1 files changed, 147 insertions, 0 deletions
diff --git a/src/time_crate/date.rs b/src/time_crate/date.rs
new file mode 100644
index 0000000..981630e
--- /dev/null
+++ b/src/time_crate/date.rs
@@ -0,0 +1,147 @@
+use super::Weekday::{self, Friday, Monday, Saturday, Sunday, Thursday, Tuesday, Wednesday};
+#[allow(unused_imports)]
+use standback::prelude::*;
+
+fn is_leap_year(year: i32) -> bool {
+    (year % 4 == 0) && ((year % 100 != 0) || (year % 400 == 0))
+}
+
+pub(crate) fn days_in_year(year: i32) -> u16 {
+    365 + is_leap_year(year) as u16
+}
+
+/// The number of days in a month in both common and leap years.
+const DAYS_IN_MONTH_COMMON_LEAP: [[u16; 12]; 2] = [
+    [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31],
+    [31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31],
+];
+
+#[allow(clippy::cast_possible_truncation)]
+pub(crate) fn days_in_year_month(year: i32, month: u8) -> u8 {
+    DAYS_IN_MONTH_COMMON_LEAP[is_leap_year(year) as usize][month as usize - 1] as u8
+}
+
+pub(crate) fn weeks_in_year(year: i32) -> u8 {
+    let weekday = Date { year, ordinal: 1 }.weekday();
+
+    if (weekday == Thursday) || (weekday == Wednesday && is_leap_year(year)) {
+        53
+    } else {
+        52
+    }
+}
+
+pub(crate) struct Date {
+    year: i32,
+    pub(crate) ordinal: u16,
+}
+
+impl Date {
+    pub(crate) const fn as_yo(&self) -> (i32, u16) {
+        (self.year, self.ordinal)
+    }
+
+    pub(crate) fn month_day(&self) -> (u8, u8) {
+        const CUMULATIVE_DAYS_IN_MONTH_COMMON_LEAP: [[u16; 11]; 2] = [
+            [31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334],
+            [31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335],
+        ];
+
+        let days = CUMULATIVE_DAYS_IN_MONTH_COMMON_LEAP[is_leap_year(self.year) as usize];
+        let ordinal = self.ordinal;
+
+        #[allow(clippy::cast_possible_truncation)]
+        {
+            if ordinal > days[10] {
+                (12, (ordinal - days[10]) as u8)
+            } else if ordinal > days[9] {
+                (11, (ordinal - days[9]) as u8)
+            } else if ordinal > days[8] {
+                (10, (ordinal - days[8]) as u8)
+            } else if ordinal > days[7] {
+                (9, (ordinal - days[7]) as u8)
+            } else if ordinal > days[6] {
+                (8, (ordinal - days[6]) as u8)
+            } else if ordinal > days[5] {
+                (7, (ordinal - days[5]) as u8)
+            } else if ordinal > days[4] {
+                (6, (ordinal - days[4]) as u8)
+            } else if ordinal > days[3] {
+                (5, (ordinal - days[3]) as u8)
+            } else if ordinal > days[2] {
+                (4, (ordinal - days[2]) as u8)
+            } else if ordinal > days[1] {
+                (3, (ordinal - days[1]) as u8)
+            } else if ordinal > days[0] {
+                (2, (ordinal - days[0]) as u8)
+            } else {
+                (1, ordinal as u8)
+            }
+        }
+    }
+
+    #[allow(unstable_name_collisions)]
+    pub(crate) fn weekday(&self) -> Weekday {
+        let (month, day) = self.month_day();
+
+        let (month, adjusted_year) = if month < 3 {
+            (month + 12, self.year - 1)
+        } else {
+            (month, self.year)
+        };
+
+        match (day as i32 + (13 * (month as i32 + 1)) / 5 + adjusted_year + adjusted_year / 4
+            - adjusted_year / 100
+            + adjusted_year / 400)
+            .rem_euclid(7)
+        {
+            0 => Saturday,
+            1 => Sunday,
+            2 => Monday,
+            3 => Tuesday,
+            4 => Wednesday,
+            5 => Thursday,
+            6 => Friday,
+            _ => unreachable!("A value mod 7 is always in the range 0..7"),
+        }
+    }
+
+    pub(crate) fn from_iso_ywd_unchecked(year: i32, week: u8, iso_weekday_number: u8) -> Date {
+        let ordinal = week as u16 * 7 + iso_weekday_number as u16
+            - (Self::from_yo_unchecked(year, 4)
+                .weekday()
+                .iso_weekday_number() as u16
+                + 3);
+
+        if ordinal < 1 {
+            return Self::from_yo_unchecked(year - 1, ordinal + days_in_year(year - 1));
+        }
+
+        let days_in_cur_year = days_in_year(year);
+        if ordinal > days_in_cur_year {
+            Self::from_yo_unchecked(year + 1, ordinal - days_in_cur_year)
+        } else {
+            Self::from_yo_unchecked(year, ordinal)
+        }
+    }
+
+    pub(crate) fn from_ymd_unchecked(year: i32, month: u8, day: u8) -> Date {
+        /// Cumulative days through the beginning of a month in both common and
+        /// leap years.
+        const DAYS_CUMULATIVE_COMMON_LEAP: [[u16; 12]; 2] = [
+            [0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334],
+            [0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335],
+        ];
+
+        let ordinal = DAYS_CUMULATIVE_COMMON_LEAP[is_leap_year(year) as usize][month as usize - 1];
+
+        Date {
+            year,
+            ordinal: ordinal + day as u16,
+        }
+    }
+
+    pub(crate) const fn from_yo_unchecked(year: i32, ordinal: u16) -> Date {
+        Date { year, ordinal }
+    }
+}