From 2413c29fc0534e39ec7f2e3476511845770aca57 Mon Sep 17 00:00:00 2001
From: Josh Wright <josh@thewrightserver.net>
Date: Sun, 4 Oct 2026 17:19:15 -0400
Subject: [PATCH] Fix pausing log auto-refresh and cancel stale reads

---
 src/lib/ui/components/LogPanel.svelte |  70 ++++--------
 src/lib/ui/log-refresh.ts             |  91 +++++++++++++++
 tests/unit/log-refresh.test.ts        | 155 ++++++++++++++++++++++++++
 3 files changed, 268 insertions(+), 48 deletions(-)
 create mode 100644 src/lib/ui/log-refresh.ts
 create mode 100644 tests/unit/log-refresh.test.ts

diff --git a/src/lib/ui/components/LogPanel.svelte b/src/lib/ui/components/LogPanel.svelte
index 9a979ac..a951534 100644
--- a/src/lib/ui/components/LogPanel.svelte
+++ b/src/lib/ui/components/LogPanel.svelte
@@ -1,9 +1,9 @@
 <script lang="ts">
-    import { tick, untrack, onMount } from 'svelte';
+    import { tick, untrack, onMount, onDestroy } from 'svelte';
     import { page } from '$app/stores';
     import { goto } from '$app/navigation';
     import { toast } from '$ui/toast.js';
-    import { pollVisible } from '$ui/poll.js';
+    import { createLogRefresh, type LogResponse } from '$ui/log-refresh.js';
     import Tabs from './primitives/Tabs.svelte';
     import Button from './primitives/Button.svelte';
     const uid = $props.id();
@@ -21,18 +21,6 @@
     }
     let { server, tabs, lines = 1000, pollMs = 5000 }: Props = $props();
 
-    interface LogResponse {
-        ok: boolean;
-        key?: string;
-        path?: string;
-        lines?: string[];
-        size?: number;
-        mtime?: string | null;
-        truncated?: boolean;
-        missing?: boolean;
-        reason?: string;
-    }
-
     const active = $derived(tabs.find(tab => tab.key === $page.url.searchParams.get('log'))?.key ?? tabs[0]?.key ?? '');
     let data = $state<Record<string, LogResponse | null>>({});
 
@@ -45,33 +33,21 @@
     let loading = $state(false);
     let autoRefresh = $state(true);
     let refreshError = $state('');
-    const pending = new Set<string>();
     let bodyEl = $state<HTMLPreElement | null>(null);
     let stickToBottom = $state(true);
 
-    async function fetchLog(key: string): Promise<void> {
-        const currentServer = server;
-        const requestKey = currentServer + ':' + key;
-        if (pending.has(requestKey)) return;
-        pending.add(requestKey); loading = true;
-        try {
-            const res = await fetch(
-                `/api/servers/${encodeURIComponent(server)}/logs/${encodeURIComponent(key)}?lines=${lines}`
-            );
-            const body = (await res.json()) as LogResponse;
-            if (!res.ok || !body.ok) throw new Error(body.reason ?? 'Could not refresh log.');
-            if (server === currentServer) { data = { ...data, [key]: body }; if (key === active) refreshError = ''; }
-        } catch (err) {
-            if (server === currentServer && key === active) refreshError = (err as Error).message;
-        } finally {
-            pending.delete(requestKey);
-            if (server === currentServer && key === active) loading = false;
-            if (stickToBottom && !query && server === currentServer && key === active) {
-                await tick();
-                if (bodyEl) bodyEl.scrollTop = bodyEl.scrollHeight;
-            }
+    const refresh = createLogRefresh({
+        onLoading: value => { loading = value; },
+        onError: message => { refreshError = message; },
+        onData: (key, body) => {
+            data = { ...data, [key]: body };
+            const currentServer = server;
+            void tick().then(() => {
+                if (server === currentServer && active === key && stickToBottom && !query && bodyEl) bodyEl.scrollTop = bodyEl.scrollHeight;
+            });
         }
-    }
+    });
+    onDestroy(() => refresh.dispose());
 
     function onScroll(): void {
         if (!bodyEl) return;
@@ -81,7 +57,10 @@
         stickToBottom = nearBottom;
     }
 
