#include <sys/types.h>
#include <sys/stat.h>
#include <sys/select.h>
#include <sys/time.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>

/*
 * Scale interface
 *
 * Simon Kirby, 2013-02-14

Capacity (kg)                           5
Outline Size (mm)                       130X30X22
Non-Linearity (%FS)                     0.017
Hysteresis, Non-Repeatability (%FS)     0.01
Creep (%FS/30min)                       0.015
Temperature effect on span (%FS/10C)    0.014
Temperature effect on zero (%FS/10C)    0.017
Temperature, compensated(C)             -10-to +40
Temperature, operation(C)               -35 to +65
Safe Overload(%FS)                      150
Ultimate Overload(%FS)                  300
Protection Class                        IP65
Cable Length (m)                        1.5

 */

char *dev = "/dev/hidraw1";

void usage_exit(void) { 
	fprintf(stderr, "usage: tmc [<device>]\n");
	exit(1); 
}

#define BUFSIZE 4096
unsigned char buf[BUFSIZE];

int main(int argc, char *argv[]) {
	const char *f;
	ssize_t r;
	int fd;
	int input;
	double grams = 0, tare = 0;
	double k = 0;
	double x = 0;
	double p = 1;
	long o = 0;

	if (argc > 1)
		f = argv[1];
	else
		f = dev;
	fd = open(f, O_RDONLY | O_APPEND);
	if (fd == -1) {
		fprintf(stderr, "open(%s): %s\n", f,
			strerror(errno));
		exit(1);
	}
	for (;;) {
		r = read(fd, buf, 8);
		if (r == -1) {
			perror("read");
			break;
		} else if (r == 0) {
			break;
		} else if (r != 8) {
			fprintf(stderr, "read() returned %zi?\n", r);
			break;
		}
		if (buf[0] != 3) {
			fprintf(stderr, "First byte is %u instead of 3",
				buf[0]);
			break;
		}
		if (buf[1] != 4) {
			fprintf(stderr, "Second byte is %u instead of 4",
				buf[1]);
			break;
		}
		input = (buf[4] << 16) | (buf[5] << 8) | buf[6];

		/*
		 * Calibration 2013-02-14 with 245.7g powerball
		 * 245.7 / (8609030 - 8375600)
		 */
//		grams = input * .00105256393779719830;
		/*
		 * Calibration 2013-02-18 with 48.68g lipo
		 */
		grams = input * .00105040616014693754;

		if (!x) {
			x = grams;
		} else {
			k = p / (p + .2);		// Compute Kalman gain
			x+= k * (grams - x);		// Update estimate
//			p*= 1 - k;			// Update error covariance
			k = grams > x ? grams - x : x - grams;
			p = (1 - p) * p + (p * (k / (k + 10)));
		}

		if (++o == 160)
			tare = x;

		fprintf(stderr, "\rScale (%i): grams: %8.2fg x: %8.2fg k: %7.2f p: %7.4f\033[K",
			buf[2], grams - tare, x - tare, k, p);
	}
	close(fd);
	return 1;
}