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Improve handling of ambiguous overstrike sequences. A sequence of _\b_
can either mean an underlined underscore or a bold underscore. This
ambiguity can be 'resolved' by takeing the state of the surrounding text
into account. If surrounded by bold text, the result should probably be
bold and likewise for underlined. less(1) previously only looked at the
preceding text and ul(1) didn't examine the context at all.

tweaks and ok schwarze
ok tb (on a previous version of the diff)

/*	$OpenBSD: ul.c,v 1.21 2016/03/26 08:59:29 natano Exp $	*/
/*	$NetBSD: ul.c,v 1.3 1994/12/07 00:28:24 jtc Exp $	*/

/*
 * Copyright (c) 1980, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <curses.h>
#include <err.h>
#include <errno.h>
#include <locale.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <term.h>
#include <unistd.h>
#include <wchar.h>

#define	IESC	L'\033'
#define	SO	L'\016'
#define	SI	L'\017'
#define	HFWD	'9'
#define	HREV	'8'
#define	FREV	'7'
#define	MAXBUF	512

#define	NORMAL	000
#define	ALTSET	001	/* Reverse */
#define	SUPERSC	002	/* Dim */
#define	SUBSC	004	/* Dim | Ul */
#define	UNDERL	010	/* Ul */
#define	BOLD	020	/* Bold */
#define	INDET	040	/* Indeterminate: either Bold or Ul */

int	must_use_uc, must_overstrike;
char	*CURS_UP, *CURS_RIGHT, *CURS_LEFT,
	*ENTER_STANDOUT, *EXIT_STANDOUT, *ENTER_UNDERLINE, *EXIT_UNDERLINE,
	*ENTER_DIM, *ENTER_BOLD, *ENTER_REVERSE, *UNDER_CHAR, *EXIT_ATTRIBUTES;

struct	CHAR	{
	char	c_mode;
	wchar_t	c_char;
	int	c_width;
	int	c_pos;
} ;

struct	CHAR	obuf[MAXBUF];
int	col, maxcol;
int	mode;
int	halfpos;
int	upln;
int	iflag;

int	outchar(int);
void	initcap(void);
void	initbuf(void);
void	mfilter(FILE *);
void	reverse(void);
void	fwd(void);
void	flushln(void);
void	msetmode(int);
void	outc(wchar_t, int);
void	overstrike(void);
void	iattr(void);

#define	PRINT(s) \
	do { \
		if (s) \
			tputs(s, 1, outchar); \
	} while (0)

int
main(int argc, char *argv[])
{
	extern int optind;
	extern char *optarg;
	int c;
	char *termtype;
	FILE *f;
	char termcap[1024];

	setlocale(LC_CTYPE, "");

	if (pledge("stdio rpath tty", NULL) == -1)
		err(1, "pledge");

	termtype = getenv("TERM");
	if (termtype == NULL || (argv[0][0] == 'c' && !isatty(1)))
		termtype = "lpr";
	while ((c = getopt(argc, argv, "it:T:")) != -1)
		switch (c) {
		case 't':
		case 'T': /* for nroff compatibility */
			termtype = optarg;
			break;
		case 'i':
			iflag = 1;
			break;

		default:
			fprintf(stderr,
			    "usage: %s [-i] [-t terminal] [file ...]\n",
			    argv[0]);
			exit(1);
		}

	switch (tgetent(termcap, termtype)) {
	case 1:
		break;
	default:
		warnx("trouble reading termcap");
		/* FALLTHROUGH */
	case 0:
		/* No such terminal type - assume dumb */
		(void)strlcpy(termcap, "dumb:os:col#80:cr=^M:sf=^J:am:",
		    sizeof termcap);
		break;
	}
	initcap();
	if ((tgetflag("os") && ENTER_BOLD == NULL ) ||
	    (tgetflag("ul") && ENTER_UNDERLINE == NULL && UNDER_CHAR == NULL))
		must_overstrike = 1;
	initbuf();
	if (optind == argc)
		mfilter(stdin);
	else for (; optind<argc; optind++) {
		f = fopen(argv[optind],"r");
		if (f == NULL)
			err(1, "%s", argv[optind]);

