Feat: Implemented geohashToEnvelope Esri#213

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

@@ -1,28 +1,82 @@
 package com.esri.core.geometry;
 
+import java.security.InvalidParameterException;
 
 /**
  * Helper class to work with geohash
  */
 public class Geohash {
 
+    private static final String base32 = "0123456789bcdefghjkmnpqrstuvwxyz";
+
+    private static final String INVALID_CHARACTER_MESSAGE = "Invalid character in geohash: ";
+    private static final String GEOHASH_EXCEED_MAX_PRECISION_MESSAGE = "Precision to high in geohash (max 24)";
+
     /**
      * Create an evelope from a given geohash
      * @param geoHash
      * @return The envelope that corresponds to the geohash
+     * @throws InvalidParameterException if the precision of geoHash is greater than 24 characters
      */
     public static Envelope2D geohashToEnvelope(String geoHash){
-        return null;
+        if(geoHash.length() > 24){
+            throw new InvalidParameterException(GEOHASH_EXCEED_MAX_PRECISION_MESSAGE);
+        } 
+
+        long latBits = 0;
+        long lonBits = 0;
+        for(int i=0; i < geoHash.length(); i++){
+            int pos = base32.indexOf(geoHash.charAt(i));
+            if(pos == -1){
+                throw new InvalidParameterException(
+                    new StringBuilder(INVALID_CHARACTER_MESSAGE)
+                        .append('\'')
+                        .append(geoHash.charAt(i))
+                        .append('\'').toString());
+            } 
+
+            if(i%2 == 0){
+                lonBits = (lonBits << 3) | ((pos>>2) & 4) | ((pos>>1) & 2) | (pos & 1); 
+                latBits = (latBits << 2) | ((pos>>2) & 2) | ((pos>>1) & 1);
+            }else{
+                latBits = (latBits << 3) | ((pos>>2) & 4) | ((pos>>1) & 2) | (pos & 1); 
+                lonBits = (lonBits << 2) | ((pos>>2) & 2) | ((pos>>1) & 1);
+            }
+        }
+
+        int lonBitsSize = (int) Math.ceil(geoHash.length()*5/2.0);
+        int latBitsSize = geoHash.length()*5 - lonBitsSize;
+
+        double lat = -90;
+        double latPrecision = 90;
+        for(int i = 0; i < latBitsSize; i++){
+            if(((1 << (latBitsSize-1-i)) & latBits) != 0){
+                lat += latPrecision;
+            }
+            latPrecision /= 2;
+        }
+
+        double lon = -180;
+        double lonPrecision = 180;
+        for(int i = 0; i < lonBitsSize; i++){
+            if(((1 << (lonBitsSize-1-i)) & lonBits) != 0){
+                lon += lonPrecision;
+            }
+            lonPrecision /= 2;
+        }
+
+        return new Envelope2D(lon, lat, lon + lonPrecision*2, lat + latPrecision*2);
     }
 
     /**
      * Computes the geohash that contains a point at a certain precision
-     * @param pt 
+     * @param pt A point represented as lat/long pair
      * @param characterLength - The precision of the geohash
      * @return The geohash of containing pt as a String
      */
     public static String toGeohash(Point2D pt, int characterLength){
-        return "";
+
+        return "";      
     }
 
     /**