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Enable dirty buffer detection in mg.
Emulate the emacs behavior: after suspend/resume, buffer switch,
or at save time, warn (prompt) the user if the file has been modified
on disk in the interim.
This has already saved my butt numerous times.
ok phessler

/*	$OpenBSD: tty.c,v 1.30 2008/09/15 16:11:35 kjell Exp $	*/

/* This file is in the public domain. */

/*
 * Terminfo display driver
 *
 * Terminfo is a terminal information database and routines to describe
 * terminals on most modern UNIX systems.  Many other systems have adopted
 * this as a reasonable way to allow for widely varying and ever changing
 * varieties of terminal types.	 This should be used where practical.
 */
/*
 * Known problems: If you have a terminal with no clear to end of screen and
 * memory of lines below the ones visible on the screen, display will be
 * wrong in some cases.  I doubt that any such terminal was ever made, but I
 * thought everyone with delete line would have clear to end of screen too...
 *
 * Code for terminals without clear to end of screen and/or clear to end of line
 * has not been extensively tested.
 *
 * Cost calculations are very rough.  Costs of insert/delete line may be far
 * from the truth.  This is accentuated by display.c not knowing about
 * multi-line insert/delete.
 *
 * Using scrolling region vs insert/delete line should probably be based on cost
 * rather than the assumption that scrolling region operations look better.
 */

#include "def.h"

#include <sys/types.h>
#include <sys/time.h>
#include <sys/ioctl.h>

#include <term.h>

static int	 charcost(char *);

static int	 cci;
static int	 insdel;	/* Do we have both insert & delete line? */
static char	*scroll_fwd;	/* How to scroll forward. */

static void	 winchhandler(int);

/* ARGSUSED */
static void
winchhandler(int sig)
{
	winch_flag = 1;
}

/*
 * Initialize the terminal when the editor
 * gets started up.
 */
void
ttinit(void)
{
	int errret;

	if (setupterm(NULL, 1, &errret))
		panic("Terminal setup failed");

	signal(SIGWINCH, winchhandler);
	signal(SIGCONT, winchhandler);
	siginterrupt(SIGWINCH, 1);

	scroll_fwd = scroll_forward;
	if (scroll_fwd == NULL || *scroll_fwd == '\0') {
		/* this is what GNU Emacs does */
		scroll_fwd = parm_down_cursor;
		if (scroll_fwd == NULL || *scroll_fwd == '\0')
			scroll_fwd = "\n";
	}

	if (cursor_address == NULL || cursor_up == NULL)
		panic("This terminal is too stupid to run mg");

	/* set nrow & ncol */
	ttresize();

	if (!clr_eol)
		tceeol = ncol;
	else
		tceeol = charcost(clr_eol);

	/* Estimate cost of inserting a line */
	if (change_scroll_region && scroll_reverse)
		tcinsl = charcost(change_scroll_region) * 2 +
		    charcost(scroll_reverse);
	else if (parm_insert_line)
		tcinsl = charcost(parm_insert_line);
	else if (insert_line)
		tcinsl = charcost(insert_line);
	else
		/* make this cost high enough */
		tcinsl = nrow * ncol;

	/* Estimate cost of deleting a line */
	if (change_scroll_region)
		tcdell = charcost(change_scroll_region) * 2 +
		    charcost(scroll_fwd);
	else if (parm_delete_line)
		tcdell = charcost(parm_delete_line);
	else if (delete_line)
		tcdell = charcost(delete_line);
	else
		/* make this cost high enough */
		tcdell = nrow * ncol;

	/* Flag to indicate that we can both insert and delete lines */
	insdel = (insert_line || parm_insert_line) &&
	    (delete_line || parm_delete_line);

	if (enter_ca_mode)
		/* enter application mode */
		putpad(enter_ca_mode, 1);

	ttresize();
}

/*
 * Re-initialize the terminal when the editor is resumed.
 * The keypad_xmit doesn't really belong here but...
 */
void
ttreinit(void)
{
	/* check if file was modified while we were gone */
	if (fchecktime(curbp) != TRUE) {
		curbp->b_flag |= BFDIRTY;
	}

	if (enter_ca_mode)
		/* enter application mode */
		putpad(enter_ca_mode, 1);

	if (keypad_xmit)
		/* turn on keypad */
		putpad(keypad_xmit, 1);

	ttresize();
}

/*
 * Clean up the terminal, in anticipation of a return to the command
 * interpreter. This is a no-op on the ANSI display. On the SCALD display,
 * it sets the window back to half screen scrolling. Perhaps it should
 * query the display for the increment, and put it back to what it was.
 */
void
tttidy(void)
{
#ifdef	XKEYS
	ttykeymaptidy();
#endif /* XKEYS */

