        "  void BaseClassMustBeDerivedFromService(const Service */*service*/) "
        "{}\n");
    printer->Print(" public:\n");
    printer->Indent();
    printer->Print(*vars,
                   "WithStreamedUnaryMethod_$Method$() {\n"
                   "  ::grpc::Service::MarkMethodStreamed($Idx$,\n"
                   "    new ::grpc::internal::StreamedUnaryHandler< $Request$, "
                   "$Response$>(std::bind"
                   "(&WithStreamedUnaryMethod_$Method$<BaseClass>::"
                   "Streamed$Method$, this, std::placeholders::_1, "
                   "std::placeholders::_2)));\n"
                   "}\n");
    printer->Print(*vars,
                   "~WithStreamedUnaryMethod_$Method$() override {\n"
                   "  BaseClassMustBeDerivedFromService(this);\n"
                   "}\n");
    printer->Print(
        *vars,
        "// disable regular version of this method\n"
        "::grpc::Status $Method$("
        "::grpc::ServerContext* /*context*/, const $Request$* /*request*/, "
        "$Response$* /*response*/) final override {\n"
        "  abort();\n"
        "  return ::grpc::Status(::grpc::StatusCode::UNIMPLEMENTED, \"\");\n"
        "}\n");
    printer->Print(*vars,
                   "// replace default version of method with streamed unary\n"
                   "virtual ::grpc::Status Streamed$Method$("
                   "::grpc::ServerContext* context, "
                   "::grpc::ServerUnaryStreamer< "
                   "$Request$,$Response$>* server_unary_streamer)"
                   " = 0;\n");
    printer->Outdent();
    printer->Print(*vars, "};\n");
  }
}

static void PrintHeaderServerMethodSplitStreaming(
    grpc_generator::Printer* printer, const grpc_generator::Method* method,
    std::map<grpc::string, grpc::string>* vars) {
  (*vars)["Method"] = method->name();
  (*vars)["Request"] = method->input_type_name();
  (*vars)["Response"] = method->output_type_name();
  if (ServerOnlyStreaming(method)) {
    printer->Print(*vars, "template <class BaseClass>\n");
    printer->Print(*vars,
                   "class WithSplitStreamingMethod_$Method$ : "
                   "public BaseClass {\n");
    printer->Print(
        " private:\n"
        "  void BaseClassMustBeDerivedFromService(const Service */*service*/) "
        "{ }\n");
    printer->Print(" public:\n");
    printer->Indent();
    printer->Print(
        *vars,
        "WithSplitStreamingMethod_$Method$() {\n"
        "  ::grpc::Service::MarkMethodStreamed($Idx$,\n"
        "    new ::grpc::internal::SplitServerStreamingHandler< $Request$, "
        "$Response$>(std::bind"
        "(&WithSplitStreamingMethod_$Method$<BaseClass>::"
        "Streamed$Method$, this, std::placeholders::_1, "
        "std::placeholders::_2)));\n"
        "}\n");
    printer->Print(*vars,
                   "~WithSplitStreamingMethod_$Method$() override {\n"
                   "  BaseClassMustBeDerivedFromService(this);\n"
                   "}\n");
    printer->Print(
        *vars,
        "// disable regular version of this method\n"
        "::grpc::Status $Method$("
        "::grpc::ServerContext* /*context*/, const $Request$* /*request*/, "
        "::grpc::ServerWriter< $Response$>* /*writer*/) final override "
        "{\n"
        "  abort();\n"
        "  return ::grpc::Status(::grpc::StatusCode::UNIMPLEMENTED, \"\");\n"
        "}\n");
    printer->Print(*vars,
                   "// replace default version of method with split streamed\n"
                   "virtual ::grpc::Status Streamed$Method$("
                   "::grpc::ServerContext* context, "
                   "::grpc::ServerSplitStreamer< "
                   "$Request$,$Response$>* server_split_streamer)"
                   " = 0;\n");
    printer->Outdent();
    printer->Print(*vars, "};\n");
  }
}

static void PrintHeaderServerMethodGeneric(
    grpc_generator::Printer* printer, const grpc_generator::Method* method,
    std::map<grpc::string, grpc::string>* vars) {
  (*vars)["Method"] = method->name();
  (*vars)["Request"] = method->input_type_name();
  (*vars)["Response"] = method->output_type_name();
  printer->Print(*vars, "template <class BaseClass>\n");
  printer->Print(*vars,
                 "class WithGenericMethod_$Method$ : public BaseClass {\n");
  printer->Print(
      " private:\n"
      "  void BaseClassMustBeDerivedFromService(const Service */*service*/) "
      "{}\n");
  printer->Print(" public:\n");
  printer->Indent();
  printer->Print(*vars,
                 "WithGenericMethod_$Method$() {\n"
                 "  ::grpc::Service::MarkMethodGeneric($Idx$);\n"
                 "}\n");
  printer->Print(*vars,
                 "~WithGenericMethod_$Method$() override {\n"
                 "  BaseClassMustBeDerivedFromService(this);\n"
                 "}\n");
  if (method->NoStreaming()) {
    printer->Print(
        *vars,
        "// disable synchronous version of this method\n"
        "::grpc::Status $Method$("
        "::grpc::ServerContext* /*context*/, const $Request$* /*request*/, "
        "$Response$* /*response*/) final override {\n"
        "  abort();\n"
        "  return ::grpc::Status(::grpc::StatusCode::UNIMPLEMENTED, \"\");\n"
        "}\n");
  } else if (ClientOnlyStreaming(method)) {
    printer->Print(
        *vars,
        "// disable synchronous version of this method\n"
        "::grpc::Status $Method$("
        "::grpc::ServerContext* /*context*/, "
        "::grpc::ServerReader< $Request$>* /*reader*/, "
        "$Response$* /*response*/) final override {\n"
        "  abort();\n"
        "  return ::grpc::Status(::grpc::StatusCode::UNIMPLEMENTED, \"\");\n"
        "}\n");
  } else if (ServerOnlyStreaming(method)) {
    printer->Print(
        *vars,
        "// disable synchronous version of this method\n"
        "::grpc::Status $Method$("
        "::grpc::ServerContext* /*context*/, const $Request$* /*request*/, "
        "::grpc::ServerWriter< $Response$>* /*writer*/) final override "
        "{\n"
        "  abort();\n"
        "  return ::grpc::Status(::grpc::StatusCode::UNIMPLEMENTED, \"\");\n"
        "}\n");
  } else if (method->BidiStreaming()) {
    printer->Print(
        *vars,
        "// disable synchronous version of this method\n"
        "::grpc::Status $Method$("
        "::grpc::ServerContext* /*context*/, "
        "::grpc::ServerReaderWriter< $Response$, $Request$>* /*stream*/) "
        "final override {\n"
        "  abort();\n"
        "  return ::grpc::Status(::grpc::StatusCode::UNIMPLEMENTED, \"\");\n"
        "}\n");
  }
  printer->Outdent();
  printer->Print(*vars, "};\n");
}

static void PrintHeaderService(grpc_generator::Printer* printer,
                               const grpc_generator::Service* service,
                               std::map<grpc::string, grpc::string>* vars) {
  (*vars)["Service"] = service->name();

  printer->Print(service->GetLeadingComments("//").c_str());
  printer->Print(*vars,
                 "class $Service$ final {\n"
                 " public:\n");
  printer->Indent();

