/* Copyright (c) 2008-2022 the MRtrix3 contributors.
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * Covered Software is provided under this License on an "as is"
 * basis, without warranty of any kind, either expressed, implied, or
 * statutory, including, without limitation, warranties that the
 * Covered Software is free of defects, merchantable, fit for a
 * particular purpose or non-infringing.
 * See the Mozilla Public License v. 2.0 for more details.
 *
 * For more details, see http://www.mrtrix.org/.
 */

#include <unistd.h>
#include <fcntl.h>
#include <locale>
#include <clocale>
#include <algorithm>


#include "app.h"
#include "debug.h"
#include "progressbar.h"
#include "file/path.h"
#include "file/config.h"
#include "signal_handler.h"

#define MRTRIX_HELP_COMMAND "less -X"

#define HELP_WIDTH  80

#define HELP_PURPOSE_INDENT 0, 4
#define HELP_ARG_INDENT 8, 20
#define HELP_OPTION_INDENT 2, 20
#define HELP_EXAMPLE_INDENT 7

#define MRTRIX_CORE_REFERENCE "Tournier, J.-D.; Smith, R. E.; Raffelt, D.; Tabbara, R.; Dhollander, T.; Pietsch, M.; Christiaens, D.; Jeurissen, B.; Yeh, C.-H. & Connelly, A. " \
"MRtrix3: A fast, flexible and open software framework for medical image processing and visualisation. " \
"NeuroImage, 2019, 202, 116137"


namespace MR
{

  namespace App
  {

    Description DESCRIPTION;
    ExampleList EXAMPLES;
    ArgumentList ARGUMENTS;
    OptionList OPTIONS;
    Description REFERENCES;
    bool REQUIRES_AT_LEAST_ONE_ARGUMENT = true;

    OptionGroup __standard_options = OptionGroup ("Standard options")
      + Option ("info", "display information messages.")
      + Option ("quiet", "do not display information messages or progress status; "
                         "alternatively, this can be achieved by setting the MRTRIX_QUIET environment variable to a non-empty string.")
      + Option ("debug", "display debugging messages.")
      + Option ("force", "force overwrite of output files "
                         "(caution: using the same file as input and output might cause unexpected behaviour).")
      + Option ("nthreads", "use this number of threads in multi-threaded applications (set to 0 to disable multi-threading).")
        + Argument ("number").type_integer (0)
      + Option ("config", "temporarily set the value of an MRtrix config file entry.").allow_multiple()
        + Argument ("key").type_text()
        + Argument ("value").type_text()
      + Option ("help", "display this information page and exit.")
      + Option ("version", "display version information and exit.");

    const char* AUTHOR = nullptr;
    const char* COPYRIGHT =
       "Copyright (c) 2008-2022 the MRtrix3 contributors.\n"
       "\n"
       "This Source Code Form is subject to the terms of the Mozilla Public\n"
       "License, v. 2.0. If a copy of the MPL was not distributed with this\n"
       "file, You can obtain one at http://mozilla.org/MPL/2.0/.\n"
       "\n"
       "Covered Software is provided under this License on an \"as is\"\n"
       "basis, without warranty of any kind, either expressed, implied, or\n"
       "statutory, including, without limitation, warranties that the\n"
       "Covered Software is free of defects, merchantable, fit for a\n"
       "particular purpose or non-infringing.\n"
       "See the Mozilla Public License v. 2.0 for more details.\n"
       "\n"
       "For more details, see http://www.mrtrix.org/.\n";
    const char* SYNOPSIS = nullptr;


    std::string NAME;
    std::string command_history_string;
    vector<ParsedArgument> argument;
    vector<ParsedOption> option;

    //ENVVAR name: MRTRIX_QUIET
    //ENVVAR Do not display information messages or progress status. This has
    //ENVVAR the same effect as the ``-quiet`` command-line option. If set,
    //ENVVAR supersedes the MRTRIX_LOGLEVEL environment variable.

    //ENVVAR name: MRTRIX_LOGLEVEL
    //ENVVAR Set the default terminal verbosity. Default terminal verbosity
    //ENVVAR is 1. This has the same effect as the ``-quiet`` (0),
    //ENVVAR ``-info`` (2) or ``-debug`` (3) comand-line options.
    int log_level = getenv("MRTRIX_QUIET") ?
                    0 :
                    (getenv("MRTRIX_LOGLEVEL") ? to<int>(getenv("MRTRIX_LOGLEVEL")) : 1);

    int exit_error_code = 0;
    bool fail_on_warn = false;
    bool terminal_use_colour = true;
    const std::thread::id main_thread_ID = std::this_thread::get_id();

    const char* project_version = nullptr;
    const char* project_build_date = nullptr;
    const char* executable_uses_mrtrix_version = nullptr;

    int argc = 0;
    const char* const* argv = nullptr;

    bool overwrite_files = false;
    void (*check_overwrite_files_func) (const std::string& name) = nullptr;

    namespace
    {

      inline void get_matches (vector<const Option*>& candidates, const OptionGroup& group, const std::string& stub)
      {
        for (size_t i = 0; i < group.size(); ++i) {
          if (stub.compare (0, stub.size(), group[i].id, stub.size()) == 0)
            candidates.push_back (&group[i]);
        }
      }


      inline int size (const std::string& text)
      {
        return text.size() - 2*std::count (text.begin(), text.end(), 0x08U);
      }

      inline void resize (std::string& text, size_t new_size, char fill)
      {
        text.resize (text.size() + new_size - size(text), fill);
      }



      std::string paragraph (
          const std::string& header,
          const std::string& text,
          int header_indent,
          int indent)
      {
        std::string out, line = std::string (header_indent, ' ') + header + " ";
        if (size (line) < indent)
          resize (line, indent, ' ');