-    function toggleAuto() { autoRefresh = !autoRefresh; }
+    function toggleAuto(event: Event) {
+        autoRefresh = (event.currentTarget as HTMLInputElement).checked;
+        refresh.configure({ server, key: active, lines }, autoRefresh, pollMs);
+    }
     async function jumpToLatest() {
         query = ''; stickToBottom = true;
         await tick(); if (bodyEl) bodyEl.scrollTop = bodyEl.scrollHeight;
@@ -111,15 +90,10 @@
     }
     $effect(() => { server; data = {}; refreshError = ''; });
     $effect(() => {
-        server;
-        const key = active;
+        const target = { server, key: active, lines };
         const auto = autoRefresh;
         const interval = pollMs;
-        if (!key) return;
-        return untrack(() => {
-            if (auto) return pollVisible(() => fetchLog(key), interval);
-            void fetchLog(key);
-        });
+        untrack(() => refresh.configure(target, auto, interval));
     });
 
     function ago(iso: string | null | undefined): string {
@@ -154,7 +128,7 @@
                 <input type="checkbox" checked={autoRefresh} onchange={toggleAuto} />
                 Auto-refresh · {pollMs / 1000}s
             </label>
-            <button class="refresh" onclick={() => fetchLog(active)} disabled={loading}>
+            <button class="refresh" onclick={() => refresh.refresh()} disabled={loading}>
                 {loading ? 'Refreshing…' : 'Refresh'}
             </button>
         </div>
@@ -163,9 +137,9 @@
     <div class="follow-state"><span>{!autoRefresh ? 'Refresh paused' : 'Auto-refresh on'} · {query ? `${visibleLines.length} matching lines` : stickToBottom ? 'Following latest lines' : 'Reading earlier lines'}</span>{#if !stickToBottom || query}<Button size="sm" variant="ghost" onclick={jumpToLatest}>Jump to latest</Button>{/if}</div>
 
