#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <termios.h>
#include <fcntl.h>
#include <sys/file.h>
#include <sys/select.h>
#include "flow.h"

#define DATA_CANCEL 0xffffffff

static bool debug = false;

static void print_debug(const char* const msg, int en)
{
	if (debug) {
		if (errno == 0) {
			fprintf(stderr, "%s", msg);
		} else {
			fprintf(stderr, "%s: %d\n", msg, en);
		}
		fflush(stderr);
	}
}

void serial_debug(bool value)
{
	debug = value;
}

//contains file descriptors used in managing a serial port
struct serial_config {
	int port_fd; // file descriptor of serial port

	/* a pipe is used to abort a serial read by writing something into the
	 * write end of the pipe */
	int pipe_read_fd; // file descriptor, read end of pipe
	int pipe_write_fd; // file descriptor, write end of pipe
};

int serial_open(
	const char* const port_name,
	int baud,
	int char_size,
	bool two_stop_bits,
	int parity,
	struct serial_config** serial)
{

	int fd = open(port_name, O_RDWR | O_NOCTTY | O_NONBLOCK);

	if (fd < 0) {
		int en = errno;
		print_debug("Error obtaining file descriptor for port", en);
		if (en == EACCES) return -E_ACCESS_DENIED;
		if (en == ENOENT) return -E_NO_PORT;
		return -E_IO;
	}

	if (flock(fd, LOCK_EX | LOCK_NB) < 0) {
		print_debug("Error acquiring lock on port", errno);
		close(fd);
		return -E_BUSY;
	}

	/* configure new port settings */
	struct termios newtio;

	/* initialize serial interface */
	newtio.c_iflag = 0;
	newtio.c_oflag = 0;
	newtio.c_lflag = 0;
	newtio.c_cflag = CREAD;

	/* set speed */
	speed_t bd;
	switch (baud) {
        case 50: bd = B50; break;
        case 75: bd = B75; break;
        case 110: bd = B110; break;
        case 134: bd = B134; break;
        case 150: bd = B150; break;
        case 200: bd = B200; break;
        case 300: bd = B300; break;
        case 600: bd = B600; break;
        case 1200: bd = B1200; break;
        case 1800: bd = B1800; break;
        case 2400: bd = B2400; break;
        case 4800: bd = B4800; break;
        case 9600: bd = B9600; break;
        case 19200: bd = B19200; break;
        case 38400: bd = B38400; break;
        case 57600: bd = B57600; break;
        case 115200: bd = B115200; break;
        case 230400: bd = B230400; break;
        default:
		close(fd);
	        print_debug("Invalid baud rate", 0);
		return -E_INVALID_SETTINGS;
	}

	if (cfsetspeed(&newtio, bd) < 0) {
		print_debug("Error setting baud rate", errno);
		close(fd);
		return -E_IO;
	}

	/* set char size*/
	switch (char_size) {
        case 5: newtio.c_cflag |= CS5; break;
        case 6: newtio.c_cflag |= CS6; break;
        case 7: newtio.c_cflag |= CS7; break;
        case 8: newtio.c_cflag |= CS8; break;
        default:
		close(fd);
		print_debug("Invalid character size", 0);
		return -E_INVALID_SETTINGS;
	}

	/* use two stop bits */
	if (two_stop_bits){
		newtio.c_cflag |= CSTOPB;
	}

	/* set parity */
	switch (parity) {
        case PARITY_NONE: break;
        case PARITY_ODD: newtio.c_cflag |= (PARENB | PARODD); break;
        case PARITY_EVEN: newtio.c_cflag |= PARENB; break;
        default:
		close(fd);
		print_debug("Invalid parity", 0);
		return -E_INVALID_SETTINGS;
	}

	if (tcflush(fd, TCIOFLUSH) < 0) {
		print_debug("Error flushing serial settings", errno);
		close(fd);
		return -E_IO;
	}

	if (tcsetattr(fd, TCSANOW, &newtio) < 0) {
		print_debug("Error applying serial settings", errno);
		close(fd);
		return -E_IO;
	}

	int pipe_fd[2];
	if (pipe(pipe_fd) < 0) {
		print_debug("Error opening pipe", errno);
		close(fd);
		return -E_IO;
	}

	if (fcntl(pipe_fd[0], F_SETFL, O_NONBLOCK) < 0 || fcntl(pipe_fd[1], F_SETFL, O_NONBLOCK) < 0) {
		print_debug("Error setting pipe to non-blocking", errno);
		close(fd);
		close(pipe_fd[0]);
		close(pipe_fd[1]);
		return -E_IO;
	}

	struct serial_config* s = malloc(sizeof(s));
	if (s == NULL) {
		print_debug("Error allocating memory for serial configuration", errno);
		close(fd);
		close(pipe_fd[0]);
		close(pipe_fd[1]);
		return -E_IO;
	}

	s->port_fd = fd;
	s->pipe_read_fd = pipe_fd[0];
	s->pipe_write_fd = pipe_fd[1];
	(*serial) = s;

	return 0;
}

int serial_close(struct serial_config* const serial)
{
	if (close(serial->pipe_write_fd) < 0) {
		print_debug("Error closing write end of pipe", errno);
		return -E_IO;
	}
	if (close(serial->pipe_read_fd) < 0) {
		print_debug("Error closing read end of pipe", errno);
		return -E_IO;
	}

	if (flock(serial->port_fd, LOCK_UN) < 0){
		print_debug("Error releasing lock on port", errno);
		return -E_IO;
	}
	if (close(serial->port_fd) < 0) {
		print_debug("Error closing port", errno);
		return -E_IO;
	}

	free(serial);
	return 0;
}

int serial_read(struct serial_config* const serial, char* const buffer, size_t size)
{
	int port = serial->port_fd;
	int pipe = serial->pipe_read_fd;

	fd_set rfds;
	FD_ZERO(&rfds);
	FD_SET(port, &rfds);
	FD_SET(pipe, &rfds);

	int nfds = pipe + 1;
	if (pipe < port) nfds = port + 1;

	int n = select(nfds, &rfds, NULL, NULL, NULL);
	if (n < 0) {
		print_debug("Error trying to call select on port and pipe", errno);
		return -E_IO;
	}

	if (FD_ISSET(pipe, &rfds)) {
		return -E_INTERRUPT;
	} else if (FD_ISSET(port, &rfds)) {
		int r = read(port, buffer, size);

		// treat 0 bytes read as an error to avoid problems on disconnect
		// anyway, after a poll there should be more than 0 bytes available to read
		if (r <= 0) {
			print_debug("Error data not available after select", errno);
			return -E_IO;
		}
		return r;
	} else {
		print_debug("Select returned unknown read sets", 0);
		return -E_IO;
	}
}

int serial_cancel_read(struct serial_config* const serial)
{
	int data = DATA_CANCEL;

	//write to pipe to wake up any blocked read thread (self-pipe trick)
	if (write(serial->pipe_write_fd, &data, 1) < 0) {
		print_debug("Error writing to pipe during read cancel", errno);
		return -E_IO;
	}

	return 0;
}

int serial_write(struct serial_config* const serial, char* const data, size_t size)
{
	int r = write(serial->port_fd, data, size);
	if (r < 0) {
		print_debug("Error writing to port", errno);
		return -E_IO;
	}
	return r;
}