	/* set the term back to normal mode */
	if (exit_ca_mode)
		putpad(exit_ca_mode, 1);
}

/*
 * Move the cursor to the specified origin 0 row and column position. Try to
 * optimize out extra moves; redisplay may have left the cursor in the right
 * location last time!
 */
void
ttmove(int row, int col)
{
	if (ttrow != row || ttcol != col) {
		putpad(tgoto(cursor_address, col, row), 1);
		ttrow = row;
		ttcol = col;
	}
}

/*
 * Erase to end of line.
 */
void
tteeol(void)
{
	int	i;

	if (clr_eol)
		putpad(clr_eol, 1);
	else {
		i = ncol - ttcol;
		while (i--)
			ttputc(' ');
		ttrow = ttcol = HUGE;
	}
}

/*
 * Erase to end of page.
 */
void
tteeop(void)
{
	int	line;

	if (clr_eos)
		putpad(clr_eos, nrow - ttrow);
	else {
		putpad(clr_eol, 1);
		if (insdel)
			ttdell(ttrow + 1, lines, lines - ttrow - 1);
		else {
			/* do it by hand */
			for (line = ttrow + 1; line <= lines; ++line) {
				ttmove(line, 0);
				tteeol();
			}
		}
		ttrow = ttcol = HUGE;
	}
}

/*
 * Make a noise.
 */
void
ttbeep(void)
{
	putpad(bell, 1);
	ttflush();
}

/*
 * Insert nchunk blank line(s) onto the screen, scrolling the last line on
 * the screen off the bottom.  Use the scrolling region if possible for a
 * smoother display.  If there is no scrolling region, use a set of insert
 * and delete line sequences.
 */
void
ttinsl(int row, int bot, int nchunk)
{
	int	i, nl;

	/* Case of one line insert is special. */
	if (row == bot) {
		ttmove(row, 0);
		tteeol();
		return;
	}
	if (change_scroll_region && scroll_reverse) {
		/* Use scroll region and back index	 */
		nl = bot - row;
		ttwindow(row, bot);
		ttmove(row, 0);
		while (nchunk--)
			putpad(scroll_reverse, nl);
		ttnowindow();
		return;
	} else if (insdel) {
		ttmove(1 + bot - nchunk, 0);
		nl = nrow - ttrow;
		if (parm_delete_line)
			putpad(tgoto(parm_delete_line, 0, nchunk), nl);
		else
			/* For all lines in the chunk... */
			for (i = 0; i < nchunk; i++)
				putpad(delete_line, nl);
		ttmove(row, 0);

		/* ttmove() changes ttrow */
		nl = nrow - ttrow;

		if (parm_insert_line)
			putpad(tgoto(parm_insert_line, 0, nchunk), nl);
		else
			/* For all lines in the chunk */
			for (i = 0; i < nchunk; i++)
				putpad(insert_line, nl);
		ttrow = HUGE;
		ttcol = HUGE;
	} else
		panic("ttinsl: Can't insert/delete line");
}

/*
 * Delete nchunk line(s) from "row", replacing the bottom line on the
 * screen with a blank line.  Unless we're using the scrolling region,
 * this is done with crafty sequences of insert and delete lines.  The
 * presence of the echo area makes a boundary condition go away.
 */
void
ttdell(int row, int bot, int nchunk)
{
	int	i, nl;

