/*
 * Copyright (C) 2017 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <map>
#include <memory>
#include <set>
#include <string>

#include <google/protobuf/compiler/code_generator.h>
#include <google/protobuf/compiler/plugin.h>
#include <google/protobuf/descriptor.h>
#include <google/protobuf/io/printer.h>
#include <google/protobuf/io/zero_copy_stream.h>
#include <google/protobuf/stubs/strutil.h>

namespace protozero {
namespace {

using google::protobuf::Descriptor;
using google::protobuf::EnumDescriptor;
using google::protobuf::EnumValueDescriptor;
using google::protobuf::FieldDescriptor;
using google::protobuf::FileDescriptor;
using google::protobuf::Split;
using google::protobuf::StripPrefixString;
using google::protobuf::StripString;
using google::protobuf::StripSuffixString;
using google::protobuf::UpperString;
using google::protobuf::compiler::GeneratorContext;
using google::protobuf::io::Printer;
using google::protobuf::io::ZeroCopyOutputStream;

// Keep this value in sync with ProtoDecoder::kMaxDecoderFieldId. If they go out
// of sync pbzero.h files will stop compiling, hitting the at() static_assert.
// Not worth an extra dependency.
constexpr int kMaxDecoderFieldId = 999;

void Assert(bool condition) {
  if (!condition)
    __builtin_trap();
}

struct FileDescriptorComp {
  bool operator()(const FileDescriptor* lhs, const FileDescriptor* rhs) const {
    int comp = lhs->name().compare(rhs->name());
    Assert(comp != 0 || lhs == rhs);
    return comp < 0;
  }
};

struct DescriptorComp {
  bool operator()(const Descriptor* lhs, const Descriptor* rhs) const {
    int comp = lhs->full_name().compare(rhs->full_name());
    Assert(comp != 0 || lhs == rhs);
    return comp < 0;
  }
};

struct EnumDescriptorComp {
  bool operator()(const EnumDescriptor* lhs, const EnumDescriptor* rhs) const {
    int comp = lhs->full_name().compare(rhs->full_name());
    Assert(comp != 0 || lhs == rhs);
    return comp < 0;
  }
};

inline std::string ProtoStubName(const FileDescriptor* proto) {
  return StripSuffixString(proto->name(), ".proto") + ".pbzero";
}

class GeneratorJob {
 public:
  GeneratorJob(const FileDescriptor* file, Printer* stub_h_printer)
      : source_(file), stub_h_(stub_h_printer) {}

  bool GenerateStubs() {
    Preprocess();
    GeneratePrologue();
    for (const EnumDescriptor* enumeration : enums_)
      GenerateEnumDescriptor(enumeration);
    for (const Descriptor* message : messages_)
      GenerateMessageDescriptor(message);
    GenerateEpilogue();
    return error_.empty();
  }

  void SetOption(const std::string& name, const std::string& value) {
    if (name == "wrapper_namespace") {
      wrapper_namespace_ = value;
    } else {
      Abort(std::string() + "Unknown plugin option '" + name + "'.");
    }
  }

  // If generator fails to produce stubs for a particular proto definitions
  // it finishes with undefined output and writes the first error occured.
  const std::string& GetFirstError() const { return error_; }

 private:
  // Only the first error will be recorded.
  void Abort(const std::string& reason) {
    if (error_.empty())
      error_ = reason;
  }

  // Get full name (including outer descriptors) of proto descriptor.
  template <class T>
  inline std::string GetDescriptorName(const T* descriptor) {
    if (!package_.empty()) {
      return StripPrefixString(descriptor->full_name(), package_ + ".");
    } else {
      return descriptor->full_name();
    }
  }

  // Get C++ class name corresponding to proto descriptor.
  // Nested names are splitted by underscores. Underscores in type names aren't
  // prohibited but not recommended in order to avoid name collisions.
  template <class T>
  inline std::string GetCppClassName(const T* descriptor, bool full = false) {
    std::string name = GetDescriptorName(descriptor);
    StripString(&name, ".", '_');
    if (full)
      name = full_namespace_prefix_ + name;
    return name;
  }

  inline std::string GetFieldNumberConstant(const FieldDescriptor* field) {
    std::string name = field->camelcase_name();
    if (!name.empty()) {
      name.at(0) = static_cast<char>(toupper(name.at(0)));
      name = "k" + name + "FieldNumber";
    } else {
      // Protoc allows fields like 'bool _ = 1'.
      Abort("Empty field name in camel case notation.");
    }
    return name;
  }