		mfilter(f);
		fclose(f);
	}
	exit(0);
}

void
mfilter(FILE *f)
{
	struct CHAR	*cp;
	wint_t		 c;
	int		 skip_bs, w, wt;

	col = 1;
	skip_bs = 0;
	while (col < MAXBUF) {
		switch (c = fgetwc(f)) {
		case WEOF:
			/* Discard invalid bytes. */
			if (ferror(f)) {
				if (errno != EILSEQ)
					err(1, NULL);
				clearerr(f);
				break;
			}

			/* End of file. */
			if (maxcol)
				flushln();
			return;

		case L'\b':
			/*
			 * Back up one character position, not one
			 * display column, but ignore a second
			 * backspace after a double-width character.
			 */
			if (skip_bs > 0)
				skip_bs--;
			else if (col > 1)
				if (obuf[--col].c_width > 1)
					skip_bs = obuf[col].c_width - 1;
			continue;

		case L'\t':
			/* Calculate the target position. */
			wt = (obuf[col - 1].c_pos + 8) & ~7;

			/* Advance past known positions. */
			while ((w = obuf[col].c_pos) > 0 && w <= wt)
				col++;

			/* Advance beyond the end. */
			if (w == 0) {
				w = obuf[col - 1].c_pos;
				while (w < wt) {
					obuf[col].c_width = 1;
					obuf[col++].c_pos = ++w;
				}
			}
			if (col > maxcol)
				maxcol = col;
			break;

		case L'\r':
			col = 1;
			break;

		case SO:
			mode |= ALTSET;
			break;

		case SI:
			mode &= ~ALTSET;
			break;

		case IESC:
			switch (c = fgetwc(f)) {
			case HREV:
				if (halfpos == 0) {
					mode |= SUPERSC;
					halfpos--;
				} else if (halfpos > 0) {
					mode &= ~SUBSC;
					halfpos--;
				} else {
					halfpos = 0;
					reverse();
				}
				break;
			case HFWD:
				if (halfpos == 0) {
					mode |= SUBSC;
					halfpos++;
				} else if (halfpos < 0) {
					mode &= ~SUPERSC;
					halfpos++;
				} else {
					halfpos = 0;
					fwd();
				}
				break;
			case FREV:
				reverse();
				break;
			default:
				errx(1, "0%o: unknown escape sequence", c);
			}
			break;

		case L'_':
			if (obuf[col].c_char == L'\0') {
				obuf[col].c_char = L'_';
				obuf[col].c_width = 1;
			} else if (obuf[col].c_char == L'_') {
				if (obuf[col - 1].c_mode & UNDERL)
					obuf[col].c_mode |= UNDERL | mode;
				else if (obuf[col - 1].c_mode & BOLD)
					obuf[col].c_mode |= BOLD | mode;
				else
					obuf[col].c_mode |= INDET | mode;
			} else
				obuf[col].c_mode |= UNDERL | mode;
			/* FALLTHROUGH */

		case L' ':
			if (obuf[col].c_pos == 0) {
				obuf[col].c_width = 1;
				obuf[col].c_pos = obuf[col - 1].c_pos + 1;
			}
			col++;
			if (col > maxcol)
				maxcol = col;
			break;

		case L'\n':
			flushln();
			break;

		case L'\f':
			flushln();
			putwchar(L'\f');
			break;

		default:
			/* Discard valid, but non-printable characters. */
			if ((w = wcwidth(c)) == -1)
				break;

