// Copyright: (2012-2015) Ben Strasser <code@ben-strasser.net>
// License: BSD-3
//
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
// 1. Redistributions of source code must retain the above copyright notice,
//    this list of conditions and the following disclaimer.
//
// 2. Redistributions in binary form must reproduce the above copyright notice,
//    this list of conditions and the following disclaimer in the documentation
//    and/or other materials provided with the distribution.
//
// 3. Neither the name of the copyright holder nor the names of its contributors
//    may be used to endorse or promote products derived from this software
//    without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
// POSSIBILITY OF SUCH DAMAGE.

#ifndef CSV_H
#define CSV_H

#include <algorithm>
#include <cstdio>
#include <cstring>
#include <exception>
#include <string>
#include <utility>
#include <vector>
#ifndef CSV_IO_NO_THREAD
#include <condition_variable>
#include <mutex>
#include <thread>
#endif
#include <cassert>
#include <cerrno>
#include <istream>
#include <limits>
#include <memory>
#include <fstream>

namespace io
{
  ////////////////////////////////////////////////////////////////////////////
  //                                 LineReader                             //
  ////////////////////////////////////////////////////////////////////////////

  namespace error
  {
    struct base : std::exception
    {
      virtual void format_error_message() const = 0;

      const char *what() const noexcept override
      {
        format_error_message();
        return error_message_buffer;
      }

      mutable char error_message_buffer[2048];
    };

    // this only affects the file name in the error message
    const int max_file_name_length = 1024;

    struct with_file_name
    {
      with_file_name() { std::memset(file_name, 0, sizeof(file_name)); }

      void set_file_name(const char *file_name)
      {
        if (file_name != nullptr)
        {
          // This call to strncpy has parenthesis around it
          // to silence the GCC -Wstringop-truncation warning
          (strncpy(this->file_name, file_name, sizeof(this->file_name)));
          this->file_name[sizeof(this->file_name) - 1] = '\0';
        }
        else
        {
          this->file_name[0] = '\0';
        }
      }

      char file_name[max_file_name_length + 1];
    };

    struct with_file_line
    {
      with_file_line() { file_line = -1; }

      void set_file_line(int file_line) { this->file_line = file_line; }

      int file_line;
    };

    struct with_errno
    {
      with_errno() { errno_value = 0; }

      void set_errno(int errno_value) { this->errno_value = errno_value; }

      int errno_value;
    };

    struct can_not_open_file : base, with_file_name, with_errno
    {
      void format_error_message() const override
      {
        if (errno_value != 0)
          std::snprintf(error_message_buffer, sizeof(error_message_buffer),
                        "Can not open file \"%s\" because \"%s\".", file_name,
                        std::strerror(errno_value));
        else
          std::snprintf(error_message_buffer, sizeof(error_message_buffer),
                        "Can not open file \"%s\".", file_name);
      }
    };

    struct line_length_limit_exceeded : base, with_file_name, with_file_line
    {
      void format_error_message() const override
      {
        std::snprintf(
            error_message_buffer, sizeof(error_message_buffer),
            "Line number %d in file \"%s\" exceeds the maximum length of 2^24-1.",
            file_line, file_name);
      }
    };
  } // namespace error

  class ByteSourceBase
  {
  public:
    virtual int read(char *buffer, int size) = 0;
    virtual ~ByteSourceBase() {}
  };

  namespace detail
  {

    class OwningStdIOByteSourceBase : public ByteSourceBase
    {
    public:
      explicit OwningStdIOByteSourceBase(FILE *file) : file(file)
      {
        // Tell the std library that we want to do the buffering ourself.
        std::setvbuf(file, 0, _IONBF, 0);
      }

      int read(char *buffer, int size) { return std::fread(buffer, 1, size, file); }

      ~OwningStdIOByteSourceBase() { std::fclose(file); }

    private:
      FILE *file;
    };

    class NonOwningIStreamByteSource : public ByteSourceBase
    {
    public:
      explicit NonOwningIStreamByteSource(std::istream &in) : in(in) {}

      int read(char *buffer, int size)
      {
        in.read(buffer, size);
        return in.gcount();
      }

      ~NonOwningIStreamByteSource() {}

    private:
      std::istream &in;
    };

    class NonOwningStringByteSource : public ByteSourceBase
    {
    public:
      NonOwningStringByteSource(const char *str, long long size)
          : str(str), remaining_byte_count(size) {}

      int read(char *buffer, int desired_byte_count)
      {
        int to_copy_byte_count = desired_byte_count;
        if (remaining_byte_count < to_copy_byte_count)
          to_copy_byte_count = remaining_byte_count;
        std::memcpy(buffer, str, to_copy_byte_count);
        remaining_byte_count -= to_copy_byte_count;
        str += to_copy_byte_count;
        return to_copy_byte_count;
      }

