#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <fcntl.h>
#include <unistd.h>
#include <termios.h>
#include <errno.h>

#include "smg_rsa.h"


int set_usb_attribs(int fd, int speed) {
	struct termios tty;
	if (tcgetattr(fd, &tty) < 0) {
		return -1;
	}

	//input and output speeds
	cfsetospeed(&tty, (speed_t)speed);
	cfsetispeed(&tty, (speed_t)speed);

	tty.c_cflag |= (CLOCAL | CREAD);	//ignore modem controls
	tty.c_cflag &= ~CSIZE;
	tty.c_cflag |= CS8;			//8 bit characters
	tty.c_cflag &= ~PARENB;	//no parity bit
	tty.c_cflag &= ~CSTOPB;	//only need 1 stop bit
	tty.c_cflag &= ~CRTSCTS;	//no hardware flow control

	//non-canonical mode
	tty.c_cflag &= ~(IGNBRK | BRKINT | PARMRK | ISTRIP | INLCR | IGNCR | ICRNL | IXON);
	tty.c_cflag &= ~(ECHO | ECHONL | ICANON | ISIG | IEXTEN);
	tty.c_cflag &= ~OPOST;

	//read at least one octet at a time; timeout 1 tenth of second between octets read
	tty.c_cc[VMIN] = 1;
	tty.c_cc[VTIME] = 1;

	if (tcsetattr(fd, TCSANOW, &tty) != 0)
		return -1;

	return 0;
}

int open_entropy_source(char* source_name) {
	int in, err;

	in = open(source_name, O_RDONLY | O_NOCTTY | O_NDELAY);
	if (in == -1) {
		printf("ERROR: failure to open entropy source %s: %s\n", source_name, strerror(errno));
		return in;	//failed to access entropy source
	}

	fcntl(in, F_SETFL, 0);

	err = set_usb_attribs(in, B115200);
	if (err==-1) {
		printf("Error setting attributes on %s: %s\n", source_name, strerror(errno));
		return err;
	}

	return in;	//source opened, return its descriptor
}

int get_random_octets_from(int noctets, unsigned char *out, int from) {

	int nread;
	int total = 0;

	while (total < noctets) {
		errno = 0;
		nread = read(from, out+total, noctets-total);
		//on interrupt received just try again
		if (nread == -1 && errno == EINTR)
			continue;
		//on error condition abort
		if (errno != 0 && (nread == -1 || nread == 0)) {
			printf("Error reading from entropy source %s after %d read: %s\n", ENTROPY_SOURCE, total, strerror(errno));
			return total;		//total read so far
		}

		if (nread > 0)
			total = total + nread;
	}
	return total;	//return number of octets read
}

int get_random_octets(int noctets, unsigned char *out) {
	int in;
	int nread = 0;

	in = open_entropy_source(ENTROPY_SOURCE);
	if (in > 0) {
		nread = get_random_octets_from(noctets, out, in);
		close(in);
	}
	return nread;
}