  // Service metadata
  printer->Print(*vars,
                 "static constexpr char const* service_full_name() {\n"
                 "  return \"$Package$$Service$\";\n"
                 "}\n");

  // Client side
  printer->Print(
      "class StubInterface {\n"
      " public:\n");
  printer->Indent();
  printer->Print("virtual ~StubInterface() {}\n");
  for (int i = 0; i < service->method_count(); ++i) {
    printer->Print(service->method(i)->GetLeadingComments("//").c_str());
    PrintHeaderClientMethodInterfaces(printer, service->method(i).get(), vars,
                                      true);
    printer->Print(service->method(i)->GetTrailingComments("//").c_str());
  }
  printer->Outdent();
  printer->Print("private:\n");
  printer->Indent();
  for (int i = 0; i < service->method_count(); ++i) {
    PrintHeaderClientMethodInterfaces(printer, service->method(i).get(), vars,
                                      false);
  }
  printer->Outdent();
  // Forward declaration of nested CallbackService if callback API enabled.
  if ((*vars)["generate_callback_api"] == "1") {
    printer->Print("class CallbackService;\n");
  }
  printer->Print("};\n");
  printer->Print(
      "class Stub final : public StubInterface"
      " {\n public:\n");
  printer->Indent();
  printer->Print(
      "Stub(const std::shared_ptr< ::grpc::ChannelInterface>& "
      "channel);\n");
  for (int i = 0; i < service->method_count(); ++i) {
    PrintHeaderClientMethod(printer, service->method(i).get(), vars, true);
  }
  printer->Outdent();
  printer->Print("\n private:\n");
  printer->Indent();
  printer->Print("std::shared_ptr< ::grpc::ChannelInterface> channel_;\n");
  for (int i = 0; i < service->method_count(); ++i) {
    PrintHeaderClientMethod(printer, service->method(i).get(), vars, false);
  }
  for (int i = 0; i < service->method_count(); ++i) {
    PrintHeaderClientMethodData(printer, service->method(i).get(), vars);
  }
  printer->Outdent();
  printer->Print("};\n");
  printer->Print(
      "static std::unique_ptr<Stub> NewStub(const std::shared_ptr< "
      "::grpc::ChannelInterface>& channel, "
      "const ::grpc::StubOptions& options = ::grpc::StubOptions());\n");

  printer->Print("\n");

  // Server side - base
  printer->Print(
      "class Service : public ::grpc::Service {\n"
      " public:\n");
  printer->Indent();
  printer->Print("Service();\n");
  printer->Print("virtual ~Service();\n");
  for (int i = 0; i < service->method_count(); ++i) {
    PrintHeaderServerMethodSync(printer, service->method(i).get(), vars);
  }
  printer->Outdent();
  printer->Print("};\n");

  // Server side - Asynchronous
  for (int i = 0; i < service->method_count(); ++i) {
    (*vars)["Idx"] = as_string(i);
    PrintHeaderServerMethodAsync(printer, service->method(i).get(), vars);
  }

  printer->Print("typedef ");

  for (int i = 0; i < service->method_count(); ++i) {
    (*vars)["method_name"] = service->method(i).get()->name();
    printer->Print(*vars, "WithAsyncMethod_$method_name$<");
  }
  printer->Print("Service");
  for (int i = 0; i < service->method_count(); ++i) {
    printer->Print(" >");
  }
  printer->Print(" AsyncService;\n");

  // Server side - Generic
  for (int i = 0; i < service->method_count(); ++i) {
    (*vars)["Idx"] = as_string(i);
    PrintHeaderServerMethodGeneric(printer, service->method(i).get(), vars);
  }

  // Server side - Streamed Unary
  for (int i = 0; i < service->method_count(); ++i) {
    (*vars)["Idx"] = as_string(i);
    PrintHeaderServerMethodStreamedUnary(printer, service->method(i).get(),
                                         vars);
  }

  printer->Print("typedef ");
  for (int i = 0; i < service->method_count(); ++i) {
    (*vars)["method_name"] = service->method(i).get()->name();
    if (service->method(i)->NoStreaming()) {
      printer->Print(*vars, "WithStreamedUnaryMethod_$method_name$<");
    }
  }
  printer->Print("Service");
  for (int i = 0; i < service->method_count(); ++i) {
    if (service->method(i)->NoStreaming()) {
      printer->Print(" >");
    }
  }
  printer->Print(" StreamedUnaryService;\n");

  // Server side - controlled server-side streaming
  for (int i = 0; i < service->method_count(); ++i) {
    (*vars)["Idx"] = as_string(i);
    PrintHeaderServerMethodSplitStreaming(printer, service->method(i).get(),
                                          vars);
  }

  printer->Print("typedef ");
  for (int i = 0; i < service->method_count(); ++i) {
    (*vars)["method_name"] = service->method(i).get()->name();
    auto method = service->method(i);
    if (ServerOnlyStreaming(method.get())) {
      printer->Print(*vars, "WithSplitStreamingMethod_$method_name$<");
    }
  }
  printer->Print("Service");
  for (int i = 0; i < service->method_count(); ++i) {
    auto method = service->method(i);
    if (ServerOnlyStreaming(method.get())) {
      printer->Print(" >");
    }
  }
  printer->Print(" SplitStreamedService;\n");

  // Server side - typedef for controlled both unary and server-side streaming
  printer->Print("typedef ");
  for (int i = 0; i < service->method_count(); ++i) {
    (*vars)["method_name"] = service->method(i).get()->name();
    auto method = service->method(i);
    if (ServerOnlyStreaming(method.get())) {
      printer->Print(*vars, "WithSplitStreamingMethod_$method_name$<");
    }
    if (service->method(i)->NoStreaming()) {
      printer->Print(*vars, "WithStreamedUnaryMethod_$method_name$<");
    }
  }
  printer->Print("Service");
  for (int i = 0; i < service->method_count(); ++i) {
    auto method = service->method(i);
    if (service->method(i)->NoStreaming() ||
        ServerOnlyStreaming(method.get())) {
      printer->Print(" >");
    }
  }
  printer->Print(" StreamedService;\n");

  printer->Outdent();
  printer->Print("};\n");
  printer->Print(service->GetTrailingComments("//").c_str());

