Start of work for a structural modification of the player

app/src/main/java/com/cappielloantonio/play/helper/recyclerview/NestedScrollableHost.kt

@@ -0,0 +1,88 @@
+package com.cappielloantonio.play.helper.recyclerview
+
+import android.content.Context
+import android.util.AttributeSet
+import android.view.MotionEvent
+import android.view.View
+import android.view.ViewConfiguration
+import android.widget.FrameLayout
+import androidx.viewpager2.widget.ViewPager2
+import androidx.viewpager2.widget.ViewPager2.ORIENTATION_HORIZONTAL
+import kotlin.math.absoluteValue
+import kotlin.math.sign
+
+class NestedScrollableHost : FrameLayout {
+    constructor(context: Context) : super(context)
+    constructor(context: Context, attrs: AttributeSet?) : super(context, attrs)
+
+    private var touchSlop = 0
+    private var initialX = 0f
+    private var initialY = 0f
+    private val parentViewPager: ViewPager2?
+        get() {
+            var v: View? = parent as? View
+            while (v != null && v !is ViewPager2) {
+                v = v.parent as? View
+            }
+            return v as? ViewPager2
+        }
+
+    private val child: View? get() = if (childCount > 0) getChildAt(0) else null
+
+    init {
+        touchSlop = ViewConfiguration.get(context).scaledTouchSlop
+    }
+
+    private fun canChildScroll(orientation: Int, delta: Float): Boolean {
+        val direction = -delta.sign.toInt()
+        return when (orientation) {
+            0 -> child?.canScrollHorizontally(direction) ?: false
+            1 -> child?.canScrollVertically(direction) ?: false
+            else -> throw IllegalArgumentException()
+        }
+    }
+
+    override fun onInterceptTouchEvent(e: MotionEvent): Boolean {
+        handleInterceptTouchEvent(e)
+        return super.onInterceptTouchEvent(e)
+    }
+
+    private fun handleInterceptTouchEvent(e: MotionEvent) {
+        val orientation = parentViewPager?.orientation ?: return
+
+        // Early return if child can't scroll in same direction as parent
+        if (!canChildScroll(orientation, -1f) && !canChildScroll(orientation, 1f)) {
+            return
+        }
+
+        if (e.action == MotionEvent.ACTION_DOWN) {
+            initialX = e.x
+            initialY = e.y
+            parent.requestDisallowInterceptTouchEvent(true)
+        } else if (e.action == MotionEvent.ACTION_MOVE) {
+            val dx = e.x - initialX
+            val dy = e.y - initialY
+            val isVpHorizontal = orientation == ORIENTATION_HORIZONTAL
+
+            // assuming ViewPager2 touch-slop is 2x touch-slop of child
+            val scaledDx = dx.absoluteValue * if (isVpHorizontal) .5f else 1f
+            val scaledDy = dy.absoluteValue * if (isVpHorizontal) 1f else .5f
+
+            if (scaledDx > touchSlop || scaledDy > touchSlop) {
+                if (isVpHorizontal == (scaledDy > scaledDx)) {
+                    // Gesture is perpendicular, allow all parents to intercept
+                    parent.requestDisallowInterceptTouchEvent(false)
+                } else {
+                    // Gesture is parallel, query child if movement in that direction is possible
+                    if (canChildScroll(orientation, if (isVpHorizontal) dx else dy)) {
+                        // Child can scroll, disallow all parents to intercept
+                        parent.requestDisallowInterceptTouchEvent(true)
+                    } else {
+                        // Child cannot scroll, allow all parents to intercept
+                        parent.requestDisallowInterceptTouchEvent(false)
+                    }
+                }
+            }
+        }
+    }
+}