      ~NonOwningStringByteSource() {}

    private:
      const char *str;
      long long remaining_byte_count;
    };

#ifndef CSV_IO_NO_THREAD
    class AsynchronousReader
    {
    public:
      void init(std::unique_ptr<ByteSourceBase> arg_byte_source)
      {
        std::unique_lock<std::mutex> guard(lock);
        byte_source = std::move(arg_byte_source);
        desired_byte_count = -1;
        termination_requested = false;
        worker = std::thread([&]
                             {
      std::unique_lock<std::mutex> guard(lock);
      try {
        for (;;) {
          read_requested_condition.wait(guard, [&] {
            return desired_byte_count != -1 || termination_requested;
          });
          if (termination_requested)
            return;

          read_byte_count = byte_source->read(buffer, desired_byte_count);
          desired_byte_count = -1;
          if (read_byte_count == 0)
            break;
          read_finished_condition.notify_one();
        }
      } catch (...) {
        read_error = std::current_exception();
      }
      read_finished_condition.notify_one(); });
      }

      bool is_valid() const { return byte_source != nullptr; }

      void start_read(char *arg_buffer, int arg_desired_byte_count)
      {
        std::unique_lock<std::mutex> guard(lock);
        buffer = arg_buffer;
        desired_byte_count = arg_desired_byte_count;
        read_byte_count = -1;
        read_requested_condition.notify_one();
      }

      int finish_read()
      {
        std::unique_lock<std::mutex> guard(lock);
        read_finished_condition.wait(
            guard, [&]
            { return read_byte_count != -1 || read_error; });
        if (read_error)
          std::rethrow_exception(read_error);
        else
          return read_byte_count;
      }

      ~AsynchronousReader()
      {
        if (byte_source != nullptr)
        {
          {
            std::unique_lock<std::mutex> guard(lock);
            termination_requested = true;
          }
          read_requested_condition.notify_one();
          worker.join();
        }
      }

    private:
      std::unique_ptr<ByteSourceBase> byte_source;

      std::thread worker;

      bool termination_requested;
      std::exception_ptr read_error;
      char *buffer;
      int desired_byte_count;
      int read_byte_count;

      std::mutex lock;
      std::condition_variable read_finished_condition;
      std::condition_variable read_requested_condition;
    };
#endif

    class SynchronousReader
    {
    public:
      void init(std::unique_ptr<ByteSourceBase> arg_byte_source)
      {
        byte_source = std::move(arg_byte_source);
      }

      bool is_valid() const { return byte_source != nullptr; }

      void start_read(char *arg_buffer, int arg_desired_byte_count)
      {
        buffer = arg_buffer;
        desired_byte_count = arg_desired_byte_count;
      }

      int finish_read() { return byte_source->read(buffer, desired_byte_count); }

    private:
      std::unique_ptr<ByteSourceBase> byte_source;
      char *buffer;
      int desired_byte_count;
    };
  } // namespace detail

  class LineReader
  {
  private:
    static const int block_len = 1 << 20;
    std::unique_ptr<char[]> buffer; // must be constructed before (and thus
                                    // destructed after) the reader!
#ifdef CSV_IO_NO_THREAD
    detail::SynchronousReader reader;
#else
    detail::AsynchronousReader reader;
#endif
    int data_begin;
    int data_end;

    char file_name[error::max_file_name_length + 1];
    unsigned file_line;

    static std::unique_ptr<ByteSourceBase> open_file(const char *file_name)
    {
      // We open the file in binary mode as it makes no difference under *nix
      // and under Windows we handle \r\n newlines ourself.
      FILE *file = std::fopen(file_name, "rb");
      if (file == 0)
      {
        int x = errno; // store errno as soon as possible, doing it after
                       // constructor call can fail.
        error::can_not_open_file err;
        err.set_errno(x);
        err.set_file_name(file_name);
        throw err;
      }
      return std::unique_ptr<ByteSourceBase>(
          new detail::OwningStdIOByteSourceBase(file));
    }

    void init(std::unique_ptr<ByteSourceBase> byte_source)
    {
      file_line = 0;

      buffer = std::unique_ptr<char[]>(new char[3 * block_len]);
      data_begin = 0;
      data_end = byte_source->read(buffer.get(), 2 * block_len);

