add date "library". Thanks @WoodyAtHome!
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src/date.zig
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79
src/date.zig
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// From https://gist.github.com/WoodyAtHome/3ef50b17f0fa2860ac52b97af12f8d15
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// Translated from German. We don't need any local time for this use case, and conversion
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// really requires the TZ DB.
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const std = @import("std");
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pub const DateTime = struct { day: u8, month: u8, year: u16, hour: u8, minute: u8, second: u8 };
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pub fn timestamp2DateTime(timestamp: i64) DateTime {
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// aus https://de.wikipedia.org/wiki/Unixzeit
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const unixtime = @intCast(u64, timestamp);
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const SECONDS_PER_DAY = 86400; //* 24* 60 * 60 */
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const DAYS_PER_YEAR = 365; //* Normal year (no leap year) */
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const DAYS_IN_4_YEARS = 1461; //* 4*365 + 1 */
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const DAYS_IN_100_YEARS = 36524; //* 100*365 + 25 - 1 */
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const DAYS_IN_400_YEARS = 146097; //* 400*365 + 100 - 4 + 1 */
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const DAY_NUMBER_ADJUSTED_1970_01_01 = 719468; //* Day number relates to March 1st */
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var dayN: u64 = DAY_NUMBER_ADJUSTED_1970_01_01 + unixtime / SECONDS_PER_DAY;
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var seconds_since_midnight: u64 = unixtime % SECONDS_PER_DAY;
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var temp: u64 = 0;
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// Leap year rules for Gregorian Calendars
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// Any year divisible by 100 is not a leap year unless also divisible by 400
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temp = 4 * (dayN + DAYS_IN_100_YEARS + 1) / DAYS_IN_400_YEARS - 1;
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var year = @intCast(u16, 100 * temp);
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dayN -= DAYS_IN_100_YEARS * temp + temp / 4;
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// For Julian calendars, each year divisible by 4 is a leap year
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temp = 4 * (dayN + DAYS_PER_YEAR + 1) / DAYS_IN_4_YEARS - 1;
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year += @intCast(u16, temp);
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dayN -= DAYS_PER_YEAR * temp + temp / 4;
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// TagN calculates the days of the year in relation to March 1
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var month = @intCast(u8, (5 * dayN + 2) / 153);
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var day = @intCast(u8, dayN - (@intCast(u64, month) * 153 + 2) / 5 + 1);
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// 153 = 31+30+31+30+31 Days for the 5 months from March through July
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// 153 = 31+30+31+30+31 Days for the 5 months from August through December
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// 31+28 Days for January and February (see below)
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// +2: Rounding adjustment
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// +1: The first day in March is March 1st (not March 0)
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month += 3; // Convert from the day that starts on March 1st, to a human year */
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if (month > 12) { // months 13 and 14 become 1 (January) und 2 (February) of the next year
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month -= 12;
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year += 1;
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}
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var hours = @intCast(u8, seconds_since_midnight / 3600);
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var minutes = @intCast(u8, seconds_since_midnight % 3600 / 60);
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var seconds = @intCast(u8, seconds_since_midnight % 60);
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return DateTime{ .day = day, .month = month, .year = year, .hour = hours, .minute = minutes, .second = seconds };
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}
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pub fn printDateTime(dt: DateTime) void {
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std.log.debug("{:0>4}-{:0>2}-{:0>2}T{:0>2}:{:0>2}:{:0<2}Z", .{
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dt.year,
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dt.month,
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dt.day,
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dt.hour,
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dt.minute,
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dt.second,
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});
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}
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pub fn printNowUtc() void {
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printDateTime(timestamp2DateTime(std.time.timestamp()));
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}
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test "GMT and localtime" {
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std.testing.log_level = .debug;
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std.log.debug("\n", .{});
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printDateTime(timestamp2DateTime(std.time.timestamp()));
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try std.testing.expectEqual(DateTime{ .year = 2020, .month = 8, .day = 28, .hour = 9, .minute = 32, .second = 27 }, timestamp2DateTime(1598607147));
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try std.testing.expectEqual(DateTime{ .year = 2020, .month = 11, .day = 1, .hour = 5, .minute = 6, .second = 7 }, timestamp2DateTime(1604207167));
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}
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