/*
 * display -- a simple program to display static text in a more(1)-like
 * manner.  Designed to run with simple BIOS services on a i*86-PC.
 *
 * Purpose of the program: provide a simple method for pcemu to display
 * a text when there is no DOS boot image installed.  This program will
 * run as the bootfile then.
 *
 * Author: Joerg Wunsch, 95/03/10
 * Placed in the public domain.  Neither kind of warranty applies.
 *
 * Thanks to Bruce Evans for his bcc compiler.  Made my work much
 * easier.
 */

#define MAXROW 23
#define MAXCOL 79
#asm
maxrow:	set 23
maxcol:	set 79
nl:	set 10
#endasm

#define WHITE	7
#define BROWN	6
#define MAGENTA	5
#define RED	4
#define CYAN	3
#define GREEN	2
#define BLUE	1
#define BLACK	0
#define HIGH	8
/* convenience: */
#define	YELLOW	(BROWN|HIGH)	/* foreground color */
#define	GRAY	WHITE		/* background color */

#define NOCHANGE (-1)		/* do not change color; for setattrib() */

/*
 * We use a special highlighting scheme: embedded control characters
 * in the text toggle the attribute selection.
 *
 * Define attributes used for highlighting.
 * NB: do not parenthise the macro expansions below, they are used as
 * complete parameter lists for setattrib()!
 */

#define REGULAR	BLACK, GRAY		/* ^R */
#define	BOLD	WHITE|HIGH, RED|HIGH	/* ^B */
#define	EMPHS	BLUE, GRAY		/* ^E */
#define	DOUBLE	YELLOW, BLACK		/* ^D */

#define	C_REGULAR	('R' & 0x1f)
#define	C_BOLD		('B' & 0x1f)
#define	C_EMPHS		('E' & 0x1f)
#define	C_DOUBLE	('D' & 0x1f)

#define	K_CUP	((0x48 << 8) + 0) /* extended ASCII, cursor up */
#define	K_CDN	((0x50 << 8) + 0) /* extended ASCII, cursor down */
#define	K_PREV	((0x49 << 8) + 0) /* extended ASCII, page up */
#define	K_NEXT	((0x51 << 8) + 0) /* extended ASCII, page down */

/*
 * Glue to link to the BIOS services.
 */

char attrib;
char row, col;


void scroll(nlines)
int nlines;			/* if nlines == 0, clear entire region */
{
#asm
	push	bp
	mov	bp, sp

	xor	bh, bh		; page 0
	mov	dx, *(maxcol + (maxrow << 8)); bottom/right corner
	xor	cx, cx		; top/left corner
	mov	al, 4[bp]	; nlines
	mov	bh, _attrib
	mov	ah, *6		; video bios, scroll (clear) region
	test	al, al		; scroll back?
	jns	_scroll.1	; positive value -> forward
	inc	ah		; scroll backwards
	neg	al
_scroll.1:
	int	0x10

	pop	bp
#endasm
}

void gotoxy(x, y)
int x;
int y;
{
#asm
	push	bp
	mov	bp, sp

	mov	dl, 4[bp]	; x
	mov	_col, dl
	mov	dh, 6[bp]	; y
	mov	_row, dh
	xor	bh, bh		; page 0
	mov	ah, *2		; video bios, set cursor
	int	0x10

	pop	bp
#endasm
}

void putchar(c)
int c;
{
#asm
	push	bp
	mov	bp, sp

	mov	al, 4[bp]	; c
	mov	bl, _attrib
	xor	bh, bh		; always page 0
	mov	cx, *1		; just one char
	mov	ah, *9		; video bios, write char
	int	0x10

	pop	bp
#endasm
	if(col < MAXCOL)
	  gotoxy(col + 1, row);
}


void cls()
{
  scroll(0);
}


int getchar()
{
#asm
	xor	ah, ah		; kbd bios, get keystroke
	int	0x16
#endasm
}

void setattrib(foreground, background)
int foreground;
int background;
{
  int i;
  if(foreground == -1)
    i = attrib & 0xf;
  else
    i = foreground & 0xf;
  if(background == -1)
    i |= (attrib & 0xf0);
  else
    i |= ((background & 0xf) << 4);
  attrib = i;
}