  // Optional CallbackService (modern async API)
  if ((*vars)["generate_callback_api"] == "1") {
    (*vars)["Service"] = service->name();
    printer->Print("\n#if defined(GRPC_CALLBACK_API_NONEXPERIMENTAL)\n");
    printer->Print(*vars,
                   "class $Service$::CallbackService : public ::grpc::Service "
                   "{\n public:\n  CallbackService();\n  virtual "
                   "~CallbackService();\n");
    printer->Indent();
    for (int i = 0; i < service->method_count(); ++i) {
      auto m = service->method(i);
      (*vars)["Method"] = m->name();
      (*vars)["Request"] = m->input_type_name();
      (*vars)["Response"] = m->output_type_name();
      if (m->NoStreaming()) {
        printer->Print(*vars,
                       "virtual ::grpc::ServerUnaryReactor* "
                       "$Method$(::grpc::CallbackServerContext* context, const "
                       "$Request$* request, $Response$* response);\n");
      } else if (ClientOnlyStreaming(m.get())) {
        printer->Print(*vars,
                       "virtual ::grpc::ServerReadReactor<$Request$>* "
                       "$Method$(::grpc::CallbackServerContext* context, "
                       "$Response$* response);\n");
      } else if (ServerOnlyStreaming(m.get())) {
        printer->Print(*vars,
                       "virtual ::grpc::ServerWriteReactor<$Response$>* "
                       "$Method$(::grpc::CallbackServerContext* context, const "
                       "$Request$* request);\n");
      } else if (m->BidiStreaming()) {
        printer->Print(
            *vars,
            "virtual ::grpc::ServerBidiReactor<$Request$, $Response$>* "
            "$Method$(::grpc::CallbackServerContext* context);\n");
      }
    }
    printer->Outdent();
    printer->Print(
        "};\n#else\n// Callback API requested but not available in this gRPC "
        "version.\n#endif // GRPC_CALLBACK_API_NONEXPERIMENTAL\n");
  }
}

}  // namespace

grpc::string GetHeaderServices(grpc_generator::File* file,
                               const Parameters& params) {
  grpc::string output;
  {
    // Scope the output stream so it closes and finalizes output to the string.
    auto printer = file->CreatePrinter(&output);
    std::map<grpc::string, grpc::string> vars;
    // Package string is empty or ends with a dot. It is used to fully qualify
    // method names.
    vars["Package"] = file->package();
    if (!file->package().empty()) {
      vars["Package"].append(".");
    }

    if (!params.services_namespace.empty()) {
      vars["services_namespace"] = params.services_namespace;
      printer->Print(vars, "\nnamespace $services_namespace$ {\n\n");
    }

    for (int i = 0; i < file->service_count(); ++i) {
      vars["generate_callback_api"] = params.generate_callback_api ? "1" : "0";
      PrintHeaderService(printer.get(), file->service(i).get(), &vars);
      printer->Print("\n");
    }
    if (params.generate_callback_api) {
      printer->Print("// FlatBuffers: Callback API code generated.\n");
      printer->Print("#define FLATBUFFERS_GENERATED_GRPC_CALLBACK_API 1\n\n");
    }

    if (!params.services_namespace.empty()) {
      printer->Print(vars, "}  // namespace $services_namespace$\n\n");
    }
  }
  return output;
}

grpc::string GetHeaderEpilogue(grpc_generator::File* file,
                               const Parameters& /*params*/) {
  grpc::string output;
  {
    // Scope the output stream so it closes and finalizes output to the string.
    auto printer = file->CreatePrinter(&output);
    std::map<grpc::string, grpc::string> vars;

    vars["filename"] = file->filename();
    vars["filename_identifier"] = FilenameIdentifier(file->filename());

    if (!file->package().empty()) {
      std::vector<grpc::string> parts = file->package_parts();

      for (auto part = parts.rbegin(); part != parts.rend(); part++) {
        vars["part"] = *part;
        printer->Print(vars, "}  // namespace $part$\n");
      }
      printer->Print(vars, "\n");
    }

    printer->Print(vars, "\n");
    printer->Print(vars, "#endif  // GRPC_$filename_identifier$__INCLUDED\n");

    printer->Print(file->GetTrailingComments("//").c_str());
  }
  return output;
}

grpc::string GetSourcePrologue(grpc_generator::File* file,
                               const Parameters& params) {
  grpc::string output;
  {
    // Scope the output stream so it closes and finalizes output to the string.
    auto printer = file->CreatePrinter(&output);
    std::map<grpc::string, grpc::string> vars;

    vars["filename"] = file->filename();
    vars["filename_base"] = file->filename_without_ext();
    vars["message_header_ext"] = params.message_header_extension;
    vars["service_header_ext"] = params.service_header_extension;

    printer->Print(vars, "// Generated by the gRPC C++ plugin.\n");
    printer->Print(vars,
                   "// FlatBuffers modified generator: native gRPC callback "
                   "client API enabled when --grpc-callback-api.\n");
    printer->Print(vars, "// source: $filename$\n\n");

    printer->Print(vars, "#include \"$filename_base$$message_header_ext$\"\n");
    printer->Print(vars, "#include \"$filename_base$$service_header_ext$\"\n");
    printer->Print(vars, "\n");
  }
  return output;
}

grpc::string GetSourceIncludes(grpc_generator::File* file,
                               const Parameters& params) {
  grpc::string output;
  {
    // Scope the output stream so it closes and finalizes output to the string.
    auto printer = file->CreatePrinter(&output);
    std::map<grpc::string, grpc::string> vars;

    static const char* headers_strs[] = {
        "grpcpp/impl/codegen/async_stream.h",
        "grpcpp/impl/codegen/async_unary_call.h",
        "grpcpp/impl/codegen/channel_interface.h",
        "grpcpp/impl/codegen/client_unary_call.h",
        "grpcpp/impl/codegen/method_handler.h",
        "grpcpp/impl/codegen/rpc_service_method.h",
        "grpcpp/impl/codegen/service_type.h",
        "grpcpp/impl/codegen/sync_stream.h"};
    std::vector<grpc::string> headers(headers_strs, array_end(headers_strs));
    PrintIncludes(printer.get(), headers, params);

    if (!file->package().empty()) {
      std::vector<grpc::string> parts = file->package_parts();

