Check review count up front

https://forums.ankiweb.net/t/inconsistent-number-of-reviews-when-clicking-optimize/39275/7

ftl/core/deck-config.ftl

@@ -339,7 +339,7 @@ deck-config-must-have-1000-reviews =
     { $count ->
         [one] Only { $count } review was found.
        *[other] Only { $count } reviews were found.
-    } You must have at least 1000 reviews to generate custom parameters.
+    } You must have at least 1000 reviews for this operation.
 # Numbers that control how aggressively the FSRS algorithm schedules cards
 deck-config-weights = FSRS parameters
 deck-config-compute-optimal-weights = Optimize FSRS parameters

rslib/src/backend/error.rs

@@ -48,6 +48,7 @@ impl AnkiError {
             #[cfg(windows)]
             AnkiError::WindowsError { .. } => Kind::OsError,
             AnkiError::SchedulerUpgradeRequired => Kind::SchedulerUpgradeRequired,
+            AnkiError::FsrsInsufficientReviews { .. } => Kind::InvalidInput,
         };
 
         anki_proto::backend::BackendError {

rslib/src/error/mod.rs

@@ -114,7 +114,12 @@ pub enum AnkiError {
     InvalidMethodIndex,
     InvalidServiceIndex,
     FsrsWeightsInvalid,
+    // Returned by fsrs-rs; may happen even if 1000+ reviews
     FsrsInsufficientData,
+    // Generated by our backend if count < 1000
+    FsrsInsufficientReviews {
+        count: usize,
+    },
     FsrsUnableToDetermineDesiredRetention,
     SchedulerUpgradeRequired,
 }
@@ -169,6 +174,9 @@ impl AnkiError {
             AnkiError::InvalidInput { source } => source.message(),
             AnkiError::NotFound { source } => source.message(tr),
             AnkiError::FsrsInsufficientData => tr.deck_config_not_enough_history().into(),
+            AnkiError::FsrsInsufficientReviews { count } => {
+                tr.deck_config_must_have_1000_reviews(*count).into()
+            }
             AnkiError::FsrsWeightsInvalid => tr.deck_config_invalid_weights().into(),
             AnkiError::SchedulerUpgradeRequired => {
                 tr.scheduling_update_required().replace("V2", "v3")

rslib/src/scheduler/fsrs/retention.rs

@@ -75,6 +75,11 @@ impl Collection {
             .col
             .storage
             .get_revlog_entries_for_searched_cards_in_card_order()?;
+        if revlogs.len() < 1000 {
+            return Err(AnkiError::FsrsInsufficientReviews {
+                count: revlogs.len(),
+            });
+        }
 
         let first_rating_count = revlogs
             .iter()

rslib/src/scheduler/fsrs/weights.rs

@@ -39,6 +39,11 @@ impl Collection {
         let mut anki_progress = self.new_progress_handler::<ComputeWeightsProgress>();
         let timing = self.timing_today()?;
         let revlogs = self.revlog_for_srs(search)?;
+        if revlogs.len() < 1000 {
+            return Err(AnkiError::FsrsInsufficientReviews {
+                count: revlogs.len(),
+            });
+        }
         let items = fsrs_items_for_training(revlogs, timing.next_day_at);
         let fsrs_items = items.len() as u32;
         anki_progress.update(false, |p| {
@@ -118,6 +123,11 @@ impl Collection {
             .col
             .storage
             .get_revlog_entries_for_searched_cards_in_card_order()?;
+        if revlogs.len() < 1000 {
+            return Err(AnkiError::FsrsInsufficientReviews {
+                count: revlogs.len(),
+            });
+        }
         anki_progress.state.fsrs_items = revlogs.len() as u32;
         let items = fsrs_items_for_training(revlogs, timing.next_day_at);
         let fsrs = FSRS::new(Some(weights))?;