        vector<std::string> paragraphs = split (text, "\n");

        for (size_t n = 0; n < paragraphs.size(); ++n) {
          size_t i = 0;
          vector<std::string> words = split (paragraphs[n]);
          while (i < words.size()) {
            do {
              line += " " + words[i++];
              if (i >= words.size())
                break;
            }
            while (size (line) + 1 + size (words[i]) < HELP_WIDTH);
            out += line + "\n";
            line = std::string (indent, ' ');
          }
        }
        return out;
      }



      std::string bold (const std::string& text)
      {
        std::string retval (3*text.size(), '\0');
        for (size_t n = 0; n < text.size(); ++n) {
          retval[3*n] = retval[3*n+2] = text[n];
          retval[3*n+1] = 0x08U;
        }
        return retval;
      }


      std::string underline (const std::string& text, bool ignore_whitespace = false)
      {
        size_t m (0);
        std::string retval (3*text.size(), '\0');
        for (size_t n = 0; n < text.size(); ++n) {
          if (ignore_whitespace and text[n]==' ')
            retval[m++] = ' ';
          else
            retval[m++] = '_';
          retval[m++] = 0x08U;
          retval[m++] = text[n];
        }
        return retval;
      }

    }





    const char* argtype_description (ArgType type)
    {
      switch (type) {
        case Integer:
          return ("integer");
        case Float:
          return ("float");
        case Text:
          return ("string");
        case ArgFileIn:
          return ("file in");
        case ArgFileOut:
          return ("file out");
        case ArgDirectoryIn:
          return ("directory in");
        case ArgDirectoryOut:
          return ("directory out");
        case ImageIn:
          return ("image in");
        case ImageOut:
          return ("image out");
        case Choice:
          return ("choice");
        case IntSeq:
          return ("int seq");
        case FloatSeq:
          return ("float seq");
        case TracksIn:
          return ("tracks in");
        case TracksOut:
          return ("tracks out");
        case Various:
          return ("various");
        default:
          return ("undefined");
      }
    }



    std::string help_head (int format)
    {
      if (!format) {
        return std::string (NAME) + ": " + (project_version ?
        std::string ("external MRtrix3 project, version ") + project_version + "\nbuilt against MRtrix3 version " + mrtrix_version :
        std::string ("part of the MRtrix3 package, version ") + mrtrix_version) + "\n\n";
      }

      std::string version_string = project_version ?
        std::string ("Version ") + project_version :
        std::string ("MRtrix ") + mrtrix_version;

      std::string date (project_version ? project_build_date : build_date);

      std::string topline = version_string +
          std::string (std::max (1, 40-size(version_string)-size(App::NAME)/2), ' ') +
          bold (App::NAME);
      topline += std::string (80-size(topline)-size(date), ' ') + date;

      if (project_version)
        topline += std::string("\nusing MRtrix3 ") + mrtrix_version;

      return topline + "\n\n     " + bold (NAME) + ": " +
        (project_version ? "external MRtrix3 project" : "part of the MRtrix3 package") + "\n\n";
    }




    std::string help_synopsis (int format)
    {
      if (!format)
        return SYNOPSIS;
      return bold("SYNOPSIS") + "\n\n" + paragraph ("", SYNOPSIS, HELP_PURPOSE_INDENT) + "\n";
    }




    std::string help_tail (int format)
    {
      std::string retval;
      if (!format)
        return retval;

      return bold ("AUTHOR") + "\n"
        + paragraph ("", AUTHOR, HELP_PURPOSE_INDENT) + "\n"
        + bold ("COPYRIGHT") + "\n"
        + paragraph ("", COPYRIGHT, HELP_PURPOSE_INDENT) + "\n"
        + [&](){
          std::string s = bold ("REFERENCES") + "\n";
          for (size_t n = 0; n < REFERENCES.size(); ++n)
            s += paragraph ("", REFERENCES[n], HELP_PURPOSE_INDENT) + "\n";
          s += paragraph ("", MRTRIX_CORE_REFERENCE, HELP_PURPOSE_INDENT) + "\n";
          return s;
        }();
    }



    std::string usage_syntax (int format)
    {
      std::string s = "USAGE";
      if (format)
        s = bold (s) + "\n\n     ";
      else
        s += ": ";
      s += ( format ? underline (NAME, true) : NAME ) + " [ options ]";

      for (size_t i = 0; i < ARGUMENTS.size(); ++i) {

        if (ARGUMENTS[i].flags & Optional)
          s += " [";
        s += std::string(" ") + ARGUMENTS[i].id;

        if (ARGUMENTS[i].flags & AllowMultiple) {
          if (! (ARGUMENTS[i].flags & Optional))
            s += std::string(" [ ") + ARGUMENTS[i].id;
          s += " ...";
        }
        if (ARGUMENTS[i].flags & (Optional | AllowMultiple))
          s += " ]";
      }
      return s + "\n\n";
    }






    std::string Description::syntax (int format) const
    {
      if (!size())
        return std::string();
      std::string s;
      if (format)
        s += bold ("DESCRIPTION") + "\n\n";
      for (size_t i = 0; i < size(); ++i)
        s += paragraph ("", (*this)[i], HELP_PURPOSE_INDENT) + "\n";
      return s;
    }




