Disable or enable button.

src/main/resources/eu/simstadt/regionchooser/website/script/simstadt_openlayers.js

 var regionChooser = (function(){
+	//TODO: Somehow split in classes. This file is getting too big and mixed
 	var publicScope = {};
 	var fromJavaFX = navigator.userAgent.indexOf('JavaFX') !== -1;
 	var dataPanel = $('#dataPanel');
@@ -162,7 +163,7 @@ var regionChooser = (function(){
 		intersections.addFeature(intersection);
 		var link = '<li>'
         // TODO: If possible, highlight the corresponding polygon when hovering above a name.
-		link += '<input type="checkbox" id="citygml_' + feature.getId() + '" class="select_citygml"><label for="citygml_' + feature.getId() + '">' +  feature['name'] + '</label>';
+		link += '<input type="checkbox" id="citygml_' + feature.getId() + '" class="select_citygml" onclick="regionChooser.canDownload();"><label for="citygml_' + feature.getId() + '">' +  feature['name'] + '</label>';
 
 		link += " (" + citygml_percentage + "%";
 		if (sketch_percentage == 100) {
@@ -171,6 +172,17 @@ var regionChooser = (function(){
 		dataPanel.append(link + ")\n");
 	}
 	
+	publicScope.canDownload = function(){
+		var count = 0;
+		console.log("...");
+		document.querySelectorAll("input.select_citygml").forEach(c => {
+			if (c.checked){
+				count += 1;
+			}
+		});
+		document.getElementById("download").disabled = (count == 0);
+	}
+	
 	function findIntersection(feature, polygon) {
 		try {
 			return turf.intersect(polygon, feature["geoJSON"]);
@@ -211,8 +223,6 @@ var regionChooser = (function(){
 	}
 	
 	publicScope.downloadRegionFromCityGMLs = function(checkbox_ids) {
-		// TODO: Disable all links
-		// TODO: DRY
 		var features = checkbox_ids.map(checkbox_id => {
 			var i = Number(checkbox_id.replace("citygml_", ""));
 			return kml_source.getFeatureById(i);
@@ -238,6 +248,7 @@ var regionChooser = (function(){
 				var time = end - start;
 				console.log('Download Execution time: ' + (time / 1000).toFixed(3) + 's');
 				setTimeout(function() {
+					document.getElementById("download").disabled = false;
 					document.documentElement.className = ''; // Stop waiting
 				}, 100);
 			} else {
@@ -267,8 +278,7 @@ var regionChooser = (function(){
 			dataPanel.append(wgs84_coords + "<br/>\n");
 		}
 		dataPanel.append("<h3 class='clean'>Area : " + (area / 10000).toFixed(1) + " ha\n");
-		//TODO: Hide button if empty
-		dataPanel.append('<button type="button" onclick="regionChooser.downloadFromSelectedCityGMLs()" id="download" style="visibility:hidden">Download Region</button><br/>\n');
+		dataPanel.append('<button type="button" onclick="regionChooser.downloadFromSelectedCityGMLs()" id="download" style="visibility:hidden" disabled>Download Region</button><br/>\n');
 		dataPanel.append('<a href="#" onclick="regionChooser.checkCityGMLS(true);">(Select All)</a>');
 		dataPanel.append('<a href="#" onclick="regionChooser.checkCityGMLS(false);">(Select None)</a>');
 		dataPanel.append('<br/>\n');
@@ -363,12 +373,14 @@ var regionChooser = (function(){
 		if (checkedBoxes.length === 0){
 			console.log("You should select at least one citygml, though.");
 		} else{
+			document.getElementById("download").disabled = true;
 			publicScope.downloadRegionFromCityGMLs(checkedBoxes.map(c => c.id));
 		}
 	}
 	
 	publicScope.checkCityGMLS = function(allOrNone) {
 		document.querySelectorAll("input.select_citygml").forEach(c => c.checked = allOrNone);
+		publicScope.canDownload();
 	}
 	
 	publicScope.selectRepository = function() {