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

struct yjk {
	int16_t	y;
	int16_t	j;
	int16_t	k;
} __attribute__((packed));

struct rgb {
	uint8_t	r;
	uint8_t	g;
	uint8_t	b;
} __attribute__((packed));

static	void	rgb2yjk(struct rgb *in, struct yjk *out)
{
	int16_t	y, j, k;

	// YJKは(本来の値×8)としている
	y = in->b * 4 + in->r * 2 + in->g;
	j = in->r * 8 - y;
	k = in->g * 8 - y;

	out->y = le16toh(y);
	out->j = le16toh(j);
	out->k = le16toh(k);
}

static	void	yjk2rgb(struct yjk *in, struct rgb *out)
{
	int	r, g, b;
	int16_t	y, j, k;

	y = le16toh(in->y);
	j = le16toh(in->j);
	k = le16toh(in->k);

	r = (y + j) / 8;
	g = (y + k) / 8;
	b = (y * 5 - j * 2 - k) / 32;

	if (r < 0) r = 0; else if (r > UINT8_MAX) r = UINT8_MAX;
	if (g < 0) g = 0; else if (g > UINT8_MAX) g = UINT8_MAX;
	if (b < 0) b = 0; else if (b > UINT8_MAX) b = UINT8_MAX;

	out->r = r;
	out->g = g;
	out->b = b;
}

static	void	encyjk(FILE *fpi, FILE *fpo)
{
	struct rgb	rgb;
	struct yjk	yjk;

	while (1) {
		if (fread(&rgb, 1, sizeof(rgb), fpi) < sizeof(rgb)) break;
		rgb2yjk(&rgb, &yjk);
		if (fwrite(&yjk, sizeof(yjk), 1, fpo) < 1) {
			fprintf(stderr, "encyjk: file write error\n");
			break;
		}
	}
}

static	void	encrgb(FILE *fpi, FILE *fpo)
{
	struct	yjk	yjk;
	struct	rgb	rgb;

	while (1) {
		if (fread(&yjk, 1, sizeof(yjk), fpi) < sizeof(yjk)) break;
		yjk2rgb(&yjk, &rgb);
		if (fwrite(&rgb, sizeof(rgb), 1, fpo) < 1) {
			fprintf(stderr, "encrgb: file write error\n");
			break;
		}
	}
}

int	main(int argc, char *argv[])
{
	FILE	*fpi, *fpo;

	if (argc < 2 || (*argv[1] != 'y' && *argv[1] != 'r')) {
		fprintf(stderr, "usage: %s [command] [(infile)] [(outfile)]\n", argv[0]);
		fprintf(stderr, "	command	y	RGB -> YJK\n");
		fprintf(stderr, "		r	YJK -> RGB\n");
		goto fin0;
	}

	if (argc < 3 || !strcmp(argv[2], "-")) {
		fpi = stdin;
	} else {
		fpi = fopen(argv[2], "r");
		if (fpi == NULL) {
			fprintf(stderr, "file open error (in)\n");
			goto fin0;
		}
	}

	if (argc < 4 || !strcmp(argv[3], "-")) {
		fpo = stdout;
	} else {
		fpo = fopen(argv[3], "w");
		if (fpo == NULL) {
			fprintf(stderr, "file open error (out)\n");
			goto fin1;
		}
	}

	switch (*argv[1]) {
	case	'y':
		encyjk(fpi, fpo);
		break;
	case	'r':
		encrgb(fpi, fpo);
		break;
	}

//fin2:
	if (fpo != stdout) fclose(fpo);
fin1:
	if (fpi != stdin) fclose(fpi);
fin0:
	return 0;
}