refactor(datetime,calendar): Move week_of_month implementation detail…

…s into calendar.

components/calendar/src/arithmetic.rs

@@ -184,6 +184,31 @@ pub mod week_of {
         }
     }
 
+    /// Computes & returns the week of given month or year accoding to a calendar with min_week_days = 1.
+    ///
+    /// # Arguments
+    ///  - first_weekday: The first day of a week.
+    ///  - day: 1-based day of the month or year.
+    ///  - week_day: The weekday of `day`.
+    pub fn simple_week_of(first_weekday: IsoWeekday, day: u16, week_day: IsoWeekday) -> u16 {
+        let calendar = CalendarInfo {
+            first_weekday,
+            min_week_days: 1,
+        };
+
+        week_of(
+            &calendar,
+            // The duration of the current and previous unit does not influence the result if min_week_days = 1
+            // so we only need to use a valid value.
+            MIN_UNIT_DAYS,
+            MIN_UNIT_DAYS,
+            day,
+            week_day,
+        )
+        .expect("week_of should can't fail with MIN_UNIT_DAYS")
+        .week
+    }
+
     #[cfg(test)]
     mod tests {
         use super::{week_of, CalendarInfo, RelativeUnit, RelativeWeek, UnitInfo, WeekOf};
@@ -425,4 +450,29 @@ pub mod week_of {
             Ok(())
         }
     }
+
+    #[test]
+    fn test_simple_week_of() {
+        // The 1st is a Monday and the week starts on Mondays.
+        assert_eq!(
+            simple_week_of(IsoWeekday::Monday, 2, IsoWeekday::Tuesday),
+            1
+        );
+        assert_eq!(simple_week_of(IsoWeekday::Monday, 7, IsoWeekday::Sunday), 1);
+        assert_eq!(simple_week_of(IsoWeekday::Monday, 8, IsoWeekday::Monday), 2);
+
+        // The 1st is a Wednesday and the week starts on Tuesdays.
+        assert_eq!(
+            simple_week_of(IsoWeekday::Tuesday, 1, IsoWeekday::Wednesday),
+            1
+        );
+        assert_eq!(
+            simple_week_of(IsoWeekday::Tuesday, 6, IsoWeekday::Monday),
+            1
+        );
+        assert_eq!(
+            simple_week_of(IsoWeekday::Tuesday, 7, IsoWeekday::Tuesday),
+            2
+        );
+    }
 }

components/datetime/src/date.rs

@@ -175,28 +175,18 @@ fn week_of_month<T: DateInput>(
     datetime: &T,
     first_weekday: IsoWeekday,
 ) -> Result<WeekOfMonth, DateTimeError> {
-    // This value isn't used by week_of() given that we use a calendar with min_week_days = 1.
-    const UNUSED_DAYS_IN_MONTH: u16 = 60;
-
-    let calendar = week_of::CalendarInfo {
-        first_weekday,
-        min_week_days: 1,
-    };
-
     let day_of_month = datetime
         .day_of_month()
         .ok_or(DateTimeError::MissingInput("DateTimeInput::day_of_month"))?;
 
-    let week = week_of::week_of(
-        &calendar,
-        UNUSED_DAYS_IN_MONTH,
-        UNUSED_DAYS_IN_MONTH,
+    let week = week_of::simple_week_of(
+        first_weekday,
         day_of_month.0 as u16,
         datetime
             .iso_weekday()
             .ok_or(DateTimeError::MissingInput("DateTimeInput::iso_weekday"))?,
-    )?;
-    Ok(WeekOfMonth(u32::from(week.week)))
+    );
+    Ok(WeekOfMonth(u32::from(week)))
 }
 
 impl<'data, T: DateTimeInput> DateTimeInputWithLocale<'data, T> {