	/* One line special cases */
	if (row == bot) {
		ttmove(row, 0);
		tteeol();
		return;
	}
	/* scrolling region */
	if (change_scroll_region) {
		nl = bot - row;
		ttwindow(row, bot);
		ttmove(bot, 0);
		while (nchunk--)
			putpad(scroll_fwd, nl);
		ttnowindow();
	/* else use insert/delete line */
	} else if (insdel) {
		ttmove(row, 0);
		nl = nrow - ttrow;
		if (parm_delete_line)
			putpad(tgoto(parm_delete_line, 0, nchunk), nl);
		else
			/* For all lines in the chunk	 */
			for (i = 0; i < nchunk; i++)
				putpad(delete_line, nl);
		ttmove(1 + bot - nchunk, 0);

		/* ttmove() changes ttrow */
		nl = nrow - ttrow;
		if (parm_insert_line)
			putpad(tgoto(parm_insert_line, 0, nchunk), nl);
		else
			/* For all lines in the chunk */
			for (i = 0; i < nchunk; i++)
				putpad(insert_line, nl);
		ttrow = HUGE;
		ttcol = HUGE;
	} else
		panic("ttdell: Can't insert/delete line");
}

/*
 * This routine sets the scrolling window on the display to go from line
 * "top" to line "bot" (origin 0, inclusive).  The caller checks for the
 * pathological 1-line scroll window which doesn't work right and avoids
 * it.  The "ttrow" and "ttcol" variables are set to a crazy value to
 * ensure that the next call to "ttmove" does not turn into a no-op (the
 * window adjustment moves the cursor).
 */
void
ttwindow(int top, int bot)
{
	if (change_scroll_region && (tttop != top || ttbot != bot)) {
		putpad(tgoto(change_scroll_region, bot, top), nrow - ttrow);
		ttrow = HUGE;	/* Unknown.		 */
		ttcol = HUGE;
		tttop = top;	/* Remember region.	 */
		ttbot = bot;
	}
}

/*
 * Switch to full screen scroll. This is used by "spawn.c" just before it
 * suspends the editor and by "display.c" when it is getting ready to
 * exit.  This function does a full screen scroll by telling the terminal
 * to set a scrolling region that is lines or nrow rows high, whichever is
 * larger.  This behavior seems to work right on systems where you can set
 * your terminal size.
 */
void
ttnowindow(void)
{
	if (change_scroll_region) {
		putpad(tgoto(change_scroll_region,
		    (nrow > lines ? nrow : lines) - 1, 0), nrow - ttrow);
		ttrow = HUGE;	/* Unknown.		 */
		ttcol = HUGE;
		tttop = HUGE;	/* No scroll region.	 */
		ttbot = HUGE;
	}
}

/*
 * Set the current writing color to the specified color. Watch for color
 * changes that are not going to do anything (the color is already right)
 * and don't send anything to the display.  The rainbow version does this
 * in putline.s on a line by line basis, so don't bother sending out the
 * color shift.
 */
void
ttcolor(int color)
{
	if (color != tthue) {
		if (color == CTEXT)
			/* normal video */
			putpad(exit_standout_mode, 1);
		else if (color == CMODE)
			/* reverse video */
			putpad(enter_standout_mode, 1);
		/* save the color */
		tthue = color;
	}
}

/*
 * This routine is called by the "refresh the screen" command to try
 * to resize the display. Look in "window.c" to see how
 * the caller deals with a change.
 *
 * We use `newrow' and `newcol' so vtresize() know the difference between the
 * new and old settings.
 */
void
ttresize(void)
{
	int newrow = 0, newcol = 0;

#ifdef	TIOCGWINSZ
	struct	winsize winsize;

	if (ioctl(0, TIOCGWINSZ, &winsize) == 0) {
		newrow = winsize.ws_row;
		newcol = winsize.ws_col;
	}
#endif
	if ((newrow <= 0 || newcol <= 0) &&
	    ((newrow = lines) <= 0 || (newcol = columns) <= 0)) {
		newrow = 24;
		newcol = 80;
	}
	if (vtresize(1, newrow, newcol) != TRUE)
		panic("vtresize failed");
}

/*
 * fake char output for charcost()
 */
/* ARGSUSED */
static int
fakec(int c)
{
	cci++;
	return (0);
}

/* calculate the cost of doing string s */
static int
charcost(char *s)
{
	cci = 0;

	tputs(s, nrow, fakec);
	return (cci);
}