Fix learn ahead limit not being applied after setting change

The preference was changed in the backend but the scheduler didn't
update itself so the learning cards that should have become available
weren't present in the review queue.
The preference change is now done through get/setPreferences().

Fixes #16645

AnkiDroid/src/main/java/com/ichi2/anki/preferences/ReviewingSettingsFragment.kt

@@ -15,13 +15,20 @@
  */
 package com.ichi2.anki.preferences
 
+import anki.config.copy
 import com.ichi2.anki.CollectionManager.withCol
 import com.ichi2.anki.R
 import com.ichi2.anki.launchCatchingTask
 import com.ichi2.anki.preferences.Preferences.Companion.getDayOffset
 import com.ichi2.anki.preferences.Preferences.Companion.setDayOffset
+import com.ichi2.annotations.NeedsTest
+import com.ichi2.libanki.undoableOp
 import com.ichi2.preferences.NumberRangePreferenceCompat
 import com.ichi2.preferences.SliderPreference
+import timber.log.Timber
+import kotlin.time.Duration
+import kotlin.time.DurationUnit
+import kotlin.time.toDuration
 
 class ReviewingSettingsFragment : SettingsFragment() {
     override val preferenceResource: Int
@@ -34,10 +41,11 @@ class ReviewingSettingsFragment : SettingsFragment() {
         // Represents the collections pref "collapseTime": i.e.
         // if there are no card to review now, but there are learning cards remaining for today, we show those learning cards if they are due before LEARN_CUTOFF minutes
         // Note that "collapseTime" is in second while LEARN_CUTOFF is in minute.
+        @NeedsTest("#16645, changing the learn ahead limit shows expected cards in review queue")
         requirePreference<NumberRangePreferenceCompat>(R.string.learn_cutoff_preference).apply {
-            launchCatchingTask { setValue(withCol { sched.learnAheadSeconds() / 60 }) }
+            launchCatchingTask { setValue(getLearnAheadLimit().toInt(DurationUnit.MINUTES)) }
             setOnPreferenceChangeListener { newValue ->
-                launchCatchingTask { withCol { config.set("collapseTime", (newValue as Int * 60)) } }
+                launchCatchingTask { setLearnAheadLimit((newValue as Int).toDuration(DurationUnit.MINUTES)) }
             }
         }
         // Timebox time limit
@@ -60,4 +68,17 @@ class ReviewingSettingsFragment : SettingsFragment() {
             }
         }
     }
+
+    private suspend fun getLearnAheadLimit(): Duration =
+        withCol { getPreferences().scheduling.learnAheadSecs }.toDuration(DurationUnit.SECONDS)
+
+    private suspend fun setLearnAheadLimit(limit: Duration) {
+        val prefs = withCol { getPreferences() }
+        val newPrefs = prefs.copy {
+            scheduling = prefs.scheduling.copy { learnAheadSecs = limit.toInt(DurationUnit.SECONDS) }
+        }
+
+        undoableOp { setPreferences(newPrefs) }
+        Timber.i("set learn ahead limit: '%d'", limit.toInt(DurationUnit.SECONDS))
+    }
 }