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<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("[data-message-id]");
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}
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