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1. // localtime.hl — epoch ms → "YYYY-MM-DD HH:MM" in Europe/Vienna (ticket #10).
2. //
3. // hl:time has no time zones (now() + a UTC timestamp() only; "timezones are a userland
4. // concern" — its header). This is the smallest correct userland rule for Vienna: the EU
5. // rule in force since 1996 — CEST (UTC+2) from the last Sunday of March 01:00 UTC to the
6. // last Sunday of October 01:00 UTC, CET (UTC+1) otherwise. Storage stays epoch ms (UTC);
7. // only the rendering shifts. Checked against node's Intl (tests/localtime.hl + the gate).
8. import { timestamp } from 'hl:time'
10. static DAY = 86400000
11. static HOUR = 3600000
13. // integer division for a >= 0 (the language has `%` but no floor in the core)
14. static idiv = (a, b) => { return (a - a % b) / b }
16. // days since 1970-01-01 of a civil date (H. Hinnant's days_from_civil, years >= 1970)
17. static daysFromCivil = (y, m, d) => {
18. let yy = m <= 2 ? y - 1 : y
19. let era = idiv(yy, 400)
20. let yoe = yy - era * 400
21. let mp = m > 2 ? m - 3 : m + 9
22. let doy = idiv(153 * mp + 2, 5) + d - 1
23. let doe = yoe * 365 + idiv(yoe, 4) - idiv(yoe, 100) + doy
24. return era * 146097 + doe - 719468
25. }
27. // the last Sunday of a 31-day month (March, October), 01:00 UTC, as epoch ms
28. static lastSundayAt1 = (y, m) => {
29. let days = daysFromCivil(y, m, 31)
30. let wd = (days + 4) % 7 // 0 = Sunday: 1970-01-01 was a Thursday
31. return (days - wd) * DAY + HOUR
32. }
34. static viennaOffset = (ms) => {
35. let y = toNumber(timestamp(ms).slice(0, 4))
36. return ms >= lastSundayAt1(y, 3) && ms < lastSundayAt1(y, 10) ? 2 * HOUR : HOUR
37. }
39. // "YYYY-MM-DD HH:MM", Vienna wall time
40. static localStamp = (ms) => {
41. let t = timestamp(ms + viennaOffset(ms))
42. return t.slice(0, 10) + ' ' + t.slice(11, 16)
43. }