    Example::operator std::string () const
    {
      return title + ": $ " + code + "  " + description;
    }




    std::string Example::syntax (int format) const
    {
      std::string s = paragraph ("", format ? underline (title + ":") + "\n" : title + ": ", HELP_PURPOSE_INDENT);
      s += std::string (HELP_EXAMPLE_INDENT, ' ') + "$ " + code + "\n";
      if (description.size())
        s += paragraph ("", description, HELP_PURPOSE_INDENT);
      if (format)
        s += "\n";
      return s;
    }




    std::string ExampleList::syntax (int format) const
    {
      if (!size())
        return std::string();
      std::string s;
      if (format)
        s += bold ("EXAMPLE USAGES") + "\n\n";
      for (size_t i = 0; i < size(); ++i)
        s += (*this)[i].syntax (format);
      return s;
    }




    std::string Argument::syntax (int format) const
    {
      std::string retval = paragraph (( format ? underline (id, true) : id ), desc, HELP_ARG_INDENT);
      if (format)
        retval += "\n";
      return retval;
    }





    std::string ArgumentList::syntax (int format) const
    {
      std::string s;
      for (size_t i = 0; i < size(); ++i)
        s += (*this)[i].syntax (format);
      return s + "\n";
    }





    std::string Option::syntax (int format) const
    {
      std::string opt ("-");
      opt += id;

      if (format)
        opt = underline (opt);

      for (size_t i = 0; i < size(); ++i)
        opt += std::string (" ") + (*this)[i].id;

      if (format && (flags & AllowMultiple))
        opt += "  (multiple uses permitted)";

      if (format)
        opt = "  " + opt + "\n" + paragraph ("", desc, HELP_PURPOSE_INDENT) + "\n";
      else
        opt = paragraph (opt, desc, HELP_OPTION_INDENT);
      return opt;
    }




    std::string OptionGroup::header (int format) const
    {
      return format ? bold (name) + "\n\n" : std::string (name) + ":\n";
    }

    std::string OptionGroup::contents (int format) const
    {
      std::string s;
      for (size_t i = 0; i < size(); ++i)
        s += (*this)[i].syntax (format);
      return s;
    }

    std::string OptionGroup::footer (int format)
    {
      return format ? "" : "\n";
    }



    std::string OptionList::syntax (int format) const
    {
      vector<std::string> group_names;
      for (size_t i = 0; i < size(); ++i) {
        if (std::find (group_names.begin(), group_names.end(), (*this)[i].name) == group_names.end())
          group_names.push_back ((*this)[i].name);
      }

      std::string s;
      for (size_t i = 0; i < group_names.size(); ++i) {
        size_t n = i;
        while ((*this)[n].name != group_names[i])
          ++n;
        s += (*this)[n].header (format);
        while (n < size()) {
          if ((*this)[n].name == group_names[i])
            s += (*this)[n].contents (format);
          ++n;
        }
        s += OptionGroup::footer (format);
      }

      return s;
    }








    std::string Argument::usage () const
    {
      std::ostringstream stream;
      stream << "ARGUMENT " << id << " "
        << (flags & Optional ? '1' : '0') << " "
        << (flags & AllowMultiple ? '1' : '0') << " ";

      switch (type) {
        case Undefined:
          assert (0);
          break;
        case Integer:
          stream << "INT " << limits.i.min << " " << limits.i.max;
          break;
        case Float:
          stream << "FLOAT " << limits.f.min << " " << limits.f.max;
          break;
        case Text:
          stream << "TEXT";
          break;
        case ArgFileIn:
          stream << "FILEIN";
          break;
        case ArgFileOut:
          stream << "FILEOUT";
          break;
        case ArgDirectoryIn:
          stream << "DIRIN";
          break;
        case ArgDirectoryOut:
          stream << "DIROUT";
          break;
        case Choice:
          stream << "CHOICE";
          for (const char* const* p = limits.choices; *p; ++p)
            stream << " " << *p;
          break;
        case ImageIn:
          stream << "IMAGEIN";
          break;
        case ImageOut:
          stream << "IMAGEOUT";
          break;
        case IntSeq:
          stream << "ISEQ";
          break;
        case FloatSeq:
          stream << "FSEQ";
          break;
        case TracksIn:
          stream << "TRACKSIN";
          break;
        case TracksOut:
          stream << "TRACKSOUT";
          break;
        case Various:
          stream << "VARIOUS";
          break;
        default:
          assert (0);
      }
      stream << "\n";
      if (desc.size())
        stream << desc << "\n";

      return stream.str();
    }




    std::string Option::usage () const
    {
      std::ostringstream stream;
      stream << "OPTION " << id << " "
        << (flags & Optional ? '1' : '0') << " "
        << (flags & AllowMultiple ? '1' : '0') << "\n";

      if (desc.size())
        stream << desc << "\n";

      for (size_t i = 0; i < size(); ++i)
        stream << (*this)[i].usage ();

      return stream.str();
    }



    std::string get_help_string (int format)
    {
      return
        help_head (format)
        + help_synopsis (format)
        + usage_syntax (format)
        + ARGUMENTS.syntax (format)
        + DESCRIPTION.syntax (format)
        + EXAMPLES.syntax (format)
        + OPTIONS.syntax (format)
        + __standard_options.header (format)
        + __standard_options.contents (format)
        + __standard_options.footer (format)
        + help_tail (format);
    }




    void print_help ()
    {
      File::Config::init ();

      //CONF option: HelpCommand
      //CONF default: less
      //CONF The command to use to display each command's help page (leave
      //CONF empty to send directly to the terminal).
      const std::string help_display_command = File::Config::get ("HelpCommand", MRTRIX_HELP_COMMAND);

      if (help_display_command.size()) {
        std::string help_string = get_help_string (1);
        FILE* file = popen (help_display_command.c_str(), "w");
        if (!file) {
          INFO ("error launching help display command \"" + help_display_command + "\": " + strerror (errno));
        }
        else if (fwrite (help_string.c_str(), 1, help_string.size(), file) != help_string.size()) {
          INFO ("error sending help page to display command \"" + help_display_command + "\": " + strerror (errno));
        }

        if (pclose (file) == 0)
          return;

