Do not assume a consistent order when paginating

core/src/main/kotlin/com/gitlab/kordlib/core/Util.kt

@@ -24,6 +24,7 @@ import kotlinx.atomicfu.atomic
 import kotlinx.coroutines.flow.*
 import java.time.Instant
 import java.time.format.DateTimeFormatter
+import kotlin.math.max
 import kotlin.reflect.KClass
 
 internal fun String?.toSnowflakeOrNull(): Snowflake? = when {
@@ -110,37 +111,58 @@ internal fun <C : Collection<T>, T> paginate(
  * Discord returns values in order newest -> oldest (big -> small) (confirmed for messages),
  * meaning that the first item returned is the one last created (youngest) in the batch.
  */
-internal fun <T> youngestItem(): (Collection<T>) -> T? = { it.firstOrNull() }
+internal fun <T> youngestItem(idSelector: (T) -> String): (Collection<T>) -> T? = function@{
+    if (it.size <= 1) return@function it.firstOrNull()
+
+    val first = it.first()
+    val last = it.last()
+
+    val firstId = idSelector(first).toLong()
+    val lastId = idSelector(last).toLong()
+
+    if (firstId > lastId) first
+    else last
+}
 
 /**
  * Discord returns values in order oldest -> newest (big -> small) (confirmed for messages),
  * meaning that the last item returned is the one first created (oldest) in the batch.
  */
-internal fun <T> oldestItem(): (Collection<T>) -> T? = { it.lastOrNull() }
+internal fun <T> oldestItem(idSelector: (T) -> String): (Collection<T>) -> T? = function@{
+    if (it.size <= 1) return@function it.firstOrNull()
+        val first = it.first()
+        val last = it.last()
+
+        val firstId = idSelector(first).toLong()
+        val lastId = idSelector(last).toLong()
+
+        if (firstId < lastId) first
+        else last
+}
 
 /**
  *  Selects the [Position.After] the youngest item in the batch.
  */
 internal fun <C : Collection<T>, T> paginateForwards(start: Snowflake = Snowflake("0"), batchSize: Int, idSelector: (T) -> String, request: suspend (position: Position) -> C): Flow<T> =
-        paginate(start.value, batchSize, idSelector, youngestItem(), Position::After, request)
+        paginate(start.value, batchSize, idSelector, youngestItem(idSelector), Position::After, request)
 
 /**
  *  Selects the [Position.After] the youngest item in the batch.
  */
 internal fun <C : Collection<T>, T : Entity> paginateForwards(start: Snowflake = Snowflake("0"), batchSize: Int, request: suspend (position: Position) -> C): Flow<T> =
-        paginate(start.value, batchSize, { it.id.value }, youngestItem(), Position::After, request)
+        paginate(start.value, batchSize, { it.id.value }, youngestItem { it.id.value }, Position::After, request)
 
 /**
  *  Selects the [Position.Before] the oldest item in the batch.
  */
 internal fun <C : Collection<T>, T> paginateBackwards(start: Snowflake = Snowflake(Long.MAX_VALUE), batchSize: Int, idSelector: (T) -> String, request: suspend (position: Position) -> C): Flow<T> =
-        paginate(start.value, batchSize, idSelector, oldestItem(), Position::Before, request)
+        paginate(start.value, batchSize, idSelector, oldestItem(idSelector), Position::Before, request)
 
 /**
  *  Selects the [Position.Before] the oldest item in the batch.
  */
 internal fun <C : Collection<T>, T : Entity> paginateBackwards(start: Snowflake = Snowflake(Long.MAX_VALUE), batchSize: Int, request: suspend (position: Position) -> C): Flow<T> =
-        paginate(start.value, batchSize, { it.id.value }, oldestItem(), Position::Before, request)
+        paginate(start.value, batchSize, { it.id.value }, oldestItem { it.id.value }, Position::Before, request)
 
 inline fun <reified T : Event> Intents.IntentsBuilder.enableEvent() = enableEvent(T::class)