From aa351f86d913df8ebba11a5372e2bd2e1cdc0d3d Mon Sep 17 00:00:00 2001
From: user1823 <92206575+user1823@users.noreply.github.com>
Date: Thu, 25 Sep 2025 19:01:32 +0530
Subject: [PATCH] Fix/Ensure fuzz doesn't go backward during rescheduling

Fixes https://github.com/ankitects/anki/issues/2694
---
 rslib/src/scheduler/fsrs/memory_state.rs | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/rslib/src/scheduler/fsrs/memory_state.rs b/rslib/src/scheduler/fsrs/memory_state.rs
index 420ead5a3..ce918c5c4 100644
--- a/rslib/src/scheduler/fsrs/memory_state.rs
+++ b/rslib/src/scheduler/fsrs/memory_state.rs
@@ -136,6 +136,15 @@ impl Collection {
                                             let deckconfig_id = deck.config_id().unwrap();
                                             // reschedule it
                                             let original_interval = card.interval;
+                                            // This should ideally use lastIvl from the latest revlog entry.
+                                            // days_elapsed is used for performance reasons.
+                                            let greater_than_last = |interval: u32| {
+                                                if interval > days_elapsed {
+                                                    days_elapsed + 1
+                                                } else {
+                                                    0
+                                                }
+                                            };
                                             let interval = fsrs.next_interval(
                                                 Some(state.stability),
                                                 desired_retention,
@@ -146,7 +155,7 @@ impl Collection {
                                                 .and_then(|r| {
                                                     r.find_interval(
                                                         interval,
-                                                        1,
+                                                        greater_than_last(interval as u32).max(1),
                                                         req.max_interval,
                                                         days_elapsed as u32,
                                                         deckconfig_id,
@@ -157,7 +166,7 @@ impl Collection {
                                                     with_review_fuzz(
                                                         card.get_fuzz_factor(true),
                                                         interval,
-                                                        1,
+                                                        greater_than_last(interval as u32).max(1),
                                                         req.max_interval,
                                                     )
                                                 });