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Instead of representing colours in several different forms with various
cell flags, convert to use an int with flags marking 256 or RGB colours
in the top byte (except in cells, which we don't want to make any
bigger). From Brad Town.

/* $OpenBSD: colour.c,v 1.14 2016/07/15 00:42:56 nicm Exp $ */

/*
 * Copyright (c) 2008 Nicholas Marriott <nicholas.marriott@gmail.com>
 * Copyright (c) 2016 Avi Halachmi <avihpit@yahoo.com>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF MIND, USE, DATA OR PROFITS, WHETHER
 * IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
 * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <sys/types.h>

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

#include "tmux.h"

static int
colour_dist_sq(int R, int G, int B, int r, int g, int b)
{
	return ((R - r) * (R - r) + (G - g) * (G - g) + (B - b) * (B - b));
}

static int
colour_to_6cube(int v)
{
	if (v < 48)
		return (0);
	if (v < 114)
		return (1);
	return ((v - 35) / 40);
}

/*
 * Convert an RGB triplet to the xterm(1) 256 colour palette.
 *
 * xterm provides a 6x6x6 colour cube (16 - 231) and 24 greys (232 - 255). We
 * map our RGB colour to the closest in the cube, also work out the closest
 * grey, and use the nearest of the two.
 *
 * Note that the xterm has much lower resolution for darker colors (they are
 * not evenly spread out), so our 6 levels are not evenly spread: 0x0, 0x5f
 * (95), 0x87 (135), 0xaf (175), 0xd7 (215) and 0xff (255). Greys are more
 * evenly spread (8, 18, 28 ... 238).
 */
int
colour_find_rgb(u_char r, u_char g, u_char b)
{
	static const int	q2c[6] = { 0x00, 0x5f, 0x87, 0xaf, 0xd7, 0xff };
	int			qr, qg, qb, cr, cg, cb, d, idx;
	int			grey_avg, grey_idx, grey;

	/* Map RGB to 6x6x6 cube. */
	qr = colour_to_6cube(r); cr = q2c[qr];
	qg = colour_to_6cube(g); cg = q2c[qg];
	qb = colour_to_6cube(b); cb = q2c[qb];

	/* If we have hit the colour exactly, return early. */
	if (cr == r && cg == g && cb == b)
		return ((16 + (36 * qr) + (6 * qg) + qb) | COLOUR_FLAG_256);

	/* Work out the closest grey (average of RGB). */
	grey_avg = (r + g + b) / 3;
	if (grey_avg > 238)
		grey_idx = 23;
	else
		grey_idx = (grey_avg - 3) / 10;
	grey = 8 + (10 * grey_idx);

	/* Is grey or 6x6x6 colour closest? */
	d = colour_dist_sq(cr, cg, cb, r, g, b);
	if (colour_dist_sq(grey, grey, grey, r, g, b) < d)
		idx = 232 + grey_idx;
	else
		idx = 16 + (36 * qr) + (6 * qg) + qb;
	return (idx | COLOUR_FLAG_256);
}

/* Join RGB into a colour. */
int
colour_join_rgb(u_char r, u_char g, u_char b)
{
	return ((((int)((r) & 0xff)) << 16) |
	    (((int)((g) & 0xff)) << 8) |
	    (((int)((b) & 0xff))) | COLOUR_FLAG_RGB);
}

/* Split colour into RGB. */
void
colour_split_rgb(int c, u_char *r, u_char *g, u_char *b)
{
	*r = (c >> 16) & 0xff;
	*g = (c >> 8) & 0xff;
	*b = c & 0xff;
}

/* Convert colour to a string. */
const char *
colour_tostring(int c)
{
	static char	s[32];
	u_char		r, g, b;

	if (c & COLOUR_FLAG_RGB) {
		colour_split_rgb(c, &r, &g, &b);
		xsnprintf(s, sizeof s, "#%02x%02x%02x", r, g, b);
		return (s);
	}

	if (c & COLOUR_FLAG_256) {
		xsnprintf(s, sizeof s, "colour%u", c & 0xff);
		return (s);
	}

	switch (c) {
	case 0:
		return ("black");
	case 1:
		return ("red");
	case 2:
		return ("green");
	case 3:
		return ("yellow");
	case 4:
		return ("blue");
	case 5:
		return ("magenta");
	case 6:
		return ("cyan");
	case 7:
		return ("white");
	case 8:
		return ("default");
	case 90:
		return ("brightblack");
	case 91:
		return ("brightred");
	case 92:
		return ("brightgreen");
	case 93:
		return ("brightyellow");
	case 94:
		return ("brightblue");
	case 95:
		return ("brightmagenta");
	case 96:
		return ("brightcyan");
	case 97:
		return ("brightwhite");
	}
	return (NULL);
}

