/*
 * Copyright (c) 2021 joshua stein <jcs@jcs.org>
 *
 * 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 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.
 */

/*
 * Implements tab spacing in TextEdit controls with a fixed-width font.
 * Only works on styled TextEdit controls (created with TEStylNew) and
 * assumes that functions get called with a text buffer that starts at the
 * beginning of the line.
 *  
 * Usage is per-TextEdit control, so these hooks need to be established
 * on all controls where tabs should be expanded:
 *
 * 	TEHandle te;
 * 	ProcPtr teproc;
 *
 *  [..]
 * 	te = TEStylNew(&bounds, &bounds);
 * 	TEAutoView(true, te);
 * 	TETabEnable(te);
 *
 * The tab width is set to 4 by default in the TETabWidth global.
 *
 * Thanks to Ari Halberstadt for their 1989 Usenet post on
 * comp.sys.mac.programmer with HitTestHook assembly.
 */

#include <Script.h>
#include <SetUpA4.h>

#include "tetab.h"

pascal void TETabDrawHook(void);
pascal void TETabWidthHook(void);
pascal void TETabHitTestHook(void);

short TETabWidth = 4;

void
TETabEnable(TEHandle te)
{
	ProcPtr teproc;

	TEAutoView(true, te);
	teproc = StripAddress(TETabWidthHook);
	TECustomHook(intWidthHook, &teproc, te);
	teproc = StripAddress(TETabDrawHook);
	TECustomHook(intDrawHook, &teproc, te);
	teproc = StripAddress(TETabHitTestHook);
	TECustomHook(intHitTestHook, &teproc, te);
}

pascal void
TETabDrawHook(void)
{
	/* entry registers, in order */
	short offset;
	short length;
	Ptr text;
	
	/* locals */
	short i, cwidth, cpos, space, startdraw;
	char c;
	
	asm {
		movem.l	d3-d7/a0-a3, -(a7)
		move.w	d0, offset
		move.w	d1, length
		move.l	a0, text
	}
	SetUpA4();
	
	cwidth = CharWidth(' ');
	
	/*
	 * This startdraw stuff is to try to draw long blocks of non-tab text
	 * with one call to DrawText() instead of DrawChar()ing every character
	 * one at a time, for speed.
	 */
	for (i = 0, cpos = 0, startdraw = 0; i < length; i++) {
		c = text[offset + i];
		
		if (c == '\t') {
			if (i - startdraw)
				DrawText(text, startdraw, i - startdraw);
			
			space = (TETabWidth - (cpos % TETabWidth));
			if (!space)
				space = TETabWidth;
			cpos += space;
			Move(cwidth * space, 0);
			startdraw = i + 1;
		} else {
			cpos++;
		}
	}
	
	if (startdraw != i)
		DrawText(text, startdraw, i - startdraw);
	
	/* return nothing */
	
	/* restore registers */
	RestoreA4();
	asm {
		movem.l	(a7)+, d3-d7/a0-a3
	}
}

pascal void
TETabWidthHook(void)
{
	/* entry registers, in order */
	short length;
	short offset;
	Ptr text;
	
	/* exit */
	short width;
	
	short i, cwidth, cpos, space;
	char c;
	
	asm {
		movem.l	d3-d7/a0-a3, -(a7)
		move.w	d0, length
		move.w	d1, offset
		move.l	a0, text
	}
	SetUpA4();

	cwidth = CharWidth(' ');
	
	for (i = 0, cpos = 0; i < length; i++) {
		c = text[offset + i];
		
		if (c == '\t') {
			space = (TETabWidth - (cpos % TETabWidth));
			if (!space)
				space = TETabWidth;
			cpos += space;
		} else {
			cpos++;
		}
	}
	
	width = cwidth * cpos;

	/* return length */
	asm {
		move.w	width, d1
	}

	/* restore registers */
	RestoreA4();
	asm {
		movem.l	(a7)+, d3-d7/a0-a3
	}
}

pascal void
TETabHitTestHook(void)
{
	/* entry registers, in order */
	short length;
	short poffset;
	Ptr text;
	
	/* exit */
	short width;
	short offset = 0;
	short leftside = 0;
	 
	/* locals */
	short i, cwidth, cpos, wpos, space, found;
	char c;
	
	asm {
		movem.l	d3-d7/a0-a3, -(a7)
		move.w	d0, length
		move.w	d1, poffset
		move.l	a0, text
	}
	SetUpA4();

	cwidth = CharWidth(' ');
	
	for (i = 0, wpos = 0, cpos = 0, found = 0; i < length; i++) {
		c = text[i];
		
		if (c == '\t') {
			space = (TETabWidth - (wpos % TETabWidth));
			if (!space)
				space = TETabWidth;
			wpos += space;
		} else if (c == '\r')
			break;
		else
			wpos++;
		
		cpos++;
		
		if (poffset <= (wpos * cwidth)) {
			found = 1;
			cpos++;
			break;
		}
	}
	
	/* put found in hi word */
	width = (wpos * cwidth) | (found << 8);
	offset = cpos;
	leftside = (poffset < (width - (cwidth / 2)));

	asm {
		move.w	width, d0
		move.w	offset, d1
		move.w	leftside, d2
	}

	/* restore registers */
	RestoreA4();
	asm {
		movem.l	(a7)+, d3-d7/a0-a3
	}
}