        INFO ("error launching help display command \"" + help_display_command + "\"");
      }

      if (help_display_command.size())
        INFO ("displaying help page using fail-safe output:\n");

      print (get_help_string (0));
    }




#ifndef MRTRIX_BUILD_TYPE
#error "MRtrix build type is not defined; you need to re-run configure script"
#endif

    std::string version_string ()
    {
      std::string version =
        "== " + App::NAME + " " + ( project_version ? project_version : mrtrix_version ) + " ==\n" +
        str(8*sizeof (size_t)) + " bit " + MRTRIX_BUILD_TYPE + ", built " + build_date
        + ( project_version ? std::string(" against MRtrix ") + mrtrix_version : std::string("") )
        + ", using Eigen " + str(EIGEN_WORLD_VERSION) + "." + str(EIGEN_MAJOR_VERSION) + "." + str(EIGEN_MINOR_VERSION) + "\n"
        "Author(s): " + AUTHOR + "\n" +
        COPYRIGHT + "\n";

      return version;
    }





    std::string full_usage ()
    {
      std::string s;
      s += SYNOPSIS + std::string("\n");

      for (size_t i = 0; i < DESCRIPTION.size(); ++i)
        s += DESCRIPTION[i] + std::string("\n");

      for (size_t i = 0; i < EXAMPLES.size(); ++i)
        s += std::string (EXAMPLES[i]) + std::string("\n");

      for (size_t i = 0; i < ARGUMENTS.size(); ++i)
        s += ARGUMENTS[i].usage();

      for (size_t i = 0; i < OPTIONS.size(); ++i)
        for (size_t j = 0; j < OPTIONS[i].size(); ++j)
          s += OPTIONS[i][j].usage();

      for (size_t i = 0; i < __standard_options.size(); ++i)
        s += __standard_options[i].usage ();

      return s;
    }





    std::string markdown_usage ()
    {
      /*
         help_head (format)
         + help_synopsis (format)
         + usage_syntax (format)
         + ARGUMENTS.syntax (format)
         + DESCRIPTION.syntax (format)
         + EXAMPLES.syntax (format)
         + OPTIONS.syntax (format)
         + __standard_options.header (format)
         + __standard_options.contents (format)
         + __standard_options.footer (format)
         + help_tail (format);
         */
      std::string s = std::string("## Synopsis\n\n") + SYNOPSIS + "\n\n";

      s += "## Usage\n\n    "
        + std::string(NAME) + " [ options ] ";

      // Syntax line:
      for (size_t i = 0; i < ARGUMENTS.size(); ++i) {

        if (ARGUMENTS[i].flags & Optional)
          s += "[";
        s += std::string(" ") + ARGUMENTS[i].id;

        if (ARGUMENTS[i].flags & AllowMultiple) {
          if (! (ARGUMENTS[i].flags & Optional))
            s += std::string(" [ ") + ARGUMENTS[i].id;
          s += " ...";
        }
        if (ARGUMENTS[i].flags & (Optional | AllowMultiple))
          s += " ]";
      }
      s += "\n\n";

      // Argument description:
      for (size_t i = 0; i < ARGUMENTS.size(); ++i)
        s += std::string("- *") + ARGUMENTS[i].id + "*: " + ARGUMENTS[i].desc + "\n";

      if (DESCRIPTION.size()) {
        s += "\n## Description\n\n";
        for (size_t i = 0; i < DESCRIPTION.size(); ++i)
          s += std::string (DESCRIPTION[i]) + "\n\n";
      }

      if (EXAMPLES.size()) {
        s += "\n## Example usages\n\n";
        for (size_t i = 0; i < EXAMPLES.size(); ++i) {
          s += std::string ("__") + EXAMPLES[i].title + ":__\n";
          s += std::string ("`$ ") + EXAMPLES[i].code + "`\n";
          if (EXAMPLES[i].description.size())
            s += EXAMPLES[i].description + "\n";
          s += "\n";
        }
      }


      vector<std::string> group_names;
      for (size_t i = 0; i < OPTIONS.size(); ++i) {
        if (std::find (group_names.begin(), group_names.end(), OPTIONS[i].name) == group_names.end())
          group_names.push_back (OPTIONS[i].name);
      }

      auto format_option = [&](const Option& opt) {
        std::string f = std::string ("+ **-") + opt.id;
        for (size_t a = 0; a < opt.size(); ++a)
          f += std::string (" ") + opt[a].id;
        f += "**";
        if (opt.flags & AllowMultiple)
          f+= "  *(multiple uses permitted)*";
        f += std::string("<br>") + opt.desc + "\n\n";
        return f;
      };

      s += "\n## Options\n\n";
      for (size_t i = 0; i < group_names.size(); ++i) {
        size_t n = i;
        while (OPTIONS[n].name != group_names[i])
          ++n;
        if (OPTIONS[n].name != std::string("OPTIONS"))
          s += std::string ("#### ") + OPTIONS[n].name + "\n\n";
        while (n < OPTIONS.size()) {
          if (OPTIONS[n].name == group_names[i]) {
            for (size_t o = 0; o < OPTIONS[n].size(); ++o)
              s += format_option (OPTIONS[n][o]);
          }
          ++n;
        }
      }

      s += "#### Standard options\n\n";
      for (size_t i = 0; i < __standard_options.size(); ++i)
        s += format_option (__standard_options[i]);

