source.url = function()

in modules/renderer/background_source.js [92:169]
73 lines of code
16 McCabe index (conditional complexity)

    source.url = function(coord) {
        if (this.type === 'wms') {
            var tileToProjectedCoords = (function(x, y, z) {
                //polyfill for IE11, PhantomJS
                var sinh = Math.sinh || function(x) {
                    var y = Math.exp(x);
                    return (y - 1 / y) / 2;
                };

                var zoomSize = Math.pow(2, z);
                var lon = x / zoomSize * Math.PI * 2 - Math.PI;
                var lat = Math.atan(sinh(Math.PI * (1 - 2 * y / zoomSize)));

                switch (this.projection) {
                    case 'EPSG:4326':
                        return {
                            x: lon * 180 / Math.PI,
                            y: lat * 180 / Math.PI
                        };
                    default: // EPSG:3857 and synonyms
                        var mercCoords = d3_geoMercatorRaw(lon, lat);
                        return {
                            x: 20037508.34 / Math.PI * mercCoords[0],
                            y: 20037508.34 / Math.PI * mercCoords[1]
                        };
                }
            }).bind(this);

            var tileSize = this.tileSize;
            var projection = this.projection;
            var minXmaxY = tileToProjectedCoords(coord[0], coord[1], coord[2]);
            var maxXminY = tileToProjectedCoords(coord[0]+1, coord[1]+1, coord[2]);
            return template.replace(/\{(\w+)\}/g, function (token, key) {
              switch (key) {
                case 'width':
                case 'height':
                  return tileSize;
                case 'proj':
                  return projection;
                case 'wkid':
                  return projection.replace(/^EPSG:/, '');
                case 'bbox':
                  return minXmaxY.x + ',' + maxXminY.y + ',' + maxXminY.x + ',' + minXmaxY.y;
                case 'w':
                  return minXmaxY.x;
                case 's':
                  return maxXminY.y;
                case 'n':
                  return maxXminY.x;
                case 'e':
                  return minXmaxY.y;
                default:
                  return token;
              }
            });
        }
        return template
            .replace('{x}', coord[0])
            .replace('{y}', coord[1])
            // TMS-flipped y coordinate
            .replace(/\{[t-]y\}/, Math.pow(2, coord[2]) - coord[1] - 1)
            .replace(/\{z(oom)?\}/, coord[2])
            .replace(/\{switch:([^}]+)\}/, function(s, r) {
                var subdomains = r.split(',');
                return subdomains[(coord[0] + coord[1]) % subdomains.length];
            })
            .replace('{u}', function() {
                var u = '';
                for (var zoom = coord[2]; zoom > 0; zoom--) {
                    var b = 0;
                    var mask = 1 << (zoom - 1);
                    if ((coord[0] & mask) !== 0) b++;
                    if ((coord[1] & mask) !== 0) b += 2;
                    u += b.toString();
                }
                return u;
            });
    };