Fix/set due date on intraday learning card (#4101)

- Introduced `next_day_start` parameter to `set_due_date` for improved due date handling.
- Updated logic to account for Unix epoch timestamps when calculating due dates.

rslib/src/scheduler/reviews.rs

@@ -17,6 +17,7 @@ use crate::collection::Collection;
 use crate::config::StringKey;
 use crate::error::Result;
 use crate::prelude::*;
+use crate::scheduler::timing::is_unix_epoch_timestamp;
 
 impl Card {
     /// Make card due in `days_from_today`.
@@ -27,6 +28,7 @@ impl Card {
     fn set_due_date(
         &mut self,
         today: u32,
+        next_day_start: i64,
         days_from_today: u32,
         ease_factor: f32,
         force_reset: bool,
@@ -34,8 +36,15 @@ impl Card {
         let new_due = (today + days_from_today) as i32;
         let fsrs_enabled = self.memory_state.is_some();
         let new_interval = if fsrs_enabled {
-            self.interval
+            let due = self.original_or_current_due();
-                .saturating_add_signed(new_due - self.original_or_current_due())
+            let due_diff = if is_unix_epoch_timestamp(due) {
+                let offset = (due as i64 - next_day_start) / 86_400;
+                let due = (today as i64 + offset) as i32;
+                new_due - due
+            } else {
+                new_due - due
+            };
+            self.interval.saturating_add_signed(due_diff)
         } else if force_reset || !matches!(self.ctype, CardType::Review | CardType::Relearn) {
             days_from_today.max(1)
         } else {
@@ -114,6 +123,7 @@ impl Collection {
         let spec = parse_due_date_str(days)?;
         let usn = self.usn()?;
         let today = self.timing_today()?.days_elapsed;
+        let next_day_start = self.timing_today()?.next_day_at.0;
         let mut rng = rand::rng();
         let distribution = Uniform::new_inclusive(spec.min, spec.max).unwrap();
         let mut decks_initial_ease: HashMap<DeckId, f32> = HashMap::new();
@@ -137,7 +147,13 @@ impl Collection {
                 };
                 let original = card.clone();
                 let days_from_today = distribution.sample(&mut rng);
-                card.set_due_date(today, days_from_today, ease_factor, spec.force_reset);
+                card.set_due_date(
+                    today,
+                    next_day_start,
+                    days_from_today,
+                    ease_factor,
+                    spec.force_reset,
+                );
                 col.log_manually_scheduled_review(&card, original.interval, usn)?;
                 col.update_card_inner(&mut card, original, usn)?;
             }
@@ -228,26 +244,26 @@ mod test {
         let mut c = Card::new(NoteId(0), 0, DeckId(0), 0);
 
         // setting the due date of a new card will convert it
-        c.set_due_date(5, 2, 1.8, false);
+        c.set_due_date(5, 0, 2, 1.8, false);
         assert_eq!(c.ctype, CardType::Review);
         assert_eq!(c.due, 7);
         assert_eq!(c.interval, 2);
         assert_eq!(c.ease_factor, 1800);
 
         // reschedule it again the next day, shifting it from day 7 to day 9
-        c.set_due_date(6, 3, 2.5, false);
+        c.set_due_date(6, 0, 3, 2.5, false);
         assert_eq!(c.due, 9);
         assert_eq!(c.interval, 2);
         assert_eq!(c.ease_factor, 1800); // interval doesn't change
 
         // we can bring cards forward too - return it to its original due date
-        c.set_due_date(6, 1, 2.4, false);
+        c.set_due_date(6, 0, 1, 2.4, false);
         assert_eq!(c.due, 7);
         assert_eq!(c.interval, 2);
         assert_eq!(c.ease_factor, 1800); // interval doesn't change
 
         // we can force the interval to be reset instead of shifted
-        c.set_due_date(6, 3, 2.3, true);
+        c.set_due_date(6, 0, 3, 2.3, true);
         assert_eq!(c.due, 9);
         assert_eq!(c.interval, 3);
         assert_eq!(c.ease_factor, 1800); // interval doesn't change
@@ -259,7 +275,7 @@ mod test {
         c.original_deck_id = DeckId(1);
         c.due = -10000;
         c.queue = CardQueue::New;
-        c.set_due_date(6, 1, 2.2, false);
+        c.set_due_date(6, 0, 1, 2.2, false);
         assert_eq!(c.due, 7);
         assert_eq!(c.interval, 2);
         assert_eq!(c.ease_factor, 2200);
@@ -271,7 +287,7 @@ mod test {
         c.ctype = CardType::Relearn;
         c.original_due = c.due;
         c.due = 12345678;
-        c.set_due_date(6, 10, 2.1, false);
+        c.set_due_date(6, 0, 10, 2.1, false);
         assert_eq!(c.due, 16);
         assert_eq!(c.interval, 2);
         assert_eq!(c.ease_factor, 2200); // interval doesn't change