      s += std::string ("## References\n\n");
      for (size_t i = 0; i < REFERENCES.size(); ++i)
        s += std::string (REFERENCES[i]) + "\n\n";
      s += std::string (MRTRIX_CORE_REFERENCE) + "\n\n";

      s += std::string("---\n\nMRtrix ") + mrtrix_version + ", built " + build_date + "\n\n"
        "\n\n**Author:** " + AUTHOR
        + "\n\n**Copyright:** " + COPYRIGHT + "\n\n";

      return s;
    }




    std::string restructured_text_usage ()
    {
      /*
         help_head (format)
         + help_synopsis (format)
         + usage_syntax (format)
         + ARGUMENTS.syntax (format)
         + DESCRIPTION.syntax (format)
         + EXAMPLES.syntax (format)
         + OPTIONS.syntax (format)
         + __standard_options.header (format)
         + __standard_options.contents (format)
         + __standard_options.footer (format)
         + help_tail (format);
         */

      std::string s = std::string("Synopsis\n--------\n\n") + SYNOPSIS + "\n\n";

      s += "Usage\n--------\n\n::\n\n    "
        + std::string(NAME) + " [ options ] ";

      // Syntax line:
      for (size_t i = 0; i < ARGUMENTS.size(); ++i) {

        if (ARGUMENTS[i].flags & Optional)
          s += "[";
        s += std::string(" ") + ARGUMENTS[i].id;

        if (ARGUMENTS[i].flags & AllowMultiple) {
          if (! (ARGUMENTS[i].flags & Optional))
            s += std::string(" [ ") + ARGUMENTS[i].id;
          s += " ...";
        }
        if (ARGUMENTS[i].flags & (Optional | AllowMultiple))
          s += " ]";
      }
      s += "\n\n";

      // Will need more sophisticated escaping of special characters
      //   if they start popping up in argument / option descriptions
      auto escape_special = [] (std::string text) {
        size_t index = 0;
        while ((index = text.find("|", index)) != std::string::npos) {
          text.replace (index, 1, "\\|");
          index += 2;
        }
        return text;
      };

      // Argument description:
      for (size_t i = 0; i < ARGUMENTS.size(); ++i) {
        auto desc = split_lines (escape_special (ARGUMENTS[i].desc), false);
        s += std::string("-  *") + ARGUMENTS[i].id + "*: " + desc[0];
        for (size_t n = 1; n < desc.size(); ++n)
          s += " |br|\n   " + desc[n];
        s+= "\n";
      }
      s += "\n";


      if (DESCRIPTION.size()) {
        s += "Description\n-----------\n\n";
        for (size_t i = 0; i < DESCRIPTION.size(); ++i) {
          auto desc = split_lines (DESCRIPTION[i], false);
          s += desc[0];
          for (size_t n = 1; n < desc.size(); ++n)
            s += " |br|\n" + desc[n];
          s += "\n\n";
        }
      }

      if (EXAMPLES.size()) {
        s += "Example usages\n--------------\n\n";
        for (size_t i = 0; i < EXAMPLES.size(); ++i) {
          s += std::string ("-   *") + EXAMPLES[i].title + "*::\n\n";
          s += std::string ("        $ ") + EXAMPLES[i].code + "\n\n";
          if (EXAMPLES[i].description.size())
            s += std::string ("    ") + EXAMPLES[i].description + "\n\n";
        }
      }


      vector<std::string> group_names;
      for (size_t i = 0; i < OPTIONS.size(); ++i) {
        if (std::find (group_names.begin(), group_names.end(), OPTIONS[i].name) == group_names.end())
          group_names.push_back (OPTIONS[i].name);
      }

      auto format_option = [&](const Option& opt) {
        std::string f = std::string ("-  **-") + opt.id;
        for (size_t a = 0; a < opt.size(); ++a)
          f += std::string (" ") + opt[a].id;
        f += std::string("** ");
        if (opt.flags & AllowMultiple)
          f += "*(multiple uses permitted)* ";
        auto desc = split_lines (opt.desc, false);
        f += escape_special (desc[0]);
        for (size_t n = 1; n < desc.size(); ++n)
          f += " |br|\n   " + escape_special (desc[n]);
        f += "\n\n";
        return f;
      };

      s += "Options\n-------\n\n";
      for (size_t i = 0; i < group_names.size(); ++i) {
        size_t n = i;
        while (OPTIONS[n].name != group_names[i])
          ++n;
        if (OPTIONS[n].name != std::string("OPTIONS"))
          s += OPTIONS[n].name + std::string("\n") + std::string(std::strlen(OPTIONS[n].name), '^') + "\n\n";
        while (n < OPTIONS.size()) {
          if (OPTIONS[n].name == group_names[i]) {
            for (size_t o = 0; o < OPTIONS[n].size(); ++o)
              s += format_option (OPTIONS[n][o]);
          }
          ++n;
        }
      }

      s += "Standard options\n^^^^^^^^^^^^^^^^\n\n";
      for (size_t i = 0; i < __standard_options.size(); ++i)
        s += format_option (__standard_options[i]);

      s += std::string ("References\n^^^^^^^^^^\n\n");
      for (size_t i = 0; i < REFERENCES.size(); ++i) {
        auto refs = split_lines (REFERENCES[i], false);
        s += refs[0];
        for (size_t n = 1; n < refs.size(); ++n)
          s += " |br|\n  " + refs[n];
        s += "\n\n";
      }
      s += std::string(MRTRIX_CORE_REFERENCE) + "\n\n";

      s += std::string("--------------\n\n") +
        "\n\n**Author:** " + (char*)AUTHOR
        + "\n\n**Copyright:** " + COPYRIGHT + "\n\n";

      return s;
    }





    const Option* match_option (const char* arg)
    {
      if (consume_dash (arg) && *arg && !isdigit (*arg) && *arg != '.') {
        while (consume_dash(arg));
        vector<const Option*> candidates;
        std::string root (arg);

        for (size_t i = 0; i < OPTIONS.size(); ++i)
          get_matches (candidates, OPTIONS[i], root);
        get_matches (candidates, __standard_options, root);