      for (auto part = parts.begin(); part != parts.end(); part++) {
        vars["part"] = *part;
        printer->Print(vars, "namespace $part$ {\n");
      }
    }

    printer->Print(vars, "\n");
  }
  return output;
}

namespace {

static void PrintSourceClientMethod(
    grpc_generator::Printer* printer, const grpc_generator::Method* method,
    std::map<grpc::string, grpc::string>* vars) {
  (*vars)["Method"] = method->name();
  (*vars)["Request"] = method->input_type_name();
  (*vars)["Response"] = method->output_type_name();
  struct {
    grpc::string prefix;
    grpc::string start;          // bool literal expressed as string
    grpc::string method_params;  // extra arguments to method
    grpc::string create_args;    // extra arguments to creator
  } async_prefixes[] = {{"Async", "true", ", void* tag", ", tag"},
                        {"PrepareAsync", "false", "", ", nullptr"}};
  if (method->NoStreaming()) {
    printer->Print(*vars,
                   "::grpc::Status $ns$$Service$::Stub::$Method$("
                   "::grpc::ClientContext* context, "
                   "const $Request$& request, $Response$* response) {\n");
    printer->Print(*vars,
                   "  return ::grpc::internal::BlockingUnaryCall"
                   "(channel_.get(), rpcmethod_$Method$_, "
                   "context, request, response);\n}\n\n");
    if ((*vars)["generate_callback_api"] == "1") {
      printer->Print(
          *vars,
          "void $ns$$Service$::Stub::async_$Method$(::grpc::ClientContext* "
          "context, const $Request$& request, $Response$* response, "
          "std::function<void(::grpc::Status)> on_done) {\n");
      printer->Print(*vars,
                     "  ::grpc::internal::CallbackUnaryCall(channel_.get(), "
                     "rpcmethod_$Method$_, context, &request, response, "
                     "std::move(on_done));\n}\n\n");
      printer->Print(
          *vars,
          "void $ns$$Service$::Stub::async_$Method$(::grpc::ClientContext* "
          "context, const $Request$& request, $Response$* response, "
          "::grpc::ClientUnaryReactor* reactor) {\n");
      printer->Print(
          *vars,
          "  "
          "::grpc::internal::ClientCallbackUnaryFactory::Create(channel_.get(),"
          " rpcmethod_$Method$_, context, &request, response, "
          "reactor);\n}\n\n");
    }
    for (size_t i = 0; i < sizeof(async_prefixes) / sizeof(async_prefixes[0]);
         i++) {
      auto& async_prefix = async_prefixes[i];
      (*vars)["AsyncPrefix"] = async_prefix.prefix;
      (*vars)["AsyncStart"] = async_prefix.start;
      printer->Print(*vars,
                     "::grpc::ClientAsyncResponseReader< $Response$>* "
                     "$ns$$Service$::Stub::$AsyncPrefix$$Method$Raw(::grpc::"
                     "ClientContext* context, "
                     "const $Request$& request, "
                     "::grpc::CompletionQueue* cq) {\n");
      printer->Print(
          *vars,
          "  return "
          "::grpc::internal::ClientAsyncResponseReaderFactory< $Response$>"
          "::Create(channel_.get(), cq, "
          "rpcmethod_$Method$_, "
          "context, request, $AsyncStart$);\n"
          "}\n\n");
    }
  } else if (ClientOnlyStreaming(method)) {
    printer->Print(*vars,
                   "::grpc::ClientWriter< $Request$>* "
                   "$ns$$Service$::Stub::$Method$Raw("
                   "::grpc::ClientContext* context, $Response$* response) {\n");
    printer->Print(
        *vars,
        "  return ::grpc::internal::ClientWriterFactory< $Request$>::Create("
        "channel_.get(), "
        "rpcmethod_$Method$_, "
        "context, response);\n"
        "}\n\n");
    if ((*vars)["generate_callback_api"] == "1") {
      printer->Print(
          *vars,
          "void $ns$$Service$::Stub::async_$Method$(::grpc::ClientContext* "
          "context, $Response$* response, ::grpc::ClientWriteReactor< "
          "$Request$ >* reactor) {\n");
      printer->Print(*vars,
                     "  ::grpc::internal::ClientCallbackWriterFactory< "
                     "$Request$ >::Create(channel_.get(), rpcmethod_$Method$_, "
                     "context, response, reactor);\n}\n\n");
    }
    for (size_t i = 0; i < sizeof(async_prefixes) / sizeof(async_prefixes[0]);
         i++) {
      auto& async_prefix = async_prefixes[i];
      (*vars)["AsyncPrefix"] = async_prefix.prefix;
      (*vars)["AsyncStart"] = async_prefix.start;
      (*vars)["AsyncMethodParams"] = async_prefix.method_params;
      (*vars)["AsyncCreateArgs"] = async_prefix.create_args;
      printer->Print(*vars,
                     "::grpc::ClientAsyncWriter< $Request$>* "
                     "$ns$$Service$::Stub::$AsyncPrefix$$Method$Raw("
                     "::grpc::ClientContext* context, $Response$* response, "
                     "::grpc::CompletionQueue* cq$AsyncMethodParams$) {\n");
      printer->Print(
          *vars,
          "  return ::grpc::internal::ClientAsyncWriterFactory< $Request$>"
          "::Create(channel_.get(), cq, "
          "rpcmethod_$Method$_, "
          "context, response, $AsyncStart$$AsyncCreateArgs$);\n"
          "}\n\n");
    }
  } else if (ServerOnlyStreaming(method)) {
    printer->Print(
        *vars,
        "::grpc::ClientReader< $Response$>* "
        "$ns$$Service$::Stub::$Method$Raw("
        "::grpc::ClientContext* context, const $Request$& request) {\n");
    printer->Print(
        *vars,
        "  return ::grpc::internal::ClientReaderFactory< $Response$>::Create("
        "channel_.get(), "
        "rpcmethod_$Method$_, "
        "context, request);\n"
        "}\n\n");
    if ((*vars)["generate_callback_api"] == "1") {
      printer->Print(
          *vars,
          "void $ns$$Service$::Stub::async_$Method$(::grpc::ClientContext* "
          "context, const $Request$& request, ::grpc::ClientReadReactor< "
          "$Response$ >* reactor) {\n");
      printer->Print(
          *vars,
          "  ::grpc::internal::ClientCallbackReaderFactory< "
          "$Response$ >::Create(channel_.get(), "
          "rpcmethod_$Method$_, context, &request, reactor);\n}\n\n");
    }
    for (size_t i = 0; i < sizeof(async_prefixes) / sizeof(async_prefixes[0]);
         i++) {
      auto& async_prefix = async_prefixes[i];
      (*vars)["AsyncPrefix"] = async_prefix.prefix;
      (*vars)["AsyncStart"] = async_prefix.start;
      (*vars)["AsyncMethodParams"] = async_prefix.method_params;
      (*vars)["AsyncCreateArgs"] = async_prefix.create_args;
      printer->Print(
          *vars,
          "::grpc::ClientAsyncReader< $Response$>* "
          "$ns$$Service$::Stub::$AsyncPrefix$$Method$Raw("
          "::grpc::ClientContext* context, const $Request$& request, "
          "::grpc::CompletionQueue* cq$AsyncMethodParams$) {\n");
      printer->Print(
          *vars,
          "  return ::grpc::internal::ClientAsyncReaderFactory< $Response$>"
          "::Create(channel_.get(), cq, "
          "rpcmethod_$Method$_, "
          "context, request, $AsyncStart$$AsyncCreateArgs$);\n"
          "}\n\n");
    }
  } else if (method->BidiStreaming()) {
    printer->Print(
        *vars,
        "::grpc::ClientReaderWriter< $Request$, $Response$>* "
        "$ns$$Service$::Stub::$Method$Raw(::grpc::ClientContext* context) {\n");
    printer->Print(*vars,
                   "  return ::grpc::internal::ClientReaderWriterFactory< "
                   "$Request$, $Response$>::Create("
                   "channel_.get(), "
                   "rpcmethod_$Method$_, "
                   "context);\n"
                   "}\n\n");
    if ((*vars)["generate_callback_api"] == "1") {
      printer->Print(
          *vars,
          "void $ns$$Service$::Stub::async_$Method$(::grpc::ClientContext* "
          "context, ::grpc::ClientBidiReactor< $Request$, $Response$ >* "
          "reactor) {\n");
      printer->Print(*vars,
                     "  ::grpc::internal::ClientCallbackReaderWriterFactory< "
                     "$Request$, $Response$ >::Create(channel_.get(), "
                     "rpcmethod_$Method$_, context, reactor);\n}\n\n");
    }
    for (size_t i = 0; i < sizeof(async_prefixes) / sizeof(async_prefixes[0]);
         i++) {
      auto& async_prefix = async_prefixes[i];
      (*vars)["AsyncPrefix"] = async_prefix.prefix;
      (*vars)["AsyncStart"] = async_prefix.start;
      (*vars)["AsyncMethodParams"] = async_prefix.method_params;
      (*vars)["AsyncCreateArgs"] = async_prefix.create_args;
      printer->Print(*vars,
                     "::grpc::ClientAsyncReaderWriter< $Request$, $Response$>* "
                     "$ns$$Service$::Stub::$AsyncPrefix$$Method$Raw(::grpc::"
                     "ClientContext* context, "
                     "::grpc::CompletionQueue* cq$AsyncMethodParams$) {\n");
      printer->Print(*vars,
                     "  return "
                     "::grpc::internal::ClientAsyncReaderWriterFactory< "
                     "$Request$, $Response$>::Create("
                     "channel_.get(), cq, "
                     "rpcmethod_$Method$_, "
                     "context, $AsyncStart$$AsyncCreateArgs$);\n"
                     "}\n\n");
    }
  }
}

