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Add support for underscore colours with Setulc capability, mostly from
Kai Moschcau.

/* $OpenBSD: colour.c,v 1.18 2019/06/27 15:17:41 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 colours (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 9:
		return ("terminal");
	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 ("invalid");
}

/* 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, "default") == 0)
		return (8);
	if (strcasecmp(s, "terminal") == 0)
		return (9);

	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, "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 to RGB colour. */
int
colour_256toRGB(int c)
{
	static const int table[256] = {
		0x000000, 0x800000, 0x008000, 0x808000,
		0x000080, 0x800080, 0x008080, 0xc0c0c0,
		0x808080, 0xff0000, 0x00ff00, 0xffff00,
		0x0000ff, 0xff00ff, 0x00ffff, 0xffffff,
		0x000000, 0x00005f, 0x000087, 0x0000af,
		0x0000d7, 0x0000ff, 0x005f00, 0x005f5f,
		0x005f87, 0x005faf, 0x005fd7, 0x005fff,
		0x008700, 0x00875f, 0x008787, 0x0087af,
		0x0087d7, 0x0087ff, 0x00af00, 0x00af5f,
		0x00af87, 0x00afaf, 0x00afd7, 0x00afff,
		0x00d700, 0x00d75f, 0x00d787, 0x00d7af,
		0x00d7d7, 0x00d7ff, 0x00ff00, 0x00ff5f,
		0x00ff87, 0x00ffaf, 0x00ffd7, 0x00ffff,
		0x5f0000, 0x5f005f, 0x5f0087, 0x5f00af,
		0x5f00d7, 0x5f00ff, 0x5f5f00, 0x5f5f5f,
		0x5f5f87, 0x5f5faf, 0x5f5fd7, 0x5f5fff,
		0x5f8700, 0x5f875f, 0x5f8787, 0x5f87af,
		0x5f87d7, 0x5f87ff, 0x5faf00, 0x5faf5f,
		0x5faf87, 0x5fafaf, 0x5fafd7, 0x5fafff,
		0x5fd700, 0x5fd75f, 0x5fd787, 0x5fd7af,
		0x5fd7d7, 0x5fd7ff, 0x5fff00, 0x5fff5f,
		0x5fff87, 0x5fffaf, 0x5fffd7, 0x5fffff,
		0x870000, 0x87005f, 0x870087, 0x8700af,
		0x8700d7, 0x8700ff, 0x875f00, 0x875f5f,
		0x875f87, 0x875faf, 0x875fd7, 0x875fff,
		0x878700, 0x87875f, 0x878787, 0x8787af,
		0x8787d7, 0x8787ff, 0x87af00, 0x87af5f,
		0x87af87, 0x87afaf, 0x87afd7, 0x87afff,
		0x87d700, 0x87d75f, 0x87d787, 0x87d7af,
		0x87d7d7, 0x87d7ff, 0x87ff00, 0x87ff5f,
		0x87ff87, 0x87ffaf, 0x87ffd7, 0x87ffff,
		0xaf0000, 0xaf005f, 0xaf0087, 0xaf00af,
		0xaf00d7, 0xaf00ff, 0xaf5f00, 0xaf5f5f,
		0xaf5f87, 0xaf5faf, 0xaf5fd7, 0xaf5fff,
		0xaf8700, 0xaf875f, 0xaf8787, 0xaf87af,
		0xaf87d7, 0xaf87ff, 0xafaf00, 0xafaf5f,
		0xafaf87, 0xafafaf, 0xafafd7, 0xafafff,
		0xafd700, 0xafd75f, 0xafd787, 0xafd7af,
		0xafd7d7, 0xafd7ff, 0xafff00, 0xafff5f,
		0xafff87, 0xafffaf, 0xafffd7, 0xafffff,
		0xd70000, 0xd7005f, 0xd70087, 0xd700af,
		0xd700d7, 0xd700ff, 0xd75f00, 0xd75f5f,
		0xd75f87, 0xd75faf, 0xd75fd7, 0xd75fff,
		0xd78700, 0xd7875f, 0xd78787, 0xd787af,
		0xd787d7, 0xd787ff, 0xd7af00, 0xd7af5f,
		0xd7af87, 0xd7afaf, 0xd7afd7, 0xd7afff,
		0xd7d700, 0xd7d75f, 0xd7d787, 0xd7d7af,
		0xd7d7d7, 0xd7d7ff, 0xd7ff00, 0xd7ff5f,
		0xd7ff87, 0xd7ffaf, 0xd7ffd7, 0xd7ffff,
		0xff0000, 0xff005f, 0xff0087, 0xff00af,
		0xff00d7, 0xff00ff, 0xff5f00, 0xff5f5f,
		0xff5f87, 0xff5faf, 0xff5fd7, 0xff5fff,
		0xff8700, 0xff875f, 0xff8787, 0xff87af,
		0xff87d7, 0xff87ff, 0xffaf00, 0xffaf5f,
		0xffaf87, 0xffafaf, 0xffafd7, 0xffafff,
		0xffd700, 0xffd75f, 0xffd787, 0xffd7af,
		0xffd7d7, 0xffd7ff, 0xffff00, 0xffff5f,
		0xffff87, 0xffffaf, 0xffffd7, 0xffffff,
		0x080808, 0x121212, 0x1c1c1c, 0x262626,
		0x303030, 0x3a3a3a, 0x444444, 0x4e4e4e,
		0x585858, 0x626262, 0x6c6c6c, 0x767676,
		0x808080, 0x8a8a8a, 0x949494, 0x9e9e9e,
		0xa8a8a8, 0xb2b2b2, 0xbcbcbc, 0xc6c6c6,
		0xd0d0d0, 0xdadada, 0xe4e4e4, 0xeeeeee
	};

	return (table[c & 0xff] | COLOUR_FLAG_RGB);
}

/* Convert 256 colour to 16 colour. */
int
colour_256to16(int c)
{
	static const 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 & 0xff]);
}