feat: go back to last chat on back to chat button (#47)

src/lib/components/model-picker/model-picker.svelte

@@ -272,7 +272,7 @@
 
 		<Popover.Content
 			portalProps={{
-				disabled: isFirefox
+				disabled: isFirefox,
 			}}
 			align="start"
 			sideOffset={5}
@@ -524,7 +524,7 @@
 		</div>
 
 		<div
-			class="bg-popover absolute top-1 right-1 scale-75 rounded-md p-1 md:opacity-0 transition-all group-hover/item:scale-100 group-hover/item:opacity-100"
+			class="bg-popover absolute top-1 right-1 scale-75 rounded-md p-1 transition-all group-hover/item:scale-100 group-hover/item:opacity-100 md:opacity-0"
 		>
 			<Button
 				variant="ghost"

src/lib/state/last-chat.svelte.ts

@@ -0,0 +1,23 @@
+import { Context } from 'runed';
+
+class LastChatState {
+	constructor(readonly opts: { lastChat: string | null }) {}
+
+	get current() {
+		return this.opts.lastChat;
+	}
+
+	set current(chat: string | null) {
+		this.opts.lastChat = chat;
+	}
+}
+
+const ctx = new Context<LastChatState>('last-chat');
+
+export function setupLastChat() {
+	return ctx.set(new LastChatState({ lastChat: null }));
+}
+
+export function useLastChat() {
+	return ctx.get();
+}

src/routes/+layout.svelte

@@ -10,11 +10,19 @@
 	import { browser } from '$app/environment';
 	import { MetaTags } from 'svelte-meta-tags';
 	import { page } from '$app/state';
+	import { setupLastChat } from '$lib/state/last-chat.svelte';
 
 	let { children } = $props();
 
 	setupConvex(PUBLIC_CONVEX_URL);
+	const lastChat = setupLastChat();
 	models.init();
+
+	$effect(() => {
+		if (page.url.pathname.startsWith('/chat')) {
+			lastChat.current = page.params?.id ?? null;
+		}
+	});
 </script>
 
 <MetaTags

src/routes/account/+layout.svelte

@@ -12,6 +12,7 @@
 	import { session } from '$lib/state/session.svelte.js';
 	import { api } from '$lib/backend/convex/_generated/api.js';
 	import { cn } from '$lib/utils/utils.js';
+	import { useLastChat } from '$lib/state/last-chat.svelte.js';
 
 	let { data, children } = $props();
 
@@ -71,11 +72,15 @@
 
 		await goto('/login');
 	}
+
+	const lastChat = useLastChat();
+
+	const backToChat = $derived(lastChat.current ? `/chat/${lastChat.current}` : '/chat');
 </script>
 
 <div class="container mx-auto max-w-[1200px] space-y-8 pt-6 pb-24">
 	<header class="flex place-items-center justify-between px-4">
-		<Button href="/chat" variant="ghost" class="flex place-items-center gap-2 text-sm">
+		<Button href={backToChat} variant="ghost" class="flex place-items-center gap-2 text-sm">
 			<ArrowLeftIcon class="size-4" />
 			Back to Chat
 		</Button>