     <div id={uid + '-panel'} role="tabpanel" aria-labelledby={uid + '-' + active}>
-    {#if refreshError}<div class="ui-error" role="alert">{refreshError} {current ? 'Showing the last loaded log.' : ''}<Button size="sm" onclick={() => fetchLog(active)} disabled={loading}>Retry</Button></div>{/if}
+    {#if refreshError}<div class="ui-error" role="alert">{refreshError} {current ? 'Showing the last loaded log.' : ''}<Button size="sm" onclick={() => refresh.refresh()} disabled={loading}>Retry</Button></div>{/if}
     {#if !current && !refreshError}
-        <div class="empty">loading…</div>
+        <div class="empty">{loading ? 'loading…' : 'No log loaded. Select Refresh to load it.'}</div>
     {:else if current && !current.ok}
         <div class="error">error: {current.reason ?? 'unknown'}</div>
     {:else if current?.missing}
diff --git a/src/lib/ui/log-refresh.ts b/src/lib/ui/log-refresh.ts
new file mode 100644
index 0000000..4c6a45b
--- /dev/null
+++ b/src/lib/ui/log-refresh.ts
@@ -0,0 +1,91 @@
+import { pollVisible } from './poll.js';
+
+export interface LogResponse {
+    ok: boolean;
+    key?: string;
+    path?: string;
+    lines?: string[];
+    size?: number;
+    mtime?: string | null;
+    truncated?: boolean;
+    missing?: boolean;
+    reason?: string;
+}
+
+interface Selection { server: string; key: string; lines: number }
+interface Options {
+    onData: (key: string, response: LogResponse) => void;
+    onError: (message: string) => void;
+    onLoading: (loading: boolean) => void;
+    fetcher?: typeof fetch;
+}
+
+/** Pausing freezes the displayed tail, including replies already in flight. */
+export function createLogRefresh(options: Options) {
+    const request = options.fetcher ?? fetch;
+    let selection: Selection | null = null;
+    let automatic = true;
+    let interval = 5000;
+    let stopPolling: (() => void) | undefined;
+    let pending: { controller: AbortController; promise: Promise<void> } | null = null;
+    let generation = 0;
+    let disposed = false;
+
+    function cancel() {
+        generation++;
+        pending?.controller.abort();
+        pending = null;
+        options.onLoading(false);
+    }
+
+    function refresh(): Promise<void> {
+        if (disposed || !selection?.key) return Promise.resolve();
+        if (pending) return pending.promise;
+        const target = selection;
+        const version = generation;
+        const current = () => !disposed && generation === version && selection === target;
+        const entry = { controller: new AbortController(), promise: Promise.resolve() };
+        pending = entry;
+        options.onLoading(true);
+        entry.promise = (async () => {
+            try {
+                const response = await request(`/api/servers/${encodeURIComponent(target.server)}/logs/${encodeURIComponent(target.key)}?lines=${target.lines}`,
+                    { signal: entry.controller.signal, cache: 'no-store' });
+                const body = await response.json() as LogResponse;
+                if (!response.ok || !body.ok) throw new Error(body.reason ?? 'Could not refresh log.');
+                if (current()) { options.onError(''); options.onData(target.key, body); }
+            } catch (error) {
+                if (current() && !entry.controller.signal.aborted) options.onError(error instanceof Error ? error.message : 'Could not refresh log.');
+            } finally {
+                if (pending === entry) pending = null;
+                if (current()) options.onLoading(false);
+            }
+        })();
+        return entry.promise;
+    }
+
+    function configure(target: Selection, enabled: boolean, pollMs: number) {
+        if (disposed) return;
+        const changed = !selection || selection.server !== target.server || selection.key !== target.key || selection.lines !== target.lines;
+        if (!changed && automatic === enabled && interval === pollMs) return;
+        stopPolling?.(); stopPolling = undefined;
+        const pausing = automatic && !enabled;
+        automatic = enabled;
+        interval = pollMs;
+        if (changed || pausing) cancel();
+        if (changed) { selection = target; options.onError(''); }
+        if (!selection?.key) return;
+        if (automatic) stopPolling = pollVisible(refresh, interval);
+        // Changing the selected log is an explicit load, even while paused.
+        else if (changed) void refresh();
+    }
+
+    function dispose() {
+        if (disposed) return;
+        disposed = true;
+        stopPolling?.(); stopPolling = undefined;
+        cancel();
+    }
+
+    return { configure, refresh, dispose };
+}
diff --git a/tests/unit/log-refresh.test.ts b/tests/unit/log-refresh.test.ts
new file mode 100644
index 0000000..e820381
--- /dev/null
+++ b/tests/unit/log-refresh.test.ts
@@ -0,0 +1,155 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+import { createLogRefresh } from '../../src/lib/ui/log-refresh.js';
+
+const target = { server: 't6_zombie_town_1', key: 'console', lines: 1000 };
+const response = (line: string) => new Response(JSON.stringify({ ok: true, lines: [line] }));
+function deferred<T>() {
+    let resolve!: (value: T) => void;
+    let reject!: (error: Error) => void;
+    const promise = new Promise<T>((done, fail) => { resolve = done; reject = fail; });
+    return { promise, resolve, reject };
+}
+let documentStub: EventTarget & { visibilityState: string };
+let controller: ReturnType<typeof createLogRefresh>;
+beforeEach(() => {
+    vi.useFakeTimers();
+    documentStub = Object.assign(new EventTarget(), { visibilityState: 'visible' });
+    vi.stubGlobal('document', documentStub);
+});
+afterEach(() => { controller?.dispose(); vi.useRealTimers(); vi.unstubAllGlobals(); });
+
+function setup() {
+    const fetcher = vi.fn<typeof fetch>();
+    const onData = vi.fn(); const onError = vi.fn(); const onLoading = vi.fn();
+    controller = createLogRefresh({ fetcher, onData, onError, onLoading });
+    return { fetcher, onData, onError, onLoading };
+}
+const visibility = (state: string) => {
+    documentStub.visibilityState = state;
+    documentStub.dispatchEvent(new Event('visibilitychange'));
+};
+
+describe('log refresh controls', () => {
+    it('pauses without fetching again and remains paused across intervals and visibility changes', async () => {
