fixing authority on server

nextjs/src/app/course/[courseName]/lecture/[lectureDay]/EditLecture.tsx

@@ -1,5 +1,4 @@
 "use client";
-
 import { MonacoEditor } from "@/components/editor/MonacoEditor";
 import {
   useLecturesSuspenseQuery,
@@ -9,47 +8,63 @@ import {
   lectureToString,
   parseLecture,
 } from "@/services/fileStorage/utils/lectureUtils";
-import { useEffect, useState } from "react";
+import { useCallback, useEffect, useState } from "react";
 import LecturePreview from "./LecturePreview";
 import EditLectureTitle from "./EditLectureTitle";
 import LectureButtons from "./LectureButtons";
 import { useCourseContext } from "../../context/courseContext";
 import { useLocalCourseSettingsQuery } from "@/hooks/localCourse/localCoursesHooks";
+import { Lecture } from "@/models/local/lecture";
 
 export default function EditLecture({ lectureDay }: { lectureDay: string }) {
-  const [_, {dataUpdatedAt}] = useLecturesSuspenseQuery();
-  return (
-    <InnerEditLecture key={dataUpdatedAt} lectureDay={lectureDay} />
-  );
-}
-export function InnerEditLecture({ lectureDay }: { lectureDay: string }) {
   const { courseName } = useCourseContext();
   const [settings] = useLocalCourseSettingsQuery();
-  const [weeks] = useLecturesSuspenseQuery();
+  const [weeks, { dataUpdatedAt: serverDataUpdatedAt }] =
+    useLecturesSuspenseQuery();
   const updateLecture = useLectureUpdateMutation();
 
   const lecture = weeks
     .flatMap(({ lectures }) => lectures.map((lecture) => lecture))
     .find((l) => l.date === lectureDay);
 
-  const startingText = lecture
-    ? lectureToString(lecture)
-    : `Name: 
-Date: ${lectureDay}
----
-`;
+  const serverVersionOfText = getLectureTextOrDefault(lecture, lectureDay);
 
-  const [text, setText] = useState(startingText);
+  const [text, setText] = useState(serverVersionOfText);
+  const [updateMonacoKey, setUpdateMonacoKey] = useState(1);
   const [error, setError] = useState("");
 
+  const [clientDataUpdatedAt, setClientDataUpdatedAt] =
+    useState(serverDataUpdatedAt);
+  const clientIsAuthoritative = serverDataUpdatedAt <= clientDataUpdatedAt;
+  console.log("client it authoritative", clientIsAuthoritative);
+
+  const textUpdate = useCallback((t: string) => {
+    setText(t);
+    setClientDataUpdatedAt(Date.now());
+  }, []);
+
   useEffect(() => {
     const delay = 500;
     const handler = setTimeout(() => {
       try {
         const parsed = parseLecture(text);
         if (!lecture || lectureToString(parsed) !== lectureToString(lecture)) {
+          if (clientIsAuthoritative) {
             console.log("updating lecture");
             updateLecture.mutate({ lecture: parsed, settings, courseName });
+          } else {
+            if (lecture) {
+              console.log(
+                "client not authoritative, updating client with server data"
+              );
+              textUpdate(lectureToString(lecture));
+              setUpdateMonacoKey((k) => k + 1);
+            } else {
+              console.log(
+                "client not authoritative, but no lecture on server, this is a bug"
+              );
+            }
+          }
         }
         setError("");
       } catch (e: any) {
@@ -60,14 +75,26 @@ Date: ${lectureDay}
     return () => {
       clearTimeout(handler);
     };
-  }, [courseName, lecture, settings, text, updateLecture]);
+  }, [
+    clientIsAuthoritative,
+    courseName,
+    lecture,
+    settings,
+    text,
+    textUpdate,
+    updateLecture,
+  ]);
 
   return (
     <div className="h-full flex flex-col">
       <EditLectureTitle lectureDay={lectureDay} />
       <div className="sm:columns-2 min-h-0 flex-1">
         <div className="flex-1 h-full">
-          <MonacoEditor value={text} onChange={setText} />
+          <MonacoEditor
+            key={updateMonacoKey}
+            value={text}
+            onChange={textUpdate}
+          />
         </div>
         <div className="h-full sm:block none overflow-auto">
           <div className="text-red-300">{error && error}</div>
@@ -78,3 +105,15 @@ Date: ${lectureDay}
     </div>
   );
 }
+
+function getLectureTextOrDefault(
+  lecture: Lecture | undefined,
+  lectureDay: string
+) {
+  return lecture
+    ? lectureToString(lecture)
+    : `Name: 
+Date: ${lectureDay}
+---
+`;
+}