Feature - Scroll to Previous Message (#1440)

* Added "Scroll to Previous Message" button.

* update mobile positioning to 50%

* fix linting issues in ScrollToPreviousBtn

---------

Co-authored-by: Nathan Sarrazin <sarrazin.nathan@gmail.com>

src/lib/components/ScrollToPreviousBtn.svelte

@@ -0,0 +1,70 @@
+<script lang="ts">
+	import { fade } from "svelte/transition";
+	import { onDestroy } from "svelte";
+	import IconChevron from "./icons/IconChevron.svelte";
+
+	export let scrollNode: HTMLElement;
+	export { className as class };
+
+	let visible = false;
+	let className = "";
+	let observer: ResizeObserver | null = null;
+
+	$: if (scrollNode) {
+		destroy();
+
+		if (window.ResizeObserver) {
+			observer = new ResizeObserver(() => {
+				updateVisibility();
+			});
+			observer.observe(scrollNode);
+		}
+		scrollNode.addEventListener("scroll", updateVisibility);
+	}
+
+	function updateVisibility() {
+		if (!scrollNode) return;
+		visible =
+			Math.ceil(scrollNode.scrollTop) + 200 < scrollNode.scrollHeight - scrollNode.clientHeight &&
+			scrollNode.scrollTop > 200;
+	}
+
+	function scrollToPrevious() {
+		if (!scrollNode) return;
+		const messages = scrollNode.querySelectorAll('[id^="message-"]');
+		const scrollTop = scrollNode.scrollTop;
+		let previousMessage: Element | null = null;
+
+		for (let i = messages.length - 1; i >= 0; i--) {
+			const messageTop =
+				messages[i].getBoundingClientRect().top +
+				scrollTop -
+				scrollNode.getBoundingClientRect().top;
+			if (messageTop < scrollTop - 1) {
+				previousMessage = messages[i];
+				break;
+			}
+		}
+
+		if (previousMessage) {
+			previousMessage.scrollIntoView({ behavior: "smooth", block: "start" });
+		}
+	}
+
+	function destroy() {
+		observer?.disconnect();
+		scrollNode?.removeEventListener("scroll", updateVisibility);
+	}
+
+	onDestroy(destroy);
+</script>
+
+{#if visible}
+	<button
+		transition:fade={{ duration: 150 }}
+		on:click={scrollToPrevious}
+		class="btn absolute flex h-[41px] w-[41px] rounded-full border bg-white shadow-md transition-all hover:bg-gray-100 dark:border-gray-600 dark:bg-gray-700 dark:shadow-gray-950 dark:hover:bg-gray-600 {className}"
+	>
+		<IconChevron classNames="rotate-180 mt-[2px]" />
+	</button>
+{/if}

src/lib/components/chat/ChatMessage.svelte

@@ -230,6 +230,7 @@
 {#if message.from === "assistant"}
 	<div
 		class="group relative -mb-4 flex items-start justify-start gap-4 pb-4 leading-relaxed"
+		id="message-assistant-{message.id}"
 		role="presentation"
 		on:click={() => (isTapped = !isTapped)}
 		on:keydown={() => (isTapped = !isTapped)}
@@ -372,6 +373,7 @@
 {#if message.from === "user"}
 	<div
 		class="group relative w-full items-start justify-start gap-4 max-sm:text-sm"
+		id="message-user-{message.id}"
 		role="presentation"
 		on:click={() => (isTapped = !isTapped)}
 		on:keydown={() => (isTapped = !isTapped)}

src/lib/components/chat/ChatWindow.svelte

@@ -27,6 +27,7 @@
 	import AssistantIntroduction from "./AssistantIntroduction.svelte";
 	import ChatMessage from "./ChatMessage.svelte";
 	import ScrollToBottomBtn from "../ScrollToBottomBtn.svelte";
+	import ScrollToPreviousBtn from "../ScrollToPreviousBtn.svelte";
 	import { browser } from "$app/environment";
 	import { snapScrollToBottom } from "$lib/actions/snapScrollToBottom";
 	import SystemPromptModal from "../SystemPromptModal.svelte";
@@ -328,8 +329,14 @@
 				/>
 			{/if}
 		</div>
+
+		<ScrollToPreviousBtn
+			class="fixed right-4 max-md:bottom-[calc(50%+26px)] md:bottom-48 lg:right-10"
+			scrollNode={chatContainer}
+		/>
+
 		<ScrollToBottomBtn
-			class="bottom-36 right-4 max-md:hidden lg:right-10"
+			class="fixed right-4 max-md:bottom-[calc(50%-26px)] md:bottom-36 lg:right-10"
 			scrollNode={chatContainer}
 		/>
 	</div>