  // Small enums can be written faster without involving VarInt encoder.
  inline bool IsTinyEnumField(const FieldDescriptor* field) {
    if (field->type() != FieldDescriptor::TYPE_ENUM)
      return false;
    const EnumDescriptor* enumeration = field->enum_type();

    for (int i = 0; i < enumeration->value_count(); ++i) {
      int32_t value = enumeration->value(i)->number();
      if (value < 0 || value > 0x7F)
        return false;
    }
    return true;
  }

  void CollectDescriptors() {
    // Collect message descriptors in DFS order.
    std::vector<const Descriptor*> stack;
    for (int i = 0; i < source_->message_type_count(); ++i)
      stack.push_back(source_->message_type(i));

    while (!stack.empty()) {
      const Descriptor* message = stack.back();
      stack.pop_back();
      messages_.push_back(message);
      for (int i = 0; i < message->nested_type_count(); ++i) {
        stack.push_back(message->nested_type(i));
      }
    }

    // Collect enums.
    for (int i = 0; i < source_->enum_type_count(); ++i)
      enums_.push_back(source_->enum_type(i));

    for (const Descriptor* message : messages_) {
      for (int i = 0; i < message->enum_type_count(); ++i) {
        enums_.push_back(message->enum_type(i));
      }
    }
  }

  void CollectDependencies() {
    // Public import basically means that callers only need to import this
    // proto in order to use the stuff publicly imported by this proto.
    for (int i = 0; i < source_->public_dependency_count(); ++i)
      public_imports_.insert(source_->public_dependency(i));

    if (source_->weak_dependency_count() > 0)
      Abort("Weak imports are not supported.");

    // Sanity check. Collect public imports (of collected imports) in DFS order.
    // Visibilty for current proto:
    // - all imports listed in current proto,
    // - public imports of everything imported (recursive).
    std::vector<const FileDescriptor*> stack;
    for (int i = 0; i < source_->dependency_count(); ++i) {
      const FileDescriptor* import = source_->dependency(i);
      stack.push_back(import);
      if (public_imports_.count(import) == 0) {
        private_imports_.insert(import);
      }
    }

    while (!stack.empty()) {
      const FileDescriptor* import = stack.back();
      stack.pop_back();
      // Having imports under different packages leads to unnecessary
      // complexity with namespaces.
      if (import->package() != package_)
        Abort("Imported proto must be in the same package.");

      for (int i = 0; i < import->public_dependency_count(); ++i) {
        stack.push_back(import->public_dependency(i));
      }
    }

    // Collect descriptors of messages and enums used in current proto.
    // It will be used to generate necessary forward declarations and performed
    // sanity check guarantees that everything lays in the same namespace.
    for (const Descriptor* message : messages_) {
      for (int i = 0; i < message->field_count(); ++i) {
        const FieldDescriptor* field = message->field(i);

        if (field->type() == FieldDescriptor::TYPE_MESSAGE) {
          if (public_imports_.count(field->message_type()->file()) == 0) {
            // Avoid multiple forward declarations since
            // public imports have been already included.
            referenced_messages_.insert(field->message_type());
          }
        } else if (field->type() == FieldDescriptor::TYPE_ENUM) {
          if (public_imports_.count(field->enum_type()->file()) == 0) {
            referenced_enums_.insert(field->enum_type());
          }
        }
      }
    }
  }

  void Preprocess() {
    // Package name maps to a series of namespaces.
    package_ = source_->package();
    namespaces_ = Split(package_, ".");
    if (!wrapper_namespace_.empty())
      namespaces_.push_back(wrapper_namespace_);

    full_namespace_prefix_ = "::";
    for (const std::string& ns : namespaces_)
      full_namespace_prefix_ += ns + "::";

    CollectDescriptors();
    CollectDependencies();
  }

  // Print top header, namespaces and forward declarations.
  void GeneratePrologue() {
    std::string greeting =
        "// Autogenerated by the ProtoZero compiler plugin. DO NOT EDIT.\n";
    std::string guard = package_ + "_" + source_->name() + "_H_";
    UpperString(&guard);
    StripString(&guard, ".-/\\", '_');

    stub_h_->Print(
        "$greeting$\n"
        "#ifndef $guard$\n"
        "#define $guard$\n\n"
        "#include <stddef.h>\n"
        "#include <stdint.h>\n\n"
        "#include \"perfetto/protozero/proto_decoder.h\"\n"
        "#include \"perfetto/protozero/message.h\"\n",
        "greeting", greeting, "guard", guard);

