Renamed some stuff, courtesy of sensiolabs.

app/Generator/Chart/Bill/BillChartGeneratorInterface.php

@@ -0,0 +1,40 @@
+<?php
+/**
+ * BillChartGeneratorInterface.php
+ * Copyright (C) 2016 Sander Dorigo
+ *
+ * This software may be modified and distributed under the terms
+ * of the MIT license.  See the LICENSE file for details.
+ */
+
+namespace FireflyIII\Generator\Chart\Bill;
+
+
+use FireflyIII\Models\Bill;
+use Illuminate\Support\Collection;
+
+/**
+ * Interface BillChartGeneratorInterface
+ *
+ * @package FireflyIII\Generator\Chart\Bill
+ */
+interface BillChartGeneratorInterface
+{
+
+    /**
+     * @param string $paid
+     * @param string $unpaid
+     *
+     * @return array
+     */
+    public function frontpage($paid, $unpaid);
+
+    /**
+     * @param Bill       $bill
+     * @param Collection $entries
+     *
+     * @return array
+     */
+    public function single(Bill $bill, Collection $entries);
+
+}