logic and a bit of cleanup

app/src/main/java/eu/kanade/presentation/library/LibraryScreen.kt

@@ -70,6 +70,7 @@ fun LibraryScreen(
                     onChangeCurrentPage = { presenter.activeCategory = it },
                     onMangaClicked = onMangaClicked,
                     onToggleSelection = { presenter.toggleSelection(it) },
+                    onToggleMultiSelection = { presenter.toggleMultiSelection(it) },
                     onRefresh = onClickRefresh,
                     onGlobalSearchClicked = onGlobalSearchClicked,
                     getNumberOfMangaForCategory = { presenter.getMangaCountForCategory(it) },

app/src/main/java/eu/kanade/presentation/library/components/LibraryContent.kt

@@ -45,6 +45,7 @@ fun LibraryContent(
     onChangeCurrentPage: (Int) -> Unit,
     onMangaClicked: (Long) -> Unit,
     onToggleSelection: (LibraryManga) -> Unit,
+    onToggleMultiSelection: (LibraryManga) -> Unit,
     onRefresh: (Category?) -> Boolean,
     onGlobalSearchClicked: () -> Unit,
     getNumberOfMangaForCategory: @Composable (Long) -> State<Int?>,
@@ -85,7 +86,7 @@ fun LibraryContent(
             }
         }
         val onLongClickManga = { manga: LibraryManga ->
-            onToggleSelection(manga)
+            onToggleMultiSelection(manga)
         }
 
         SwipeRefresh(

app/src/main/java/eu/kanade/tachiyomi/ui/library/LibraryPresenter.kt

@@ -667,10 +667,37 @@ class LibraryPresenter(
         val mutableList = state.selection.toMutableList()
         if (selection.fastAny { it.manga.id == manga.manga.id }) {
             mutableList.remove(manga)
+            state.selection = mutableList
         } else {
             mutableList.add(manga)
+            state.selection = mutableList
+        }
+    }
+
+    fun toggleMultiSelection(manga: LibraryManga) {
+        val mutableList = state.selection.toMutableList()
+        if (selection.fastAny { it.manga.id == manga.manga.id }) {
+            mutableList.remove(manga)
+            state.selection = mutableList
+        } else if (mutableList.fastAny{ it.category == manga.category }) {
+            val items = (loadedManga[manga.category] ?: emptyList()).map { it.libraryManga }
+
+            val lastMangaIndex =
+                items.indexOf(mutableList.findLast { it.category == manga.category })
+            val curMangaIndex = items.indexOf(manga)
+
+            val newList = when (lastMangaIndex >= curMangaIndex + 1) {
+                true -> items.subList(curMangaIndex, lastMangaIndex)
+                false -> items.subList(lastMangaIndex, curMangaIndex + 1)
+            }
+
+            state.selection = state.selection.toMutableList().apply {
+                addAll(newList.filterNot { it in selection }.map { it })
+            }
+        } else {
+            mutableList.add(manga)
+            state.selection = mutableList
         }
-        state.selection = mutableList
     }
 
     fun selectAll(index: Int) {