use proper grid position at thumbnails with grouping and section titles

app/src/main/kotlin/com/simplemobiletools/gallery/pro/activities/MediaActivity.kt

@@ -747,7 +747,9 @@ class MediaActivity : SimpleActivity(), MediaOperationsListener {
         if (viewType == VIEW_TYPE_GRID) {
             val spanCount = config.mediaColumnCnt
             val spacing = config.thumbnailSpacing
-            media_grid.addItemDecoration(GridSpacingItemDecoration(spanCount, spacing, config.scrollHorizontally, config.fileRoundedCorners))
+            val useGridPosition = mMedia.firstOrNull() is ThumbnailSection
+            val decoration = GridSpacingItemDecoration(spanCount, spacing, config.scrollHorizontally, config.fileRoundedCorners, mMedia, useGridPosition)
+            media_grid.addItemDecoration(decoration)
         }
     }
 

app/src/main/kotlin/com/simplemobiletools/gallery/pro/helpers/GridSpacingItemDecoration.kt

@@ -3,12 +3,17 @@ package com.simplemobiletools.gallery.pro.helpers
 import android.graphics.Rect
 import android.view.View
 import androidx.recyclerview.widget.RecyclerView
+import com.simplemobiletools.gallery.pro.models.Medium
+import com.simplemobiletools.gallery.pro.models.ThumbnailItem
 
-class GridSpacingItemDecoration(val spanCount: Int, val spacing: Int, val isScrollingHorizontally: Boolean, val addSideSpacing: Boolean) : RecyclerView.ItemDecoration() {
+class GridSpacingItemDecoration(val spanCount: Int, val spacing: Int, val isScrollingHorizontally: Boolean, val addSideSpacing: Boolean,
+                                val items: ArrayList<ThumbnailItem>, val useGridPosition: Boolean) : RecyclerView.ItemDecoration() {
 
     override fun getItemOffsets(outRect: Rect, view: View, parent: RecyclerView, state: RecyclerView.State) {
         val position = parent.getChildAdapterPosition(view)
-        val column = position % spanCount
+        val medium = items[position] as? Medium ?: return
+        val gridPositionToUse = if (useGridPosition) medium.gridPosition else position
+        val column = gridPositionToUse % spanCount
 
         if (isScrollingHorizontally) {
             if (addSideSpacing) {
@@ -32,13 +37,14 @@ class GridSpacingItemDecoration(val spanCount: Int, val spacing: Int, val isScro
                 outRect.right = (column + 1) * spacing / spanCount
                 outRect.bottom = spacing
 
-                if (position < spanCount) {
+                if (position < spanCount && !useGridPosition) {
                     outRect.top = spacing
                 }
             } else {
                 outRect.left = column * spacing / spanCount
                 outRect.right = spacing - (column + 1) * spacing / spanCount
-                if (position >= spanCount) {
+
+                if (gridPositionToUse >= spanCount) {
                     outRect.top = spacing
                 }
             }

app/src/main/kotlin/com/simplemobiletools/gallery/pro/helpers/MediaFetcher.kt

@@ -635,12 +635,15 @@ class MediaFetcher(val context: Context) {
             return thumbnailItems
         }
 
+        var currentGridPosition = 0
         val mediumGroups = LinkedHashMap<String, ArrayList<Medium>>()
         media.forEach {
             val key = it.getGroupingKey(currentGrouping)
             if (!mediumGroups.containsKey(key)) {
                 mediumGroups[key] = ArrayList()
+                currentGridPosition = 0
             }
+            it.gridPosition = currentGridPosition++
             mediumGroups[key]!!.add(it)
         }
 

app/src/main/kotlin/com/simplemobiletools/gallery/pro/models/Medium.kt

@@ -1,10 +1,7 @@
 package com.simplemobiletools.gallery.pro.models
 
 import android.content.Context
-import androidx.room.ColumnInfo
+import androidx.room.*
-import androidx.room.Entity
-import androidx.room.Index
-import androidx.room.PrimaryKey
 import com.bumptech.glide.signature.ObjectKey
 import com.simplemobiletools.commons.extensions.formatDate
 import com.simplemobiletools.commons.extensions.formatSize
@@ -25,13 +22,18 @@ data class Medium(
     @ColumnInfo(name = "filename") var name: String,
     @ColumnInfo(name = "full_path") var path: String,
     @ColumnInfo(name = "parent_path") var parentPath: String,
-    @ColumnInfo(name = "last_modified") val modified: Long,
+    @ColumnInfo(name = "last_modified") var modified: Long,
     @ColumnInfo(name = "date_taken") var taken: Long,
-    @ColumnInfo(name = "size") val size: Long,
+    @ColumnInfo(name = "size") var size: Long,
-    @ColumnInfo(name = "type") val type: Int,
+    @ColumnInfo(name = "type") var type: Int,
-    @ColumnInfo(name = "video_duration") val videoDuration: Int,
+    @ColumnInfo(name = "video_duration") var videoDuration: Int,
     @ColumnInfo(name = "is_favorite") var isFavorite: Boolean,
-    @ColumnInfo(name = "deleted_ts") var deletedTS: Long) : Serializable, ThumbnailItem() {
+    @ColumnInfo(name = "deleted_ts") var deletedTS: Long,
+
+    @Ignore var gridPosition: Int = 0   // used at grid view decoration at Grouping enabled
+) : Serializable, ThumbnailItem() {
+
+    constructor() : this(null, "", "", "", 0L, 0L, 0L, 0, 0, false, 0L, 0)
 
     companion object {
         private const val serialVersionUID = -6553149366975655L