/**

 * 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:

		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();

	}

};

}

}

}