+        const { fetcher, onData, onLoading } = setup();
+        fetcher.mockResolvedValueOnce(response('saved log'));
+        controller.configure(target, true, 5000);
+        await controller.refresh();
+        controller.configure(target, false, 5000);
+        await vi.advanceTimersByTimeAsync(30_000);
+        visibility('hidden'); visibility('visible');
+        await vi.advanceTimersByTimeAsync(30_000);
+        expect(fetcher).toHaveBeenCalledTimes(1);
+        expect(onData).toHaveBeenCalledTimes(1);
+        expect(onLoading).toHaveBeenLastCalledWith(false);
+    });
+
+    it('aborts a pending refresh immediately and ignores its late data and loading updates after resume', async () => {
+        const { fetcher, onData, onLoading, onError } = setup();
+        const old = deferred<Response>(); const fresh = deferred<Response>();
+        fetcher.mockReturnValueOnce(old.promise).mockReturnValueOnce(fresh.promise);
+        controller.configure(target, true, 5000);
+        const pending = controller.refresh();
+        const signal = fetcher.mock.calls[0][1]!.signal!;
+        controller.configure(target, false, 5000);
+        expect(signal.aborted).toBe(true);
+        expect(onLoading).toHaveBeenLastCalledWith(false);
+        expect(fetcher).toHaveBeenCalledTimes(1);
+        controller.configure(target, true, 5000);
+        const resumed = controller.refresh();
+        expect(fetcher).toHaveBeenCalledTimes(2);
+        onData.mockClear(); onError.mockClear(); onLoading.mockClear();
+        // Simulate a transport that delivers a response despite cancellation.
+        old.resolve(response('obsolete'));
+        await pending;
+        expect(onData).not.toHaveBeenCalled();
+        expect(onError).not.toHaveBeenCalled();
+        expect(onLoading).not.toHaveBeenCalled();
+        fresh.resolve(response('current'));
+        await resumed;
+        expect(onData).toHaveBeenCalledWith('console', expect.objectContaining({ lines: ['current'] }));
+        expect(onLoading).toHaveBeenLastCalledWith(false);
+    });
+
+    it('preserves the loaded tail and suppresses a pending refresh error on pause', async () => {
+        const { fetcher, onData, onError } = setup();
+        const next = deferred<Response>();
+        fetcher.mockResolvedValueOnce(response('saved')).mockReturnValueOnce(next.promise);
+        controller.configure(target, true, 5000);
+        await controller.refresh();
+        await vi.advanceTimersByTimeAsync(5000);
+        const pending = controller.refresh();
+        controller.configure(target, false, 5000);
+        onError.mockClear();
+        next.reject(new Error('cancelled response'));
+        await pending;
+        expect(onData).toHaveBeenCalledTimes(1);
+        expect(onData).toHaveBeenLastCalledWith('console', expect.objectContaining({ lines: ['saved'] }));
+        expect(onError).not.toHaveBeenCalled();
+    });
+
+    it('allows a manual refresh while paused without restarting automatic polling', async () => {
+        const { fetcher, onData } = setup();
+        fetcher.mockResolvedValueOnce(response('initial')).mockResolvedValueOnce(response('manual'));
+        controller.configure(target, true, 5000);
+        await controller.refresh();
+        controller.configure(target, false, 5000);
+        await controller.refresh();
+        await vi.advanceTimersByTimeAsync(30_000);
+        expect(fetcher).toHaveBeenCalledTimes(2);
+        expect(onData).toHaveBeenLastCalledWith('console', expect.objectContaining({ lines: ['manual'] }));
+    });
+
+    it('loads a selected log while paused and never accepts a reply from the prior server or tab', async () => {
+        const { fetcher, onData } = setup();
+        const old = deferred<Response>();
+        fetcher.mockReturnValueOnce(old.promise).mockResolvedValueOnce(response('selected log'));
+        controller.configure(target, false, 5000);
+        const pending = controller.refresh();
+        controller.configure({ ...target, server: 'another-server', key: 'games_zm' }, false, 5000);
+        await controller.refresh();
+        old.resolve(response('prior server'));
+        await pending;
+        await vi.advanceTimersByTimeAsync(30_000);
+        expect(fetcher.mock.calls[0][1]!.signal!.aborted).toBe(true);
+        expect(fetcher).toHaveBeenCalledTimes(2);
+        expect(fetcher.mock.calls[1][0]).toContain('/another-server/logs/games_zm?lines=1000');
+        expect(onData).toHaveBeenCalledTimes(1);
+        expect(onData).toHaveBeenLastCalledWith('games_zm', expect.objectContaining({ lines: ['selected log'] }));
+    });
+
+    it('resumes one polling loop and coalesces manual and scheduled reads', async () => {
+        const { fetcher } = setup();
+        fetcher.mockImplementation(async () => response('log'));
+        controller.configure(target, false, 5000);
+        await controller.refresh();
+        controller.configure(target, true, 5000);
+        controller.configure({ ...target }, true, 5000);
+        await Promise.all([controller.refresh(), controller.refresh()]);
+        expect(fetcher).toHaveBeenCalledTimes(2);
+        await vi.advanceTimersByTimeAsync(5000);
+        expect(fetcher).toHaveBeenCalledTimes(3);
+        await vi.advanceTimersByTimeAsync(5000);
+        expect(fetcher).toHaveBeenCalledTimes(4);
+    });
+
+    it('cancels outstanding work and polling on unmount, including a late response body', async () => {
+        const { fetcher, onData, onError, onLoading } = setup();
+        const body = deferred<unknown>();
+        fetcher.mockResolvedValue({ ok: true, json: () => body.promise } as Response);
+        controller.configure(target, true, 5000);
+        const pending = controller.refresh();
+        await Promise.resolve();
+        controller.dispose();
+        expect(fetcher.mock.calls[0][1]!.signal!.aborted).toBe(true);
+        onData.mockClear(); onError.mockClear(); onLoading.mockClear();
+        body.resolve({ ok: true, lines: ['late body'] });
+        await pending;
+        visibility('visible');
+        await vi.advanceTimersByTimeAsync(30_000);
+        expect(fetcher).toHaveBeenCalledTimes(1);
+        expect(onData).not.toHaveBeenCalled();
+        expect(onError).not.toHaveBeenCalled();
+        expect(onLoading).not.toHaveBeenCalled();
+    });
+});