        // no matches
        if (candidates.size() == 0)
          throw Exception (std::string ("unknown option \"-") + root + "\"");

        // return match if unique:
        if (candidates.size() == 1)
          return candidates[0];

        // return match if fully specified:
        for (size_t i = 0; i < candidates.size(); ++i)
          if (root == candidates[i]->id)
            return candidates[i];

        // check if there is only one *unique* candidate
        const auto cid = candidates[0]->id;
        if ( std::all_of(++candidates.begin(), candidates.end(), [& cid](const Option* cand){return cand->id == cid;}) )
          return candidates[0];

        // report something useful:
        root = "several matches possible for option \"-" + root + "\": \"-" + candidates[0]->id;

        for (size_t i = 1; i < candidates.size(); ++i)
          root += std::string ("\", \"-") + candidates[i]->id + "\"";

        throw Exception (root);
      }

      return nullptr;
    }




    void sort_arguments (int argc, const char* const* argv)
    {
      for (int n = 1; n < argc; ++n) {
        if (argv[n]) {
          const Option* opt = match_option (argv[n]);
          if (opt) {
            if (n + int (opt->size()) >= argc)
              throw Exception (std::string ("not enough parameters to option \"-") + opt->id + "\"");

            option.push_back (ParsedOption (opt, argv+n+1));
            n += opt->size();
          }
          else
            argument.push_back (ParsedArgument (nullptr, nullptr, argv[n]));
        }
      }
    }




    void parse_standard_options()
    {
      if (get_options ("info").size()) {
        if (log_level < 2)
          log_level = 2;
      }
      if (get_options ("debug").size())
        log_level = 3;
      if (get_options ("quiet").size())
        log_level = 0;
      if (get_options ("force").size()) {
        WARN ("existing output files will be overwritten");
        overwrite_files = true;
      }
    }



    void verify_usage ()
    {
      if (!AUTHOR)
        throw Exception ("No author specified for command " + std::string(NAME));
      if (!SYNOPSIS)
        throw Exception ("No synopsis specified for command " + std::string(NAME));
    }



    void parse_special_options ()
    {
      if (argc != 2) return;
      if (strcmp (argv[1], "__print_full_usage__") == 0) {
        print (full_usage ());
        throw 0;
      }
      if (strcmp (argv[1], "__print_usage_markdown__") == 0) {
        print (markdown_usage ());
        throw 0;
      }
      if (strcmp (argv[1], "__print_usage_rst__") == 0) {
        print (restructured_text_usage ());
        throw 0;
      }
      if (strcmp (argv[1], "__print_synopsis__") == 0) {
        print (SYNOPSIS);
        throw 0;
      }
    }



    void parse ()
    {
      argument.clear();
      option.clear();

      sort_arguments (argc, argv);

      if (get_options ("help").size()) {
        print_help();
        throw 0;
      }
      if (get_options ("version").size()) {
        print (version_string());
        throw 0;
      }

      size_t num_args_required = 0, num_command_arguments = 0;
      size_t num_optional_arguments = 0;

      ArgFlags flags = None;
      for (size_t i = 0; i < ARGUMENTS.size(); ++i) {
        ++num_command_arguments;
        if (ARGUMENTS[i].flags) {
          if (flags && flags != ARGUMENTS[i].flags)
            throw Exception ("FIXME: all arguments declared optional() or allow_multiple() should have matching flags in command-line syntax");
          flags = ARGUMENTS[i].flags;
          ++num_optional_arguments;
          if (!(flags & Optional))
            ++num_args_required;
        }
        else
          ++num_args_required;
      }

      if (!option.size() && !argument.size() && REQUIRES_AT_LEAST_ONE_ARGUMENT) {
        print_help ();
        throw 0;
      }

      if (num_optional_arguments && num_args_required > argument.size())
        throw Exception ("Expected at least " + str (num_args_required)
            + " arguments (" + str (argument.size()) + " supplied)");

      if (num_optional_arguments == 0 && num_args_required != argument.size()) {
        Exception e ("Expected exactly " + str (num_args_required)
            + " arguments (" + str (argument.size()) + " supplied)");
        std::string s = "Usage: " + NAME;
        for (const auto& a : ARGUMENTS)
          s += " " + std::string(a.id);
        e.push_back (s);
        s = "Yours: " + NAME;
        for (const auto& a : argument)
          s += " " + std::string(a);
        e.push_back (s);
        if (argument.size() > num_args_required) {
          vector<std::string> potential_options;
          for (const auto& a : argument) {
            for (const auto& og : OPTIONS) {
              for (const auto& o : og) {
                if (std::string(a) == std::string(o.id))
                  potential_options.push_back ("'-" + a + "'");
              }
            }
          }
          if (potential_options.size())
            e.push_back ("(Did you mean " + join(potential_options, " or ") + "?)");
        }
        throw e;
      }

      size_t num_extra_arguments = argument.size() - num_args_required;
      size_t num_arg_per_multi = num_optional_arguments ? num_extra_arguments / num_optional_arguments : 0;
      if (num_arg_per_multi*num_optional_arguments != num_extra_arguments)
        throw Exception ("number of optional arguments provided are not equal for all arguments");
      if (!(flags & Optional))
        ++num_arg_per_multi;

