ST_ClusterIntersecting as a window function

cluster_impl.c

PG_FUNCTION_INFO_V1(cluster_intersecting_window);
Datum cluster_intersecting_window(PG_FUNCTION_ARGS)
{
	WindowObject win_obj = PG_WINDOW_OBJECT();
	uint32_t row = WinGetCurrentPosition(win_obj);
	uint32_t ngeoms = WinGetPartitionRowCount(win_obj);	
	uint32_t* cluster_assignments = WinGetPartitionLocalMemory(win_obj, ngeoms * sizeof(uint32_t));

	if (row == 0) /* beginning of the partition; do all of the work now */
	{
		uint32_t i;
		GEOSGeometry** geos_geoms = lwalloc(ngeoms * sizeof(GEOSGeometry*));
		UNIONFIND* uf = UF_create(ngeoms);

		initGEOS(lwnotice, lwgeom_geos_error);
		for (i = 0; i < ngeoms; i++)
		{
			GSERIALIZED* g;
			bool is_null;
			Datum arg = WinGetFuncArgInPartition(win_obj, 0, i, WINDOW_SEEK_HEAD, false, &is_null, NULL);

			if (is_null) {
				/* TODO */
				continue;
			}

			g = (GSERIALIZED*) PG_DETOAST_DATUM(arg);// DatumGetPointer(arg);
			geos_geoms[i] = POSTGIS2GEOS(g);

			if (!geos_geoms[i]) {
				/* TODO */
			}
		}

		union_intersecting_pairs(geos_geoms, ngeoms, uf);
		/* TODO check for error */

		for (i = 0; i < ngeoms; i++)
		{
			cluster_assignments[i] = uf->clusters[i];
			GEOSGeom_destroy(geos_geoms[i]);
		}
		UF_destroy(uf);
	}

	PG_RETURN_INT32(cluster_assignments[row]);
}

def.sql

CREATE OR REPLACE FUNCTION ST_ClusterIntersectingW(geometry)
	RETURNS int
	AS 'MODULE_PATHNAME', 'cluster_intersecting_window'
	LANGUAGE 'c' IMMUTABLE STRICT WINDOW;