adding handling for an external static method

README.md

@@ -44,6 +44,21 @@ the error like (via the `Psecio\Canary\Notify\ErrorLog` handler). The JSON encod
 > **NOTE:** Canary automatically pulls in the `$_GET` and `$_POST` superglobal values for evaluation so you don't need to manually pass
 then in.
 
+### Using an external data source
+
+`Canary` also allows you to use a (static) class method to provide the `if` portion of the evaluation with data. To use it, just pass in the class
+and static method name as a string:
+
+```
+<?php
+$classMethod = '\Foo\Bar::criteria';
+
+\Psecio\Canary\Instance::build()->if($classMethod)->execute();
+?>
+```
+
+The return from this method must be an array otherwise an exception will be thrown.
+
 ### Supported Notifier Methods
 
 Currently `Canary` supports the following notification methods:

src/Instance.php

@@ -131,6 +131,22 @@ public function if(...$params) : \Psecio\Canary\Instance
     {
         if (count($params) == 1 && $params[0] instanceof CriteriaSet) {
             $this->criteria = $params[0];
+        } elseif (count($params) == 1 && is_string($params[0])) {
+            // Try to load it like a class
+            list($classNs, $method) = explode('::', $params[0]);
+            if (!class_exists($classNs)) {
+                throw new \InvalidArgumentException('Invalid data source: '.$classNs);
+            }
+            $result = call_user_func($classNs.'::'.$method);
+
+            if (!is_array($result)) {
+                throw new \InvalidArgumentException('Method call must return an array');
+            }
+            foreach ($result as $index => $value) {
+                $equals = new Equals($index, $value);
+                $this->criteria->add($equals);
+            }
+
         } elseif (count($params) == 1 && $params[0] instanceof Criteria) {
             $this->criteria->add($params[0]);