      // assign arguments to their corresponding definitions:
      for (size_t n = 0, index = 0, next = 0; n < argument.size(); ++n) {
        if (n == next) {
          if (n) ++index;
          if (ARGUMENTS[index].flags != None)
            next = n + num_arg_per_multi;
          else
            ++next;
        }
        argument[n].arg = &ARGUMENTS[index];
      }

      // check for multiple instances of options:
      for (size_t i = 0; i < OPTIONS.size(); ++i) {
        for (size_t j = 0; j < OPTIONS[i].size(); ++j) {
          size_t count = 0;
          for (size_t k = 0; k < option.size(); ++k)
            if (option[k].opt == &OPTIONS[i][j])
              count++;

          if (count < 1 && ! (OPTIONS[i][j].flags & Optional))
            throw Exception (std::string ("mandatory option \"-") + OPTIONS[i][j].id + "\" must be specified");

          if (count > 1 && ! (OPTIONS[i][j].flags & AllowMultiple))
            throw Exception (std::string ("multiple instances of option \"-") +  OPTIONS[i][j].id + "\" are not allowed");
        }
      }

      parse_standard_options();

      File::Config::init ();

      //CONF option: FailOnWarn
      //CONF default: 0 (false)
      //CONF A boolean value specifying whether MRtrix applications should
      //CONF abort as soon as any (otherwise non-fatal) warning is issued.
      fail_on_warn = File::Config::get_bool ("FailOnWarn", false);

      //CONF option: TerminalColor
      //CONF default: 1 (true)
      //CONF A boolean value to indicate whether colours should be used in the terminal.
      terminal_use_colour = File::Config::get_bool ("TerminalColor", terminal_use_colour);

      // check for the existence of all specified input files (including optional ones that have been provided)
      // if necessary, also check for pre-existence of any output files with known paths
      //   (if the output is e.g. given as a prefix, the argument should be flagged as type_text())
      for (const auto& i : argument) {
        const std::string text = std::string (i);
        if (i.arg->type == ArgFileIn || i.arg->type == TracksIn) {
          if (!Path::exists (text))
            throw Exception ("required input file \"" + text + "\" not found");
          if (!Path::is_file (text))
            throw Exception ("required input \"" + text + "\" is not a file");
        }
        if (i.arg->type == ArgDirectoryIn) {
          if (!Path::exists (text))
            throw Exception ("required input directory \"" + text + "\" not found");
          if (!Path::is_dir (text))
            throw Exception ("required input \"" + text + "\" is not a directory");
        }
        if (i.arg->type == ArgFileOut || i.arg->type == TracksOut) {
          if (text.find_last_of (PATH_SEPARATORS) == text.size() - 1)
            throw Exception ("output path \"" + std::string(i) + "\" is not a valid file path (ends with directory path separator)");
          check_overwrite (text);
        }
        if (i.arg->type == ArgDirectoryOut)
          check_overwrite (text);
        if (i.arg->type == TracksIn && !Path::has_suffix (text, ".tck"))
          throw Exception ("input file \"" + text + "\" is not a valid track file");
        if (i.arg->type == TracksOut && !Path::has_suffix (text, ".tck"))
          throw Exception ("output track file \"" + text + "\" must use the .tck suffix");
      }
      for (const auto& i : option) {
        for (size_t j = 0; j != i.opt->size(); ++j) {
          const Argument& arg = i.opt->operator [](j);
          const std::string text = std::string (i.args[j]);
          if (arg.type == ArgFileIn || arg.type == TracksIn) {
            if (!Path::exists (text))
              throw Exception ("input file \"" + text + "\" for option \"-" + std::string(i.opt->id) + "\" not found");
            if (!Path::is_file (text))
              throw Exception ("input \"" + text + "\" for option \"-" + std::string(i.opt->id) + "\" is not a file");
          }
          if (arg.type == ArgDirectoryIn) {
            if (!Path::exists (text))
              throw Exception ("input directory \"" + text + "\" for option \"-" + std::string(i.opt->id) + "\" not found");
            if (!Path::is_dir (text))
              throw Exception ("input \"" + text + "\" for option \"-" + std::string(i.opt->id) + "\" is not a directory");
          }
          if (arg.type == ArgFileOut || arg.type == TracksOut) {
            if (text.find_last_of (PATH_SEPARATORS) == text.size() - 1)
              throw Exception ("output path \"" + text + "\" for option \"-" + std::string(i.opt->id) + "\" is not a valid file path (ends with directory path separator)");
            check_overwrite (text);
          }
          if (arg.type == ArgDirectoryOut)
            check_overwrite (text);
          if (arg.type == TracksIn && !Path::has_suffix (text, ".tck"))
            throw Exception ("input file \"" + text + "\" for option \"-" + std::string(i.opt->id) + "\" is not a valid track file");
          if (arg.type == TracksOut && !Path::has_suffix (text, ".tck"))
            throw Exception ("output track file \"" + text + "\" for option \"-" + std::string(i.opt->id) + "\" must use the .tck suffix");
        }
      }

      SignalHandler::init();
    }




    void init (int cmdline_argc, const char* const* cmdline_argv)
    {
#ifdef MRTRIX_WINDOWS
      // force stderr to be unbuffered, and stdout to be line-buffered:
      setvbuf (stderr, nullptr, _IONBF, 0);
      setvbuf (stdout, nullptr, _IOLBF, 0);
#endif

      terminal_use_colour = !ProgressBar::set_update_method();

      argc = cmdline_argc;
      argv = cmdline_argv;

