auto-detect data interval and match default period

main.js

@@ -564,6 +564,22 @@ function bindToolbar() {
   setActiveIndicatorButtons()
 }
 
+function detectDefaultPeriod(data) {
+  if (data.len < 2) return '1m'
+  let minGap = Infinity
+  for (let i = 1; i < Math.min(data.len, 100); i++) {
+    const gap = data.ts[i] - data.ts[i - 1]
+    if (gap > 0 && gap < minGap) minGap = gap
+  }
+  const gapMin = minGap / MINUTE
+  const candidates = PERIODS.map(p => ({ key: p.key, span: getSpanMinutes(p.period) }))
+  let best = candidates[0]
+  for (const c of candidates) {
+    if (c.span <= gapMin + 0.01) best = c
+  }
+  return best.key
+}
+
 function mountChart(source) {
   const chartDom = document.getElementById('chart')
   if (chartDom === null) return
@@ -574,6 +590,11 @@ function mountChart(source) {
     rawLoaded = true
     if (loadingEl) loadingEl.style.display = 'none'
     console.log(`Loaded ${data.len} bars, ${new Date(data.ts[0])} → ${new Date(data.ts[data.len - 1])}`)
+    const defaultPeriod = detectDefaultPeriod(data)
+    if (defaultPeriod !== activePeriodKey) {
+      activePeriodKey = defaultPeriod
+      setActivePeriodButton()
+    }
     if (chart) dispose(chartDom)
     chart = init(chartDom, {
       styles: {