add assignment completion api

backend/app/Schedule/UseCases/SetAssignmentCompletion/SetAssignmentCompletion.php

@@ -0,0 +1,47 @@
+<?php
+
+namespace App\Schedule\UseCases\SetAssignmentCompletion;
+
+use App\Auth\Clock;
+use App\Exceptions\BadRequestException;
+use App\Exceptions\NotFoundException;
+use App\Schedule\ScheduleAssignment;
+use App\Schedule\ScheduleRepository;
+
+class SetAssignmentCompletion
+{
+    public function __construct(
+        private ScheduleRepository $scheduleRepository,
+        private Clock $clock,
+    ) {}
+
+    /**
+     * @throws BadRequestException
+     * @throws NotFoundException
+     */
+    public function execute(
+        SetAssignmentCompletionRequest $request,
+    ): ScheduleAssignment {
+        if ($request->completed === null) {
+            throw new BadRequestException(
+                'completed must be a boolean',
+            );
+        }
+
+        $assignment = $this->scheduleRepository->findAssignmentForUser(
+            $request->assignmentId,
+            $request->user,
+        );
+        if ($assignment === null) {
+            throw new NotFoundException('assignment not found');
+        }
+
+        if ($request->completed) {
+            $assignment->complete($this->clock->now());
+        } else {
+            $assignment->reopen();
+        }
+
+        return $this->scheduleRepository->updateAssignment($assignment);
+    }
+}