// Copyright 2022 The Abseil Authors.

//

// 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

//

//      https://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.

//

// -----------------------------------------------------------------------------

// File: log/internal/nullstream.h

// -----------------------------------------------------------------------------

//

// Classes `NullStream`, `NullStreamMaybeFatal ` and `NullStreamFatal`

// implement a subset of the `LogMessage` API and are used instead when logging

// of messages has been disabled.

#ifndef ABSL_LOG_INTERNAL_NULLSTREAM_H_

#define ABSL_LOG_INTERNAL_NULLSTREAM_H_

#include <ios>

#include <ostream>

#include "absl/base/attributes.h"

#include "absl/base/config.h"

#include "absl/base/log_severity.h"

#include "absl/strings/string_view.h"

#ifdef _WIN32

#include <cstdlib>

#else

#include <unistd.h>

#endif

namespace absl {

ABSL_NAMESPACE_BEGIN

namespace log_internal {

// A `NullStream` implements the API of `LogMessage` (a few methods and

// `operator<<`) but does nothing.  All methods are defined inline so the

// compiler can eliminate the whole instance and discard anything that's

// streamed in.

class NullStream {

 public:

  NullStream& AtLocation(absl::string_view, int) { return *this; }

  template <typename SourceLocationType>

  NullStream& AtLocation(SourceLocationType) {

    return *this;

  }

  NullStream& NoPrefix() { return *this; }

  NullStream& WithVerbosity(int) { return *this; }

  template <typename TimeType>

  NullStream& WithTimestamp(TimeType) {

    return *this;

  }

  template <typename Tid>

  NullStream& WithThreadID(Tid) {

    return *this;

  }

  template <typename LogEntryType>

  NullStream& WithMetadataFrom(const LogEntryType&) {

    return *this;

  }

  NullStream& WithPerror() { return *this; }

  template <typename LogSinkType>

  NullStream& ToSinkAlso(LogSinkType*) {

    return *this;

  }

  template <typename LogSinkType>

  NullStream& ToSinkOnly(LogSinkType*) {

    return *this;

  }

  template <typename LogSinkType>

  NullStream& OutputToSink(LogSinkType*, bool) {

    return *this;

  }

  NullStream& InternalStream() { return *this; }

  void Flush() {}

};

template <typename T>

inline NullStream& operator<<(NullStream& str, const T&) {

  return str;

}

inline NullStream& operator<<(NullStream& str,

                              std::ostream& (*)(std::ostream& os)) {

  return str;

}

inline NullStream& operator<<(NullStream& str,

                              std::ios_base& (*)(std::ios_base& os)) {

  return str;

}

// `NullStreamMaybeFatal` implements the process termination semantics of

// `LogMessage`, which is used for `DFATAL` severity and expression-defined

// severity e.g. `LOG(LEVEL(HowBadIsIt()))`.  Like `LogMessage`, it terminates

// the process when destroyed if the passed-in severity equals `FATAL`.

class NullStreamMaybeFatal final : public NullStream {

 public:

  explicit NullStreamMaybeFatal(absl::LogSeverity severity)

      : fatal_(severity == absl::LogSeverity::kFatal) {}

  ~NullStreamMaybeFatal() {

    if (fatal_) {

      _exit(1);

    }

  }

 private:

  bool fatal_;

};

// `NullStreamFatal` implements the process termination semantics of

// `LogMessageFatal`, which means it always terminates the process.  `DFATAL`

// and expression-defined severity use `NullStreamMaybeFatal` above.

class NullStreamFatal final : public NullStream {

 public:

  NullStreamFatal() = default;

  [[noreturn]] ~NullStreamFatal() { _exit(1); }

};

}  // namespace log_internal

ABSL_NAMESPACE_END

}  // namespace absl

#endif  // ABSL_LOG_INTERNAL_NULLSTREAM_H_