Add basic !if function

app/Engine/Cfnpp/Functions.php

@@ -111,4 +111,41 @@ class Functions
 		$value = $this->options->getVariable($function->getValue());
 		return new NodeValue(null, $node->hasName() ? $node->getName() : null, $value);
 	}
+
+	/**
+	 * Conditionally include part of the file.
+	 *
+	 * @param  Node         $node
+	 * @param  NodeFunction $function
+	 * @return ?Node
+	 */
+	public function f_if(Node $node, NodeFunction $function): ?Node
+	{
+		if (!($function instanceof NodeFunction))
+		{
+			throw new \Exception('!if expects array of parameters');
+		}
+
+		$nodes = $function->getChildren();
+
+		$condition = $nodes[0]; // expects NodeValue
+		$if_true = $nodes[1];
+		$if_false = sizeof($nodes) == 3 ? $nodes[2] : null;
+
+		$parser = new \App\Engine\Cfnpp\Expression\Parser();
+		$expression = $parser->parse($condition->getValue());
+		$result = $expression->evaluate($this->options->getVariables());
+
+		if ($result)
+		{
+			$if_true->setName($node->hasName() ? $node->getName() : null);
+			return $if_true;
+		}
+
+		if (isset($if_false))
+		{
+			$if_false->setName($node->hasName() ? $node->getName() : null);
+		}
+		return $if_false;
+	}
 }