static void PrintSourceServerMethod(
    grpc_generator::Printer* printer, const grpc_generator::Method* method,
    std::map<grpc::string, grpc::string>* vars) {
  (*vars)["Method"] = method->name();
  (*vars)["Request"] = method->input_type_name();
  (*vars)["Response"] = method->output_type_name();
  if (method->NoStreaming()) {
    printer->Print(
        *vars,
        "::grpc::Status $ns$$Service$::Service::$Method$("
        "::grpc::ServerContext* /*context*/, "
        "const $Request$* /*request*/, $Response$* /*response*/) {\n");
    printer->Print(
        "  return ::grpc::Status("
        "::grpc::StatusCode::UNIMPLEMENTED, \"\");\n");
    printer->Print("}\n\n");
  } else if (ClientOnlyStreaming(method)) {
    printer->Print(*vars,
                   "::grpc::Status $ns$$Service$::Service::$Method$("
                   "::grpc::ServerContext* /*context*/, "
                   "::grpc::ServerReader< $Request$>* /*reader*/, "
                   "$Response$* /*response*/) {\n");
    printer->Print(
        "  return ::grpc::Status("
        "::grpc::StatusCode::UNIMPLEMENTED, \"\");\n");
    printer->Print("}\n\n");
  } else if (ServerOnlyStreaming(method)) {
    printer->Print(*vars,
                   "::grpc::Status $ns$$Service$::Service::$Method$("
                   "::grpc::ServerContext* /*context*/, "
                   "const $Request$* /*request*/, "
                   "::grpc::ServerWriter< $Response$>* /*writer*/) {\n");
    printer->Print(
        "  return ::grpc::Status("
        "::grpc::StatusCode::UNIMPLEMENTED, \"\");\n");
    printer->Print("}\n\n");
  } else if (method->BidiStreaming()) {
    printer->Print(*vars,
                   "::grpc::Status $ns$$Service$::Service::$Method$("
                   "::grpc::ServerContext* /*context*/, "
                   "::grpc::ServerReaderWriter< $Response$, $Request$>* "
                   "/*stream*/) {\n");
    printer->Print(
        "  return ::grpc::Status("
        "::grpc::StatusCode::UNIMPLEMENTED, \"\");\n");
    printer->Print("}\n\n");
  }
}

static void PrintSourceService(grpc_generator::Printer* printer,
                               const grpc_generator::Service* service,
                               std::map<grpc::string, grpc::string>* vars) {
  (*vars)["Service"] = service->name();

  if (service->method_count() > 0) {
    printer->Print(*vars,
                   "static const char* $prefix$$Service$_method_names[] = {\n");
    for (int i = 0; i < service->method_count(); ++i) {
      (*vars)["Method"] = service->method(i).get()->name();
      printer->Print(*vars, "  \"/$Package$$Service$/$Method$\",\n");
    }
    printer->Print(*vars, "};\n\n");
  }

