Issues-83: Custom function pipe error

src/main/java/com/dashjoin/jsonata/Jsonata.java

@@ -2184,9 +2184,20 @@ public static class JFunction implements JFunctionCallable, JFunctionSignatureVa
         Signature signature;
         Method method;
         Object methodInstance;
+        int numberOfArgs;
 
         public JFunction(JFunctionCallable function, String signature) {
+            this(null, function, signature);
+        }
+
+        public JFunction(String functionName, JFunctionCallable function, String signature) {
+            this(functionName, function, signature, 0);
+        }
+
+        public JFunction(String functionName, JFunctionCallable function, String signature, int numberOfArgs) {
+            this.functionName = functionName;
             this.function = function;
+            this.numberOfArgs = numberOfArgs;
             if (signature!=null)
                 // use classname as default, gets overwritten once the function is registered
                 this.signature = new Signature(signature, function.getClass().getName());
@@ -2231,7 +2242,7 @@ public Object validate(Object args, Object context) {
         }
 
         public int getNumberOfArgs() {
-            return method != null ? method.getParameterTypes().length : 0;
+            return method != null ? method.getParameterTypes().length : numberOfArgs;
         }
     }
 

src/test/java/com/dashjoin/jsonata/CustomFunctionTest.java

@@ -58,6 +58,48 @@ public Object call(Object input, List args) throws Throwable {
     Assertions.assertEquals("abc", expression.evaluate(Map.of("a", "a", "b", "b", "c", "c")));
   }
 
+  @Test
+  public void testFunctionWithInputData() {
+    JFunction addWithFactor = new JFunction("addWithFactor", (input, args) -> {
+      var inputMap = (Map<String, Object>)input;
+      String factor = inputMap.get("factor").toString();
+      int factorInt = Integer.parseInt(factor);
+      return ((Integer) args.get(0) + (Integer) args.get(1)) * factorInt;
+    }, null);
+
+    var expression = Jsonata.jsonata("$addWithFactor(1, 2)");
+    expression.registerFunction(addWithFactor.functionName, addWithFactor);
+    Assertions.assertEquals(9, expression.evaluate(Map.of("factor", "3")));
+  }
+
+  @Test
+  public void testFunctionWithInputData2() {
+    JFunction addWithFactor = new JFunction("multiply", (input, args) -> {
+      Object first = args.get(0);
+      Object second;
+      if (args.size() > 1) {
+        second = args.get(1);
+      } else {
+        var inputMap = (Map<String, Object>)input;
+        String factor = inputMap.get("factor").toString();
+        second = Integer.parseInt(factor);
+      }
+      return (Integer) first * (Integer) second;
+    }, null, 2);
+
+    var expression = Jsonata.jsonata("$multiply(3) ~> $multiply(?, 2)");
+    expression.registerFunction(addWithFactor.functionName, addWithFactor);
+    Assertions.assertEquals(18, expression.evaluate(Map.of("factor", "3")));
+  }
+
+  @Test
+  public void testCustomFunctionPipe() {
+    JFunction add = new JFunction("add", (input, args) -> (Integer) args.get(0) + (Integer) args.get(1), null, 2);
+    var expression = Jsonata.jsonata("$add(1, 2) ~> $add(?, 3)");
+    expression.registerFunction(add.functionName, add);
+    Assertions.assertEquals(6, expression.evaluate(null));
+  }
+
   /**
    * Lambdas use no signature - in case of an error, a ClassCastException is thrown
    */