// Copyright (c) 2011 The LevelDB Authors. All rights reserved.

// Use of this source code is governed by a BSD-style license that can be

// found in the LICENSE file. See the AUTHORS file for names of contributors.

//

// Logger implementation that can be shared by all environments

// where enough posix functionality is available.

#ifndef STORAGE_LEVELDB_UTIL_POSIX_LOGGER_H_

#define STORAGE_LEVELDB_UTIL_POSIX_LOGGER_H_

#include <sys/time.h>

#include <cassert>

#include <cstdarg>

#include <cstdio>

#include <ctime>

#include <sstream>

#include <thread>

#include "leveldb/env.h"

namespace leveldb {

class PosixLogger final : public Logger {

 public:

  // Creates a logger that writes to the given file.

  //

  // The PosixLogger instance takes ownership of the file handle.

  explicit PosixLogger(std::FILE* fp) : fp_(fp) { assert(fp != nullptr); }

  ~PosixLogger() override { std::fclose(fp_); }

  void Logv(const char* format, std::va_list arguments) override {

    // Record the time as close to the Logv() call as possible.

    struct ::timeval now_timeval;

    ::gettimeofday(&now_timeval, nullptr);

    const std::time_t now_seconds = now_timeval.tv_sec;

    struct std::tm now_components;

    ::localtime_r(&now_seconds, &now_components);

    // Record the thread ID.

    constexpr const int kMaxThreadIdSize = 32;

    std::ostringstream thread_stream;

    thread_stream << std::this_thread::get_id();

    std::string thread_id = thread_stream.str();

    if (thread_id.size() > kMaxThreadIdSize) {

      thread_id.resize(kMaxThreadIdSize);

    }

    // We first attempt to print into a stack-allocated buffer. If this attempt

    // fails, we make a second attempt with a dynamically allocated buffer.

    constexpr const int kStackBufferSize = 512;

    char stack_buffer[kStackBufferSize];

    static_assert(sizeof(stack_buffer) == static_cast<size_t>(kStackBufferSize),

                  "sizeof(char) is expected to be 1 in C++");

    int dynamic_buffer_size = 0;  // Computed in the first iteration.

    for (int iteration = 0; iteration < 2; ++iteration) {

      const int buffer_size =

          (iteration == 0) ? kStackBufferSize : dynamic_buffer_size;

      char* const buffer =

          (iteration == 0) ? stack_buffer : new char[dynamic_buffer_size];

      // Print the header into the buffer.

      int buffer_offset = std::snprintf(

          buffer, buffer_size, "%04d/%02d/%02d-%02d:%02d:%02d.%06d %s ",

          now_components.tm_year + 1900, now_components.tm_mon + 1,

          now_components.tm_mday, now_components.tm_hour, now_components.tm_min,

          now_components.tm_sec, static_cast<int>(now_timeval.tv_usec),

          thread_id.c_str());

      // The header can be at most 28 characters (10 date + 15 time +

      // 3 delimiters) plus the thread ID, which should fit comfortably into the

      // static buffer.

      assert(buffer_offset <= 28 + kMaxThreadIdSize);

      static_assert(28 + kMaxThreadIdSize < kStackBufferSize,

                    "stack-allocated buffer may not fit the message header");

      assert(buffer_offset < buffer_size);

      // Print the message into the buffer.

      std::va_list arguments_copy;

      va_copy(arguments_copy, arguments);

      buffer_offset +=

          std::vsnprintf(buffer + buffer_offset, buffer_size - buffer_offset,

                         format, arguments_copy);

      va_end(arguments_copy);

      // The code below may append a newline at the end of the buffer, which

      // requires an extra character.

      if (buffer_offset >= buffer_size - 1) {

        // The message did not fit into the buffer.

        if (iteration == 0) {

          // Re-run the loop and use a dynamically-allocated buffer. The buffer

          // will be large enough for the log message, an extra newline and a

          // null terminator.

          dynamic_buffer_size = buffer_offset + 2;

          continue;

        }

        // The dynamically-allocated buffer was incorrectly sized. This should

        // not happen, assuming a correct implementation of std::(v)snprintf.

        // Fail in tests, recover by truncating the log message in production.

        assert(false);

        buffer_offset = buffer_size - 1;

      }

      // Add a newline if necessary.

      if (buffer[buffer_offset - 1] != '\n') {

        buffer[buffer_offset] = '\n';

        ++buffer_offset;

      }

      assert(buffer_offset <= buffer_size);

      std::fwrite(buffer, 1, buffer_offset, fp_);

      std::fflush(fp_);

      if (iteration != 0) {

        delete[] buffer;

      }

      break;

    }

  }

 private:

  std::FILE* const fp_;

};

}  // namespace leveldb

#endif  // STORAGE_LEVELDB_UTIL_POSIX_LOGGER_H_