      // Ignore UTF-8 BOM
      if (data_end >= 3 && buffer[0] == '\xEF' && buffer[1] == '\xBB' &&
          buffer[2] == '\xBF')
        data_begin = 3;

      if (data_end == 2 * block_len)
      {
        reader.init(std::move(byte_source));
        reader.start_read(buffer.get() + 2 * block_len, block_len);
      }
    }

  public:
    LineReader() = delete;
    LineReader(const LineReader &) = delete;
    LineReader &operator=(const LineReader &) = delete;

    explicit LineReader(const char *file_name)
    {
      set_file_name(file_name);
      init(open_file(file_name));
    }

    explicit LineReader(const std::string &file_name)
    {
      set_file_name(file_name.c_str());
      init(open_file(file_name.c_str()));
    }

    LineReader(const char *file_name,
               std::unique_ptr<ByteSourceBase> byte_source)
    {
      set_file_name(file_name);
      init(std::move(byte_source));
    }

    LineReader(const std::string &file_name,
               std::unique_ptr<ByteSourceBase> byte_source)
    {
      set_file_name(file_name.c_str());
      init(std::move(byte_source));
    }

    LineReader(const char *file_name, const char *data_begin,
               const char *data_end)
    {
      set_file_name(file_name);
      init(std::unique_ptr<ByteSourceBase>(new detail::NonOwningStringByteSource(
          data_begin, data_end - data_begin)));
    }

    LineReader(const std::string &file_name, const char *data_begin,
               const char *data_end)
    {
      set_file_name(file_name.c_str());
      init(std::unique_ptr<ByteSourceBase>(new detail::NonOwningStringByteSource(
          data_begin, data_end - data_begin)));
    }

    LineReader(const char *file_name, FILE *file)
    {
      set_file_name(file_name);
      init(std::unique_ptr<ByteSourceBase>(
          new detail::OwningStdIOByteSourceBase(file)));
    }

    LineReader(const std::string &file_name, FILE *file)
    {
      set_file_name(file_name.c_str());
      init(std::unique_ptr<ByteSourceBase>(
          new detail::OwningStdIOByteSourceBase(file)));
    }

    LineReader(const char *file_name, std::istream &in)
    {
      set_file_name(file_name);
      init(std::unique_ptr<ByteSourceBase>(
          new detail::NonOwningIStreamByteSource(in)));
    }

    LineReader(const std::string &file_name, std::istream &in)
    {
      set_file_name(file_name.c_str());
      init(std::unique_ptr<ByteSourceBase>(
          new detail::NonOwningIStreamByteSource(in)));
    }

    void set_file_name(const std::string &file_name)
    {
      set_file_name(file_name.c_str());
    }

    void set_file_name(const char *file_name)
    {
      if (file_name != nullptr)
      {
        strncpy(this->file_name, file_name, sizeof(this->file_name));
        this->file_name[sizeof(this->file_name) - 1] = '\0';
      }
      else
      {
        this->file_name[0] = '\0';
      }
    }

    const char *get_truncated_file_name() const { return file_name; }

    void set_file_line(unsigned file_line) { this->file_line = file_line; }

    unsigned get_file_line() const { return file_line; }

    char *next_line()
    {
      if (data_begin == data_end)
        return nullptr;

      ++file_line;

      assert(data_begin < data_end);
      assert(data_end <= block_len * 2);

      if (data_begin >= block_len)
      {
        std::memcpy(buffer.get(), buffer.get() + block_len, block_len);
        data_begin -= block_len;
        data_end -= block_len;
        if (reader.is_valid())
        {
          data_end += reader.finish_read();
          std::memcpy(buffer.get() + block_len, buffer.get() + 2 * block_len,
                      block_len);
          reader.start_read(buffer.get() + 2 * block_len, block_len);
        }
      }

      int line_end = data_begin;
      while (line_end != data_end && buffer[line_end] != '\n')
      {
        ++line_end;
      }

      if (line_end - data_begin + 1 > block_len)
      {
        error::line_length_limit_exceeded err;
        err.set_file_name(file_name);
        err.set_file_line(file_line);
        throw err;
      }

      if (line_end != data_end && buffer[line_end] == '\n')
      {
        buffer[line_end] = '\0';
      }
      else
      {
        // some files are missing the newline at the end of the
        // last line
        ++data_end;
        buffer[line_end] = '\0';
      }

      // handle windows \r\n-line breaks
      if (line_end != data_begin && buffer[line_end - 1] == '\r')
        buffer[line_end - 1] = '\0';

      char *ret = buffer.get() + data_begin;
      data_begin = line_end + 1;
      return ret;
    }
  };