    // Print includes for public imports.
    for (const FileDescriptor* dependency : public_imports_) {
      // Dependency name could contain slashes but importing from upper-level
      // directories is not possible anyway since build system processes each
      // proto file individually. Hence proto lookup path is always equal to the
      // directory where particular proto file is located and protoc does not
      // allow reference to upper directory (aka ..) in import path.
      //
      // Laconically said:
      // - source_->name() may never have slashes,
      // - dependency->name() may have slashes but always refers to inner path.
      stub_h_->Print("#include \"$name$.h\"\n", "name",
                     ProtoStubName(dependency));
    }
    stub_h_->Print("\n");

    // Print namespaces.
    for (const std::string& ns : namespaces_) {
      stub_h_->Print("namespace $ns$ {\n", "ns", ns);
    }
    stub_h_->Print("\n");

    // Print forward declarations.
    for (const Descriptor* message : referenced_messages_) {
      stub_h_->Print("class $class$;\n", "class", GetCppClassName(message));
    }
    for (const EnumDescriptor* enumeration : referenced_enums_) {
      stub_h_->Print("enum $class$ : int32_t;\n", "class",
                     GetCppClassName(enumeration));
    }
    stub_h_->Print("\n");
  }

  void GenerateEnumDescriptor(const EnumDescriptor* enumeration) {
    stub_h_->Print("enum $class$ : int32_t {\n", "class",
                   GetCppClassName(enumeration));
    stub_h_->Indent();

    std::string value_name_prefix;
    if (enumeration->containing_type() != nullptr)
      value_name_prefix = GetCppClassName(enumeration) + "_";

    std::string min_name, max_name;
    int min_val = std::numeric_limits<int>::max();
    int max_val = -1;
    for (int i = 0; i < enumeration->value_count(); ++i) {
      const EnumValueDescriptor* value = enumeration->value(i);
      stub_h_->Print("$name$ = $number$,\n", "name",
                     value_name_prefix + value->name(), "number",
                     std::to_string(value->number()));
      if (value->number() < min_val) {
        min_val = value->number();
        min_name = value_name_prefix + value->name();
      }
      if (value->number() > max_val) {
        max_val = value->number();
        max_name = value_name_prefix + value->name();
      }
    }
    stub_h_->Outdent();
    stub_h_->Print("};\n\n");
    stub_h_->Print("const $class$ $class$_MIN = $min$;\n", "class",
                   GetCppClassName(enumeration), "min", min_name);
    stub_h_->Print("const $class$ $class$_MAX = $max$;\n", "class",
                   GetCppClassName(enumeration), "max", max_name);
    stub_h_->Print("\n");
  }

  void GenerateSimpleFieldDescriptor(const FieldDescriptor* field) {
    std::map<std::string, std::string> setter;
    setter["id"] = std::to_string(field->number());
    setter["name"] = field->name();
    setter["action"] = field->is_repeated() ? "add" : "set";

    std::string appender;
    std::string cpp_type;

