re-add lesson page extra props

Author: samsaksfithian

src/App.js

@@ -111,13 +111,23 @@ class App extends React.Component {
               const courseObj = courses.find(
                 course => course.slug === props.match.params.course,
               );
-              if (!courseObj) return <ErrorPage />;
+              const prevCourse = courses.find(
+                course => course.order === courseObj.order - 1,
+              );
+              const nextCourse = courses.find(
+                course => course.order === courseObj.order + 1,
+              );
+              const order = parseInt(props.match.params.order, 10);
+              if (!courseObj || order >= courseObj.lessons.length) return <ErrorPage />;
               return (
                 <LessonPage
                   {...props}
+                  course_title={courseObj.title}
                   lessons={courseObj.lessons}
-                  curr_lesson_num={parseInt(props.match.params.order, 10)}
-                  base_path={props.match.params.course}
+                  curr_lesson_num={order}
+                  base_path={courseObj.slug}
+                  prev_slug={prevCourse ? prevCourse.slug : undefined}
+                  next_slug={nextCourse ? nextCourse.slug : undefined}
                 />
               );
             }}