From 66d0046b8a847df3b460207ed4ed52964da44063 Mon Sep 17 00:00:00 2001
From: Damien Elmes <gpg@ankiweb.net>
Date: Mon, 8 Jan 2024 14:05:09 +1000
Subject: [PATCH] Check review count up front

https://forums.ankiweb.net/t/inconsistent-number-of-reviews-when-clicking-optimize/39275/7
---
 ftl/core/deck-config.ftl              |  2 +-
 rslib/src/backend/error.rs            |  1 +
 rslib/src/error/mod.rs                |  8 ++++++++
 rslib/src/scheduler/fsrs/retention.rs |  5 +++++
 rslib/src/scheduler/fsrs/weights.rs   | 10 ++++++++++
 5 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/ftl/core/deck-config.ftl b/ftl/core/deck-config.ftl
index d5530d401..10120d905 100644
--- a/ftl/core/deck-config.ftl
+++ b/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
diff --git a/rslib/src/backend/error.rs b/rslib/src/backend/error.rs
index da7addf51..d1671f074 100644
--- a/rslib/src/backend/error.rs
+++ b/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 {
diff --git a/rslib/src/error/mod.rs b/rslib/src/error/mod.rs
index 47ad88fbe..77c6b164e 100644
--- a/rslib/src/error/mod.rs
+++ b/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")
diff --git a/rslib/src/scheduler/fsrs/retention.rs b/rslib/src/scheduler/fsrs/retention.rs
index 509008605..375e5870b 100644
--- a/rslib/src/scheduler/fsrs/retention.rs
+++ b/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()
diff --git a/rslib/src/scheduler/fsrs/weights.rs b/rslib/src/scheduler/fsrs/weights.rs
index dfaa007b4..e8049225b 100644
--- a/rslib/src/scheduler/fsrs/weights.rs
+++ b/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))?;