/**
 * Relational pipes
 * Copyright © 2019 František Kučera (Frantovo.cz, GlobalCode.info)
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, version 3 of the License.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
 */
#pragma once

#include <vector>
#include <sstream>
#include <fcntl.h>
#include <unistd.h>
#include <sys/wait.h>
#include <ext/stdio_filebuf.h>

#include <relpipe/writer/typedefs.h>
#include <relpipe/cli/RelpipeCLIException.h>

namespace relpipe {
namespace in {
namespace filesystem {

/**
 * Simple wrapper for a system process (fork+exec) that captures and returns just the STDOUT.
 */
class SystemProcess {
private:
	/**
	 * the command + its arguments
	 */
	std::vector<std::string> commandLine;
	int nullFile = -1;

	/**
	 * TODO: move to a common library (copied from the AWK module) 
	 * @param args
	 */
	void execp(const std::vector<std::string>& args) {
		const char** a = new const char*[args.size() + 1];
		for (size_t i = 0; i < args.size(); i++) a[i] = args[i].c_str();
		a[args.size()] = nullptr;

		execvp(a[0], (char*const*) a);

		delete[] a;
		throw relpipe::cli::RelpipeCLIException(L"Unable to do execvp().", relpipe::cli::CLI::EXIT_CODE_UNEXPECTED_ERROR); // TODO: better exception?
	}

	/**
	 * TODO: move to a common library (copied from the AWK module) 
	 * @param readerFD
	 * @param writerFD
	 */
	void createPipe(int& readerFD, int& writerFD) {
		int fds[2];
		int result = pipe(fds);
		readerFD = fds[0];
		writerFD = fds[1];
		if (result < 0) throw relpipe::cli::RelpipeCLIException(L"Unable to create a pipe.", relpipe::cli::CLI::EXIT_CODE_UNEXPECTED_ERROR); // TODO: better exception?
	}

	/**
	 * TODO: move to a common library (copied from the AWK module) 
	 */
	void redirectFD(int oldfd, int newfd) {
		int result = dup2(oldfd, newfd);
		if (result < 0) throw relpipe::cli::RelpipeCLIException(L"Unable redirect FD.", relpipe::cli::CLI::EXIT_CODE_UNEXPECTED_ERROR); // TODO: better exception?
	}

	/**
	 * TODO: move to a common library (copied from the AWK module) 
	 */
	void closeOrThrow(int fd) {
		int error = close(fd);
		if (error) throw relpipe::cli::RelpipeCLIException(L"Unable to close FD: " + to_wstring(fd) + L" from PID: " + to_wstring(getpid()), relpipe::cli::CLI::EXIT_CODE_UNEXPECTED_ERROR); // TODO: better exception?
	}

public:

	SystemProcess(std::vector<std::string> commandLine) : commandLine(commandLine) {
		nullFile = open("/dev/null", O_RDWR);
	}

	virtual ~SystemProcess() {
		close(nullFile);
	}

	std::string execute() {

		std::stringstream result;

		int hashReaderFD;
		int hashWriterFD;
		createPipe(hashReaderFD, hashWriterFD);
		
		__pid_t hashPid = fork();

		if (hashPid < 0) {
			throw relpipe::cli::RelpipeCLIException(L"Unable to fork the hash process.", relpipe::cli::CLI::EXIT_CODE_UNEXPECTED_ERROR); // TODO: better exception?
		} else if (hashPid == 0) {
			// Child process
			closeOrThrow(hashReaderFD);
			redirectFD(nullFile, STDIN_FILENO);
			redirectFD(nullFile, STDERR_FILENO);
			redirectFD(hashWriterFD, STDOUT_FILENO);
			execp(commandLine);
		} else {
			// Parent process
			closeOrThrow(hashWriterFD);

			__gnu_cxx::stdio_filebuf<char> hashReaderBuffer(hashReaderFD, std::ios::in);
			std::istream hashReader(&hashReaderBuffer);
			
			for (char ch; hashReader.read(&ch, 1).good();) result.put(ch);
			
			int waitError;
			__pid_t waitPID = wait(&waitError);
			if (waitError) throw relpipe::cli::RelpipeCLIException(L"The child process returned an error exit code.", relpipe::cli::CLI::EXIT_CODE_UNEXPECTED_ERROR); // TODO: better exception?
		}

		return result.str();
	}
};

}
}
}