C++ Program to Convert .TXT files to .EML Email Format. Useful to save notes to email folder.

txttoeml.cpp

//============================================================================
// Name        : txttoeml.cpp
// Author      : 
// Version     :
// Copyright   : Your copyright notice
// Description : Hello World in C++, Ansi-style
//============================================================================

#include <iostream>
#include <string>
#include <iostream>
#include <filesystem>
#include <regex>
#include <fstream>

namespace fs = std::filesystem;

// Converting `std::filesystem::file_time_type` to a string
// https://stackoverflow.com/questions/56788745/how-to-convert-stdfilesystemfile-time-type-to-a-string-using-gcc-9
template <typename TP>
std::time_t to_time_t(TP tp)
{
    using namespace std::chrono;
    auto sctp = time_point_cast<system_clock::duration>(tp - TP::clock::now()
              + system_clock::now());
    return system_clock::to_time_t(sctp);
}

// Get EML format string from `std::filesystem::file_time_type` timestamp
std::string format_time_eml(fs::file_time_type file_time){
  std::time_t tt = to_time_t(file_time);
  std::tm *gmt = std::gmtime(&tt);
  std::stringstream buffer;
  buffer << std::put_time(gmt, "%a, %d %b %Y %H:%M:%S");
  std::string formattedFileTime = buffer.str();
  return formattedFileTime;
}

// Convert file function
int convertTxtFile(std::string inPathFilename){
  std::cout << "Processing " << inPathFilename << std::endl;

  std::ifstream inFile (inPathFilename);
  if (!inFile.is_open()) {\
    std::cout << "   Error opening file." << std::endl;
    return 1;
  }

  // Create output note file
  std::regex outputRegex("(.*)\\/(.+)\\.txt");
  std::string outPathFilename = std::regex_replace(inPathFilename, outputRegex, "$1-eml/$2.eml");
  std::ofstream outFile(outPathFilename, std::ofstream::out);

  // Write note header (basic)
  outFile << "From: hello@petrstepanov.com" << std::endl;
  outFile << "Content-Type: text/plain; charset=\"utf-8\"" << std::endl;
  outFile << "Content-Transfer-Encoding: quoted-printable" << std::endl;
  outFile << "MIME-Version: 1.0" << std::endl;

  // Write note header (modified time)
  fs::file_time_type modifiedDate = fs::last_write_time(inPathFilename);
  std::string dateStringEml = format_time_eml(modifiedDate);
  outFile << "Date: " << dateStringEml << std::endl;
  outFile << "X-Mail-Created-Date: "  << dateStringEml << std::endl;

  // Write note header (subject)
  std::string line;
  std::getline (inFile, line);

  std::string subject = line.empty() ? "No Title" : line;
  outFile << "Subject: "  << subject << std::endl;

  // Write note header (separator)
  outFile << std::endl;

  // Write note content
  outFile << line << std::endl;
  while (std::getline (inFile,line)) {
    outFile << line << std::endl;
  }
  inFile.close();
  outFile.close();

  // Set Modified Date
  fs::last_write_time(outPathFilename, modifiedDate);

  std::cout << "   Created " << outPathFilename << '\n';
  return 0;
}

// Entry point
int main(int argc, char *argv[]) {
  if (argc != 2) {
    std::cout << "Missing parameter - input directory path with .txt files" << std::endl;
    return 1;
  }

  // Create output directory
  std::string inPath = argv[1];
  std::regex r("(.*)\\/(.+)");
  std::string outPath = std::regex_replace(inPath, r, "$1/$2-eml");\

  // Check if output directory exists
  if (!fs::exists(outPath)){
    // Create output dierectory
    if (fs::create_directories(outPath) == false){
      std::cout << "Cannot create output directory: " << outPath << std::endl;
      return 1;
    }
    std::cout << "Created output directory: " << outPath << std::endl;
  }

  // Convert all txt files
  for (const auto & entry : fs::directory_iterator(inPath)){
    convertTxtFile(entry.path());
  }

  std::cout << "Success." << std::endl; // prints !!!Hello World!!!
	return 0;
}