invoice calculator to group entries by activity (#380)

src/Invoice/Calculator/ActivityInvoiceCalculator.php

@@ -0,0 +1,51 @@
+<?php
+
+/*
+ * This file is part of the Kimai time-tracking app.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace App\Invoice\Calculator;
+
+use App\Entity\Timesheet;
+use App\Invoice\CalculatorInterface;
+
+/**
+ * A calculator that sums up the timesheet records by activity.
+ */
+class ActivityInvoiceCalculator extends AbstractMergedCalculator implements CalculatorInterface
+{
+    /**
+     * @return Timesheet[]
+     */
+    public function getEntries()
+    {
+        $entries = $this->model->getEntries();
+        if (empty($entries)) {
+            return [];
+        }
+
+        /** @var Timesheet[] $timesheets */
+        $timesheets = [];
+
+        foreach ($entries as $entry) {
+            if (!isset($timesheets[$entry->getActivity()->getId()])) {
+                $timesheets[$entry->getActivity()->getId()] = new Timesheet();
+            }
+            $timesheet = $timesheets[$entry->getActivity()->getId()];
+            $this->mergeTimesheets($timesheet, $entry);
+        }
+
+        return array_values($timesheets);
+    }
+
+    /**
+     * @return string
+     */
+    public function getId(): string
+    {
+        return 'activity';
+    }
+}