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Remember the number of lines scrolled into the history (versus cleared
into the history) and when resizing only use scrolled lines and not
cleared lines (which are probably not intended to reappear). From
Chaoren Lin.

/* $OpenBSD: screen.c,v 1.40 2016/09/02 20:57:20 nicm Exp $ */

/*
 * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.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 <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "tmux.h"

void	screen_resize_x(struct screen *, u_int);
void	screen_resize_y(struct screen *, u_int);

/* Create a new screen. */
void
screen_init(struct screen *s, u_int sx, u_int sy, u_int hlimit)
{
	s->grid = grid_create(sx, sy, hlimit);
	s->title = xstrdup("");

	s->cstyle = 0;
	s->ccolour = xstrdup("");
	s->tabs = NULL;

	s->dirty = NULL;
	s->dirtysize = 0;

	screen_reinit(s);
}

/* Reinitialise screen. */
void
screen_reinit(struct screen *s)
{
	s->cx = 0;
	s->cy = 0;

	s->rupper = 0;
	s->rlower = screen_size_y(s) - 1;

	s->mode = MODE_CURSOR | MODE_WRAP;

	screen_reset_tabs(s);

	grid_clear_lines(s->grid, s->grid->hsize, s->grid->sy);

	screen_clear_selection(s);
}

/* Destroy a screen. */
void
screen_free(struct screen *s)
{
	free(s->dirty);
	free(s->tabs);
	free(s->title);
	free(s->ccolour);
	grid_destroy(s->grid);
}

/* Reset tabs to default, eight spaces apart. */
void
screen_reset_tabs(struct screen *s)
{
	u_int	i;

	free(s->tabs);

	if ((s->tabs = bit_alloc(screen_size_x(s))) == NULL)
		fatal("bit_alloc failed");
	for (i = 8; i < screen_size_x(s); i += 8)
		bit_set(s->tabs, i);
}

/* Set screen cursor style. */
void
screen_set_cursor_style(struct screen *s, u_int style)
{
	if (style <= 6)
		s->cstyle = style;
}

/* Set screen cursor colour. */
void
screen_set_cursor_colour(struct screen *s, const char *colour)
{
	free(s->ccolour);
	s->ccolour = xstrdup(colour);
}

/* Set screen title. */
void
screen_set_title(struct screen *s, const char *title)
{
	free(s->title);
	s->title = xstrdup(title);
}

/* Resize screen. */
void
screen_resize(struct screen *s, u_int sx, u_int sy, int reflow)
{
	if (sx < 1)
		sx = 1;
	if (sy < 1)
		sy = 1;

	if (sx != screen_size_x(s)) {
		screen_resize_x(s, sx);

		/*
		 * It is unclear what should happen to tabs on resize. xterm
		 * seems to try and maintain them, rxvt resets them. Resetting
		 * is simpler and more reliable so let's do that.
		 */
		screen_reset_tabs(s);
	}

	if (sy != screen_size_y(s))
		screen_resize_y(s, sy);

	if (reflow)
		screen_reflow(s, sx);
}

void
screen_resize_x(struct screen *s, u_int sx)
{
	struct grid		*gd = s->grid;

	if (sx == 0)
		fatalx("zero size");

	/*
	 * Treat resizing horizontally simply: just ensure the cursor is
	 * on-screen and change the size. Don't bother to truncate any lines -
	 * then the data should be accessible if the size is then increased.
	 *
	 * The only potential wrinkle is if UTF-8 double-width characters are
	 * left in the last column, but UTF-8 terminals should deal with this
	 * sanely.
	 */
	if (s->cx >= sx)
		s->cx = sx - 1;
	gd->sx = sx;
}

void
screen_resize_y(struct screen *s, u_int sy)
{
	struct grid	*gd = s->grid;
	u_int		 needed, available, oldy, i;

	if (sy == 0)
		fatalx("zero size");
	oldy = screen_size_y(s);

	/*
	 * When resizing:
	 *
	 * If the height is decreasing, delete lines from the bottom until
	 * hitting the cursor, then push lines from the top into the history.
	 *
	 * When increasing, pull as many lines as possible from scrolled
	 * history (not explicitly cleared from view) to the top, then fill the
	 * remaining with blanks at the bottom.
	 */

	/* Size decreasing. */
	if (sy < oldy) {
		needed = oldy - sy;

		/* Delete as many lines as possible from the bottom. */
		available = oldy - 1 - s->cy;
		if (available > 0) {
			if (available > needed)
				available = needed;
			grid_view_delete_lines(gd, oldy - available, available);
		}
		needed -= available;

		/*
		 * Now just increase the history size, if possible, to take
		 * over the lines which are left. If history is off, delete
		 * lines from the top.
		 */
		available = s->cy;
		if (gd->flags & GRID_HISTORY) {
			gd->hscrolled += needed;
			gd->hsize += needed;
		} else if (needed > 0 && available > 0) {
			if (available > needed)
				available = needed;
			grid_view_delete_lines(gd, 0, available);
		}
		s->cy -= needed;
	}

