frontend: Highlight files not downloaded

frontend/fic/src/lib/components/ExerciceDownloads.svelte

@@ -9,6 +9,7 @@
      ListGroupItem,
  } from '@sveltestrap/sveltestrap';
 
+ import { hasDownloaded } from '$lib/stores/downloaded.js';
  import FileSize from './FileSize.svelte';
 
  export let files = [];
@@ -27,8 +28,8 @@
         </CardBody>
         <ListGroup flush class="border-secondary">
             {#each files as file, index}
-                <ListGroupItem tag="a" href={file.path} target={(file.name.endsWith(".txt") || file.name.endsWith(".xml") || file.name.endsWith(".jpg") || file.name.endsWith(".png") || file.name.endsWith(".pdf"))?"_blank":"_self"} class="d-flex">
-		    <h1 class="me-3">
+                <ListGroupItem tag="a" href={file.path} target={(file.name.endsWith(".txt") || file.name.endsWith(".xml") || file.name.endsWith(".jpg") || file.name.endsWith(".png") || file.name.endsWith(".pdf"))?"_blank":"_self"} class="d-flex" action on:click={() => hasDownloaded.update((u) => {u[file.path] = true; return u;})}>
+		    <h1 class="me-3" class:text-info={!$hasDownloaded[file.path]}>
                         <Icon name="arrow-down-circle" />
                     </h1>
                     <div style="min-width: 0">

frontend/fic/src/lib/stores/downloaded.js

@@ -0,0 +1,25 @@
+import { writable } from 'svelte/store';
+
+function createDownloadedStore() {
+  let init = { };
+  try {
+    if (window.localStorage && window.localStorage.getItem("downloadedStore")) {
+      init = JSON.parse(window.localStorage.getItem("downloadedStore"));
+    }
+  } catch {
+    init = { };
+  }
+
+  const { subscribe, set, update } = writable(init);
+
+  return {
+    subscribe,
+
+    update: (u) => {
+      update(u);
+      if (window.localStorage) localStorage.setItem("downloadedStore", JSON.stringify(init));
+    },
+  }
+}
+
+export const hasDownloaded = createDownloadedStore();