preserver infinite scroll positions (#615)

modules/desktop/src/components/packages/packages.svelte

@@ -10,7 +10,8 @@
   import Package from "./package.svelte";
   import NoInstalls from "./no-installs.svelte";
   import NoUpdates from "./no-updates.svelte";
-  import { packagesStore } from "$libs/stores";
+  import { packagesStore, scrollStore } from "$libs/stores";
+  import { afterUpdate, beforeUpdate } from "svelte";
 
   const { packageList: allPackages } = packagesStore;
   export let packageFilter: SideMenuOptions = SideMenuOptions.all;
@@ -20,6 +21,11 @@
   let loadMore = 9;
   let limit = loadMore + 9;
 
+  const updateLimit = (value: number) => {
+    limit += value;
+    scrollStore.setLimit(packageFilter, limit);
+  };
+
   // TODO: figure out a better type strategy here so that this breaks if SideMenuOptions is updated
   const pkgFilters: { [key: string]: (pkg: GUIPackage) => boolean } = {
     [SideMenuOptions.all]: (_pkg: GUIPackage) => true,
@@ -46,6 +52,7 @@
   const onScroll = (e: Event) => {
     const target = e.target as HTMLInputElement;
     scrollY = target.scrollTop || 0;
+    scrollStore.setScrollPosition(packageFilter, scrollY);
   };
 
   $: packages = $allPackages.filter(pkgFilters[packageFilter] || pkgFilters.all);
@@ -56,13 +63,37 @@
     const minCardRows = Math.floor(node.scrollHeight / assumedCardHeight);
     if (cardRows < minCardRows) {
       const addLimit = 3 * (minCardRows - cardRows);
-      limit += addLimit;
+      updateLimit(addLimit);
     }
   };
+
+  let scrollElement: any = null;
+  let prevFilter: SideMenuOptions | null;
+
+  // Restore the limit before the update...
+  beforeUpdate(() => {
+    if (prevFilter !== packageFilter) {
+      limit = scrollStore.getLimit(packageFilter);
+    }
+  });
+
+  // ...and scroll position after the update
+  afterUpdate(() => {
+    if (prevFilter !== packageFilter && scrollElement) {
+      prevFilter = packageFilter;
+      const scrollPosition = scrollStore.getScrollPosition(packageFilter);
+      scrollElement.scrollTop = scrollPosition;
+    }
+  });
 </script>
 
 <div class="relative h-full w-full">
-  <ul class="flex flex-wrap content-start bg-black" use:watchResize={onResize} on:scroll={onScroll}>
+  <ul
+    bind:this={scrollElement}
+    class="flex flex-wrap content-start bg-black"
+    use:watchResize={onResize}
+    on:scroll={onScroll}
+  >
     {#if packages.length > 0}
       {#each packages as pkg, index}
         {#if index < limit}
@@ -84,7 +115,7 @@
         </section>
       {/each}
     {/if}
-    <InfiniteScroll threshold={100} on:loadMore={() => (limit += loadMore)} />
+    <InfiniteScroll threshold={100} on:loadMore={() => updateLimit(loadMore)} />
   </ul>
 </div>
 

modules/desktop/src/libs/stores.ts

@@ -11,6 +11,7 @@ import pkgStore from "./stores/pkgs";
 import initNotificationStore from "./stores/notifications";
 import initAppUpdateStore from "./stores/update";
 import { trackSearch } from "./analytics";
+import initScrollStore from "./stores/scroll";
 
 export const featuredPackages = writable<Package[]>([]);
 
@@ -140,3 +141,5 @@ export const navStore = initNavStore();
 export const notificationStore = initNotificationStore();
 
 export const appUpdateStore = initAppUpdateStore();
+
+export const scrollStore = initScrollStore();

modules/desktop/src/libs/stores/scroll.ts

@@ -0,0 +1,33 @@
+import type { SideMenuOptions } from "$libs/types";
+import { get, writable } from "svelte/store";
+
+type ScrollValue = Record<SideMenuOptions, number>;
+
+const defaultLimit = 18;
+
+// keep track of the scroll position of each side menu filter so it's not lost after navigation
+export default function initScrollStore() {
+  const scrollPositions = writable<ScrollValue>({} as ScrollValue);
+  const limits = writable<ScrollValue>({} as ScrollValue);
+
+  return {
+    setScrollPosition: (filter: SideMenuOptions, pos: number) => {
+      scrollPositions.update((prev) => {
+        prev[filter] = pos;
+        return prev;
+      });
+    },
+    getScrollPosition: (filter: SideMenuOptions) => {
+      return get(scrollPositions)[filter] || 0;
+    },
+    setLimit: (filter: SideMenuOptions, limit: number) => {
+      limits.update((prev) => {
+        prev[filter] = limit;
+        return prev;
+      });
+    },
+    getLimit: (filter: SideMenuOptions) => {
+      return get(limits)[filter] || defaultLimit;
+    }
+  };
+}