feat: coveringGeohash funciton added

Adds funtion which given an envelope returns up to four geohashes
which cover the envelope.

src/main/java/com/esri/core/geometry/Geohash.java

@@ -176,6 +176,44 @@ public static String containingGeohash(Envelope2D envelope) {
    * @return up to four geohashes that completely cover given envelope
    */
   public static String[] coveringGeohash(Envelope2D envelope) {
-    return new String[] {};
+
+    String[] geoHashes = new String[4];
+
+    double xmin = envelope.xmin;
+    double ymin = envelope.ymin;
+    double xmax = envelope.xmax;
+    double ymax = envelope.ymax;
+
+    if (NumberUtils.isNaN(xmax)) {
+      return new String[] {""};
+    }
+    String[] geoHash = {containingGeohash(envelope)};
+    if (xmin == xmax && ymin == ymax) {
+      Point2D p = new Point2D(xmax, ymax);
+      return geoHash;
+    }
+    if (geoHash[0] != ""){
+      return geoHash;
+    }
+
+    int grid = 45;
+    int gridMaxLon = (int)Math.floor(xmax/grid);
+    int gridMinLon = (int)Math.floor(xmin/grid);
+    int gridMaxLat = (int)Math.floor(ymax/grid);
+    int gridMinLat = (int)Math.floor(ymin/grid);
+    int deltaLon = gridMaxLon - gridMinLon + 1;
+    int deltaLat = gridMaxLat - gridMinLat + 1;
+
+    if (deltaLon * deltaLat > 4){
+      return geoHashes;
+    } else {
+      for (int i = 0; i < deltaLon; i++){
+        for (int j = 0; j < deltaLat; j++){
+          Point2D p = new Point2D(gridMinLon + i * grid, gridMinLat + j * grid);
+          geoHashes[i*deltaLat] = toGeohash(p, 1);
+        }
+      }
+    }
+    return geoHashes;
   }
 }