	/* Resize line arrays. */
	gd->linedata = xreallocarray(gd->linedata, gd->hsize + sy,
	    sizeof *gd->linedata);

	/* Size increasing. */
	if (sy > oldy) {
		needed = sy - oldy;

		/*
		 * Try to pull as much as possible out of scrolled history, if is
		 * is enabled.
		 */
		available = gd->hscrolled;
		if (gd->flags & GRID_HISTORY && available > 0) {
			if (available > needed)
				available = needed;
			gd->hscrolled -= available;
			gd->hsize -= available;
			s->cy += available;
		} else
			available = 0;
		needed -= available;

		/* Then fill the rest in with blanks. */
		for (i = gd->hsize + sy - needed; i < gd->hsize + sy; i++)
			memset(&gd->linedata[i], 0, sizeof gd->linedata[i]);
	}

	/* Set the new size, and reset the scroll region. */
	gd->sy = sy;
	s->rupper = 0;
	s->rlower = screen_size_y(s) - 1;
}

/* Set selection. */
void
screen_set_selection(struct screen *s, u_int sx, u_int sy,
    u_int ex, u_int ey, u_int rectflag, struct grid_cell *gc)
{
	struct screen_sel	*sel = &s->sel;

	memcpy(&sel->cell, gc, sizeof sel->cell);
	sel->flag = 1;
	sel->rectflag = rectflag;

	sel->sx = sx; sel->sy = sy;
	sel->ex = ex; sel->ey = ey;
}

/* Clear selection. */
void
screen_clear_selection(struct screen *s)
{
	struct screen_sel	*sel = &s->sel;

	sel->flag = 0;
	sel->lineflag = LINE_SEL_NONE;
}

/* Check if cell in selection. */
int
screen_check_selection(struct screen *s, u_int px, u_int py)
{
	struct screen_sel	*sel = &s->sel;
	u_int			 xx;

	if (!sel->flag)
		return (0);

	if (sel->rectflag) {
		if (sel->sy < sel->ey) {
			/* start line < end line -- downward selection. */
			if (py < sel->sy || py > sel->ey)
				return (0);
		} else if (sel->sy > sel->ey) {
			/* start line > end line -- upward selection. */
			if (py > sel->sy || py < sel->ey)
				return (0);
		} else {
			/* starting line == ending line. */
			if (py != sel->sy)
				return (0);
		}

		/*
		 * Need to include the selection start row, but not the cursor
		 * row, which means the selection changes depending on which
		 * one is on the left.
		 */
		if (sel->ex < sel->sx) {
			/* Cursor (ex) is on the left. */
			if (px < sel->ex)
				return (0);

			if (px > sel->sx)
				return (0);
		} else {
			/* Selection start (sx) is on the left. */
			if (px < sel->sx)
				return (0);

			if (px > sel->ex)
				return (0);
		}
	} else {
		/*
		 * Like emacs, keep the top-left-most character, and drop the
		 * bottom-right-most, regardless of copy direction.
		 */
		if (sel->sy < sel->ey) {
			/* starting line < ending line -- downward selection. */
			if (py < sel->sy || py > sel->ey)
				return (0);

			if (py == sel->sy && px < sel->sx)
				return (0);

			if (py == sel->ey && px > sel->ex)
				return (0);
		} else if (sel->sy > sel->ey) {
			/* starting line > ending line -- upward selection. */
			if (py > sel->sy || py < sel->ey)
				return (0);

			if (py == sel->ey && px < sel->ex)
				return (0);

			if (sel->modekeys == MODEKEY_EMACS)
				xx = sel->sx - 1;
			else
				xx = sel->sx;
			if (py == sel->sy && px > xx)
				return (0);
		} else {
			/* starting line == ending line. */
			if (py != sel->sy)
				return (0);

			if (sel->ex < sel->sx) {
				/* cursor (ex) is on the left */
				if (sel->modekeys == MODEKEY_EMACS)
					xx = sel->sx - 1;
				else
					xx = sel->sx;
				if (px > xx || px < sel->ex)
					return (0);
			} else {
				/* selection start (sx) is on the left */
				if (px < sel->sx || px > sel->ex)
					return (0);
			}
		}
	}

	return (1);
}

/* Reflow wrapped lines. */
void
screen_reflow(struct screen *s, u_int new_x)
{
	struct grid	*old = s->grid;
	u_int		 change;

	s->grid = grid_create(old->sx, old->sy, old->hlimit);

	change = grid_reflow(s->grid, old, new_x);
	if (change < s->cy)
		s->cy -= change;
	else
		s->cy = 0;
}