/**

 * Relational pipes

 * Copyright © 2020 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/>.

 */

#include <iostream>

#include <sstream>

#include <codecvt>

#include <locale>

#include <fcntl.h>

#include <unistd.h>

#include <sys/wait.h>

#include <ext/stdio_filebuf.h>

#include <algorithm>

#include "SubProcess.h"

using namespace relpipe::writer;

/**

 * TODO: have a separate side process for forking new processes.

 */

class SubProcessImpl : public SubProcess {

private:

	__pid_t subPid;

	std::istream subOutputReader;

	std::ostream subInputWriter;

	__gnu_cxx::stdio_filebuf<char> subOutputReaderBuffer;

	__gnu_cxx::stdio_filebuf<char> subInputWriterBuffer;

	static const char SEPARATOR = '\0';

	std::wstring_convert < std::codecvt_utf8<wchar_t>> convertor; // TODO: support also other encodings. Or use always UTF-8 for communication with subprocesses.

	int readInt() {

		return std::stoi(readString());

	}

	string_t readString() {

		std::stringstream s;

		for (char ch; subOutputReader.read(&ch, 1).good() && ch != SEPARATOR;) s.put(ch);

		return convertor.from_bytes(s.str());

	}

	void write(string_t s) {

		subInputWriter << convertor.to_bytes(s).c_str();

		subInputWriter.put(SEPARATOR);

		if (subInputWriter.bad()) throw SubProcess::Exception(L"Unable to write to sub-process.");

	}

	void write(int i) {

		write(std::to_wstring(i));

	}

	void flush() {

		subInputWriter.flush();

	}

public:

	/**

	 * TODO: move to a common library (copied from the AWK module) 

	 * @param args

	 */

	static 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;

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

		delete[] a;

		throw SubProcess::Exception(L"Unable to do execvp().");

	}

	/**

	 * TODO: move to a common library (copied from the AWK module) 

	 * @param readerFD

	 * @param writerFD

	 */

	static void createPipe(int& readerFD, int& writerFD) {

		int fds[2];

		int result = pipe(fds);

		readerFD = fds[0];

		writerFD = fds[1];

		if (result < 0) throw SubProcess::Exception(L"Unable to create a pipe.");

	}

	/**

	 * TODO: move to a common library (copied from the AWK module) 

	 */

	static void redirectFD(int oldfd, int newfd) {

		int result = dup2(oldfd, newfd);

		if (result < 0) throw SubProcess::Exception(L"Unable redirect FD.");

	}

	/**

	 * TODO: move to a common library (copied from the AWK module) 

	 */

	static void closeOrThrow(int fd) {

		int error = close(fd);

		if (error) throw SubProcess::Exception(L"Unable to close FD: " + std::to_wstring(fd) + L" from PID: " + std::to_wstring(getpid()));

	}

	static SubProcess* createSubProcess(std::vector<string_t> commandLine, std::map<string_t, string_t> environment, bool dropErrorOutput) {

		int subInputReaderFD;

		int subInputWriterFD;

		int subOutputReaderFD;

		int subOutputWriterFD;

		createPipe(subInputReaderFD, subInputWriterFD);

		createPipe(subOutputReaderFD, subOutputWriterFD);

		__pid_t subPid = fork();

		if (subPid < 0) {

			throw SubProcess::Exception(L"Unable to fork the hash process.");

		} else if (subPid == 0) {

			// Child process

			redirectFD(subInputReaderFD, STDIN_FILENO);

			redirectFD(subOutputWriterFD, STDOUT_FILENO);

			closeOrThrow(subInputWriterFD);

			closeOrThrow(subOutputReaderFD);

			if (dropErrorOutput) redirectFD(open("/dev/null", O_RDWR), STDERR_FILENO);

			std::wstring_convert < std::codecvt_utf8<wchar_t>> convertor; // TODO: support also other encodings. Or use always UTF-8 for communication with subprocesses.

			for (auto const & entry : environment) setenv(convertor.to_bytes(entry.first).c_str(), convertor.to_bytes(entry.second).c_str(), true);

			std::vector<std::string> commandLineRaw;

			for (string_t s : commandLine) commandLineRaw.push_back(convertor.to_bytes(s));

			execp(commandLineRaw);

			throw SubProcess::Exception(L"Unexpected exception after execp(commandLineRaw)"); // will never happen, look inside the method above (throws exception)

		} else {

			// Parent process

			closeOrThrow(subInputReaderFD);

			closeOrThrow(subOutputWriterFD);

			fcntl(subInputWriterFD, F_SETFD, FD_CLOEXEC);

			fcntl(subOutputReaderFD, F_SETFD, FD_CLOEXEC);

			return new SubProcessImpl(subPid, subInputWriterFD, subOutputReaderFD);

		}

	}

	SubProcessImpl(__pid_t subPid, int subInputWriterFD, int subOutputReaderFD) :

	subPid(subPid),

	subOutputReaderBuffer(__gnu_cxx::stdio_filebuf<char>(subOutputReaderFD, std::ios::in)),

	subInputWriterBuffer(__gnu_cxx::stdio_filebuf<char>(subInputWriterFD, std::ios::out)),

	subOutputReader(&subOutputReaderBuffer),

	subInputWriter(&subInputWriterBuffer) {

	}

	virtual ~SubProcessImpl() {

	}

	SubProcess::Message read() {

		Message m;

		m.code = readInt();

		int count = readInt();

		for (int i = 0; i < count; i++) m.parameters.push_back(readString());

		return m;

	}

	void write(Message m) {

		write(m.code);

		write(m.parameters.size());

		for (auto p : m.parameters) write(p);

		flush();

	}

	int wait() {

		closeOrThrow(subInputWriterBuffer.fd());

		closeOrThrow(subOutputReaderBuffer.fd());

		int status = -1;

		::waitpid(subPid, &status, 0);

		return status;

	}

};

SubProcess* SubProcess::create(std::vector<string_t> commandLine, std::map<string_t, string_t> environment, bool dropErrorOutput) {

	return SubProcessImpl::createSubProcess(commandLine, environment, dropErrorOutput);

}