From da0e42ea0374f8d18c3cd1b893e4511b1c032f0f Mon Sep 17 00:00:00 2001
From: Damien Elmes <gpg@ankiweb.net>
Date: Mon, 25 Sep 2023 14:40:44 +1000
Subject: [PATCH] Fix extract_fsrs_retrievabilty()

- Need to use fuzzed interval to accurately determine elapsed days
- saturating_sub on an i32 is not useful
---
 rslib/src/search/mod.rs       |  2 +-
 rslib/src/search/sqlwriter.rs |  2 +-
 rslib/src/storage/sqlite.rs   | 17 ++++++++---------
 3 files changed, 10 insertions(+), 11 deletions(-)

diff --git a/rslib/src/search/mod.rs b/rslib/src/search/mod.rs
index 5fe7a0195..5d983defc 100644
--- a/rslib/src/search/mod.rs
+++ b/rslib/src/search/mod.rs
@@ -377,7 +377,7 @@ fn card_order_from_sort_column(column: Column, timing: SchedTimingToday) -> Cow<
         Column::Stability => "extract_fsrs_variable(c.data, 's') desc".into(),
         Column::Difficulty => "extract_fsrs_variable(c.data, 'd') desc".into(),
         Column::Retrievability => format!(
-            "extract_fsrs_retrievability(c.data, c.due, {})",
+            "extract_fsrs_retrievability(c.data, c.due, c.ivl, {})",
             timing.days_elapsed
         )
         .into(),
diff --git a/rslib/src/search/sqlwriter.rs b/rslib/src/search/sqlwriter.rs
index 639c55b73..fd1456f5d 100644
--- a/rslib/src/search/sqlwriter.rs
+++ b/rslib/src/search/sqlwriter.rs
@@ -383,7 +383,7 @@ impl SqlWriter<'_> {
                 let elap = self.col.timing_today()?.days_elapsed;
                 write!(
                     self.sql,
-                    "extract_fsrs_retrievability(c.data, c.due, {elap}) {op} {r}"
+                    "extract_fsrs_retrievability(c.data, c.due, c.ivl, {elap}) {op} {r}"
                 )
                 .unwrap()
             }
diff --git a/rslib/src/storage/sqlite.rs b/rslib/src/storage/sqlite.rs
index 30390a954..216837e69 100644
--- a/rslib/src/storage/sqlite.rs
+++ b/rslib/src/storage/sqlite.rs
@@ -265,15 +265,15 @@ fn add_extract_fsrs_variable(db: &Connection) -> rusqlite::Result<()> {
     )
 }
 
-/// eg. extract_fsrs_retrievability(card.data, card.due, timing.days_elapsed) ->
-/// float | null
+/// eg. extract_fsrs_retrievability(card.data, card.due, card.ivl,
+/// timing.days_elapsed) -> float | null
 fn add_extract_fsrs_retrievability(db: &Connection) -> rusqlite::Result<()> {
     db.create_scalar_function(
         "extract_fsrs_retrievability",
-        3,
+        4,
         FunctionFlags::SQLITE_DETERMINISTIC,
         move |ctx| {
-            assert_eq!(ctx.len(), 3, "called with unexpected number of arguments");
+            assert_eq!(ctx.len(), 4, "called with unexpected number of arguments");
 
             let Ok(card_data) = ctx.get_raw(0).as_str() else {
                 return Ok(None);
@@ -289,15 +289,14 @@ fn add_extract_fsrs_retrievability(db: &Connection) -> rusqlite::Result<()> {
                 // learning card
                 return Ok(None);
             }
-            let Ok(days_elapsed) = ctx.get_raw(2).as_i64() else {
+            let Ok(ivl) = ctx.get_raw(2).as_i64() else {
                 return Ok(None);
             };
-            let Some(stability) = card_data.fsrs_stability else {
+            let Ok(days_elapsed) = ctx.get_raw(3).as_i64() else {
                 return Ok(None);
             };
-
-            let review_day = due.saturating_sub(stability as i64);
-            let days_elapsed = days_elapsed.saturating_sub(review_day) as u32;
+            let review_day = (due.max(0) as u32).saturating_sub(ivl as u32);
+            let days_elapsed = (days_elapsed.max(0) as u32).saturating_sub(review_day);
             Ok(card_data.memory_state().map(|state| {
                 FSRS::new(None)
                     .unwrap()