  ////////////////////////////////////////////////////////////////////////////
  //                                 CSV                                    //
  ////////////////////////////////////////////////////////////////////////////

  namespace error
  {
    const int max_column_name_length = 63;
    struct with_column_name
    {
      with_column_name()
      {
        std::memset(column_name, 0, max_column_name_length + 1);
      }

      void set_column_name(const char *column_name)
      {
        if (column_name != nullptr)
        {
          std::strncpy(this->column_name, column_name, max_column_name_length);
          this->column_name[max_column_name_length] = '\0';
        }
        else
        {
          this->column_name[0] = '\0';
        }
      }

      char column_name[max_column_name_length + 1];
    };

    const int max_column_content_length = 63;

    struct with_column_content
    {
      with_column_content()
      {
        std::memset(column_content, 0, max_column_content_length + 1);
      }

      void set_column_content(const char *column_content)
      {
        if (column_content != nullptr)
        {
          std::strncpy(this->column_content, column_content,
                       max_column_content_length);
          this->column_content[max_column_content_length] = '\0';
        }
        else
        {
          this->column_content[0] = '\0';
        }
      }

      char column_content[max_column_content_length + 1];
    };

    struct extra_column_in_header : base, with_file_name, with_column_name
    {
      void format_error_message() const override
      {
        std::snprintf(error_message_buffer, sizeof(error_message_buffer),
                      R"(Extra column "%s" in header of file "%s".)", column_name,
                      file_name);
      }
    };

    struct missing_column_in_header : base, with_file_name, with_column_name
    {
      void format_error_message() const override
      {
        std::snprintf(error_message_buffer, sizeof(error_message_buffer),
                      R"(Missing column "%s" in header of file "%s".)", column_name,
                      file_name);
      }
    };

    struct duplicated_column_in_header : base, with_file_name, with_column_name
    {
      void format_error_message() const override
      {
        std::snprintf(error_message_buffer, sizeof(error_message_buffer),
                      R"(Duplicated column "%s" in header of file "%s".)",
                      column_name, file_name);
      }
    };

    struct header_missing : base, with_file_name
    {
      void format_error_message() const override
      {
        std::snprintf(error_message_buffer, sizeof(error_message_buffer),
                      "Header missing in file \"%s\".", file_name);
      }
    };

    struct too_few_columns : base, with_file_name, with_file_line
    {
      void format_error_message() const override
      {
        std::snprintf(error_message_buffer, sizeof(error_message_buffer),
                      "Too few columns in line %d in file \"%s\".", file_line,
                      file_name);
      }
    };

    struct too_many_columns : base, with_file_name, with_file_line
    {
      void format_error_message() const override
      {
        std::snprintf(error_message_buffer, sizeof(error_message_buffer),
                      "Too many columns in line %d in file \"%s\".", file_line,
                      file_name);
      }
    };

    struct escaped_string_not_closed : base, with_file_name, with_file_line
    {
      void format_error_message() const override
      {
        std::snprintf(error_message_buffer, sizeof(error_message_buffer),
                      "Escaped string was not closed in line %d in file \"%s\".",
                      file_line, file_name);
      }
    };

    struct integer_must_be_positive : base,
                                      with_file_name,
                                      with_file_line,
                                      with_column_name,
                                      with_column_content
    {
      void format_error_message() const override
      {
        std::snprintf(
            error_message_buffer, sizeof(error_message_buffer),
            R"(The integer "%s" must be positive or 0 in column "%s" in file "%s" in line "%d".)",
            column_content, column_name, file_name, file_line);
      }
    };

    struct no_digit : base,
                      with_file_name,
                      with_file_line,
                      with_column_name,
                      with_column_content
    {
      void format_error_message() const override
      {
        std::snprintf(
            error_message_buffer, sizeof(error_message_buffer),
            R"(The integer "%s" contains an invalid digit in column "%s" in file "%s" in line "%d".)",
            column_content, column_name, file_name, file_line);
      }
    };

    struct integer_overflow : base,
                              with_file_name,
                              with_file_line,
                              with_column_name,
                              with_column_content
    {
      void format_error_message() const override
      {
        std::snprintf(
            error_message_buffer, sizeof(error_message_buffer),
            R"(The integer "%s" overflows in column "%s" in file "%s" in line "%d".)",
            column_content, column_name, file_name, file_line);
      }
    };

    struct integer_underflow : base,
                               with_file_name,
                               with_file_line,
                               with_column_name,
                               with_column_content
    {
      void format_error_message() const override
      {
        std::snprintf(
            error_message_buffer, sizeof(error_message_buffer),
            R"(The integer "%s" underflows in column "%s" in file "%s" in line "%d".)",
            column_content, column_name, file_name, file_line);
      }
    };

    struct invalid_single_character : base,
                                      with_file_name,
                                      with_file_line,
                                      with_column_name,
                                      with_column_content
    {
      void format_error_message() const override
      {
        std::snprintf(
            error_message_buffer, sizeof(error_message_buffer),
            R"(The content "%s" of column "%s" in file "%s" in line "%d" is not a single character.)",
            column_content, column_name, file_name, file_line);
      }
    };
  } // namespace error

