feat: Implement market hours and intelligent sleep duration calculation

m5paper-stockticker.ino

@@ -231,6 +231,68 @@ void fmtMoney(char* buf, size_t len, float val) {
     snprintf(buf, len, "%d.%02d", dollars, cents);
 }
 
+// -------------------------------------------------------
+// US market hours (Eastern time) helpers
+// -------------------------------------------------------
+// Approximate US Eastern DST window: 2nd Sunday of March .. 1st Sunday of Nov.
+// (The exact 2 AM changeover happens on a Sunday when markets are closed, so
+//  day-level precision is sufficient here.)
+bool usEasternDST(const struct tm& u) {
+  int m = u.tm_mon + 1, d = u.tm_mday, wday = u.tm_wday;
+  if (m < 3 || m > 11) return false;
+  if (m > 3 && m < 11) return true;
+  int prevSunday = d - wday;
+  if (m == 3) return prevSunday >= 8;   // on/after 2nd Sunday -> DST
+  return prevSunday <= 0;               // Nov: before 1st Sunday -> DST
+}
+
+// Break current UTC time down into US Eastern local time.
+void getEasternTime(struct tm& etTm) {
+  time_t utc = time(nullptr);
+  struct tm u;
+  gmtime_r(&utc, &u);
+  int off = usEasternDST(u) ? -4 * 3600 : -5 * 3600;
+  time_t et = utc + off;
+  gmtime_r(&et, &etTm);
+}
+
+// Daily market events, as seconds-of-day in US Eastern time.
+const long EVT_OPEN  = 9 * 3600 + 30 * 60;   // 09:30 -> 34200 s
+const long EVT_MID   = 12 * 3600 + 45 * 60;   // 12:45 -> 45900 s (session midpoint)
+const long EVT_CLOSE = 16 * 3600;             // 16:00 -> 57600 s
+
+// Which event this update corresponds to: nearest of open / mid / close.
+const char* marketPhase(const struct tm& et) {
+  long s = et.tm_hour * 3600 + et.tm_min * 60 + et.tm_sec;
+  long dOpen  = labs(s - EVT_OPEN);
+  long dMid   = labs(s - EVT_MID);
+  long dClose = labs(s - EVT_CLOSE);
+  if (dOpen <= dMid && dOpen <= dClose) return "open";
+  if (dClose <= dMid && dClose <= dOpen) return "close";
+  return "mid";
+}
+
+// Microseconds until the next market event: the opening bell (9:30 AM ET),
+// midday (12:45 PM ET), or the closing bell (4:00 PM ET), whichever comes
+// first, Mon-Fri only. We wake for these three events, so the ticker refreshes
+// three times per session.
+uint64_t usUntilNextEvent(const struct tm& et) {
+  const long events[3] = { EVT_OPEN, EVT_MID, EVT_CLOSE };
+  long secsToday = et.tm_hour * 3600 + et.tm_min * 60 + et.tm_sec;
+  for (int d = 0; d <= 7; d++) {
+    int wd = (et.tm_wday + d) % 7;
+    if (wd < 1 || wd > 5) continue;                     // skip Sat/Sun
+    long base = (long)d * 86400 - secsToday;
+    long best = -1;
+    for (int e = 0; e < 3; e++) {
+      long cand = base + events[e];
+      if (cand > 0 && (best < 0 || cand < best)) best = cand;
+    }
+    if (best > 0) return (uint64_t)best * 1000000ULL;
+  }
+  return 24ULL * 3600ULL * 1000000ULL;                  // fallback: 24h
+}
+
 // -------------------------------------------------------
 // Setup
 // -------------------------------------------------------