add Day<Tz>

src/day.rs

@@ -0,0 +1,236 @@
+use core::cmp::Ordering;
+use core::convert::TryFrom;
+use core::fmt;
+use core::fmt::Debug;
+use core::fmt::Display;
+use core::fmt::Write;
+use core::ops::Add;
+use core::ops::Sub;
+
+use crate::oldtime;
+use crate::DateTime;
+use crate::Days;
+use crate::NaiveDate;
+use crate::NaiveTime;
+use crate::TimeZone;
+use oldtime::Duration;
+
+/// Represents the full range of local timestamps in the day
+///
+///
+#[derive(Clone, Copy)]
+pub struct Day<Tz>
+where
+    Tz: TimeZone + Copy + Display,
+{
+    date: NaiveDate,
+    tz: Tz,
+}
+
+impl<Tz> Day<Tz>
+where
+    Tz: TimeZone + Copy + Display,
+{
+    ///
+    pub fn date(&self) -> NaiveDate {
+        self.date
+    }
+
+    ///
+    pub fn zone(&self) -> Tz {
+        self.tz
+    }
+
+    ///
+    pub fn new(date: NaiveDate, tz: Tz) -> Day<Tz> {
+        Day { date, tz }
+    }
+
+    /// Returns the earliest datetime on the given day
+    ///
+    /// panics: This will panic in the following cases:
+    ///   * There are no valid local times in the first six hours of the day
+    /// other: This will return the incorrect value when:
+    ///   * There are valid local times not aligned to a 15-minute reslution
+    pub fn start(&self) -> DateTime<Tz> {
+        // All possible offsets: https://en.wikipedia.org/wiki/List_of_UTC_offsets
+        // means a gap of 15 minutes should be reasonable
+
+        // while looping here is less than ideal, in the vast majority of cases
+        // the inital start time guess will be valid. We have to loop here because
+        // we don't know ex-ante what the earliest valid local time on the day will be
+        // and so we have to attempt a number of reasonable local times until we find one.
+        //
+        // Reasonable in this case means that this function will work for all timezones
+        // mentioned in the above wikipedia list, but will panic in custom implementations
+        // that allow offsets not aligned to a 15-minute resolution.
+
+        let base = NaiveTime::MIN;
+        for multiple in 0..=24 {
+            let start_time = base + oldtime::Duration::minutes(multiple * 15);
+            match self.tz.from_local_datetime(&self.date.and_time(start_time)) {
+                crate::LocalResult::None => continue,
+                crate::LocalResult::Single(dt) => return dt,
+                // in the ambiguous case we pick the one which has an
+                // earlier UTC timestamp
+                // (this could be done without calling `naive_utc`, but
+                // this potentially better expresses the intent)
+                crate::LocalResult::Ambiguous(dt1, dt2) => {
+                    if dt1.naive_utc() < dt2.naive_utc() {
+                        return dt1;
+                    } else {
+                        return dt2;
+                    }
+                }
+            }
+        }
+
+        panic!("Unable to calculate start time for date {} and time zone {}", self.date, self.tz)
+    }
+
+    ///
+    pub fn checked_add_days(self, days: Days) -> Option<Self> {
+        if days.0 == 0 {
+            return Some(self);
+        }
+
+        i64::try_from(days.0).ok().and_then(|d| self.diff_days(d))
+    }
+
+    ///
+    pub fn checked_sub_days(self, days: Days) -> Option<Self> {
+        if days.0 == 0 {
+            return Some(self);
+        }
+
+        i64::try_from(days.0).ok().and_then(|d| self.diff_days(-d))
