From bd474133fcb3688aa18449519acd1713cf04579e Mon Sep 17 00:00:00 2001
From: DynamycSound <sm.stefan.miloje@gmail.com>
Date: Sun, 7 Jun 2026 23:54:21 +0000
Subject: [PATCH] fix(android): stop home hero carousel reshuffling while
 loading

The home hero pool is rebuilt every time a catalog batch finishes
loading, then shuffled with a one-shot Random seeded on the request
key. Re-permuting the growing pool on each intermediate publish made
the carousel visibly reshuffle/reorder several times on app open
before settling.

Order the hero candidates by a stable per-item hash instead, so the
relative order of already-loaded items stays fixed while later items
slot into place. The carousel now settles instead of reshuffling, and
ordering remains deterministic per catalog set and stable across app
opens.

Fixes #1133
---
 .../nuvio/app/features/home/HomeRepository.kt | 24 ++++++++-
 .../app/features/home/HomeHeroOrderingTest.kt | 54 +++++++++++++++++++
 2 files changed, 76 insertions(+), 2 deletions(-)
 create mode 100644 composeApp/src/commonTest/kotlin/com/nuvio/app/features/home/HomeHeroOrderingTest.kt

diff --git a/composeApp/src/commonMain/kotlin/com/nuvio/app/features/home/HomeRepository.kt b/composeApp/src/commonMain/kotlin/com/nuvio/app/features/home/HomeRepository.kt
index 54b1e30e7..4d96dec97 100644
--- a/composeApp/src/commonMain/kotlin/com/nuvio/app/features/home/HomeRepository.kt
+++ b/composeApp/src/commonMain/kotlin/com/nuvio/app/features/home/HomeRepository.kt
@@ -197,14 +197,14 @@ object HomeRepository {
             }
 
         val catalogHeroItems = if (snapshot.heroEnabled) {
-            val heroRandom = Random((requestKey?.hashCode() ?: 0).absoluteValue + 1)
+            val heroOrderSeed = requestKey?.hashCode() ?: 0
             currentDefinitions
                 .filter { definition -> preferences[definition.key]?.heroSourceEnabled != false }
                 .mapNotNull { definition -> cachedSections[definition.key] }
                 .map { section -> section.withReleaseFilter() }
                 .flatMap { section -> section.items }
                 .distinctBy { item -> "${item.type}:${item.id}" }
-                .shuffled(heroRandom)
+                .orderedForHero(heroOrderSeed) { item -> "${item.type}:${item.id}" }
                 .take(HOME_HERO_ITEM_LIMIT)
         } else {
             emptyList()
@@ -433,6 +433,26 @@ private const val HOME_CATALOG_FETCH_BATCH_SIZE = 4
 private const val HOME_CATALOG_PREVIEW_FETCH_LIMIT = 18
 private const val HOME_CATALOG_PUBLISH_INTERVAL = 2
 
+internal fun <T> List<T>.orderedForHero(seed: Int, keySelector: (T) -> String): List<T> =
+    sortedWith(
+        compareBy(
+            { item -> stableHeroOrderRank(seed, keySelector(item)) },
+            { item -> keySelector(item) },
+        ),
+    )
+
+internal fun stableHeroOrderRank(seed: Int, itemKey: String): Int {
+    var hash = seed
+    for (index in itemKey.indices) {
+        hash = hash * 31 + itemKey[index].code
+    }
+    // Avalanche mix so items from the same catalog (similar ids) don't cluster together.
+    hash = hash xor (hash ushr 16)
+    hash *= 0x7feb352d
+    hash = hash xor (hash ushr 15)
+    return hash
+}
+
 private fun prioritizeDefinitions(
     definitions: List<HomeCatalogDefinition>,
     snapshot: HomeCatalogSettingsSnapshot,
diff --git a/composeApp/src/commonTest/kotlin/com/nuvio/app/features/home/HomeHeroOrderingTest.kt b/composeApp/src/commonTest/kotlin/com/nuvio/app/features/home/HomeHeroOrderingTest.kt
new file mode 100644
index 000000000..060dcb9ef
--- /dev/null
+++ b/composeApp/src/commonTest/kotlin/com/nuvio/app/features/home/HomeHeroOrderingTest.kt
@@ -0,0 +1,54 @@
+package com.nuvio.app.features.home
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertTrue
+
+class HomeHeroOrderingTest {
+
+    @Test
+    fun `ordering is deterministic for a given seed`() {
+        val items = listOf("series:a", "movie:b", "series:c", "movie:d", "series:e")
+
+        assertEquals(
+            items.orderedForHero(seed = 42) { it },
+            items.orderedForHero(seed = 42) { it },
+        )
+    }
+
+    @Test
+    fun `ordering does not depend on the input order`() {
+        val seed = 7
+        val ascending = listOf("a", "b", "c", "d", "e").orderedForHero(seed) { it }
+        val descending = listOf("e", "d", "c", "b", "a").orderedForHero(seed) { it }
+
+        assertEquals(ascending, descending)
+    }
+
+    @Test
+    fun `adding more items keeps the relative order of already-loaded items`() {
+        // Regression guard for the hero carousel reshuffle bug: the hero pool is rebuilt as more
+        // catalog batches load, so the ordering must keep already-shown items in place instead of
+        // re-permuting the whole carousel. The previous Random.shuffled() implementation failed
+        // this because shuffling lists of different sizes produces unrelated orders.
+        val seed = 123
+        val firstBatch = listOf("s1", "s2", "s3", "s4")
+        val grownPool = firstBatch + listOf("s5", "s6", "s7", "s8", "s9")
+
+        val firstBatchOrder = firstBatch.orderedForHero(seed) { it }
+        val grownOrderFilteredToFirstBatch = grownPool
+            .orderedForHero(seed) { it }
+            .filter { it in firstBatch }
+
+        assertEquals(firstBatchOrder, grownOrderFilteredToFirstBatch)
+    }
+
+    @Test
+    fun `ordering is shuffled rather than sorted alphabetically`() {
+        val items = (1..20).map { "series:tt$it" }
+        val ordered = items.orderedForHero(seed = 99) { it }
+
+        assertTrue(ordered != items.sortedBy { it }, "hero order should not be a plain sort")
+        assertEquals(items.toSet(), ordered.toSet(), "ordering must not drop or add items")
+    }
+}