man.cpp

#include "ArgumentParsing.h"
#include "Parameter.h"

#include <array>
#include <csignal>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <string>
#include <unistd.h>

namespace sargp {

namespace {

void printManPage();
auto manPage =
	Flag("man", "show a man compatible help for the active (sub) command(s)",
		 printManPage);

void printManPage() {
	auto commands = getActiveCommands();
	Command *activeCommand = commands.back();
	std::string command_names =
		std::accumulate(next(begin(commands)), end(commands), std::string{},
		            [](std::string const &l, Command const *c) {
		                return l + " " + c->getName();
		            });
	std::string groff = ".TH man 1\n.SH NAME\n" + command_names + "\n";
	groff += ".SH SYNOPSIS\n" + command_names;
	if (not activeCommand->getSubCommands().empty()) {
		groff += " [subcommand]...";
	}
	if (not activeCommand->getParameters().empty()) {
		groff += " [arguments]...";
	}
	groff += "\n.SH DESCRIPTION\n" + activeCommand->getDescription() + "\n";

	auto const &subCommands = activeCommand->getSubCommands();
	if (not subCommands.empty()) { // if there is at least one subcommand
		groff += ".SH SUB COMMANDS\n";
		for (auto const &subC : subCommands) {
			groff += ".TP\n\\fB" + subC->getName() + "\\fR\n" +
			         subC->getDescription() + "\n";
		}
		groff += "\n";
	}

	Command const *command = activeCommand;
	while (command->getParentCommand()) {
		if (command->getParameters().size() > 1
		    or (command->getParameters().size() == 1 and command->findParameter("") == nullptr)) {
			groff += ".SH OPTIONS FOR " + command->getName() + "\n";
			for (ParameterBase const *param : command->getParameters()) {
				if (param->getArgName() == "") continue;
				groff += ".TP\n";
				groff += "\\fR--" + param->getArgName() + "\\fR\n";
				groff += param->describe() + "\n";
			}
		}
		command = command->getParentCommand();
	}
	if (command->getParameters().size() > 1
	    or (command->getParameters().size() == 1 and command->findParameter("") == nullptr)) {
		groff += ".SH GLOBAL OPTIONS\n";
		for (ParameterBase const *param : command->getParameters()) {
			if (param->getArgName() == "") continue;
			groff += ".TP\n";
			groff += "\\fR--" + param->getArgName() + "\\fR\n";
			groff += param->describe() + "\n";
		}
	}

	char tmp_file_name[] = "/tmp/groff_tempfileXXXXXX";
	int fd = mkstemp(tmp_file_name);
	if (fd == -1) {
		throw std::runtime_error("cannot create tempfile" +
		                         std::string{std::strerror(errno)});
	}

	std::array<char, 4096> absPath{'\0'};
	std::string procPat = "/proc/self/fd/" + std::to_string(fd);
	int r = readlink(procPat.c_str(), absPath.data(), absPath.size());
	if (r == -1 || r == static_cast<int>(absPath.size())) {
		throw std::runtime_error("cannot do readlink");
	}

	std::size_t written{0};
	while (written < groff.size()) {
		int w = ::write(fd, groff.data() + written, groff.size() - written);
		if (w <= 0) {
			break;
		}
		written += w;
	}

	pid_t parentPID = getpid();
	pid_t childPID = fork();
	if (not childPID) {
		// wait for parent process to terminate
		while (1) {
			sleep(1);
			if (parentPID != getppid()) {
				break;
			}
		}
		unlink(tmp_file_name);
		exit(0);
	}

	int e = ::execlp("man", "man", "-l", absPath.data(), nullptr);

	exit(e);
}

}
}