  using ignore_column = unsigned int;
  static const ignore_column ignore_no_column = 0;
  static const ignore_column ignore_extra_column = 1;
  static const ignore_column ignore_missing_column = 2;

  template <char... trim_char_list>
  struct trim_chars
  {
  private:
    constexpr static bool is_trim_char(char) { return false; }

    template <class... OtherTrimChars>
    constexpr static bool is_trim_char(char c, char trim_char,
                                       OtherTrimChars... other_trim_chars)
    {
      return c == trim_char || is_trim_char(c, other_trim_chars...);
    }

  public:
    static void trim(char *&str_begin, char *&str_end)
    {
      while (str_begin != str_end && is_trim_char(*str_begin, trim_char_list...))
        ++str_begin;
      while (str_begin != str_end &&
             is_trim_char(*(str_end - 1), trim_char_list...))
        --str_end;
      *str_end = '\0';
    }
  };

  struct no_comment
  {
    static bool is_comment(const char *) { return false; }
  };

  template <char... comment_start_char_list>
  struct single_line_comment
  {
  private:
    constexpr static bool is_comment_start_char(char) { return false; }

    template <class... OtherCommentStartChars>
    constexpr static bool
    is_comment_start_char(char c, char comment_start_char,
                          OtherCommentStartChars... other_comment_start_chars)
    {
      return c == comment_start_char ||
             is_comment_start_char(c, other_comment_start_chars...);
    }

  public:
    static bool is_comment(const char *line)
    {
      return is_comment_start_char(*line, comment_start_char_list...);
    }
  };

  struct empty_line_comment
  {
    static bool is_comment(const char *line)
    {
      if (*line == '\0')
        return true;
      while (*line == ' ' || *line == '\t')
      {
        ++line;
        if (*line == 0)
          return true;
      }
      return false;
    }
  };

  template <char... comment_start_char_list>
  struct single_and_empty_line_comment
  {
    static bool is_comment(const char *line)
    {
      return single_line_comment<comment_start_char_list...>::is_comment(line) ||
             empty_line_comment::is_comment(line);
    }
  };

  template <char sep>
  struct no_quote_escape
  {
    static const char *find_next_column_end(const char *col_begin)
    {
      while (*col_begin != sep && *col_begin != '\0')
        ++col_begin;
      return col_begin;
    }

    static void unescape(char *&, char *&) {}
  };

  template <char sep, char quote>
  struct double_quote_escape
  {
    static const char *find_next_column_end(const char *col_begin)
    {
      while (*col_begin != sep && *col_begin != '\0')
        if (*col_begin != quote)
          ++col_begin;
        else
        {
          do
          {
            ++col_begin;
            while (*col_begin != quote)
            {
              if (*col_begin == '\0')
                throw error::escaped_string_not_closed();
              ++col_begin;
            }
            ++col_begin;
          } while (*col_begin == quote);
        }
      return col_begin;
    }

    static void unescape(char *&col_begin, char *&col_end)
    {
      if (col_end - col_begin >= 2)
      {
        if (*col_begin == quote && *(col_end - 1) == quote)
        {
          ++col_begin;
          --col_end;
          char *out = col_begin;
          for (char *in = col_begin; in != col_end; ++in)
          {
            if (*in == quote && (in + 1) != col_end && *(in + 1) == quote)
            {
              ++in;
            }
            *out = *in;
            ++out;
          }
          col_end = out;
          *col_end = '\0';
        }
      }
    }
  };

  struct throw_on_overflow
  {
    template <class T>
    static void on_overflow(T &)
    {
      throw error::integer_overflow();
    }

    template <class T>
    static void on_underflow(T &)
    {
      throw error::integer_underflow();
    }
  };

  struct ignore_overflow
  {
    template <class T>
    static void on_overflow(T &) {}

    template <class T>
    static void on_underflow(T &) {}
  };

  struct set_to_max_on_overflow
  {
    template <class T>
    static void on_overflow(T &x)
    {
      // using (std::numeric_limits<T>::max) instead of
      // std::numeric_limits<T>::max to make code including windows.h with its max
      // macro happy
      x = (std::numeric_limits<T>::max)();
    }

    template <class T>
    static void on_underflow(T &x)
    {
      x = (std::numeric_limits<T>::min)();
    }
  };

  namespace detail
  {
    template <class quote_policy>
    void chop_next_column(char *&line, char *&col_begin, char *&col_end)
    {
      assert(line != nullptr);

