Disabling drag and drop in library unless selected as the sort option

So the option for DnD now appears in sort list, otherwise categories not in DnD mode are locked

app/src/main/java/eu/kanade/tachiyomi/data/database/models/Category.kt

@@ -34,7 +34,7 @@ interface Category : Serializable {
         return ((mangaSort?.minus('a') ?: 0) % 2) != 1
     }
 
-    fun sortingMode(): Int? = when (mangaSort) {
+    fun sortingMode(nullAsDND: Boolean = false): Int? = when (mangaSort) {
         ALPHA_ASC, ALPHA_DSC -> LibrarySort.ALPHA
         UPDATED_ASC, UPDATED_DSC -> LibrarySort.LATEST_CHAPTER
         UNREAD_ASC, UNREAD_DSC -> LibrarySort.UNREAD
@@ -42,9 +42,12 @@ interface Category : Serializable {
         TOTAL_ASC, TOTAL_DSC -> LibrarySort.TOTAL
         DRAG_AND_DROP -> LibrarySort.DRAG_AND_DROP
         DATE_ADDED_ASC, DATE_ADDED_DSC -> LibrarySort.DATE_ADDED
-        else -> null
+        else -> if (nullAsDND && !isDynamic) LibrarySort.DRAG_AND_DROP else null
     }
 
+    val isDragAndDrop
+        get() = (mangaSort == null || mangaSort == DRAG_AND_DROP) && !isDynamic
+
     fun sortRes(): Int = when (mangaSort) {
         ALPHA_ASC, ALPHA_DSC -> R.string.title
         UPDATED_ASC, UPDATED_DSC -> R.string.latest_chapter

app/src/main/java/eu/kanade/tachiyomi/data/database/models/Manga.kt

@@ -30,6 +30,7 @@ interface Manga : SManga {
     var hide_title: Boolean
 
     fun isBlank() = id == Long.MIN_VALUE
+    fun isHidden() = status == -1
 
     fun setChapterOrder(order: Int) {
         setFlags(order, SORT_MASK)

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

@@ -64,6 +64,17 @@ class LibraryCategoryAdapter(val controller: LibraryController) :
         }
     }
 
+    /**
+     * Returns the position in the adapter for the given manga.
+     *
+     * @param manga the manga to find.
+     */
+    fun findCategoryHeader(catId: Int): LibraryHeaderItem? {
+        return currentItems.find {
+            (it is LibraryHeaderItem) && it.category.id == catId
+        } as LibraryHeaderItem
+    }
+
     /**
      * Returns the position in the adapter for the given manga.
      *

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

@@ -1402,7 +1402,16 @@ class LibraryController(
     }
 
     override fun sortCategory(catId: Int, sortBy: Int) {
-        presenter.sortCategory(catId, sortBy)
+        val category = presenter.categories.find { it.id == catId }
+        if (category?.isDynamic == false && ('a' + (sortBy - 1)) == Category.DRAG_AND_DROP) {
+            val item = adapter.findCategoryHeader(catId) ?: return
+            val libraryItems = adapter.getSectionItems(item)
+                .filterIsInstance<LibraryItem>()
+            val mangaIds = libraryItems.mapNotNull { (it as? LibraryItem)?.manga?.id }
+            presenter.rearrangeCategory(catId, mangaIds)
+        } else {
+            presenter.sortCategory(catId, sortBy)
+        }
     }
 
     override fun selectAll(position: Int) {

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

@@ -184,8 +184,16 @@ class LibraryHeaderHolder(val view: View, private val adapter: LibraryCategoryAd
                         R.string.category
                     )
                 )
+            } else {
+                items.add(
+                    MaterialMenuSheet.MenuSheetItem(
+                        LibrarySort.DRAG_AND_DROP,
+                        R.drawable.ic_swap_vert_24dp,
+                        R.string.drag_and_drop
+                    )
+                )
             }
-            val sortingMode = category.sortingMode()
+            val sortingMode = category.sortingMode(true)
             val sheet = MaterialMenuSheet(
                 activity,
                 items,

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

@@ -61,8 +61,17 @@ abstract class LibraryHolder(
 
     override fun onLongClick(view: View?): Boolean {
         return if (adapter.isLongPressDragEnabled) {
+            val manga = (adapter.getItem(flexibleAdapterPosition) as LibraryItem).manga
+            if (!isDraggable && !manga.isBlank() && !manga.isHidden()) {
+                adapter.mItemLongClickListener.onItemLongClick(flexibleAdapterPosition)
+                toggleActivation()
+                true
+            } else {
+                super.onLongClick(view)
+                false
+            }
+        } else {
             super.onLongClick(view)
-            false
+        }
-        } else super.onLongClick(view)
     }
 }

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

@@ -125,7 +125,7 @@ class LibraryItem(
      * Returns true if this item is draggable.
      */
     override fun isDraggable(): Boolean {
-        return !manga.isBlank()
+        return !manga.isBlank() && header.category.isDragAndDrop
     }
 
     override fun isEnabled(): Boolean {