    switch (field->type()) {
      case FieldDescriptor::TYPE_BOOL: {
        appender = "AppendTinyVarInt";
        cpp_type = "bool";
        break;
      }
      case FieldDescriptor::TYPE_INT32: {
        appender = "AppendVarInt";
        cpp_type = "int32_t";
        break;
      }
      case FieldDescriptor::TYPE_INT64: {
        appender = "AppendVarInt";
        cpp_type = "int64_t";
        break;
      }
      case FieldDescriptor::TYPE_UINT32: {
        appender = "AppendVarInt";
        cpp_type = "uint32_t";
        break;
      }
      case FieldDescriptor::TYPE_UINT64: {
        appender = "AppendVarInt";
        cpp_type = "uint64_t";
        break;
      }
      case FieldDescriptor::TYPE_SINT32: {
        appender = "AppendSignedVarInt";
        cpp_type = "int32_t";
        break;
      }
      case FieldDescriptor::TYPE_SINT64: {
        appender = "AppendSignedVarInt";
        cpp_type = "int64_t";
        break;
      }
      case FieldDescriptor::TYPE_FIXED32: {
        appender = "AppendFixed";
        cpp_type = "uint32_t";
        break;
      }
      case FieldDescriptor::TYPE_FIXED64: {
        appender = "AppendFixed";
        cpp_type = "uint64_t";
        break;
      }
      case FieldDescriptor::TYPE_SFIXED32: {
        appender = "AppendFixed";
        cpp_type = "int32_t";
        break;
      }
      case FieldDescriptor::TYPE_SFIXED64: {
        appender = "AppendFixed";
        cpp_type = "int64_t";
        break;
      }
      case FieldDescriptor::TYPE_FLOAT: {
        appender = "AppendFixed";
        cpp_type = "float";
        break;
      }
      case FieldDescriptor::TYPE_DOUBLE: {
        appender = "AppendFixed";
        cpp_type = "double";
        break;
      }
      case FieldDescriptor::TYPE_ENUM: {
        appender = IsTinyEnumField(field) ? "AppendTinyVarInt" : "AppendVarInt";
        cpp_type = GetCppClassName(field->enum_type(), true);
        break;
      }
      case FieldDescriptor::TYPE_STRING: {
        appender = "AppendString";
        cpp_type = "const char*";
        break;
      }
      case FieldDescriptor::TYPE_BYTES: {
        stub_h_->Print(
            setter,
            "void $action$_$name$(const uint8_t* data, size_t size) {\n"
            "  AppendBytes($id$, data, size);\n"
            "}\n");
        return;
      }
      case FieldDescriptor::TYPE_GROUP:
      case FieldDescriptor::TYPE_MESSAGE: {
        Abort("Unsupported field type.");
        return;
      }
    }
    setter["appender"] = appender;
    setter["cpp_type"] = cpp_type;
    stub_h_->Print(setter,
                   "void $action$_$name$($cpp_type$ value) {\n"
                   "  $appender$($id$, value);\n"
                   "}\n");

    // For strings also generate a variant for non-null terminated strings.
    if (field->type() == FieldDescriptor::TYPE_STRING) {
      stub_h_->Print(setter,
                     "// Doesn't check for null terminator.\n"
                     "// Expects |value| to be at least |size| long.\n"
                     "void $action$_$name$($cpp_type$ value, size_t size) {\n"
                     "  AppendBytes($id$, value, size);\n"
                     "}\n");
    }
  }

  void GenerateNestedMessageFieldDescriptor(const FieldDescriptor* field) {
    std::string action = field->is_repeated() ? "add" : "set";
    std::string inner_class = GetCppClassName(field->message_type());
    stub_h_->Print(
        "template <typename T = $inner_class$> T* $action$_$name$() {\n"
        "  return BeginNestedMessage<T>($id$);\n"
        "}\n\n",
        "id", std::to_string(field->number()), "name", field->name(), "action",
        action, "inner_class", inner_class);
  }

  void GenerateDecoder(const Descriptor* message) {
    int max_field_id = 0;
    bool has_repeated_fields = false;
    for (int i = 0; i < message->field_count(); ++i) {
      const FieldDescriptor* field = message->field(i);
      if (field->number() > kMaxDecoderFieldId)
        continue;
      max_field_id = std::max(max_field_id, field->number());
      if (field->is_repeated())
        has_repeated_fields = true;
    }

    std::string class_name = GetCppClassName(message) + "_Decoder";
    stub_h_->Print(
        "class $name$ : public "
        "::protozero::TypedProtoDecoder</*MAX_FIELD_ID=*/$max$, "
        "/*HAS_REPEATED_FIELDS=*/$rep$> {\n",
        "name", class_name, "max", std::to_string(max_field_id), "rep",
        has_repeated_fields ? "true" : "false");
    stub_h_->Print(" public:\n");
    stub_h_->Indent();
    stub_h_->Print(
        "$name$(const uint8_t* data, size_t len) "
        ": TypedProtoDecoder(data, len) {}\n",
        "name", class_name);
    stub_h_->Print(
        "explicit $name$(const std::string& raw) : "
        "TypedProtoDecoder(reinterpret_cast<const uint8_t*>(raw.data()), "
        "raw.size()) {}\n",
        "name", class_name);
    stub_h_->Print(
        "explicit $name$(const ::protozero::ConstBytes& raw) : "
        "TypedProtoDecoder(raw.data, raw.size) {}\n",
        "name", class_name);