  printer->Print(*vars,
                 "std::unique_ptr< $ns$$Service$::Stub> $ns$$Service$::NewStub("
                 "const std::shared_ptr< ::grpc::ChannelInterface>& channel, "
                 "const ::grpc::StubOptions& /*options*/) {\n"
                 "  std::unique_ptr< $ns$$Service$::Stub> stub(new "
                 "$ns$$Service$::Stub(channel));\n"
                 "  return stub;\n"
                 "}\n\n");
  printer->Print(*vars,
                 "$ns$$Service$::Stub::Stub(const std::shared_ptr< "
                 "::grpc::ChannelInterface>& channel)\n");
  printer->Indent();
  printer->Print(": channel_(channel)");
  for (int i = 0; i < service->method_count(); ++i) {
    auto method = service->method(i);
    (*vars)["Method"] = method->name();
    (*vars)["Idx"] = as_string(i);
    if (method->NoStreaming()) {
      (*vars)["StreamingType"] = "NORMAL_RPC";
      // NOTE: There is no reason to consider streamed-unary as a separate
      // category here since this part is setting up the client-side stub
      // and this appears as a NORMAL_RPC from the client-side.
    } else if (ClientOnlyStreaming(method.get())) {
      (*vars)["StreamingType"] = "CLIENT_STREAMING";
    } else if (ServerOnlyStreaming(method.get())) {
      (*vars)["StreamingType"] = "SERVER_STREAMING";
    } else {
      (*vars)["StreamingType"] = "BIDI_STREAMING";
    }
    printer->Print(*vars,
                   ", rpcmethod_$Method$_("
                   "$prefix$$Service$_method_names[$Idx$], "
                   "::grpc::internal::RpcMethod::$StreamingType$, "
                   "channel"
                   ")\n");
  }
  printer->Print("{}\n\n");
  printer->Outdent();

  for (int i = 0; i < service->method_count(); ++i) {
    (*vars)["Idx"] = as_string(i);
    PrintSourceClientMethod(printer, service->method(i).get(), vars);
  }

  printer->Print(*vars, "$ns$$Service$::Service::Service() {\n");
  printer->Indent();
  for (int i = 0; i < service->method_count(); ++i) {
    auto method = service->method(i);
    (*vars)["Idx"] = as_string(i);
    (*vars)["Method"] = method->name();
    (*vars)["Request"] = method->input_type_name();
    (*vars)["Response"] = method->output_type_name();
    if (method->NoStreaming()) {
      printer->Print(
          *vars,
          "AddMethod(new ::grpc::internal::RpcServiceMethod(\n"
          "    $prefix$$Service$_method_names[$Idx$],\n"
          "    ::grpc::internal::RpcMethod::NORMAL_RPC,\n"
          "    new ::grpc::internal::RpcMethodHandler< $ns$$Service$::Service, "
          "$Request$, "
          "$Response$>(\n"
          "        std::mem_fn(&$ns$$Service$::Service::$Method$), this)));\n");
    } else if (ClientOnlyStreaming(method.get())) {
      printer->Print(
          *vars,
          "AddMethod(new ::grpc::internal::RpcServiceMethod(\n"
          "    $prefix$$Service$_method_names[$Idx$],\n"
          "    ::grpc::internal::RpcMethod::CLIENT_STREAMING,\n"
          "    new ::grpc::internal::ClientStreamingHandler< "
          "$ns$$Service$::Service, $Request$, $Response$>(\n"
          "        std::mem_fn(&$ns$$Service$::Service::$Method$), this)));\n");
    } else if (ServerOnlyStreaming(method.get())) {
      printer->Print(
          *vars,
          "AddMethod(new ::grpc::internal::RpcServiceMethod(\n"
          "    $prefix$$Service$_method_names[$Idx$],\n"
          "    ::grpc::internal::RpcMethod::SERVER_STREAMING,\n"
          "    new ::grpc::internal::ServerStreamingHandler< "
          "$ns$$Service$::Service, $Request$, $Response$>(\n"
          "        std::mem_fn(&$ns$$Service$::Service::$Method$), this)));\n");
    } else if (method->BidiStreaming()) {
      printer->Print(
          *vars,
          "AddMethod(new ::grpc::internal::RpcServiceMethod(\n"
          "    $prefix$$Service$_method_names[$Idx$],\n"
          "    ::grpc::internal::RpcMethod::BIDI_STREAMING,\n"
          "    new ::grpc::internal::BidiStreamingHandler< "
          "$ns$$Service$::Service, $Request$, $Response$>(\n"
          "        std::mem_fn(&$ns$$Service$::Service::$Method$), this)));\n");
    }
  }
  printer->Outdent();
  printer->Print(*vars, "}\n\n");
  printer->Print(*vars,
                 "$ns$$Service$::Service::~Service() {\n"
                 "}\n\n");
  for (int i = 0; i < service->method_count(); ++i) {
    (*vars)["Idx"] = as_string(i);
    PrintSourceServerMethod(printer, service->method(i).get(), vars);
  }

