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<script lang="ts">
import { tick, untrack } from "svelte";
import { tabStore } from "../tabs.svelte.js";
import ChatMessageComponent from "./ChatMessage.svelte";
let messagesEl: HTMLDivElement | undefined;
let userScrolledUp = $state(false);
let isAutoScrolling = false;
let isLoadingMore = $state(false);
const renderGroups = $derived(tabStore.activeTab?.renderGroups ?? []);
const activeTabId = $derived(tabStore.activeTab?.id);
// Compaction placeholder state for the active tab. `compactingSource` is set on
// a transient placeholder tab while a conversation is being compacted;
// `compactionError` is set if it failed.
const compactingSource = $derived(tabStore.activeTab?.compactingSource ?? null);
const compactionError = $derived(tabStore.activeTab?.compactionError ?? null);
// Stable, turn-scoped render keys. A bubble's identity is `${turnId}:${role}:${n}`
// (n = its index among same-(turn,role) messages) rather than the underlying
// row/client id, so when the live turn reconciles into sealed chunk rows the
// bubble keeps its identity and does NOT remount (no flash). Falls back to the
// message id for anything without a turnId (e.g. optimistic/queued messages
// before turn-start, standalone system notices).
const keyedMessages = $derived.by(() => {
const counts = new Map<string, number>();
return renderGroups.map((m) => {
if (!m.turnId) return { m, key: m.id };
const base = `${m.turnId}:${m.role}`;
const n = counts.get(base) ?? 0;
counts.set(base, n + 1);
return { m, key: `${base}:${n}` };
});
});
function isNearBottom(el: HTMLElement): boolean {
return el.scrollHeight - el.scrollTop - el.clientHeight < 64;
}
function scrollToBottom(animate = false) {
if (!messagesEl) return;
messagesEl.scrollTo({
top: messagesEl.scrollHeight,
behavior: animate ? "smooth" : "instant",
});
}
async function onNearTop() {
if (isLoadingMore) return;
const tab = tabStore.activeTab;
if (!tab) return;
// Nothing older to load if we're already at the very first message, or if
// we already hold every message the backend has for this tab.
if (tab.oldestLoadedSeq !== null && tab.oldestLoadedSeq <= 0) return;
isLoadingMore = true;
const prevScrollHeight = messagesEl?.scrollHeight ?? 0;
const prevScrollTop = messagesEl?.scrollTop ?? 0;
try {
await tabStore.loadOlderChunks(tab.id);
// Wait for Svelte to flush the prepended messages into the DOM.
// Reading `scrollHeight` synchronously after the await would observe
// the OLD layout (reactive updates are batched), so the scroll
// correction would be computed against a stale height and the
// viewport would jump. `tick()` resolves once the DOM reflects the
// new message list.
await tick();
if (messagesEl) {
const newScrollHeight = messagesEl.scrollHeight;
const delta = newScrollHeight - prevScrollHeight;
// Only adjust when content was actually prepended above the
// viewport. If nothing was added (all duplicates / nothing older),
// `delta` is 0 and we leave the user where they are instead of
// snapping to the top.
if (delta > 0) {
messagesEl.scrollTop = prevScrollTop + delta;
}
}
} finally {
isLoadingMore = false;
}
}
function handleScroll() {
if (!messagesEl || isAutoScrolling) return;
const wasScrolledUp = userScrolledUp;
userScrolledUp = !isNearBottom(messagesEl);
if (activeTabId) tabStore.setScrolledUp(activeTabId, userScrolledUp);
// User just scrolled back to the bottom manually — safe to evict now.
if (wasScrolledUp && !userScrolledUp && activeTabId) {
tabStore.evictChunks(activeTabId);
}
// Near the top — pull in older history.
if (userScrolledUp && messagesEl.scrollTop < 200) {
void onNearTop();
}
}
function resumeAutoScroll() {
userScrolledUp = false;
isAutoScrolling = true;
if (activeTabId) {
tabStore.setScrolledUp(activeTabId, false);
tabStore.evictChunks(activeTabId);
}
scrollToBottom(true);
}
$effect(() => {
const count = renderGroups.length;
void count;
if (messagesEl) {
untrack(() => {
if (!userScrolledUp) scrollToBottom(false);
});
}
});
$effect(() => {
const prevTabId = activeTabId;
// Reset scroll state when switching tabs
userScrolledUp = false;
isAutoScrolling = false;
return () => {
if (prevTabId) {
tabStore.setScrolledUp(prevTabId, false);
}
};
});
</script>
<div class="flex flex-col h-full">
<!-- Messages -->
<div class="relative flex-1 min-h-0">
<div
bind:this={messagesEl}
class="h-full overflow-y-auto p-4"
onscroll={handleScroll}
onscrollend={() => {
isAutoScrolling = false;
}}
>
{#if isLoadingMore}
<div class="text-center text-xs text-base-content/40 py-2">Loading earlier messages...</div>
{/if}
{#if compactingSource || compactionError}
<div class="flex flex-col items-center justify-center h-full gap-4 px-6 text-center">
{#if compactionError}
<div class="text-2xl font-semibold text-error">Compaction failed</div>
<div class="text-base text-base-content/70 max-w-md">{compactionError}</div>
<div class="text-sm text-base-content/50">Close this tab to dismiss — your conversation was not changed.</div>
{:else}
<span class="loading loading-spinner loading-lg text-primary"></span>
<div class="text-2xl font-semibold text-base-content">Please wait, compacting conversation…</div>
<div class="text-sm text-base-content/50">You can cancel by closing this tab.</div>
{/if}
</div>
{:else if renderGroups.length === 0}
<div class="flex items-center justify-center h-full text-base-content/40 text-sm">
Send a message to start a conversation
</div>
{/if}
{#if !compactingSource && !compactionError}
{#each keyedMessages as { m, key } (key)}
<ChatMessageComponent message={m} tabId={activeTabId} />
{/each}
{/if}
</div>
<!-- Scroll-to-bottom button -->
<button
type="button"
class="absolute bottom-0 left-1/2 -translate-x-1/2 mb-4 btn btn-sm px-8 rounded-lg shadow-lg transition-opacity duration-200 {userScrolledUp ? 'opacity-100' : 'opacity-0 pointer-events-none'}"
onclick={resumeAutoScroll}
aria-label="Scroll to bottom"
tabindex={userScrolledUp ? 0 : -1}
>
▼
</button>
</div>
</div>
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