			if (obuf[col].c_char == L'\0') {
				obuf[col].c_char = c;
				obuf[col].c_mode = mode;
				obuf[col].c_width = w;
				obuf[col].c_pos = obuf[col - 1].c_pos + w;
			} else if (obuf[col].c_char == L'_') {
				obuf[col].c_char = c;
				obuf[col].c_mode |= UNDERL|mode;
				obuf[col].c_width = w;
				obuf[col].c_pos = obuf[col - 1].c_pos + w;
				for (cp = obuf + col; cp[1].c_pos > 0; cp++)
					cp[1].c_pos = cp[0].c_pos +
					    cp[1].c_width;
			} else if (obuf[col].c_char == c)
				obuf[col].c_mode |= BOLD|mode;
			else
				obuf[col].c_mode = mode;
			col++;
			if (col > maxcol)
				maxcol = col;
			break;
		}
		skip_bs = 0;
	}
}

void
flushln(void)
{
	int lastmode, i;
	int hadmodes = 0;

	for (i = maxcol; i > 0; i--) {
		if (obuf[i].c_mode & INDET) {
			obuf[i].c_mode &= ~INDET;
			if (i < maxcol && obuf[i + 1].c_mode & BOLD)
				obuf[i].c_mode |= BOLD;
			else
				obuf[i].c_mode |= UNDERL;
		}
	}

	lastmode = NORMAL;
	for (i = 1; i < maxcol; i++) {
		if (obuf[i].c_mode != lastmode) {
			hadmodes = 1;
			msetmode(obuf[i].c_mode);
			lastmode = obuf[i].c_mode;
		}
		if (obuf[i].c_char == L'\0') {
			if (upln)
				PRINT(CURS_RIGHT);
			else
				outc(L' ', 1);
		} else
			outc(obuf[i].c_char, obuf[i].c_width);
	}
	if (lastmode != NORMAL)
		msetmode(0);
	if (must_overstrike && hadmodes)
		overstrike();
	putwchar(L'\n');
	if (iflag && hadmodes)
		iattr();
	(void)fflush(stdout);
	if (upln)
		upln--;
	initbuf();
}

/*
 * For terminals that can overstrike, overstrike underlines and bolds.
 * We don't do anything with halfline ups and downs, or Greek.
 */
void
overstrike(void)
{
	wchar_t wc;
	int i, j, needspace;

	putwchar(L'\r');
	needspace = 0;
	for (i = 1; i < maxcol; i++) {
		if (obuf[i].c_mode != UNDERL && obuf[i].c_mode != BOLD) {
			needspace += obuf[i].c_width;
			continue;
		}
		while (needspace > 0) {
			putwchar(L' ');
			needspace--;
		}
		if (obuf[i].c_mode == BOLD)
			putwchar(obuf[i].c_char);
		else
			for (j = 0; j < obuf[i].c_width; j++)
				putwchar(L'_');
	}
}

void
iattr(void)
{
	int i, j, needspace;
	char c;

	needspace = 0;
	for (i = 1; i < maxcol; i++) {
		switch (obuf[i].c_mode) {
		case NORMAL:
			needspace += obuf[i].c_width;
			continue;
		case ALTSET:
			c = 'g';
			break;
		case SUPERSC:
			c = '^';
			break;
		case SUBSC:
			c = 'v';
			break;
		case UNDERL:
			c = '_';
			break;
		case BOLD:
			c = '!';
			break;
		default:
			c = 'X';
			break;
		}
		while (needspace > 0) {
			putwchar(L' ');
			needspace--;
		}
		for (j = 0; j < obuf[i].c_width; j++)
			putwchar(c);
	}
	putwchar(L'\n');
}

void
initbuf(void)
{
	bzero(obuf, sizeof (obuf));	/* depends on NORMAL == 0 */
	col = 1;
	maxcol = 0;
	mode &= ALTSET;
}

void
fwd(void)
{
	int oldcol, oldmax;

	oldcol = col;
	oldmax = maxcol;
	flushln();
	col = oldcol;
	maxcol = oldmax;
}

void
reverse(void)
{
	upln++;
	fwd();
	PRINT(CURS_UP);
	PRINT(CURS_UP);
	upln++;
}

void
initcap(void)
{
	static char tcapbuf[512];
	char *bp = tcapbuf;

