EventNotifier should show dates/times in the client's timezone

EventNotifier/tools/gen_timezones.py

@@ -0,0 +1,87 @@
+#!/usr/bin/env python3
+"""
+Generates configs/eventnotifier_timezones.cfg from the system tzdata.
+
+Each zone lists "<utc timestamp>" "<offset seconds> <abbreviation>" pairs; the
+"0" entry is the offset in effect before the first transition in range.
+Regenerate before END_YEAR runs out (32-bit timestamps end in 2038 anyway).
+"""
+
+import re
+import zoneinfo
+from datetime import datetime, timedelta, timezone
+from pathlib import Path
+
+START_YEAR = 2025
+END_YEAR = 2037
+
+OUT = Path(__file__).resolve().parent.parent / "configs" / "eventnotifier_timezones.cfg"
+
+
+def utc(ts):
+    return datetime.fromtimestamp(ts, timezone.utc)
+
+
+def state(zone, ts):
+    local = utc(ts).astimezone(zone)
+    return int(local.utcoffset().total_seconds()), local.tzname()
+
+
+def abbreviation(name, offset):
+    # tzdata uses numeric names like "+03" / "-0330" for zones without a real abbreviation.
+    if name and re.fullmatch(r"[A-Za-z]+", name):
+        return name
+    sign = "+" if offset >= 0 else "-"
+    hours, rem = divmod(abs(offset), 3600)
+    minutes = rem // 60
+    if hours == 0 and minutes == 0:
+        return "UTC"
+    return f"UTC{sign}{hours}:{minutes:02d}" if minutes else f"UTC{sign}{hours}"
+
+
+def transitions(zone):
+    start = int(datetime(START_YEAR, 1, 1, tzinfo=timezone.utc).timestamp())
+    end = int(datetime(END_YEAR, 12, 31, tzinfo=timezone.utc).timestamp())
+    step = int(timedelta(days=1).total_seconds())
+
+    periods = [(0, *state(zone, start))]
+    prev_ts, prev = start, periods[0][1:]
+    ts = start + step
+    while ts <= end:
+        cur = state(zone, ts)
+        if cur != prev:
+            # Bisect to the first second of the new state.
+            lo, hi = prev_ts, ts
+            while hi - lo > 1:
+                mid = (lo + hi) // 2
+                if state(zone, mid) == prev:
+                    lo = mid
+                else:
+                    hi = mid
+            periods.append((hi, *state(zone, hi)))
+            prev = cur
+        prev_ts = ts
+        ts += step
+    return periods
+
+
+def main():
+    lines = ["// Generated by tools/gen_timezones.py, do not edit by hand.", '"Timezones"', "{"]
+    for name in sorted(zoneinfo.available_timezones()):
+        if name.startswith(("posix/", "right/")) or name in ("Factory", "localtime"):
+            continue
+        zone = zoneinfo.ZoneInfo(name)
+        lines.append(f'\t"{name}"')
+        lines.append("\t{")
+        for ts, offset, tzname in transitions(zone):
+            lines.append(f'\t\t"{ts}"\t"{offset} {abbreviation(tzname, offset)}"')
+        lines.append("\t}")
+    lines.append("}")
+
+    OUT.parent.mkdir(parents=True, exist_ok=True)
+    OUT.write_text("\n".join(lines) + "\n")
+    print(f"Wrote {OUT}")
+
+
+if __name__ == "__main__":
+    main()