Began fixing bugs with caused by asynchronous listener calls.

#bug

src/main/java/seng302/visualiser/map/CanvasMap.java

@@ -0,0 +1,103 @@
+package seng302.visualiser.map;
+
+import java.net.URL;
+import javafx.geometry.Point2D;
+import javafx.scene.image.Image;
+import javax.net.ssl.HttpsURLConnection;
+import seng302.utilities.GeoPoint;
+
+/**
+ * CanvasMap retrieves a map image with given geo boundary from Google Map server.
+ * By passing a rectangle like geo boundary, it returns a map image with the
+ * highest resolution. However, due to free quote account usage limit, the maximum
+ * resolution is only 1280 * 1280.
+ *
+ * Created by Haoming on 15/5/2017
+ */
+public class CanvasMap {
+
+	private Boundary boundary;
+	private long width, height;  // desired image size
+	private int zoom;
+
+	private String KEY = "AIzaSyC-5oOShMCY5Oy_9L7guYMPUPFHDMr37wE";
+
+	CanvasMap(Boundary boundary) {
+		this.boundary = boundary;
+		calculateOptimalMapSize();
+	}
+
+	Image getMapImage() {
+		try {
+			URL url = new URL(getRequest());
+			HttpsURLConnection connection = (HttpsURLConnection) url.openConnection();
+
+			return new Image(connection.getInputStream());
+		} catch (Exception e) {
+			System.out.println("[CanvasMap] Exception");
+			return null;
+		}
+	}
+
+	private String getRequest() {
+		StringBuilder sb = new StringBuilder();
+		sb.append("https://maps.googleapis.com/maps/api/staticmap?");
+		sb.append(String.format("center=%f,%f", boundary.getCentreLat(), boundary.getCentreLng()));
+		sb.append(String.format("&zoom=%d", zoom));
+		sb.append(String.format("&size=%dx%d&scale=2", width, height));
+		sb.append("&style=feature:all|element:labels|visibility:off"); // hide all labels on map
+//		sb.append(String.format("&markers=%f,%f", boundary.getSouthLat(), boundary.getWestLng()));
+//		sb.append(String.format("&key=%s", KEY));
+		return sb.toString();
+	}
+
+	private void calculateOptimalMapSize() {
+		for (int z = 20; z > 0; z--) {
+			MapSize mapSize = getMapSize(z, boundary);
+			zoom = z;
+			width = mapSize.width;
+			height = mapSize.height;
+			// if map size is valid, exit the loop as we have the highest resolution
+			if (mapSize.isValid()) break;
+		}
+	}
+
+	private MapSize getMapSize(int zoom, Boundary boundary) {
+		double scale = Math.pow(2, zoom);
+		GeoPoint geoSW = new GeoPoint(boundary.getSouthLat(), boundary.getWestLng());
+		GeoPoint geoNE = new GeoPoint(boundary.getNorthLat(), boundary.getEastLng());
+		Point2D pointSW = MercatorProjection.toMapPoint(geoSW);
+		Point2D pointNE = MercatorProjection.toMapPoint(geoNE);
+		return new MapSize(Math.abs(pointNE.getX() - pointSW.getX()) * scale,
+				Math.abs(pointNE.getY() - pointSW.getY()) * scale);
+	}
+
+	class MapSize {
+		long width, height;
+
+		MapSize(double width, double height) {
+			this.width = Math.round(width);
+			this.height = Math.round(height);
+		}
+
+		/**
+		 * Map size is valid when width and height are both less than 640 pixels
+		 * @return true if both dimensions are less than 640px
+		 */
+		boolean isValid() {
+			return Math.max(width, height) <= 640;
+		}
+	}
+
+	public long getWidth() {
+		return width;
+	}
+
+	public long getHeight() {
+		return height;
+	}
+
+	public int getZoom() {
+		return zoom;
+	}
+}