Improve navigation logic

& do the TODO.
Also leave a pointer how to improve it (even) more.

aleksis/apps/alsijil/frontend/components/coursebook/Coursebook.vue

@@ -171,10 +171,10 @@ export default {
     },
   },
   methods: {
-    resetDate() {
+    resetDate(toDate) {
       // Assure current date
       console.log('Resetting date range', this.$route.hash);
-      this.currentDate = this.$route.hash?.substring(1);
+      this.currentDate = toDate || this.$route.hash?.substring(1);
       if (!this.currentDate) {
         console.log('Set default date');
         this.setDate(DateTime.now().toISODate());
@@ -285,7 +285,27 @@ export default {
         }
       };
     },
-    // TODO: only load the else if out of range / not just not present
+    // Improve me?
+    // The navigation logic could be a bit simpler if the current days
+    // where known as a sorted array (= result of groupDocsByDay) But
+    // then the list would need its own component and this gets rather
+    // complicated. Then the calendar could also show the present days
+    // / gray out the missing.
+    //
+    // Next two: arg date is ts object
+    findPrev(date) {
+      return this.$refs.days
+        .map((day) => day.date)
+        .sort()
+        .reverse()
+        .find((date2) => date2 < date);
+    },
+    findNext(date) {
+      return this.$refs.days
+        .map((day) => day.date)
+        .sort()
+        .find((date2) => date2 > date);
+    },
     gotoDate(date) {
       const present = this.$refs.days
             .find((day) => day.date.toISODate() === date);
@@ -295,26 +315,22 @@ export default {
         // Also intersect handler does not always react to scrollIntoView
         this.setDate(date);
         present.focus("smooth");
-      } else {
-        this.setDate(date);
-        this.resetDate();
+      } else if (!this.findPrev(DateTime.fromISO(date)) || !this.findNext(DateTime.fromISO(date))) {
+        console.log('resetting from cal to ', date);
+        this.resetDate(date);
       }
     },
-    // TODO: Disable navigation while loading!
     gotoPrev() {
-      const pref = this.$refs.days
-            .map((day) => day.date.toISODate())
-            .sort()
-            .reverse()
-            .find((date) => date < this.currentDate);
-      this.gotoDate(pref);
+      const prev = this.findPrev(DateTime.fromISO(this.currentDate));
+      if (prev) {
+        this.gotoDate(prev.toISODate());
+      }
     },
     gotoNext() {
-      const next = this.$refs.days
-            .map((day) => day.date.toISODate())
-            .sort()
-            .find((date) => date > this.currentDate);
-      this.gotoDate(next);
+      const next = this.findNext(DateTime.fromISO(this.currentDate));
+      if (next) {
+        this.gotoDate(next.toISODate());
+      }
     },
   },
   created() {