linear time WeekendsOnly bdays impl

src/calendars.rs

@@ -1,6 +1,6 @@
 
 use crate::HolidayCalendar;
-use ::chrono::Datelike;
+use ::chrono::{Datelike, NaiveDate};
 
 /// Holiday Calendars for Brazil.
 pub mod brazil;
@@ -16,4 +16,52 @@ impl<T: Datelike + Copy + PartialOrd> HolidayCalendar<T> for WeekendsOnly {
     fn is_holiday(&self, _date: T) -> bool {
         false
     }
+
+    fn bdays(&self, d0: T, d1: T) -> i32 {
+
+        if d0 == d1 {
+            0
+        } else {
+
+            let from: NaiveDate;
+            let to: NaiveDate;
+            let swapped: bool;
+
+            if d1 < d0 {
+                from = NaiveDate::from_num_days_from_ce(d1.num_days_from_ce());
+                to = NaiveDate::from_num_days_from_ce(d0.num_days_from_ce());
+                swapped = true;
+            } else {
+                from = NaiveDate::from_num_days_from_ce(d0.num_days_from_ce());
+                to = NaiveDate::from_num_days_from_ce(d1.num_days_from_ce());
+                swapped = false;
+            }
+
+            let mut result: i32 = 0;
+            let days = to.num_days_from_ce() - from.num_days_from_ce();
+            let whole_weeks = days / 7;
+            result += whole_weeks * 5;
+
+            let mut current_date = NaiveDate::from_num_days_from_ce(from.num_days_from_ce() + whole_weeks * 7);
+
+            if current_date < to {
+                let mut day_of_week = current_date.weekday();
+
+                while current_date < to {
+                    if day_of_week.number_from_monday() < 6 {
+                        result += 1;
+                    }
+
+                    current_date = NaiveDate::from_num_days_from_ce(current_date.num_days_from_ce() + 1);
+                    day_of_week = day_of_week.succ();
+                }
+            }
+
+            if swapped {
+                result = -result;
+            }
+
+            result
+        }
+    }
 }