From ecd1cf45e9ccb45d40881aec5e235353cd7d9ab6 Mon Sep 17 00:00:00 2001
From: Jarrett Ye <jarrett.ye@outlook.com>
Date: Wed, 17 Sep 2025 12:28:24 +0800
Subject: [PATCH 1/2] Refactor reviews_for_fsrs function for improved
 performance

Replaced the previous implementation with a more efficient approach using a single loop and pre-allocated vectors. This change reduces the complexity of creating FSRSItems and enhances overall performance, especially for larger datasets.
---
 rslib/src/scheduler/fsrs/params.rs | 34 ++++++++++++++----------------
 1 file changed, 16 insertions(+), 18 deletions(-)

diff --git a/rslib/src/scheduler/fsrs/params.rs b/rslib/src/scheduler/fsrs/params.rs
index 726870fe1..ff31b85f2 100644
--- a/rslib/src/scheduler/fsrs/params.rs
+++ b/rslib/src/scheduler/fsrs/params.rs
@@ -481,24 +481,22 @@ pub(crate) fn reviews_for_fsrs(
     let skip = if training { 1 } else { 0 };
     // Convert the remaining entries into separate FSRSItems, where each item
     // contains all reviews done until then.
-    let items: Vec<(RevlogId, FSRSItem)> = entries
-        .iter()
-        .enumerate()
-        .skip(skip)
-        .map(|(outer_idx, entry)| {
-            let reviews = entries
-                .iter()
-                .take(outer_idx + 1)
-                .enumerate()
-                .map(|(inner_idx, r)| FSRSReview {
-                    rating: r.button_chosen as u32,
-                    delta_t: delta_ts[inner_idx],
-                })
-                .collect();
-            (entry.id, FSRSItem { reviews })
-        })
-        .filter(|(_, item)| !training || item.reviews.last().unwrap().delta_t > 0)
-        .collect_vec();
+    let mut items = Vec::with_capacity(entries.len());
+    let mut current_reviews = Vec::with_capacity(entries.len());
+    for (idx, (entry, &delta_t)) in entries.iter().zip(delta_ts.iter()).enumerate() {
+        current_reviews.push(FSRSReview {
+            rating: entry.button_chosen as u32,
+            delta_t,
+        });
+        if idx >= skip {
+            if !training || current_reviews.last().unwrap().delta_t > 0 {
+                let item = FSRSItem {
+                    reviews: current_reviews.clone(),
+                };
+                items.push((entry.id, item));
+            }
+        }
+    }
     if items.is_empty() {
         None
     } else {

From 38990fe68dbefb8466ce90af26448b94907097e7 Mon Sep 17 00:00:00 2001
From: Jarrett Ye <jarrett.ye@outlook.com>
Date: Wed, 17 Sep 2025 13:38:05 +0800
Subject: [PATCH 2/2] collapse `if` statement

---
 rslib/src/scheduler/fsrs/params.rs | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/rslib/src/scheduler/fsrs/params.rs b/rslib/src/scheduler/fsrs/params.rs
index ff31b85f2..df1ec15bb 100644
--- a/rslib/src/scheduler/fsrs/params.rs
+++ b/rslib/src/scheduler/fsrs/params.rs
@@ -488,13 +488,11 @@ pub(crate) fn reviews_for_fsrs(
             rating: entry.button_chosen as u32,
             delta_t,
         });
-        if idx >= skip {
-            if !training || current_reviews.last().unwrap().delta_t > 0 {
-                let item = FSRSItem {
-                    reviews: current_reviews.clone(),
-                };
-                items.push((entry.id, item));
-            }
+        if idx >= skip && (!training || current_reviews.last().unwrap().delta_t > 0) {
+            let item = FSRSItem {
+                reviews: current_reviews.clone(),
+            };
+            items.push((entry.id, item));
         }
     }
     if items.is_empty() {