#include "postgres.h"
#include "utils/geo_decls.h"

static void
make_bound_box(POLYGON *poly)
{
	int			i;
	double		min_x, min_y;
	double		max_x, max_y;
	
	min_x = max_x = poly->p[0].x;
	min_y = max_y = poly->p[0].y;
	
	for (i = 1; i < poly->npts; i++)
	{
		if (poly->p[i].x < min_x)
			min_x = poly->p[i].x;
		if (poly->p[i].y < min_y)
			min_y = poly->p[i].y;

		if (poly->p[i].x > max_x)
			max_x = poly->p[i].x;
		if (poly->p[i].y > max_y)
			max_y = poly->p[i].y;
	}

	poly->boundbox.low.x = min_x;
	poly->boundbox.low.y = min_y;
	poly->boundbox.high.x = max_x;
	poly->boundbox.high.y = max_y;
}

PG_FUNCTION_INFO_V1(geo_part);

Datum
geo_part(PG_FUNCTION_ARGS)
{
	POLYGON	*orig = PG_GETARG_POLYGON_P(0);
	int32	 offset = PG_GETARG_INT32(1);
	int32	 limit = PG_GETARG_INT32(2);
	int32	 remaining;

	POLYGON *poly;
	int32	 size;

	int			i;
	double		min_x, min_y;
	double		max_x, max_y;
	
	if (offset < 0 || limit < 0)
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("offset and limit values have to be a "
				 		"nonnegative integer")));

	if (offset > orig->npts)
		PG_RETURN_NULL();
	
	remaining = orig->npts - offset;
	if (limit > remaining)
		limit = remaining;
	if (!limit)
		PG_RETURN_NULL();
	
	size = offsetof(POLYGON, p[0]) + sizeof(poly->p[0]) * limit;
	poly = (POLYGON *) palloc(size);

	poly->size = size;
	poly->npts = limit;
	memcpy(poly->p, orig->p + offset, sizeof(orig->p[0]) * limit);

	make_bound_box(poly);

	PG_RETURN_POLYGON_P(poly);
}