fix: mutate polyline points in place on SSE ping, no fetch, no flicker

This reverts commit 72bc11813d.

apps/web/src/utils/sparkline.ts

@@ -9,5 +9,5 @@ export function sparkline(values: number[], width = 120, height = 32): string {
     const y = height - ((v - min) / range) * (height - 4) - 2;
     return `${x},${y}`;
   }).join(' ');
-  return `<svg width="${width}" height="${height}" class="inline-block"><polyline points="${points}" fill="none" stroke="#60a5fa" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/></svg>`;
+  return `<svg width="${width}" height="${height}" class="inline-block" data-vals="${values.join(',')}"><polyline points="${points}" fill="none" stroke="#60a5fa" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/></svg>`;
 }

apps/web/src/views/home.ejs

@@ -75,43 +75,7 @@
       } catch {}
     }, 30000);
 
-    // Client-side sparkline — seed with SSR data, update locally on SSE
+    // SSE: on each ping, update text fields and redraw sparkline in place
-    const _sparkData = {
-      <% it.monitors.forEach(function(m, i) {
-        const lats = (m.pings || []).filter(p => p.latency_ms != null).map(p => p.latency_ms);
-      %>'<%= m.id %>': [<%- lats.join(',') %>]<% if (i < it.monitors.length - 1) { %>,<% } %>
-      <% }) %>
-    };
-
-    function drawSparkline(values, el) {
-      const W = 120, H = 32;
-      if (!values.length) { el.innerHTML = ''; return; }
-      const max = Math.max(...values, 1);
-      const min = Math.min(...values, 0);
-      const range = max - min || 1;
-      const step = W / Math.max(values.length - 1, 1);
-      const pts = values.map((v, i) => {
-        const x = i * step;
-        const y = H - ((v - min) / range) * (H - 4) - 2;
-        return `${x},${y}`;
-      }).join(' ');
-      const svg = document.createElementNS('http://www.w3.org/2000/svg', 'svg');
-      svg.setAttribute('viewBox', `0 0 ${W} ${H}`);
-      svg.setAttribute('width', W);
-      svg.setAttribute('height', H);
-      const pl = document.createElementNS('http://www.w3.org/2000/svg', 'polyline');
-      pl.setAttribute('points', pts);
-      pl.setAttribute('fill', 'none');
-      pl.setAttribute('stroke', '#60a5fa');
-      pl.setAttribute('stroke-width', '1.5');
-      pl.setAttribute('stroke-linecap', 'round');
-      pl.setAttribute('stroke-linejoin', 'round');
-      svg.appendChild(pl);
-      const old = el.querySelector('svg');
-      if (old) old.replaceWith(svg); else el.appendChild(svg);
-    }
-
-    // SSE: update cards in realtime
     watchAccount((ping) => {
       const card = document.querySelector(`[data-monitor-id="${ping.monitor_id}"]`);
       if (!card) return;
@@ -124,13 +88,30 @@
       if (ping.latency_ms != null) card.querySelector('.stat-latency').textContent = ping.latency_ms + 'ms';
       card.querySelector('.stat-last').innerHTML = timeAgo(ping.checked_at);
 
-      // Sparkline — update buffer and redraw locally
+      // Sparkline — append point to existing polyline, drop oldest, no refetch
       if (ping.latency_ms != null) {
-        const buf = _sparkData[ping.monitor_id] = _sparkData[ping.monitor_id] || [];
-        buf.push(ping.latency_ms);
-        if (buf.length > 20) buf.shift();
         const sparkEl = card.querySelector('.stat-sparkline');
-        if (sparkEl) drawSparkline(buf, sparkEl);
+        const polyline = sparkEl?.querySelector('polyline');
+        if (polyline) {
+          const pts = polyline.getAttribute('points').trim().split(' ').filter(Boolean);
+          const W = 120, H = 32;
+          // Parse existing points
+          let coords = pts.map(p => p.split(',').map(Number));
+          // Extract just y-values (latencies are encoded in y relative to scale)
+          // Easier: maintain a data attr on the svg with the raw values
+          const svg = sparkEl.querySelector('svg');
+          let vals = svg?.dataset.vals ? svg.dataset.vals.split(',').map(Number) : [];
+          vals.push(ping.latency_ms);
+          if (vals.length > 20) vals.shift();
+          if (svg) svg.dataset.vals = vals.join(',');
+          // Redraw polyline in place
+          const max = Math.max(...vals, 1);
+          const min = Math.min(...vals, 0);
+          const range = max - min || 1;
+          const step = W / Math.max(vals.length - 1, 1);
+          const newPts = vals.map((v, i) => `${i * step},${H - ((v - min) / range) * (H - 4) - 2}`).join(' ');
+          polyline.setAttribute('points', newPts);
+        }
       }
     });
   </script>