  // CallbackService implementation (if enabled)
  if ((*vars)["generate_callback_api"] == "1") {
    (*vars)["Service"] = service->name();
    printer->Print("#if defined(GRPC_CALLBACK_API_NONEXPERIMENTAL)\n");
    printer->Print(*vars,
                   "$ns$$Service$::CallbackService::CallbackService() {\n");
    printer->Indent();
    for (int i = 0; i < service->method_count(); ++i) {
      auto method = service->method(i);
      (*vars)["Idx"] = as_string(i);
      (*vars)["Method"] = method->name();
      (*vars)["Request"] = method->input_type_name();
      (*vars)["Response"] = method->output_type_name();
      if (method->NoStreaming()) {
        printer->Print(
            *vars,
            "AddMethod(new ::grpc::internal::RpcServiceMethod(\n"
            "    $prefix$$Service$_method_names[$Idx$],\n"
            "    ::grpc::internal::RpcMethod::NORMAL_RPC,\n"
            "    new ::grpc::internal::CallbackUnaryHandler<$Request$, "
            "$Response$>(\n"
            "      [this](::grpc::CallbackServerContext* ctx, const $Request$* "
            "req, $Response$* resp) {\n"
            "        return this->$Method$(ctx, req, resp);\n"
            "      })));\n");
      } else if (ClientOnlyStreaming(method.get())) {
        printer->Print(*vars,
                       "AddMethod(new ::grpc::internal::RpcServiceMethod(\n"
                       "    $prefix$$Service$_method_names[$Idx$],\n"
                       "    ::grpc::internal::RpcMethod::CLIENT_STREAMING,\n"
                       "    new "
                       "::grpc::internal::CallbackClientStreamingHandler<$"
                       "Request$, $Response$>(\n"
                       "      [this](::grpc::CallbackServerContext* ctx, "
                       "$Response$* resp) {\n"
                       "        return this->$Method$(ctx, resp);\n"
                       "      })));\n");
      } else if (ServerOnlyStreaming(method.get())) {
        printer->Print(*vars,
                       "AddMethod(new ::grpc::internal::RpcServiceMethod(\n"
                       "    $prefix$$Service$_method_names[$Idx$],\n"
                       "    ::grpc::internal::RpcMethod::SERVER_STREAMING,\n"
                       "    new "
                       "::grpc::internal::CallbackServerStreamingHandler<$"
                       "Request$, $Response$>(\n"
                       "      [this](::grpc::CallbackServerContext* ctx, const "
                       "$Request$* req) {\n"
                       "        return this->$Method$(ctx, req);\n"
                       "      })));\n");
      } else if (method->BidiStreaming()) {
        printer->Print(
            *vars,
            "AddMethod(new ::grpc::internal::RpcServiceMethod(\n"
            "    $prefix$$Service$_method_names[$Idx$],\n"
            "    ::grpc::internal::RpcMethod::BIDI_STREAMING,\n"
            "    new ::grpc::internal::CallbackBidiHandler<$Request$, "
            "$Response$>(\n"
            "      [this](::grpc::CallbackServerContext* ctx) {\n"
            "        return this->$Method$(ctx);\n"
            "      })));\n");
      }
    }
    printer->Outdent();
    printer->Print("}\n\n");
    printer->Print(*vars,
                   "$ns$$Service$::CallbackService::~CallbackService() {}\n\n");
    // Default method bodies returning UNIMPLEMENTED reactors.
    for (int i = 0; i < service->method_count(); ++i) {
      auto method = service->method(i);
      (*vars)["Method"] = method->name();
      (*vars)["Request"] = method->input_type_name();
      (*vars)["Response"] = method->output_type_name();
      if (method->NoStreaming()) {
        printer->Print(*vars,
                       "::grpc::ServerUnaryReactor* "
                       "$ns$$Service$::CallbackService::$Method$(::grpc::"
                       "CallbackServerContext* /*context*/, const $Request$* "
                       "/*request*/, $Response$* /*response*/) {\n"
                       "  return nullptr; // user must override\n"
                       "}\n\n");
      } else if (ClientOnlyStreaming(method.get())) {
        printer->Print(
            *vars,
            "::grpc::ServerReadReactor<$Request$>* "
            "$ns$$Service$::CallbackService::$Method$(::grpc::"
            "CallbackServerContext* /*context*/, $Response$* /*response*/) {\n"
            "  return nullptr; // user must override\n"
            "}\n\n");
      } else if (ServerOnlyStreaming(method.get())) {
        printer->Print(*vars,
                       "::grpc::ServerWriteReactor<$Response$>* "
                       "$ns$$Service$::CallbackService::$Method$(::grpc::"
                       "CallbackServerContext* /*context*/, const $Request$* "
                       "/*request*/) {\n"
                       "  return nullptr; // user must override\n"
                       "}\n\n");
      } else if (method->BidiStreaming()) {
        printer->Print(*vars,
                       "::grpc::ServerBidiReactor<$Request$, $Response$>* "
                       "$ns$$Service$::CallbackService::$Method$(::grpc::"
                       "CallbackServerContext* /*context*/) {\n"
                       "  return nullptr; // user must override\n"
                       "}\n\n");
      }
    }
    printer->Print("#endif // GRPC_CALLBACK_API_NONEXPERIMENTAL\n");
  }
}

}  // namespace

grpc::string GetSourceServices(grpc_generator::File* file,
                               const Parameters& params) {
  grpc::string output;
  {
    // Scope the output stream so it closes and finalizes output to the string.
    auto printer = file->CreatePrinter(&output);
    std::map<grpc::string, grpc::string> vars;
    // Package string is empty or ends with a dot. It is used to fully qualify
    // method names.
    vars["Package"] = file->package();
    if (!file->package().empty()) {
      vars["Package"].append(".");
    }
    if (!params.services_namespace.empty()) {
      vars["ns"] = params.services_namespace + "::";
      vars["prefix"] = params.services_namespace;
    } else {
      vars["ns"] = "";
      vars["prefix"] = "";
    }

    for (int i = 0; i < file->service_count(); ++i) {
      vars["generate_callback_api"] = params.generate_callback_api ? "1" : "0";
      PrintSourceService(printer.get(), file->service(i).get(), &vars);
      printer->Print("\n");
    }
  }
  return output;
}

grpc::string GetSourceEpilogue(grpc_generator::File* file,
                               const Parameters& /*params*/) {
  grpc::string temp;

  if (!file->package().empty()) {
    std::vector<grpc::string> parts = file->package_parts();

    for (auto part = parts.begin(); part != parts.end(); part++) {
      temp.append("}  // namespace ");
      temp.append(*part);
      temp.append("\n");
    }
    temp.append("\n");
  }

  return temp;
}

grpc::string GetMockPrologue(grpc_generator::File* file,
                             const Parameters& params) {
  grpc::string output;
  {
    // Scope the output stream so it closes and finalizes output to the string.
    auto printer = file->CreatePrinter(&output);
    std::map<grpc::string, grpc::string> vars;

    vars["filename"] = file->filename();
    vars["filename_base"] = file->filename_without_ext();
    vars["message_header_ext"] = params.message_header_extension;
    vars["service_header_ext"] = params.service_header_extension;

    printer->Print(vars, "// Generated by the gRPC C++ plugin.\n");
    printer->Print(vars,
                   "// If you make any local change, they will be lost.\n");
    printer->Print(vars, "// source: $filename$\n\n");

    printer->Print(vars, "#include \"$filename_base$$message_header_ext$\"\n");
    printer->Print(vars, "#include \"$filename_base$$service_header_ext$\"\n");
    printer->Print(vars, file->additional_headers().c_str());
    printer->Print(vars, "\n");
  }
  return output;
}