      col_begin = line;
      // the col_begin + (... - col_begin) removes the constness
      col_end =
          col_begin + (quote_policy::find_next_column_end(col_begin) - col_begin);

      if (*col_end == '\0')
      {
        line = nullptr;
      }
      else
      {
        *col_end = '\0';
        line = col_end + 1;
      }
    }

    template <class trim_policy, class quote_policy>
    void parse_line(char *line, char **sorted_col,
                    const std::vector<int> &col_order)
    {
      for (int i : col_order)
      {
        if (line == nullptr)
          throw ::io::error::too_few_columns();
        char *col_begin, *col_end;
        chop_next_column<quote_policy>(line, col_begin, col_end);

        if (i != -1)
        {
          trim_policy::trim(col_begin, col_end);
          quote_policy::unescape(col_begin, col_end);

          sorted_col[i] = col_begin;
        }
      }
      if (line != nullptr)
        throw ::io::error::too_many_columns();
    }

    template <unsigned column_count, class trim_policy, class quote_policy>
    void parse_header_line(char *line, std::vector<int> &col_order,
                           const std::string *col_name,
                           ignore_column ignore_policy)
    {
      col_order.clear();

      bool found[column_count];
      std::fill(found, found + column_count, false);
      while (line)
      {
        char *col_begin, *col_end;
        chop_next_column<quote_policy>(line, col_begin, col_end);

        trim_policy::trim(col_begin, col_end);
        quote_policy::unescape(col_begin, col_end);

        for (unsigned i = 0; i < column_count; ++i)
          if (col_begin == col_name[i])
          {
            if (found[i])
            {
              error::duplicated_column_in_header err;
              err.set_column_name(col_begin);
              throw err;
            }
            found[i] = true;
            col_order.push_back(i);
            col_begin = 0;
            break;
          }
        if (col_begin)
        {
          if (ignore_policy & ::io::ignore_extra_column)
            col_order.push_back(-1);
          else
          {
            error::extra_column_in_header err;
            err.set_column_name(col_begin);
            throw err;
          }
        }
      }
      if (!(ignore_policy & ::io::ignore_missing_column))
      {
        for (unsigned i = 0; i < column_count; ++i)
        {
          if (!found[i])
          {
            error::missing_column_in_header err;
            err.set_column_name(col_name[i].c_str());
            throw err;
          }
        }
      }
    }

    template <class overflow_policy>
    void parse(char *col, char &x)
    {
      if (!*col)
        throw error::invalid_single_character();
      x = *col;
      ++col;
      if (*col)
        throw error::invalid_single_character();
    }

    template <class overflow_policy>
    void parse(char *col, std::string &x)
    {
      x = col;
    }

    template <class overflow_policy>
    void parse(char *col, const char *&x)
    {
      x = col;
    }

    template <class overflow_policy>
    void parse(char *col, char *&x) { x = col; }

    template <class overflow_policy, class T>
    void parse_unsigned_integer(const char *col, T &x)
    {
      x = 0;
      while (*col != '\0')
      {
        if ('0' <= *col && *col <= '9')
        {
          T y = *col - '0';
          if (x > ((std::numeric_limits<T>::max)() - y) / 10)
          {
            overflow_policy::on_overflow(x);
            return;
          }
          x = 10 * x + y;
        }
        else
          throw error::no_digit();
        ++col;
      }
    }

    template <class overflow_policy>
    void parse(char *col, unsigned char &x)
    {
      parse_unsigned_integer<overflow_policy>(col, x);
    }
    template <class overflow_policy>
    void parse(char *col, unsigned short &x)
    {
      parse_unsigned_integer<overflow_policy>(col, x);
    }
    template <class overflow_policy>
    void parse(char *col, unsigned int &x)
    {
      parse_unsigned_integer<overflow_policy>(col, x);
    }
    template <class overflow_policy>
    void parse(char *col, unsigned long &x)
    {
      parse_unsigned_integer<overflow_policy>(col, x);
    }
    template <class overflow_policy>
    void parse(char *col, unsigned long long &x)
    {
      parse_unsigned_integer<overflow_policy>(col, x);
    }

    template <class overflow_policy, class T>
    void parse_signed_integer(const char *col, T &x)
    {
      if (*col == '-')
      {
        ++col;

        x = 0;
        while (*col != '\0')
        {
          if ('0' <= *col && *col <= '9')
          {
            T y = *col - '0';
            if (x < ((std::numeric_limits<T>::min)() + y) / 10)
            {
              overflow_policy::on_underflow(x);
              return;
            }
            x = 10 * x - y;
          }
          else
            throw error::no_digit();
          ++col;
        }
        return;
      }
      else if (*col == '+')
        ++col;
      parse_unsigned_integer<overflow_policy>(col, x);
    }