+    }
+
+    fn diff_days(self, days: i64) -> Option<Self> {
+        let date = self.date.checked_add_signed(Duration::days(days))?;
+        Some(Day { date, ..self })
+    }
+}
+
+impl<Tz> Debug for Day<Tz>
+where
+    Tz: TimeZone + Copy + Display,
+{
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        Debug::fmt(&self.date, f)?;
+        f.write_char(' ')?;
+        self.tz.fmt(f)
+    }
+}
+
+impl<Tz> Display for Day<Tz>
+where
+    Tz: TimeZone + Copy + Display,
+{
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        Debug::fmt(self, f)
+    }
+}
+
+impl<Tz> PartialOrd for Day<Tz>
+where
+    Tz: TimeZone + Copy + Display,
+{
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        self.date.partial_cmp(&other.date)
+    }
+}
+
+impl<Tz> Ord for Day<Tz>
+where
+    Tz: TimeZone + Copy + Display,
+{
+    fn cmp(&self, other: &Self) -> Ordering {
+        self.date.cmp(&other.date)
+    }
+}
+
+impl<Tz> PartialEq for Day<Tz>
+where
+    Tz: TimeZone + Copy + Display,
+{
+    fn eq(&self, other: &Self) -> bool {
+        self.date.eq(&other.date)
+    }
+}
+
+impl<Tz> Eq for Day<Tz> where Tz: TimeZone + Copy + Display {}
+
+impl<Tz> Add<Days> for Day<Tz>
+where
+    Tz: TimeZone + Copy + Display,
+{
+    type Output = Day<Tz>;
+
+    fn add(self, days: Days) -> Self::Output {
+        self.checked_add_days(days).unwrap()
+    }
+}
+
+impl<Tz> Sub<Days> for Day<Tz>
+where
+    Tz: TimeZone + Copy + Display,
+{
+    type Output = Day<Tz>;
+
+    fn sub(self, days: Days) -> Self::Output {
+        self.checked_sub_days(days).unwrap()
+    }
+}
+
+impl<Tz> From<DateTime<Tz>> for Day<Tz>
+where
+    Tz: TimeZone + Copy + Display,
+{
+    fn from(dt: DateTime<Tz>) -> Self {
+        Day { date: dt.date_naive(), tz: dt.timezone() }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Day;
+    use crate::Utc;
+
+    #[test]
+    fn test_start_time() {
+        assert_eq!(
+            Day::from(Utc::now()).start(),
+            Utc::now()
+                .date_naive()
+                .and_hms_opt(0, 0, 0)
+                .unwrap()
+                .and_local_timezone(Utc)
+                .single()
+                .unwrap(),
+        );
+    }
+}
+
+#[cfg(feature = "serde")]
+#[cfg_attr(docsrs, doc(cfg(feature = "serde")))]
+mod serde {
+    use crate::{Day, TimeZone};
+    use core::fmt::Display;
+    use serde::ser;
+
+    // Currently no `Deserialize` option as there is no generic way to create a timezone
+    // from a string representation of it. This could be added to the `TimeZone` trait in future
+
+    impl<Tz> ser::Serialize for Day<Tz>
+    where
+        Tz: TimeZone + Copy + Display,
+    {
+        fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+        where
+            S: ser::Serializer,
+        {
+            serializer.collect_str(&self)
+        }
+    }
+}

src/lib.rs

@@ -457,6 +457,9 @@ mod date;
 #[allow(deprecated)]
 pub use date::{Date, MAX_DATE, MIN_DATE};
 
+mod day;
+pub use day::Day;
+
 mod datetime;
 #[cfg(feature = "rustc-serialize")]
 #[cfg_attr(docsrs, doc(cfg(feature = "rustc-serialize")))]

src/naive/time/mod.rs

@@ -752,7 +752,7 @@ impl NaiveTime {
         (hour, min, sec)
     }
 
-    pub(super) const MIN: Self = Self { secs: 0, frac: 0 };
+    pub(crate) const MIN: Self = Self { secs: 0, frac: 0 };
     pub(super) const MAX: Self = Self { secs: 23 * 3600 + 59 * 60 + 59, frac: 999_999_999 };
 }