	/* This nonsense attempts to work with both old and new termcap */
	CURS_UP =		tgetstr("up", &bp);
	CURS_RIGHT =		tgetstr("ri", &bp);
	if (CURS_RIGHT == NULL)
		CURS_RIGHT =	tgetstr("nd", &bp);
	CURS_LEFT =		tgetstr("le", &bp);
	if (CURS_LEFT == NULL)
		CURS_LEFT =	tgetstr("bc", &bp);
	if (CURS_LEFT == NULL && tgetflag("bs"))
		CURS_LEFT =	"\b";

	ENTER_STANDOUT =	tgetstr("so", &bp);
	EXIT_STANDOUT =		tgetstr("se", &bp);
	ENTER_UNDERLINE =	tgetstr("us", &bp);
	EXIT_UNDERLINE =	tgetstr("ue", &bp);
	ENTER_DIM =		tgetstr("mh", &bp);
	ENTER_BOLD =		tgetstr("md", &bp);
	ENTER_REVERSE =		tgetstr("mr", &bp);
	EXIT_ATTRIBUTES =	tgetstr("me", &bp);

	if (!ENTER_BOLD && ENTER_REVERSE)
		ENTER_BOLD = ENTER_REVERSE;
	if (!ENTER_BOLD && ENTER_STANDOUT)
		ENTER_BOLD = ENTER_STANDOUT;
	if (!ENTER_UNDERLINE && ENTER_STANDOUT) {
		ENTER_UNDERLINE = ENTER_STANDOUT;
		EXIT_UNDERLINE = EXIT_STANDOUT;
	}
	if (!ENTER_DIM && ENTER_STANDOUT)
		ENTER_DIM = ENTER_STANDOUT;
	if (!ENTER_REVERSE && ENTER_STANDOUT)
		ENTER_REVERSE = ENTER_STANDOUT;
	if (!EXIT_ATTRIBUTES && EXIT_STANDOUT)
		EXIT_ATTRIBUTES = EXIT_STANDOUT;
	
	/*
	 * Note that we use REVERSE for the alternate character set,
	 * not the as/ae capabilities.  This is because we are modelling
	 * the model 37 teletype (since that's what nroff outputs) and
	 * the typical as/ae is more of a graphics set, not the greek
	 * letters the 37 has.
	 */

	UNDER_CHAR =		tgetstr("uc", &bp);
	must_use_uc = (UNDER_CHAR && !ENTER_UNDERLINE);
}

int
outchar(int c)
{
	return (putwchar(c) != WEOF ? c : EOF);
}

static int curmode = 0;

void
outc(wchar_t c, int width)
{
	int i;

	putwchar(c);
	if (must_use_uc && (curmode&UNDERL)) {
		for (i = 0; i < width; i++)
			PRINT(CURS_LEFT);
		for (i = 0; i < width; i++)
			PRINT(UNDER_CHAR);
	}
}

void
msetmode(int newmode)
{
	if (!iflag) {
		if (curmode != NORMAL && newmode != NORMAL)
			msetmode(NORMAL);
		switch (newmode) {
		case NORMAL:
			switch(curmode) {
			case NORMAL:
				break;
			case UNDERL:
				PRINT(EXIT_UNDERLINE);
				break;
			default:
				/* This includes standout */
				PRINT(EXIT_ATTRIBUTES);
				break;
			}
			break;
		case ALTSET:
			PRINT(ENTER_REVERSE);
			break;
		case SUPERSC:
			/*
			 * This only works on a few terminals.
			 * It should be fixed.
			 */
			PRINT(ENTER_UNDERLINE);
			PRINT(ENTER_DIM);
			break;
		case SUBSC:
			PRINT(ENTER_DIM);
			break;
		case UNDERL:
			PRINT(ENTER_UNDERLINE);
			break;
		case BOLD:
			PRINT(ENTER_BOLD);
			break;
		default:
			/*
			 * We should have some provision here for multiple modes
			 * on at once.  This will have to come later.
			 */
			PRINT(ENTER_STANDOUT);
			break;
		}
	}
	curmode = newmode;
}