    template <class overflow_policy>
    void parse(char *col, signed char &x)
    {
      parse_signed_integer<overflow_policy>(col, x);
    }
    template <class overflow_policy>
    void parse(char *col, signed short &x)
    {
      parse_signed_integer<overflow_policy>(col, x);
    }
    template <class overflow_policy>
    void parse(char *col, signed int &x)
    {
      parse_signed_integer<overflow_policy>(col, x);
    }
    template <class overflow_policy>
    void parse(char *col, signed long &x)
    {
      parse_signed_integer<overflow_policy>(col, x);
    }
    template <class overflow_policy>
    void parse(char *col, signed long long &x)
    {
      parse_signed_integer<overflow_policy>(col, x);
    }

    template <class T>
    void parse_float(const char *col, T &x)
    {
      bool is_neg = false;
      if (*col == '-')
      {
        is_neg = true;
        ++col;
      }
      else if (*col == '+')
        ++col;

      x = 0;
      while ('0' <= *col && *col <= '9')
      {
        int y = *col - '0';
        x *= 10;
        x += y;
        ++col;
      }

      if (*col == '.' || *col == ',')
      {
        ++col;
        T pos = 1;
        while ('0' <= *col && *col <= '9')
        {
          pos /= 10;
          int y = *col - '0';
          ++col;
          x += y * pos;
        }
      }

      if (*col == 'e' || *col == 'E')
      {
        ++col;
        int e;

        parse_signed_integer<set_to_max_on_overflow>(col, e);

        if (e != 0)
        {
          T base;
          if (e < 0)
          {
            base = T(0.1);
            e = -e;
          }
          else
          {
            base = T(10);
          }

          while (e != 1)
          {
            if ((e & 1) == 0)
            {
              base = base * base;
              e >>= 1;
            }
            else
            {
              x *= base;
              --e;
            }
          }
          x *= base;
        }
      }
      else
      {
        if (*col != '\0')
          throw error::no_digit();
      }

      if (is_neg)
        x = -x;
    }

    template <class overflow_policy>
    void parse(char *col, float &x)
    {
      parse_float(col, x);
    }
    template <class overflow_policy>
    void parse(char *col, double &x)
    {
      parse_float(col, x);
    }
    template <class overflow_policy>
    void parse(char *col, long double &x)
    {
      parse_float(col, x);
    }

    template <class overflow_policy, class T>
    void parse(char *col, T &x)
    {
      // Mute unused variable compiler warning
      (void)col;
      (void)x;
      // GCC evaluates "false" when reading the template and
      // "sizeof(T)!=sizeof(T)" only when instantiating it. This is why
      // this strange construct is used.
      static_assert(sizeof(T) != sizeof(T),
                    "Can not parse this type. Only builtin integrals, floats, "
                    "char, char*, const char* and std::string are supported");
    }

  } // namespace detail

  template <unsigned column_count, class trim_policy = trim_chars<' ', '\t'>,
            class quote_policy = no_quote_escape<','>,
            class overflow_policy = throw_on_overflow,
            class comment_policy = no_comment>
  class CSVReader
  {
  private:
    LineReader in;

    char *row[column_count];
    std::string column_names[column_count];

    std::vector<int> col_order;

    template <class... ColNames>
    void set_column_names(std::string s, ColNames... cols)
    {
      column_names[column_count - sizeof...(ColNames) - 1] = std::move(s);
      set_column_names(std::forward<ColNames>(cols)...);
    }

    void set_column_names() {}

  public:
    CSVReader() = delete;
    CSVReader(const CSVReader &) = delete;
    CSVReader &operator=(const CSVReader &);

    template <class... Args>
    explicit CSVReader(Args &&...args) : in(std::forward<Args>(args)...)
    {
      std::fill(row, row + column_count, nullptr);
      col_order.resize(column_count);
      for (unsigned i = 0; i < column_count; ++i)
        col_order[i] = i;
      for (unsigned i = 1; i <= column_count; ++i)
        column_names[i - 1] = "col" + std::to_string(i);
    }

    char *next_line() { return in.next_line(); }

    template <class... ColNames>
    void read_header(ignore_column ignore_policy, ColNames... cols)
    {
      static_assert(sizeof...(ColNames) >= column_count,
                    "not enough column names specified");
      static_assert(sizeof...(ColNames) <= column_count,
                    "too many column names specified");
      try
      {
        set_column_names(std::forward<ColNames>(cols)...);

        char *line;
        do
        {
          line = in.next_line();
          if (!line)
            throw error::header_missing();
        } while (comment_policy::is_comment(line));

