Make pager a completely separate class for easier reuse

app/src/main/kotlin/com/simplemobiletools/launcher/views/HomeScreenGrid.kt

@@ -11,6 +11,7 @@ import android.content.Context
 import android.graphics.*
 import android.graphics.drawable.BitmapDrawable
 import android.os.Bundle
+import android.os.Handler
 import android.text.Layout
 import android.text.StaticLayout
 import android.text.TextPaint
@@ -67,7 +68,14 @@ class HomeScreenGrid(context: Context, attrs: AttributeSet, defStyle: Int) : Rel
     private var redrawWidgets = false
     private var iconSize = 0
 
-    private val pager = Pager()
+    private val pager = AnimatedGridPager(
+        getMaxPage = ::getMaxPage,
+        redrawGrid = ::redrawGrid,
+        getWidth = { width },
+        getHandler = { handler },
+        getNextPageBound = { right - sideMargins.right - cellWidth / 2 },
+        getPrevPageBound = { left + sideMargins.left + cellWidth / 2 }
+    )
 
     // apply fake margins at the home screen. Real ones would cause the icons be cut at dragging at screen sides
     var sideMargins = Rect()
@@ -203,7 +211,7 @@ class HomeScreenGrid(context: Context, attrs: AttributeSet, defStyle: Int) : Rel
             return
         }
 
-        if (draggedItemCurrentCoords.first == -1 && draggedItemCurrentCoords.second == -1 && draggedItem != null) {
+        if (draggedItemCurrentCoords.first == -1 && draggedItemCurrentCoords.second == -1) {
             if (draggedItem!!.type == ITEM_TYPE_WIDGET) {
                 val draggedWidgetView = widgetViews.firstOrNull { it.tag == draggedItem?.widgetId }
                 if (draggedWidgetView != null) {
@@ -965,14 +973,40 @@ class HomeScreenGrid(context: Context, attrs: AttributeSet, defStyle: Int) : Rel
 
 
     fun setSwipeMovement(diffX: Float) {
+        if (draggedItem != null) {
             pager.setSwipeMovement(diffX)
         }
+    }
 
     fun finalizeSwipe() {
         pager.finalizeSwipe()
     }
+}
+
+/**
+ * Helper class responsible for managing current page and providing utilities for animating page changes,
+ * as well as partial dragigng between pages
+ */
+private class AnimatedGridPager(
+    private val getMaxPage: () -> Int,
+    private val redrawGrid: () -> Unit,
+    private val getWidth: () -> Int,
+    private val getHandler: () -> Handler,
+    private val getNextPageBound: () -> Int,
+    private val getPrevPageBound: () -> Int,
+) {
+
+    companion object {
+        private const val PAGE_CHANGE_HOLD_THRESHOLD = 500L
+        private const val PAGE_INDICATORS_FADE_DELAY = PAGE_CHANGE_HOLD_THRESHOLD + 300L
+
+        private enum class PageChangeArea {
+            LEFT,
+            MIDDLE,
+            RIGHT
+        }
+    }
 
-    private inner class Pager {
     private var lastPage = 0
     private var currentPage = 0
     private var pageChangeLastArea = PageChangeArea.MIDDLE
@@ -988,7 +1022,7 @@ class HomeScreenGrid(context: Context, attrs: AttributeSet, defStyle: Int) : Rel
 
     fun isItemOnLastPage(item: HomeScreenGridItem) = item.page == lastPage
 
-        fun getPageCount() = max(getMaxPage(), pager.currentPage) + 1
+    fun getPageCount() = max(getMaxPage(), currentPage) + 1
 
 
     fun isOutsideOfPageRange() = currentPage > getMaxPage()
@@ -998,12 +1032,12 @@ class HomeScreenGrid(context: Context, attrs: AttributeSet, defStyle: Int) : Rel
 
     fun isSwiped() = abs(pageChangeSwipedPercentage) > 0f
 
-        fun isAnimatingPageChange() = pager.pageChangeAnimLeftPercentage > 0f
+    fun isAnimatingPageChange() = pageChangeAnimLeftPercentage > 0f
 
     fun shouldDisplayPageChangeIndicator() = isSwiped() || isAnimatingPageChange() || pageChangeIndicatorsAlpha > 0f
 
     fun getPageChangeIndicatorsAlpha() = if (pageChangeIndicatorsAlpha != 0f) {
-            (pager.pageChangeIndicatorsAlpha * 255.0f).toInt()
+        (pageChangeIndicatorsAlpha * 255.0f).toInt()
     } else {
         255
     }
@@ -1053,12 +1087,12 @@ class HomeScreenGrid(context: Context, attrs: AttributeSet, defStyle: Int) : Rel
     }
 