    for (int i = 0; i < message->field_count(); ++i) {
      const FieldDescriptor* field = message->field(i);
      if (field->is_packed()) {
        Abort("Packed repeated fields are not supported.");
        return;
      }

      if (field->number() > max_field_id) {
        stub_h_->Print("// field $name$ omitted because its id is too high\n",
                       "name", field->name());
        continue;
      }
      std::string getter;
      std::string cpp_type;
      switch (field->type()) {
        case FieldDescriptor::TYPE_BOOL:
          getter = "as_bool";
          cpp_type = "bool";
          break;
        case FieldDescriptor::TYPE_SFIXED32:
        case FieldDescriptor::TYPE_SINT32:
        case FieldDescriptor::TYPE_INT32:
          getter = "as_int32";
          cpp_type = "int32_t";
          break;
        case FieldDescriptor::TYPE_SFIXED64:
        case FieldDescriptor::TYPE_SINT64:
        case FieldDescriptor::TYPE_INT64:
          getter = "as_int64";
          cpp_type = "int64_t";
          break;
        case FieldDescriptor::TYPE_FIXED32:
        case FieldDescriptor::TYPE_UINT32:
          getter = "as_uint32";
          cpp_type = "uint32_t";
          break;
        case FieldDescriptor::TYPE_FIXED64:
        case FieldDescriptor::TYPE_UINT64:
          getter = "as_uint64";
          cpp_type = "uint64_t";
          break;
        case FieldDescriptor::TYPE_FLOAT:
          getter = "as_float";
          cpp_type = "float";
          break;
        case FieldDescriptor::TYPE_DOUBLE:
          getter = "as_double";
          cpp_type = "double";
          break;
        case FieldDescriptor::TYPE_ENUM:
          getter = "as_int32";
          cpp_type = "int32_t";
          break;
        case FieldDescriptor::TYPE_STRING:
          getter = "as_string";
          cpp_type = "::protozero::ConstChars";
          break;
        case FieldDescriptor::TYPE_MESSAGE:
        case FieldDescriptor::TYPE_BYTES:
          getter = "as_bytes";
          cpp_type = "::protozero::ConstBytes";
          break;
        case FieldDescriptor::TYPE_GROUP:
          continue;
      }

      stub_h_->Print("bool has_$name$() const { return at<$id$>().valid(); }\n",
                     "name", field->name(), "id",
                     std::to_string(field->number()));

      if (field->is_repeated()) {
        stub_h_->Print(
            "::protozero::RepeatedFieldIterator $name$() const { return "
            "GetRepeated($id$); }\n",
            "name", field->name(), "id", std::to_string(field->number()));
      } else {
        stub_h_->Print(
            "$cpp_type$ $name$() const { return at<$id$>().$getter$(); }\n",
            "name", field->name(), "id", std::to_string(field->number()),
            "cpp_type", cpp_type, "getter", getter);
      }
    }
    stub_h_->Outdent();
    stub_h_->Print("};\n\n");
  }

  void GenerateConstantsForMessageFields(const Descriptor* message) {
    const bool has_fields = (message->field_count() > 0);

    // Field number constants.
    if (has_fields) {
      stub_h_->Print("enum : int32_t {\n");
      stub_h_->Indent();

      for (int i = 0; i < message->field_count(); ++i) {
        const FieldDescriptor* field = message->field(i);
        stub_h_->Print("$name$ = $id$,\n", "name",
                       GetFieldNumberConstant(field), "id",
                       std::to_string(field->number()));
      }
      stub_h_->Outdent();
      stub_h_->Print("};\n");
    }
  }

  void GenerateMessageDescriptor(const Descriptor* message) {
    GenerateDecoder(message);

    stub_h_->Print(
        "class $name$ : public ::protozero::Message {\n"
        " public:\n",
        "name", GetCppClassName(message));
    stub_h_->Indent();

    stub_h_->Print("using Decoder = $name$_Decoder;\n", "name",
                   GetCppClassName(message));

    GenerateConstantsForMessageFields(message);

    // Using statements for nested messages.
    for (int i = 0; i < message->nested_type_count(); ++i) {
      const Descriptor* nested_message = message->nested_type(i);
      stub_h_->Print("using $local_name$ = $global_name$;\n", "local_name",
                     nested_message->name(), "global_name",
                     GetCppClassName(nested_message, true));
    }