      NAME = Path::basename (argv[0]);
#ifdef MRTRIX_WINDOWS
      if (Path::has_suffix (NAME, ".exe"))
        NAME.erase (NAME.size()-4);
#endif

      if (strcmp (mrtrix_version, executable_uses_mrtrix_version) != 0) {
        Exception E ("executable was compiled for a different version of the MRtrix3 library!");
        E.push_back (std::string("  ") + NAME + " version: " + executable_uses_mrtrix_version);
        E.push_back (std::string("  library version: ") + mrtrix_version);
        E.push_back ("Running ./build again may correct error");
        throw E;
      }

      auto argv_quoted = [] (const std::string& s) -> std::string {
        for (size_t i = 0; i != s.size(); ++i) {
          if (!(isalnum(s[i]) || s[i] == '.' || s[i] == '_' || s[i] == '-' || s[i] == '/')) {
            std::string escaped_string ("\'");
            for (auto c : s) {
              switch (c) {
                case '\'': escaped_string.append ("\\\'"); break;
                case '\\': escaped_string.append ("\\\\"); break;
                default: escaped_string.push_back (c); break;
              }
            }
            escaped_string.push_back ('\'');
            return escaped_string;
          }
        }
        return s;
      };
      command_history_string = argv[0];
      for (int n = 1; n < argc; ++n)
        command_history_string += std::string(" ") + argv_quoted (argv[n]);
      command_history_string += std::string ("  (version=") + mrtrix_version;
      if (project_version)
        command_history_string += std::string (", project=") + project_version;
      command_history_string += ")";

      std::locale::global (std::locale::classic());
      std::setlocale (LC_ALL, "C");

      srand (time (nullptr));
    }








    const vector<ParsedOption> get_options (const std::string& name)
    {
      vector<ParsedOption> matches;
      for (size_t i = 0; i < option.size(); ++i) {
        assert (option[i].opt);
        if (option[i].opt->is (name))
          matches.push_back ({ option[i].opt, option[i].args });
      }
      return matches;
    }






    int64_t App::ParsedArgument::as_int () const
    {
      if (arg->type == Integer) {

        // Check to see if there are any alpha characters in here
        // - If a single character at the end, use as integer multiplier
        //   - Unless there's a dot point before the multiplier; in which case,
        //     parse the number as a float, multiply, then cast to integer
        // - If a single 'e' or 'E' in the middle, parse as float and convert to integer
        size_t alpha_count = 0;
        bool alpha_is_last = false;
        bool contains_dotpoint = false;
        char alpha_char = 0;
        for (const char* c = p; *c; ++c) {
          if (std::isalpha (*c)) {
            ++alpha_count;
            alpha_is_last = true;
            alpha_char = *c;
          } else {
            alpha_is_last = false;
          }
          if (*c == '.')
            contains_dotpoint = true;
        }
        if (alpha_count > 1)
          throw Exception ("error converting string " + str(p) + " to integer: too many letters");
        int64_t retval = 0;
        if (alpha_count) {
          if (alpha_is_last) {
            std::string num (p);
            const char postfix = num.back();
            num.pop_back();
            int64_t multiplier = 1.0;
            switch (postfix) {
              case 'k': case 'K': multiplier = 1000; break;
              case 'm': case 'M': multiplier = 1000000; break;
              case 'b': case 'B': multiplier = 1000000000; break;
              case 't': case 'T': multiplier = 1000000000000; break;
              default: throw Exception ("error converting string " + str(p) + " to integer: unexpected postfix \'" + postfix + "\'");
            }
            if (contains_dotpoint) {
              const default_type prefix = to<default_type> (num);
              retval = std::round (prefix * default_type(multiplier));
            } else {
              retval = to<int64_t> (num) * multiplier;
            }
          } else if (alpha_char == 'e' || alpha_char == 'E') {
            const default_type as_float = to<default_type> (p);
            retval = std::round (as_float);
          } else {
            throw Exception ("error converting string " + str(p) + " to integer: unexpected character");
          }
        } else {
          retval = to<int64_t> (p);
        }

        const int64_t min = arg->limits.i.min;
        const int64_t max = arg->limits.i.max;
        if (retval < min || retval > max) {
          std::string msg ("value supplied for ");
          if (opt) msg += std::string ("option \"") + opt->id;
          else msg += std::string ("argument \"") + arg->id;
          msg += "\" is out of bounds (valid range: " + str (min) + " to " + str (max) + ", value supplied: " + str (retval) + ")";
          throw Exception (msg);
        }
        return retval;
      }

      if (arg->type == Choice) {
        std::string selection = lowercase (p);
        const char* const* choices = arg->limits.choices;
        for (int i = 0; choices[i]; ++i) {
          if (selection == choices[i]) {
            return i;
          }
        }
        std::string msg = std::string ("unexpected value supplied for ");
        if (opt) msg += std::string ("option \"") + opt->id;
        else msg += std::string ("argument \"") + arg->id;
        msg += std::string ("\" (received \"" + std::string(p) + "\"; valid choices are: ") + join (choices, ", ") + ")";
        throw Exception (msg);
      }
      assert (0);
      return (0);
    }



    default_type App::ParsedArgument::as_float () const
    {
      assert (arg->type == Float);
      const default_type retval = to<default_type> (p);
      const default_type min = arg->limits.f.min;
      const default_type max = arg->limits.f.max;
      if (retval < min || retval > max) {
        std::string msg ("value supplied for ");
        if (opt) msg += std::string ("option \"") + opt->id;
        else msg += std::string ("argument \"") + arg->id;
        msg += "\" is out of bounds (valid range: " + str (min) + " to " + str (max) + ", value supplied: " + str (retval) + ")";
        throw Exception (msg);
      }

      return retval;
    }


  }
}