CREATE FUNCTION "URX_PUBLIC"."_add_raster_constraint_coverage_tile"(rastschema name, rasttable name, rastcolumn name) 
 RETURNS boolean AS 
$BODY$
	DECLARE
		fqtn text;
		cn name;
		sql text;

		_scalex double precision;
		_scaley double precision;
		_skewx double precision;
		_skewy double precision;
		_tilewidth integer;
		_tileheight integer;
		_alignment boolean;

		_covextent geometry;
		_covrast raster;
	BEGIN
		fqtn := '';
		IF length($1) > 0 THEN
			fqtn := quote_ident($1) || '.';
		END IF;
		fqtn := fqtn || quote_ident($2);

		cn := 'enforce_coverage_tile_' || $3;

		-- metadata
		BEGIN
			sql := 'WITH foo AS (SELECT "URX_PUBLIC".ST_Metadata(' || quote_ident($3) || ') AS meta, "URX_PUBLIC".ST_ConvexHull(' || quote_ident($3) || ') AS hull FROM ' || fqtn || ') SELECT max((meta).scalex), max((meta).scaley), max((meta).skewx), max((meta).skewy), max((meta).width), max((meta).height), "URX_PUBLIC".ST_Union(hull) FROM foo';
			EXECUTE sql INTO _scalex, _scaley, _skewx, _skewy, _tilewidth, _tileheight, _covextent;
		EXCEPTION WHEN OTHERS THEN
			RAISE DEBUG 'Unable to get coverage metadata for %.%: % (%)',
        fqtn, quote_ident($3), SQLERRM, SQLSTATE;
      -- TODO: Why not return false here ?
		END;

		-- rasterize extent
		BEGIN
			_covrast := "URX_PUBLIC".ST_AsRaster(_covextent, _scalex, _scaley, '8BUI', 1, 0, NULL, NULL, _skewx, _skewy);
			IF _covrast IS NULL THEN
				RAISE NOTICE 'Unable to create coverage raster. Cannot add coverage tile constraint: % (%)',
          SQLERRM, SQLSTATE;
				RETURN FALSE;
			END IF;

			-- remove band
			_covrast := ST_MakeEmptyRaster(_covrast);
		EXCEPTION WHEN OTHERS THEN
			RAISE NOTICE 'Unable to create coverage raster. Cannot add coverage tile constraint: % (%)',
        SQLERRM, SQLSTATE;
			RETURN FALSE;
		END;

		sql := 'ALTER TABLE ' || fqtn ||
			' ADD CONSTRAINT ' || quote_ident(cn) ||
			' CHECK (st_iscoveragetile(' || quote_ident($3) || ', ''' || _covrast || '''::raster, ' || _tilewidth || ', ' || _tileheight || '))';
		RETURN  "URX_PUBLIC"._add_raster_constraint(cn, sql);
	END;
	$BODY$
 LANGUAGE 'plpgsql' VOLATILESTRICT ;