1 files changed, 108 insertions, 0 deletions
diff --git a/system/libraries/format/date.zig b/system/libraries/format/date.zig
new file mode 100644
index 0000000..d90adec
--- /dev/null
+++ b/system/libraries/format/date.zig
@@ -0,0 +1,108 @@
+//! Date formatting
+
+const int = @import("int.zig");
+
+const SECONDS_PER_DAY: u64 = 86400;
+const SECONDS_PER_HOUR: u64 = 3600;
+const SECONDS_PER_MINUTE: u64 = 60;
+const DAYS_PER_4_YEARS: u64 = 1461;
+
+const MONTH_NAMES = [_][]const u8{ "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec" };
+const DAYS_NORMAL = [_]u64{ 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
+const DAYS_LEAP = [_]u64{ 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
+
+pub fn format(timestamp: u64, buf: []u8) []u8 {
+    if (timestamp == 0) {
+        const default = "01 Jan 1970 00:00";
+        for (default, 0..) |c, i| {
+            buf[i] = c;
+        }
+        return buf[0..default.len];
+    }
+
+    const days_since_epoch = timestamp / SECONDS_PER_DAY;
+    const seconds_today = timestamp % SECONDS_PER_DAY;
+    const hours = seconds_today / SECONDS_PER_HOUR;
+    const minutes = (seconds_today % SECONDS_PER_HOUR) / SECONDS_PER_MINUTE;
+
+    var year: u64 = 1970;
+    var remaining_days = days_since_epoch;
+
+    const four_year_cycles = remaining_days / DAYS_PER_4_YEARS;
+    year += four_year_cycles * 4;
+    remaining_days = remaining_days % DAYS_PER_4_YEARS;
+
+    while (remaining_days >= 365) {
+        const is_leap = isLeapYear(year);
+        const days_this_year: u64 = if (is_leap) 366 else 365;
+        if (remaining_days >= days_this_year) {
+            remaining_days -= days_this_year;
+            year += 1;
+        } else {
+            break;
+        }
+    }
+
+    const is_leap = isLeapYear(year);
+    const days_in_months = if (is_leap) DAYS_LEAP else DAYS_NORMAL;
+
+    var month: usize = 0;
+    var day: u64 = remaining_days + 1;
+
+    for (days_in_months, 0..) |days, m| {
+        if (day <= days) {
+            month = m;
+            break;
+        }
+        day -= days;
+    }
+
+    var pos: usize = 0;
+
+    if (day < 10) {
+        buf[pos] = '0';
+        pos += 1;
+    }
+    const day_str = int.toStr(day, buf[pos..]);
+    pos += day_str.len;
+
+    buf[pos] = ' ';
+    pos += 1;
+
+    for (MONTH_NAMES[month]) |c| {
+        buf[pos] = c;
+        pos += 1;
+    }
+
+    buf[pos] = ' ';
+    pos += 1;
+
+    const year_str = int.toStr(year, buf[pos..]);
+    pos += year_str.len;
+
+    buf[pos] = ' ';
+    pos += 1;
+
+    if (hours < 10) {
+        buf[pos] = '0';
+        pos += 1;
+    }
+    const hour_str = int.toStr(hours, buf[pos..]);
+    pos += hour_str.len;
+
+    buf[pos] = ':';
+    pos += 1;
+
+    if (minutes < 10) {
+        buf[pos] = '0';
+        pos += 1;
+    }
+    const min_str = int.toStr(minutes, buf[pos..]);
+    pos += min_str.len;
+
+    return buf[0..pos];
+}
+
+fn isLeapYear(year: u64) bool {
+    return (year % 4 == 0 and year % 100 != 0) or (year % 400 == 0);
+}