     fun setSwipeMovement(diffX: Float) {
-            if (!pageChangeEnabled || draggedItem != null) {
+        if (!pageChangeEnabled) {
             return
         }
 
         if (currentPage < getMaxPage() && diffX > 0f || currentPage > 0 && diffX < 0f) {
-                pageChangeSwipedPercentage = (-diffX / width.toFloat()).coerceIn(-1f, 1f)
+            pageChangeSwipedPercentage = (-diffX / getWidth().toFloat()).coerceIn(-1f, 1f)
             redrawGrid()
         }
     }
@@ -1089,11 +1123,11 @@ class HomeScreenGrid(context: Context, attrs: AttributeSet, defStyle: Int) : Rel
 
     fun handleItemMovement(x: Int, y: Int) {
         showIndicators()
-            if (x > right - sideMargins.right - cellWidth / 2) {
+        if (x > getNextPageBound()) {
             doWithPageChangeDelay(PageChangeArea.RIGHT) {
                 nextOrAdditionalPage()
             }
-            } else if (x < left + sideMargins.left + cellWidth / 2) {
+        } else if (x < getPrevPageBound()) {
             doWithPageChangeDelay(PageChangeArea.LEFT) {
                 prevPage()
             }
@@ -1162,23 +1196,23 @@ class HomeScreenGrid(context: Context, attrs: AttributeSet, defStyle: Int) : Rel
 
     private fun showIndicators() {
         pageChangeIndicatorsAlpha = 1f
-            removeCallbacks(startFadingIndicators)
+        getHandler().removeCallbacks(startFadingIndicators)
     }
 
     private fun clearPageChangeFlags() {
         pageChangeLastArea = PageChangeArea.MIDDLE
         pageChangeLastAreaEntryTime = 0
-            removeCallbacks(checkAndExecuteDelayedPageChange)
+        getHandler().removeCallbacks(checkAndExecuteDelayedPageChange)
     }
 
     private fun schedulePageChange() {
         pageChangeLastAreaEntryTime = System.currentTimeMillis()
-            postDelayed(checkAndExecuteDelayedPageChange, PAGE_CHANGE_HOLD_THRESHOLD)
+        getHandler().postDelayed(checkAndExecuteDelayedPageChange, PAGE_CHANGE_HOLD_THRESHOLD)
     }
 
     private fun scheduleIndicatorsFade() {
         pageChangeIndicatorsAlpha = 1f
-            postDelayed(startFadingIndicators, PAGE_INDICATORS_FADE_DELAY)
+        getHandler().postDelayed(startFadingIndicators, PAGE_INDICATORS_FADE_DELAY)
     }
 
     private fun doWithPageChangeDelay(needed: PageChangeArea, pageChangeFunction: () -> Boolean) {
@@ -1208,7 +1242,7 @@ class HomeScreenGrid(context: Context, attrs: AttributeSet, defStyle: Int) : Rel
         pageChangeIndicatorsAlpha = 0f
         val startingAt = 1 - abs(pageChangeSwipedPercentage)
         pageChangeSwipedPercentage = 0f
-            removeCallbacks(startFadingIndicators)
+        getHandler().removeCallbacks(startFadingIndicators)
         if (redraw) {
             redrawGrid()
         }
@@ -1224,11 +1258,7 @@ class HomeScreenGrid(context: Context, attrs: AttributeSet, defStyle: Int) : Rel
                         pageChangeAnimLeftPercentage = 0f
                         pageChangeEnabled = true
                         lastPage = currentPage
-                            if (draggedItem != null) {
-                                schedulePageChange()
-                            } else {
                         clearPageChangeFlags()
-                            }
                         scheduleIndicatorsFade()
                         redrawGrid()
                     }
@@ -1236,17 +1266,4 @@ class HomeScreenGrid(context: Context, attrs: AttributeSet, defStyle: Int) : Rel
                 start()
             }
     }
-    }
-
-    companion object {
-        private const val PAGE_CHANGE_HOLD_THRESHOLD = 500L
-        private const val PAGE_INDICATORS_FADE_DELAY = PAGE_CHANGE_HOLD_THRESHOLD + 300L
-
-        private enum class PageChangeArea {
-            LEFT,
-            MIDDLE,
-            RIGHT
-        }
-    }
-
 }