From 44e5ad763794a438ecfd50c8b7f6ea760ea82da5 Mon Sep 17 00:00:00 2001
From: tsne <tsne.dev@outlook.com>
Date: Wed, 1 Jan 2025 14:58:28 +0100
Subject: initial commit

---
 src/time.zig | 134 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 134 insertions(+)
 create mode 100644 src/time.zig

(limited to 'src/time.zig')

diff --git a/src/time.zig b/src/time.zig
new file mode 100644
index 0000000..290c9de
--- /dev/null
+++ b/src/time.zig
@@ -0,0 +1,134 @@
+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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