cassiopeia: adding time handling utility

apps/cassiopeia/src/time.rs

@@ -0,0 +1,95 @@
+use chrono::{
+    DateTime, FixedOffset as Offset, Local, NaiveDateTime, NaiveTime, TimeZone, Timelike, Utc,
+};
+
+/// A convenience wrapper around [DateTime][t] with fixed timezone
+///
+/// [t]: chrono::DateTime
+pub struct Time {
+    inner: DateTime<Offset>,
+}
+
+impl Time {
+    /// Get the current local time and pin it to a fixed Tz offset
+    pub fn now() -> Self {
+        let now = Local::now();
+        Self {
+            inner: build_datetime(now.time()),
+        }
+    }
+
+    #[cfg(test)]
+    pub(crate) fn fixed(hour: u32, min: u32, sec: u32) -> Self {
+        Self {
+            inner: build_datetime(NaiveTime::from_hms(hour, min, sec)),
+        }
+    }
+
+    /// Return a new instance that is rounded to nearest 15 minutes
+    ///
+    /// It uses the internally provided offset to do rounding, meaning
+    /// that the timezone information will not change, even when
+    /// rounding values that were created in a different timezone.
+    pub fn round(&self) -> Self {
+        let naive = self.inner.time();
+
+        let (new_min, incr_hour) = match naive.minute() {
+            // 0-7 => (0, false)
+            m if m > 0 && m < 7 => (0, false),
+            // 7-22 => (15, false)
+            m if m >= 7 && m < 22 => (15, false),
+            // 22-37 => (30, false)
+            m if m >= 22 && m < 37 => (30, false),
+            // 37-52 => (45, false)
+            m if m >= 37 && m < 52 => (45, false),
+            // 52-59 => (0, true)
+            m if m >= 52 && m <= 59 => (0, true),
+            _ => unreachable!(),
+        };
+
+        let hour = naive.hour();
+        let new = NaiveTime::from_hms(if incr_hour { hour + 1 } else { hour }, new_min, 0);
+        let offset = self.inner.offset();
+        let date = self.inner.date();
+
+        Self {
+            inner: DateTime::from_utc(NaiveDateTime::new(date.naive_local(), new), *offset),
+        }
+    }
+
+    pub fn hour(&self) -> u32 {
+        self.inner.hour()
+    }
+
+    pub fn minute(&self) -> u32 {
+        self.inner.minute()
+    }
+
+    pub fn second(&self) -> u32 {
+        self.inner.second()
+    }
+}
+
+/// Build a DateTime with the current local fixed offset
+fn build_datetime(nt: NaiveTime) -> DateTime<Offset> {
+    let date = Utc::now().date().naive_local();
+    let offset = Local.offset_from_utc_date(&date);
+
+    DateTime::from_utc(NaiveDateTime::new(date, nt), offset)
+}
+
+#[test]
+fn simple() {
+    let t = Time::fixed(10, 44, 0);
+    let round = t.round();
+    assert_eq!(round.minute(), 45);
+
+    let t = Time::fixed(6, 8, 0);
+    let round = t.round();
+    assert_eq!(round.minute(), 15);
+
+    let t = Time::fixed(6, 55, 0);
+    let round = t.round();
+    assert_eq!(round.minute(), 0);
+    assert_eq!(round.hour(), 7);
+}