/*
 * SAME/EAS decoder, 2006 Ben Winslow <rain bluecherry net>
 * with credit to Zinx Verituse
 */

/* FIXME:
 * - The power thresholds are completely arbitrary.  They should probably be
 *   based on some average of the sample window.
 * - No window synchronization.  This means there's some luck involved in
 *   a successful decoding, especially with a noisy signal.
 * - Doing proper FFT might yield better results?
 * - There should be an option to require a valid preamble before deciding
 *   that we're synchronized.
 */

#include <stdio.h>
#include <unistd.h>
#include <math.h>

#define ABS(x) ((x) < 0 ? ((x) * -1) : (x))
#define SRATE 44100.0
#define BAND 260.0
#define NSAMP (int)((1920.0/1000000.0) * SRATE)
#define MARK_FREQ 2083.3
#define SPACE_FREQ 1562.5

int main(int argc, char *argv[])
{
	short sample, window[NSAMP];
	int windpos = 0, havesync = 0, x;
	double mark_sine, mark_cosine;
	double space_sine, space_cosine;
	double mark_power, space_power;
	int accum = 0, accumbits = 0;
	
	printf("Window: %d samples\n", NSAMP);
	
	while (read(0, &sample, sizeof(sample)) == sizeof(sample)) {
//		printf("Sample: %d\n", sample);
		window[windpos] = sample;
		windpos++;
		
		if (windpos >= NSAMP) {
			mark_sine = mark_cosine = space_sine = space_cosine = 0.0;
			
			for (x = 0; x < NSAMP; x++) {
				mark_sine += window[x] * sin(MARK_FREQ * M_PI * 2 * (double)x / SRATE);
				space_sine += window[x] * sin(SPACE_FREQ * M_PI * 2 * (double)x / SRATE);
				mark_cosine += window[x] * cos(MARK_FREQ * M_PI * 2 * (double)x / SRATE);
				space_cosine += window[x] * cos(SPACE_FREQ * M_PI * 2 * (double)x / SRATE);
			}
			
			mark_power = sqrt(pow(mark_sine, 2) + pow(mark_cosine, 2));
			space_power = sqrt(pow(space_sine, 2) + pow(space_cosine, 2));

			if (mark_power > 10000.0 || space_power > 10000.0) {
//				printf("power[%.1fHz] = %f - power[%.1fHz] = %f :: %s\n", MARK_FREQ, mark_power, SPACE_FREQ, space_power, mark_power > space_power ? "MARK" : "SPACE");
				accum >>= 1;
				
				if (mark_power > space_power)
					accum |= 0x80;
				accumbits++;
				
//				printf("[s%d] accum[%02x]\n", havesync, accum);
				
				if (!havesync) {
					if ((accum & 0xff) == 0xab) {
						havesync = 1;
						accum = accumbits = 0;
						printf("[got sync]");
					}
				} else if (accumbits == 8) {
					if ((accum & 0xff) < 0x20 || (accum & 0xff) >= 0x80)
						printf("[%02x]", accum & 0xff);
					else
						printf("%c", accum & 0xff);
					accum = accumbits = 0;
				}
			} else if (havesync) {
				printf("[lost sync]\n");
				havesync = 0;
			}
			fflush(stdout);
			
			windpos = 0;
		}
	}
	printf("[eof!]\n");

	return 0;
}