Making it possible to access the details of error responses from the API (see #4)

src/main/java/org/neocities/api/BaseResponse.java

@@ -3,6 +3,7 @@
 public class BaseResponse {
 
     public static final String SUCCESS = "success";
+    public static final String ERROR = "error";
 
     private String result;
     private String error_type;

src/main/java/org/neocities/api/NeoCitiesApiError.java

@@ -1,7 +1,15 @@
 package org.neocities.api;
 
+import java.util.Optional;
+
 public class NeoCitiesApiError extends RuntimeException {
 
+    /**
+     * The actual error response from the neocities API.
+     * Will be null if this exception was not built from a response.
+     */
+    public final BaseResponse error;
+
     public static NeoCitiesApiError fromResponse(final BaseResponse instance) {
         final String message = new StringBuilder("API returned unexpected result: '")
                 .append(instance.getResult())
@@ -11,14 +19,28 @@ public static NeoCitiesApiError fromResponse(final BaseResponse instance) {
                 .append(instance.getMessage())
                 .append(").")
                 .toString();
-        return new NeoCitiesApiError(message);
+        return new NeoCitiesApiError(message, instance);
     }
 
-    public NeoCitiesApiError(final String message) {
+    private NeoCitiesApiError(final String message, final BaseResponse instance){
         super(message);
+        error = instance;
+    }
+
+    public NeoCitiesApiError(final String message) {
+        this(message, null);
     }
 
     public NeoCitiesApiError(final Throwable cause) {
         super(cause);
+        error = null;
+    }
+
+    /**
+     * Safely provides access to the error response from Neocities (if present)
+     * @return the value of {@link NeoCitiesApiError#error} wrapped in an {@link Optional}
+     */
+    public Optional<BaseResponse> getError() {
+        return Optional.ofNullable(error);
     }
 }