/* Convert colour from string. */
int
colour_fromstring(const char *s)
{
	const char	*errstr;
	const char	*cp;
	int		 n;
	u_char		 r, g, b;

	if (*s == '#' && strlen(s) == 7) {
		for (cp = s + 1; isxdigit((u_char) *cp); cp++)
			;
		if (*cp != '\0')
			return (-1);
		n = sscanf(s + 1, "%2hhx%2hhx%2hhx", &r, &g, &b);
		if (n != 3)
			return (-1);
		return (colour_join_rgb(r, g, b));
	}

	if (strncasecmp(s, "colour", (sizeof "colour") - 1) == 0) {
		n = strtonum(s + (sizeof "colour") - 1, 0, 255, &errstr);
		if (errstr != NULL)
			return (-1);
		return (n | COLOUR_FLAG_256);
	}

	if (strcasecmp(s, "black") == 0 || strcmp(s, "0") == 0)
		return (0);
	if (strcasecmp(s, "red") == 0 || strcmp(s, "1") == 0)
		return (1);
	if (strcasecmp(s, "green") == 0 || strcmp(s, "2") == 0)
		return (2);
	if (strcasecmp(s, "yellow") == 0 || strcmp(s, "3") == 0)
		return (3);
	if (strcasecmp(s, "blue") == 0 || strcmp(s, "4") == 0)
		return (4);
	if (strcasecmp(s, "magenta") == 0 || strcmp(s, "5") == 0)
		return (5);
	if (strcasecmp(s, "cyan") == 0 || strcmp(s, "6") == 0)
		return (6);
	if (strcasecmp(s, "white") == 0 || strcmp(s, "7") == 0)
		return (7);
	if (strcasecmp(s, "default") == 0 || strcmp(s, "8") == 0)
		return (8);
	if (strcasecmp(s, "brightblack") == 0 || strcmp(s, "90") == 0)
		return (90);
	if (strcasecmp(s, "brightred") == 0 || strcmp(s, "91") == 0)
		return (91);
	if (strcasecmp(s, "brightgreen") == 0 || strcmp(s, "92") == 0)
		return (92);
	if (strcasecmp(s, "brightyellow") == 0 || strcmp(s, "93") == 0)
		return (93);
	if (strcasecmp(s, "brightblue") == 0 || strcmp(s, "94") == 0)
		return (94);
	if (strcasecmp(s, "brightmagenta") == 0 || strcmp(s, "95") == 0)
		return (95);
	if (strcasecmp(s, "brightcyan") == 0 || strcmp(s, "96") == 0)
		return (96);
	if (strcasecmp(s, "brightwhite") == 0 || strcmp(s, "97") == 0)
		return (97);
	return (-1);
}

/* Convert 256 colour palette to 16. */
u_char
colour_256to16(u_char c)
{
	static const u_char table[256] = {
		 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15,
		 0,  4,  4,  4, 12, 12,  2,  6,  4,  4, 12, 12,  2,  2,  6,  4,
		12, 12,  2,  2,  2,  6, 12, 12, 10, 10, 10, 10, 14, 12, 10, 10,
		10, 10, 10, 14,  1,  5,  4,  4, 12, 12,  3,  8,  4,  4, 12, 12,
		 2,  2,  6,  4, 12, 12,  2,  2,  2,  6, 12, 12, 10, 10, 10, 10,
		14, 12, 10, 10, 10, 10, 10, 14,  1,  1,  5,  4, 12, 12,  1,  1,
		 5,  4, 12, 12,  3,  3,  8,  4, 12, 12,  2,  2,  2,  6, 12, 12,
		10, 10, 10, 10, 14, 12, 10, 10, 10, 10, 10, 14,  1,  1,  1,  5,
		12, 12,  1,  1,  1,  5, 12, 12,  1,  1,  1,  5, 12, 12,  3,  3,
		 3,  7, 12, 12, 10, 10, 10, 10, 14, 12, 10, 10, 10, 10, 10, 14,
		 9,  9,  9,  9, 13, 12,  9,  9,  9,  9, 13, 12,  9,  9,  9,  9,
		13, 12,  9,  9,  9,  9, 13, 12, 11, 11, 11, 11,  7, 12, 10, 10,
		10, 10, 10, 14,  9,  9,  9,  9,  9, 13,  9,  9,  9,  9,  9, 13,
		 9,  9,  9,  9,  9, 13,  9,  9,  9,  9,  9, 13,  9,  9,  9,  9,
		 9, 13, 11, 11, 11, 11, 11, 15,  0,  0,  0,  0,  0,  0,  8,  8,
		 8,  8,  8,  8,  7,  7,  7,  7,  7,  7, 15, 15, 15, 15, 15, 15
	};

	return (table[c]);
}