        detail::parse_header_line<column_count, trim_policy, quote_policy>(
            line, col_order, column_names, ignore_policy);
      }
      catch (error::with_file_name &err)
      {
        err.set_file_name(in.get_truncated_file_name());
        throw;
      }
    }

    template <class... ColNames>
    void set_header(ColNames... cols)
    {
      static_assert(sizeof...(ColNames) >= column_count,
                    "not enough column names specified");
      static_assert(sizeof...(ColNames) <= column_count,
                    "too many column names specified");
      set_column_names(std::forward<ColNames>(cols)...);
      std::fill(row, row + column_count, nullptr);
      col_order.resize(column_count);
      for (unsigned i = 0; i < column_count; ++i)
        col_order[i] = i;
    }

    bool has_column(const std::string &name) const
    {
      return col_order.end() !=
             std::find(col_order.begin(), col_order.end(),
                       std::find(std::begin(column_names), std::end(column_names),
                                 name) -
                           std::begin(column_names));
    }

    void set_file_name(const std::string &file_name)
    {
      in.set_file_name(file_name);
    }

    void set_file_name(const char *file_name) { in.set_file_name(file_name); }

    const char *get_truncated_file_name() const
    {
      return in.get_truncated_file_name();
    }

    void set_file_line(unsigned file_line) { in.set_file_line(file_line); }

    unsigned get_file_line() const { return in.get_file_line(); }

  private:
    void parse_helper(std::size_t) {}

    template <class T, class... ColType>
    void parse_helper(std::size_t r, T &t, ColType &...cols)
    {
      if (row[r])
      {
        try
        {
          try
          {
            ::io::detail::parse<overflow_policy>(row[r], t);
          }
          catch (error::with_column_content &err)
          {
            err.set_column_content(row[r]);
            throw;
          }
        }
        catch (error::with_column_name &err)
        {
          err.set_column_name(column_names[r].c_str());
          throw;
        }
      }
      parse_helper(r + 1, cols...);
    }

  public:
    template <class... ColType>
    bool read_row(ColType &...cols)
    {
      static_assert(sizeof...(ColType) >= column_count,
                    "not enough columns specified");
      static_assert(sizeof...(ColType) <= column_count,
                    "too many columns specified");
      try
      {
        try
        {

          char *line;
          do
          {
            line = in.next_line();
            if (!line)
              return false;
          } while (comment_policy::is_comment(line));

          detail::parse_line<trim_policy, quote_policy>(line, row, col_order);

          parse_helper(0, cols...);
        }
        catch (error::with_file_name &err)
        {
          err.set_file_name(in.get_truncated_file_name());
          throw;
        }
      }
      catch (error::with_file_line &err)
      {
        err.set_file_line(in.get_file_line());
        throw;
      }

      return true;
    }
  };

  // CSVWriter
  class LineWriter
  {
  private:
    std::ofstream file;

  public:
    LineWriter(const std::string &filename)
    {
      file.open(filename);
      if (!file.is_open())
      {
        throw std::runtime_error("Unable to open file");
      }
    }

    ~LineWriter()
    {
      if (file.is_open())
      {
        file.close();
      }
    }

    void write(const std::string &line)
    {
      file << line;
    }
  };

  // CSVWriter 的实现
  template <unsigned column_count,
            class trim_policy = std::string,  // 使用默认值 ' ' 和 '\t'
            class quote_policy = std::string, // 在这里我们可以简单化
            class overflow_policy = std::runtime_error>
  class CSVWriter
  {
  private:
    LineWriter out;
    std::string column_names[column_count];

    void write_header()
    {
      for (unsigned i = 0; i < column_count; ++i)
      {
        if (i > 0)
          out.write(",");
        out.write(column_names[i]);
      }
      out.write("\n");
    }

  public:
    CSVWriter(const std::string &filename, const std::initializer_list<std::string> &cols)
        : out(filename)
    {
      // 使用初始化列表设置列名
      unsigned index = 0;
      for (const auto &col : cols)
      {
        if (index < column_count)
        {
          column_names[index++] = col;
        }
        else
        {
          throw overflow_policy("Too many column names specified");
        }
      }
      write_header(); // 写入头部
    }

    template <class... ColType>
    void write_row(ColType... cols)
    {
      write_row_helper(cols...);
      out.write("\n");
    }

  private:
    template <typename T>
    void write_value(const T &value)
    {
      out.write(std::to_string(value)); // 简化，不进行引用处理
    }

    template <typename T, typename... Rest>
    void write_row_helper(const T &value, const Rest &...rest)
    {
      write_value(value);
      if constexpr (sizeof...(rest) > 0)
      {
        out.write(",");
        write_row_helper(rest...);
      }
    }
  };

} // namespace io
#endif