From d71515c7067a8bcde5b58b6055d06d6d5b755329 Mon Sep 17 00:00:00 2001
From: "Amy J. Ko" <ajko@uw.edu>
Date: Mon, 22 Jul 2024 13:55:37 -0700
Subject: [PATCH] Preserve concept on guide page refresh.

---
 CHANGELOG.md                  |  1 +
 src/routes/guide/Guide.svelte | 72 ++++++++++++++++++++++-------------
 2 files changed, 46 insertions(+), 27 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index dcc899c74..b631fa8bc 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,7 @@ Dates are in `YYYY-MM-DD` format and versions are in [semantic versioning](http:
 ### Fixed
 
 -   Fixed text sorting.
+-   Preserve concept on guide page refresh.
 
 ## 0.10.6 2024-07-20
 
diff --git a/src/routes/guide/Guide.svelte b/src/routes/guide/Guide.svelte
index c075ec8b8..f061e675f 100644
--- a/src/routes/guide/Guide.svelte
+++ b/src/routes/guide/Guide.svelte
@@ -14,12 +14,9 @@
     import { locales } from '@db/Database';
     import Project from '@models/Project';
     import Source from '@nodes/Source';
-    import { setContext } from 'svelte';
+    import { onMount, setContext } from 'svelte';
     import { writable } from 'svelte/store';
 
-    let locale: string | null = null;
-    let concept: string | null = null;
-
     // There's no actual project; the documentation component just relies on one to have contexts.
     $: project = Project.make(
         null,
@@ -30,44 +27,65 @@
     );
 
     $: index = ConceptIndex.make(project, $locales);
+    $: indexStore.set(index);
     let indexStore = writable<ConceptIndex | undefined>(index);
     setContext(ConceptIndexSymbol, indexStore);
-    $: indexStore.set(index);
 
-    // Create a concept path for children
+    function getLocaleInURL() {
+        return (
+            $page.url.searchParams.get('locale') ??
+            `${$locales.getLocales()[0].language}-${
+                $locales.getLocales()[0].region
+            }`
+        );
+    }
+
+    function getConceptFromURL() {
+        return $page.url.searchParams.get('concept');
+    }
+
+    function getConcept(concept: string | null) {
+        return concept ? index.getConceptByName(concept) : undefined;
+    }
+
+    // Initialize locale and concept with URL.
+    let locale: string | null = getLocaleInURL();
+    let concept: string | null = getConceptFromURL();
+
+    // Create a concept path for children, initialized
     let path = writable<Concept[]>([]);
     setContext(ConceptPathSymbol, path);
 
+    let mounted = false;
+    onMount(() => {
+        concept = getConceptFromURL();
+        path.set([getConcept(concept)].filter((c) => c !== undefined));
+        mounted = true;
+    });
+
     // After any navigation, extract the locale and concept from the URL and
     // ensure the concepts are set to match it.
-    afterNavigate(async () => {
-        locale =
-            $page.url.searchParams.get('locale') ??
-            `${$locales.getLocales()[0].language}-${
-                $locales.getLocales()[0].region
-            }`;
-        concept = $page.url.searchParams.get('concept');
-
-        if (concept) {
-            const match = index.getConceptByName(concept);
-            // Only update the path if the concept exists and is not already in the path.
-            if (
-                match &&
-                ($path.length === 0 ||
-                    match.getName($locales, false) !==
-                        $path[0].getName($locales, false))
-            ) {
-                path.set([match]);
-            }
+    afterNavigate(() => {
+        // Set the current locale.
+        locale = getLocaleInURL();
+        const currentConcept = getConcept(concept);
+        // Only update the path if the concept exists and is not already in the path.
+        if (
+            currentConcept &&
+            ($path.length === 0 ||
+                currentConcept.getName($locales, false) !==
+                    $path[0].getName($locales, false))
+        ) {
+            path.set([currentConcept]);
         }
         // Only update if the path isn't already empty.
-        else if ($path.length !== 0) {
+        else if (currentConcept === null && $path.length !== 0) {
             path.set([]);
         }
     });
 
     // When the concept path changes, navigate to the corresponding URL.
-    $: if (browser && $path) {
+    $: if (browser && $path && mounted) {
         const current = $path.at(-1);
         if (current) {
             concept = current.getName($locales, false);