#include <fslock.h>

#include <unistd.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>

#include <logger.h>

namespace newsboat {

void remove_lock(const std::string& lock_filepath)
{
	::unlink(lock_filepath.c_str());
	LOG(level::DEBUG, "FSLock: removed lockfile %s", lock_filepath);
}

FSLock::~FSLock()
{
	if (locked) {
		remove_lock(lock_filepath);
	}
}

bool FSLock::try_lock(const std::string& new_lock_filepath, pid_t& pid)
{
	if (locked && lock_filepath == new_lock_filepath) {
		return true;
	}

	// pid == 0 indicates that something went majorly wrong during locking
	pid = 0;

	LOG(level::DEBUG, "FSLock: trying to lock `%s'", new_lock_filepath);

	// first, we open (and possibly create) the lock file
	int fd = ::open(new_lock_filepath.c_str(), O_RDWR | O_CREAT, 0600);
	if (fd < 0) {
		return false;
	}

	// then we lock it (returns immediately if locking is not possible)
	if (lockf(fd, F_TLOCK, 0) == 0) {
		LOG(level::DEBUG, "FSLock: locked `%s', writing PID...", new_lock_filepath);
		std::string pidtext = std::to_string(getpid());
		// locking successful -> truncate file and write own PID into it
		ssize_t written = 0;
		if (ftruncate(fd, 0) == 0) {
			written = write(fd, pidtext.c_str(), pidtext.length());
		}
		bool success =
			   (written != -1)
			&& (static_cast<unsigned int>(written) == pidtext.length());
		LOG(level::DEBUG, "FSLock: PID written successfully: %i", success);
		if (success) {
			if (locked) {
				remove_lock(lock_filepath);
			}
			locked = success;
			lock_filepath = new_lock_filepath;
		}
		return success;
	} else {
		LOG(level::ERROR, "FSLock: something went wrong during locking: %s",
				strerror(errno));
	}

	// locking was not successful -> read PID of locking process from it
	fd = ::open(new_lock_filepath.c_str(), O_RDONLY);
	if (fd >= 0) {
		char buf[32];
		int len = read(fd, buf, sizeof(buf)-1);
		unsigned int upid = 0;
		buf[len] = '\0';
		sscanf(buf, "%u", &upid);
		pid = upid;
		close(fd);
	}
	LOG(level::DEBUG, "FSLock: locking failed, already locked by %u", pid);
	return false;
}

}