/*
 * Some auxiliary functions
 */

/*
 * print one line of text up to a newline or a null character
 */

char *printline(s)
char *s;
{
  register char c;

  while((c = *s++) && c != '\n')
    switch(c)
      {
      case C_REGULAR:
	setattrib(REGULAR);
	break;

      case C_BOLD:
	setattrib(BOLD);
	break;

      case C_EMPHS:
	setattrib(EMPHS);
	break;

      case C_DOUBLE:
	setattrib(DOUBLE);
	break;
	
      default:
	putchar(c);
      }
	
  if(c == 0) s--;
  return s;
}


/*
 * display a message on the bottom line; if msg == 0, clear bottom line
 */

void more(msg)
char *msg;
{
  int i;
  
  gotoxy(0, MAXROW + 1);
  if(msg) {
    setattrib(YELLOW, BLUE);
    (void)printline(msg);
    setattrib(REGULAR);
  } else {
    setattrib(WHITE, BLACK);
    for(i = 0; i < MAXCOL; i++) putchar(' ');
    setattrib(REGULAR);
  }
}


/*
 * go back for numlines newline chars, starting at current, but not before
 * initial
 */

char *goback(initial, current, numlines)
char *initial;
char *current;
int numlines;
{
  current--;
  
  while(numlines && current > initial)
    if(*--current == '\n')
      numlines--;
  if(*current == '\n')
    current++;
  return current;
}


/*
 * the static text is maintained separately in an (automatically generated)
 * .S file
 */

extern char textstr[];		/* do not declare this "char *" - bcc breaks */


int main()
{
  char *cp, *cp1;
  int c;
  int lineno;
  
  lineno = 0;
  cp = textstr;
  setattrib(REGULAR);
  cls();
  for(;;) {
    gotoxy(0, lineno);
    cp = printline(cp);
    if(*cp == 0) break;
    lineno++;
    if(lineno == MAXROW + 1) {
      for(;;) {
	more("--More--");
	c = getchar();
	more(0);

	if(c & 0xff)		/* regular ASCII */
	  c &= 0xff;		/* strip scancode */
				
	switch(c) {
	case ' ':		/* page forward */
	case K_NEXT:
	  lineno = 0;	
	  cls();
	  goto out;
					
	case 'd':		/* half page forward */
	  scroll((MAXROW + 1) / 2);
	  lineno -= (MAXROW + 1) / 2;
	  goto out;

	case 'b':		/* page backward */
	case K_PREV:
	  cp = goback(textstr, cp, 2 * (MAXROW + 1));
	  lineno = 0;
	  cls();
	  goto out;

	case '\r':		/* one more line */
	case '\n':
	case K_CDN:
	  lineno--;
	  scroll(1);
	  goto out;
	  
	case K_CUP:		/* one line less */
	  cp1 = goback(textstr, cp, 2);
	  cp = goback(textstr, cp1, MAXROW);
	  if(cp == textstr)	/* start of text, redisplay all */
	    {
	      lineno = 0;
	      cls();
	    }
	  else
	    {
	      scroll(-1);
	      gotoxy(0, 0);
	      (void)printline(cp);
	      cp = cp1;
	      lineno--;
	    }
	  goto out;

	case '?':
	case 'h':
	  more(
"space: next page, d: half page, b: back page, CR, DWN: nxt line, UP: prv line"
	      );
	  (void)getchar();
	  more(0);
	  break;

	case 'q':		/* quit the game */
	  goto done;
	}
      }
    }
    out:;
  }
  done:
  more("Hit any key to quit.");
  (void)getchar();
  more(0);
  
  return 0;
}