From 4316a42991f59fb95a7dec2c47b5fc5c7880e3ff Mon Sep 17 00:00:00 2001
From: Alex <git@pentive.com>
Date: Sat, 27 Apr 2024 09:28:10 -0500
Subject: [PATCH] add `minute_offset` and update to fsrs 0.6.2

---
 Cargo.lock           |  2 +-
 fsrs-rs              |  2 +-
 sandbox/src/train.ts | 20 +++++++++++++++++++-
 src/lib.rs           |  8 ++++++--
 4 files changed, 27 insertions(+), 5 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index fc63c76..38b60eb 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -726,7 +726,7 @@ checksum = "aa9a19cbb55df58761df49b23516a86d432839add4af60fc256da840f66ed35b"
 
 [[package]]
 name = "fsrs"
-version = "0.6.1"
+version = "0.6.2"
 dependencies = [
  "burn",
  "chrono",
diff --git a/fsrs-rs b/fsrs-rs
index 2170a29..14a6284 160000
--- a/fsrs-rs
+++ b/fsrs-rs
@@ -1 +1 @@
-Subproject commit 2170a2903699ccb99d913def9f5f6e485e1681ca
+Subproject commit 14a62849af95a0df0f97cc1251390d03a1dda19c
diff --git a/sandbox/src/train.ts b/sandbox/src/train.ts
index d1010f9..1c68fea 100644
--- a/sandbox/src/train.ts
+++ b/sandbox/src/train.ts
@@ -135,7 +135,25 @@ function computeParameters(
 		// Do not read from memory after `Stop` is posted!
 		pointer: progress.pointer(),
 	} satisfies ProgressMessage)
-	let parameters = fsrs.computeParametersAnki(cids, eases, ids, types, progress)
+	// MDN states:
+	//     The number of minutes returned by getTimezoneOffset() is positive if the
+	//     local time zone is behind UTC, and negative if the local time zone is ahead of UTC.
+	// This is useful when going from our timezone to UTC; our local time + offset = UTC.
+	// However, we want to go from UTC to our timezone. (Anki revlog id is UTC, and we want to convert it to local time.)
+	// So we flip the sign of `getTimezoneOffset()`.
+	let timeZoneMinutesOffset = new Date().getTimezoneOffset() * -1
+	let ankiNextDayStartsAtMinutes = 4 * 60
+	let parameters = fsrs.computeParametersAnki(
+		// We subtract ankiNextDayStartsAtMinutes because
+		// we want a review done at, say, 1am to be done for the *prior* day.
+		// Adding would move it into the future.
+		timeZoneMinutesOffset - ankiNextDayStartsAtMinutes,
+		cids,
+		eases,
+		ids,
+		types,
+		progress,
+	)
 	self.postMessage({
 		tag: 'Stop',
 		parameters,
diff --git a/src/lib.rs b/src/lib.rs
index 3d5b7ef..0e6d659 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -29,9 +29,11 @@ impl FSRSwasm {
         Self { model }
     }
 
+    /// `minute_offset` should be the `user's timezone offset from UTC` minus `Anki's "next day starts at"`, in minutes.
     #[wasm_bindgen(js_name = computeParametersAnki)]
     pub fn compute_parameters_anki(
         &mut self,
+        minute_offset: i32,
         cids: &[i64],
         eases: &[u8],
         ids: &[i64],
@@ -39,7 +41,7 @@ impl FSRSwasm {
         progress: Option<Progress>,
     ) -> Vec<f32> {
         let revlog_entries = to_revlog_entry(cids, eases, ids, types);
-        let items = anki_to_fsrs(revlog_entries);
+        let items = anki_to_fsrs(revlog_entries, minute_offset);
         self.train_and_set_parameters(items, progress)
     }
 
@@ -98,9 +100,11 @@ impl FSRSwasm {
     }
 
     #[wasm_bindgen(js_name = memoryStateAnki)]
+    /// `minute_offset` should be the `user's timezone offset from UTC` minus `Anki's "next day starts at"`, in minutes.
     /// Returns an array of 2 elements: `[stability, difficulty]`
     pub fn memory_state_anki(
         &self,
+        minute_offset: i32,
         cids: &mut [i64],
         eases: &[u8],
         ids: &[i64],
@@ -116,7 +120,7 @@ impl FSRSwasm {
         assert_eq!(len, 1, "Expected 1 card, but was given {}", len);
 
         let revlog_entries = to_revlog_entry(cids, eases, ids, types);
-        anki_to_fsrs(revlog_entries)
+        anki_to_fsrs(revlog_entries, minute_offset)
             .pop()
             .map(|item| self._memory_state(item))
     }