/*
 * p2d_hsort.c - Hierarchical polygon sort
 *
 * Written 2012 by Werner Almesberger
 * Copyright 2012 Werner Almesberger
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 */


#include "util.h"
#include "poly2d.h"
#include "p2d_hsort.h"


static struct p2d_hier *recurse_hsort(struct p2d *p)
{
	struct p2d *sub = NULL, *sub2 = NULL, **last = ⊂
	struct p2d **a, *b, **next;
	struct p2d_hier *res = NULL, *t;
	struct p2d **res_last = (struct p2d **) &res;

	/*
	 * Move all polygons that are inside some other polygon to "sub".
	 */
	for (a = &p; *a; a = next) {
		next = &(*a)->next;
		for (b = p; b; b = b->next)
			if (*a != b && p2d_contains_poly(b, *a)) {
				*last = *a;
				last = &(*last)->next;
				*a = *next;
				next = a;
				*last = NULL;
				break;
			}
	}

	while (p) {
		/*
		 * Begin transplanting "p" into t->p.
		 */
		t = alloc_type(struct p2d_hier);
		t->p = *p;

		/*
		 * Move all polygons inside the current one from "sub" to
		 * "sub2". (Direct and indirect subordinates.)
		 */
		sub2 = NULL;
		last = &sub2;
		for (a = ⊂ *a; a = next) {
			next = &(*a)->next;
			if (p2d_contains_poly(p, *a)) {
				*last = *a;
				last = &(*last)->next;
				*a = *next;
				next = a;
				*last = NULL;
			}
		}

		/*
		 * Sort the subordinates.
		 */
		t->holes = recurse_hsort(sub2);

		/*
		 * End transplanting "p" into t->p.
		 */
		free(p);
		p = t->p.next;

		/*
		 * Append "t" to "res".
		 */
		*res_last = &t->p;
		res_last = &t->p.next;
		t->p.next = NULL;

	}
	return res;
}


struct p2d_hier *p2d_hsort(const struct p2d *p)
{
	return recurse_hsort(p2d_copy_all(p));
}


void p2d_hier_free(struct p2d_hier *t)
{
	struct p2d_hier *next;
	struct p2d *p;

	while (t) {
		p2d_hier_free(t->holes);
		p = &t->p;
		next = p2d_to_hier(p->next);
		p2d_free(p);
		t = next;
	}
}