// TODO(mmukhi): Add client-stream and completion-queue headers.
grpc::string GetMockIncludes(grpc_generator::File* file,
                             const Parameters& params) {
  grpc::string output;
  {
    // Scope the output stream so it closes and finalizes output to the string.
    auto printer = file->CreatePrinter(&output);
    std::map<grpc::string, grpc::string> vars;

    static const char* headers_strs[] = {
        "grpcpp/impl/codegen/async_stream.h",
        "grpcpp/impl/codegen/sync_stream.h",
        "gmock/gmock.h",
    };
    std::vector<grpc::string> headers(headers_strs, array_end(headers_strs));
    PrintIncludes(printer.get(), headers, params);

    if (!file->package().empty()) {
      std::vector<grpc::string> parts = file->package_parts();

      for (auto part = parts.begin(); part != parts.end(); part++) {
        vars["part"] = *part;
        printer->Print(vars, "namespace $part$ {\n");
      }
    }

    printer->Print(vars, "\n");
  }
  return output;
}

namespace {

static void PrintMockClientMethods(grpc_generator::Printer* printer,
                                   const grpc_generator::Method* method,
                                   std::map<grpc::string, grpc::string>* vars) {
  (*vars)["Method"] = method->name();
  (*vars)["Request"] = method->input_type_name();
  (*vars)["Response"] = method->output_type_name();

  struct {
    grpc::string prefix;
    grpc::string method_params;  // extra arguments to method
    int extra_method_param_count;
  } async_prefixes[] = {{"Async", ", void* tag", 1}, {"PrepareAsync", "", 0}};

  if (method->NoStreaming()) {
    printer->Print(
        *vars,
        "MOCK_METHOD3($Method$, ::grpc::Status(::grpc::ClientContext* context, "
        "const $Request$& request, $Response$* response));\n");
    for (size_t i = 0; i < sizeof(async_prefixes) / sizeof(async_prefixes[0]);
         i++) {
      auto& async_prefix = async_prefixes[i];
      (*vars)["AsyncPrefix"] = async_prefix.prefix;
      printer->Print(
          *vars,
          "MOCK_METHOD3($AsyncPrefix$$Method$Raw, "
          "::grpc::ClientAsyncResponseReaderInterface< $Response$>*"
          "(::grpc::ClientContext* context, const $Request$& request, "
          "::grpc::CompletionQueue* cq));\n");
    }
  } else if (ClientOnlyStreaming(method)) {
    printer->Print(
        *vars,
        "MOCK_METHOD2($Method$Raw, "
        "::grpc::ClientWriterInterface< $Request$>*"
        "(::grpc::ClientContext* context, $Response$* response));\n");
    for (size_t i = 0; i < sizeof(async_prefixes) / sizeof(async_prefixes[0]);
         i++) {
      auto& async_prefix = async_prefixes[i];
      (*vars)["AsyncPrefix"] = async_prefix.prefix;
      (*vars)["AsyncMethodParams"] = async_prefix.method_params;
      (*vars)["MockArgs"] =
          flatbuffers::NumToString(3 + async_prefix.extra_method_param_count);
      printer->Print(*vars,
                     "MOCK_METHOD$MockArgs$($AsyncPrefix$$Method$Raw, "
                     "::grpc::ClientAsyncWriterInterface< $Request$>*"
                     "(::grpc::ClientContext* context, $Response$* response, "
                     "::grpc::CompletionQueue* cq$AsyncMethodParams$));\n");
    }
  } else if (ServerOnlyStreaming(method)) {
    printer->Print(
        *vars,
        "MOCK_METHOD2($Method$Raw, "
        "::grpc::ClientReaderInterface< $Response$>*"
        "(::grpc::ClientContext* context, const $Request$& request));\n");
    for (size_t i = 0; i < sizeof(async_prefixes) / sizeof(async_prefixes[0]);
         i++) {
      auto& async_prefix = async_prefixes[i];
      (*vars)["AsyncPrefix"] = async_prefix.prefix;
      (*vars)["AsyncMethodParams"] = async_prefix.method_params;
      (*vars)["MockArgs"] =
          flatbuffers::NumToString(3 + async_prefix.extra_method_param_count);
      printer->Print(
          *vars,
          "MOCK_METHOD$MockArgs$($AsyncPrefix$$Method$Raw, "
          "::grpc::ClientAsyncReaderInterface< $Response$>*"
          "(::grpc::ClientContext* context, const $Request$& request, "
          "::grpc::CompletionQueue* cq$AsyncMethodParams$));\n");
    }
  } else if (method->BidiStreaming()) {
    printer->Print(
        *vars,
        "MOCK_METHOD1($Method$Raw, "
        "::grpc::ClientReaderWriterInterface< $Request$, $Response$>*"
        "(::grpc::ClientContext* context));\n");
    for (size_t i = 0; i < sizeof(async_prefixes) / sizeof(async_prefixes[0]);
         i++) {
      auto& async_prefix = async_prefixes[i];
      (*vars)["AsyncPrefix"] = async_prefix.prefix;
      (*vars)["AsyncMethodParams"] = async_prefix.method_params;
      (*vars)["MockArgs"] =
          flatbuffers::NumToString(2 + async_prefix.extra_method_param_count);
      printer->Print(
          *vars,
          "MOCK_METHOD$MockArgs$($AsyncPrefix$$Method$Raw, "
          "::grpc::ClientAsyncReaderWriterInterface<$Request$, $Response$>*"
          "(::grpc::ClientContext* context, ::grpc::CompletionQueue* cq"
          "$AsyncMethodParams$));\n");
    }
  }
}

static void PrintMockService(grpc_generator::Printer* printer,
                             const grpc_generator::Service* service,
                             std::map<grpc::string, grpc::string>* vars) {
  (*vars)["Service"] = service->name();

  printer->Print(*vars,
                 "class Mock$Service$Stub : public $Service$::StubInterface {\n"
                 " public:\n");
  printer->Indent();
  for (int i = 0; i < service->method_count(); ++i) {
    PrintMockClientMethods(printer, service->method(i).get(), vars);
  }
  printer->Outdent();
  printer->Print("};\n");
}

}  // namespace

grpc::string GetMockServices(grpc_generator::File* file,
                             const Parameters& params) {
  grpc::string output;
  {
    // Scope the output stream so it closes and finalizes output to the string.
    auto printer = file->CreatePrinter(&output);
    std::map<grpc::string, grpc::string> vars;
    // Package string is empty or ends with a dot. It is used to fully qualify
    // method names.
    vars["Package"] = file->package();
    if (!file->package().empty()) {
      vars["Package"].append(".");
    }

    if (!params.services_namespace.empty()) {
      vars["services_namespace"] = params.services_namespace;
      printer->Print(vars, "\nnamespace $services_namespace$ {\n\n");
    }

    for (int i = 0; i < file->service_count(); i++) {
      PrintMockService(printer.get(), file->service(i).get(), &vars);
      printer->Print("\n");
    }

    if (!params.services_namespace.empty()) {
      printer->Print(vars, "} // namespace $services_namespace$\n\n");
    }
  }
  return output;
}

grpc::string GetMockEpilogue(grpc_generator::File* file,
                             const Parameters& /*params*/) {
  grpc::string temp;

  if (!file->package().empty()) {
    std::vector<grpc::string> parts = file->package_parts();

    for (auto part = parts.begin(); part != parts.end(); part++) {
      temp.append("} // namespace ");
      temp.append(*part);
      temp.append("\n");
    }
    temp.append("\n");
  }

  return temp;
}

}  // namespace grpc_cpp_generator