    // Using statements for nested enums.
    for (int i = 0; i < message->enum_type_count(); ++i) {
      const EnumDescriptor* nested_enum = message->enum_type(i);
      stub_h_->Print("using $local_name$ = $global_name$;\n", "local_name",
                     nested_enum->name(), "global_name",
                     GetCppClassName(nested_enum, true));
    }

    // Values of nested enums.
    for (int i = 0; i < message->enum_type_count(); ++i) {
      const EnumDescriptor* nested_enum = message->enum_type(i);
      std::string value_name_prefix = GetCppClassName(nested_enum) + "_";

      for (int j = 0; j < nested_enum->value_count(); ++j) {
        const EnumValueDescriptor* value = nested_enum->value(j);
        stub_h_->Print("static const $class$ $name$ = $full_name$;\n", "class",
                       nested_enum->name(), "name", value->name(), "full_name",
                       value_name_prefix + value->name());
      }
    }

    // Field descriptors.
    for (int i = 0; i < message->field_count(); ++i) {
      const FieldDescriptor* field = message->field(i);
      if (field->is_packed()) {
        Abort("Packed repeated fields are not supported.");
        return;
      }
      if (field->type() != FieldDescriptor::TYPE_MESSAGE) {
        GenerateSimpleFieldDescriptor(field);
      } else {
        GenerateNestedMessageFieldDescriptor(field);
      }
    }

    stub_h_->Outdent();
    stub_h_->Print("};\n\n");
  }

  void GenerateEpilogue() {
    for (unsigned i = 0; i < namespaces_.size(); ++i) {
      stub_h_->Print("} // Namespace.\n");
    }
    stub_h_->Print("#endif  // Include guard.\n");
  }

  const FileDescriptor* const source_;
  Printer* const stub_h_;
  std::string error_;

  std::string package_;
  std::string wrapper_namespace_;
  std::vector<std::string> namespaces_;
  std::string full_namespace_prefix_;
  std::vector<const Descriptor*> messages_;
  std::vector<const EnumDescriptor*> enums_;

  // The custom *Comp comparators are to ensure determinism of the generator.
  std::set<const FileDescriptor*, FileDescriptorComp> public_imports_;
  std::set<const FileDescriptor*, FileDescriptorComp> private_imports_;
  std::set<const Descriptor*, DescriptorComp> referenced_messages_;
  std::set<const EnumDescriptor*, EnumDescriptorComp> referenced_enums_;
};

class ProtoZeroGenerator : public ::google::protobuf::compiler::CodeGenerator {
 public:
  explicit ProtoZeroGenerator();
  ~ProtoZeroGenerator() override;

  // CodeGenerator implementation
  bool Generate(const google::protobuf::FileDescriptor* file,
                const std::string& options,
                GeneratorContext* context,
                std::string* error) const override;
};

ProtoZeroGenerator::ProtoZeroGenerator() {}

ProtoZeroGenerator::~ProtoZeroGenerator() {}

bool ProtoZeroGenerator::Generate(const FileDescriptor* file,
                                  const std::string& options,
                                  GeneratorContext* context,
                                  std::string* error) const {
  const std::unique_ptr<ZeroCopyOutputStream> stub_h_file_stream(
      context->Open(ProtoStubName(file) + ".h"));
  const std::unique_ptr<ZeroCopyOutputStream> stub_cc_file_stream(
      context->Open(ProtoStubName(file) + ".cc"));

  // Variables are delimited by $.
  Printer stub_h_printer(stub_h_file_stream.get(), '$');
  GeneratorJob job(file, &stub_h_printer);

  Printer stub_cc_printer(stub_cc_file_stream.get(), '$');
  stub_cc_printer.Print("// Intentionally empty\n");

  // Parse additional options.
  for (const std::string& option : Split(options, ",")) {
    std::vector<std::string> option_pair = Split(option, "=");
    job.SetOption(option_pair[0], option_pair[1]);
  }

  if (!job.GenerateStubs()) {
    *error = job.GetFirstError();
    return false;
  }
  return true;
}

}  // namespace
}  // namespace protozero

int main(int argc, char* argv[]) {
  ::protozero::ProtoZeroGenerator generator;
  return google::protobuf::compiler::PluginMain(argc, argv, &generator);
}