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const std = @import("std");
pub const Time = struct {
year: u16,
month: u8,
day: u8,
hour: u8,
minute: u8,
second: u8,
pub fn from_timestamp(timestamp: u64) Time {
// Source: https://git.musl-libc.org/cgit/musl/tree/src/time/__secs_to_tm.c
// Copyright: https://git.musl-libc.org/cgit/musl/tree/COPYRIGHT
const leapoch = 946684800 + 86400 * (31 + 29); // 2000-03-01 (mod 400 year, immediately after feb29)
const days_per_400y = 365 * 400 + 97;
const days_per_100y = 365 * 100 + 24;
const days_per_4y = 365 * 4 + 1;
const days_in_month = [_]i64{ 31, 30, 31, 30, 31, 31, 30, 31, 30, 31, 31, 29 };
var days: i64 = undefined;
var remsecs: i64 = undefined;
if (timestamp < leapoch) {
const secs: i64 = @as(i64, @intCast(timestamp)) - leapoch;
days = @divTrunc(secs, 86400);
remsecs = @rem(secs, 86400);
} else {
const secs: u64 = timestamp - leapoch;
days = @intCast(secs / 86400);
remsecs = @intCast(@rem(secs, 86400));
}
if (remsecs < 0) {
remsecs += 86400;
days -= 1;
}
var qc_cycles = @divTrunc(days, days_per_400y);
var remdays = @rem(days, days_per_400y);
if (remdays < 0) {
remdays += days_per_400y;
qc_cycles = -1;
}
var c_cycles = @divTrunc(remdays, days_per_100y);
if (c_cycles == 4) {
c_cycles -= 1;
}
remdays -= c_cycles * days_per_100y;
var q_cycles = @divTrunc(remdays, days_per_4y);
if (q_cycles == 25) {
q_cycles -= 1;
}
remdays -= q_cycles * days_per_4y;
var remyears = @divTrunc(remdays, 365);
if (remyears == 4) {
remyears -= 1;
}
remdays -= remyears * 365;
var years = remyears + 4 * q_cycles + 100 * c_cycles + 400 * qc_cycles;
var months: u64 = 0;
while (remdays >= days_in_month[months]) {
remdays -= days_in_month[months];
months += 1;
}
if (months < 10) {
months += 3;
} else {
months -= 9;
years += 1;
}
return .{
.year = @intCast(years + 2000),
.month = @intCast(months),
.day = @intCast(remdays + 1),
.hour = @intCast(@divTrunc(remsecs, 3600)),
.minute = @intCast(@rem(@divTrunc(remsecs, 60), 60)),
.second = @intCast(@rem(remsecs, 60)),
};
}
pub fn format(self: Time, w: *std.io.Writer) std.io.Writer.Error!void {
try w.print(
"{d:0>4}-{d:0>2}-{d:0>2} {d:0>2}:{d:0>2}:{d:0>2} UTC",
.{ self.year, self.month, self.day, self.hour, self.minute, self.second },
);
}
};
pub fn now() u64 {
const ts = std.posix.clock_gettime(.REALTIME) catch return 0;
return if (ts.sec < 0) 0 else @intCast(ts.sec);
}
test "time from timestamp" {
var t: Time = undefined;
const leapoch = 946684800 + 86400 * (31 + 29);
t = .from_timestamp(0);
try std.testing.expectEqual(1970, t.year);
try std.testing.expectEqual(1, t.month);
try std.testing.expectEqual(1, t.day);
try std.testing.expectEqual(0, t.hour);
try std.testing.expectEqual(0, t.minute);
try std.testing.expectEqual(0, t.second);
t = .from_timestamp(leapoch - 1);
try std.testing.expectEqual(2000, t.year);
try std.testing.expectEqual(2, t.month);
try std.testing.expectEqual(29, t.day);
try std.testing.expectEqual(23, t.hour);
try std.testing.expectEqual(59, t.minute);
try std.testing.expectEqual(59, t.second);
t = .from_timestamp(leapoch);
try std.testing.expectEqual(2000, t.year);
try std.testing.expectEqual(3, t.month);
try std.testing.expectEqual(1, t.day);
try std.testing.expectEqual(0, t.hour);
try std.testing.expectEqual(0, t.minute);
try std.testing.expectEqual(0, t.second);
t = .from_timestamp(leapoch + 1);
try std.testing.expectEqual(2000, t.year);
try std.testing.expectEqual(3, t.month);
try std.testing.expectEqual(1, t.day);
try std.testing.expectEqual(0, t.hour);
try std.testing.expectEqual(0, t.minute);
try std.testing.expectEqual(1, t.second);
}
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