Add scroll to bottom button plumming

app/src/main/java/org/thoughtcrime/securesms/conversation/v2/ConversationActivityV2.kt

@@ -6,11 +6,13 @@ import android.content.res.Resources
 import android.database.Cursor
 import android.graphics.Rect
 import android.os.Bundle
+import android.util.Log
 import android.view.*
 import android.widget.RelativeLayout
 import androidx.loader.app.LoaderManager
 import androidx.loader.content.Loader
 import androidx.recyclerview.widget.LinearLayoutManager
+import androidx.recyclerview.widget.RecyclerView
 import kotlinx.android.synthetic.main.activity_conversation_v2.*
 import kotlinx.android.synthetic.main.activity_conversation_v2.view.*
 import kotlinx.android.synthetic.main.activity_conversation_v2_action_bar.*
@@ -34,11 +36,12 @@ import org.thoughtcrime.securesms.database.DraftDatabase.Drafts
 import org.thoughtcrime.securesms.database.model.MessageRecord
 import org.thoughtcrime.securesms.loki.utilities.toPx
 import org.thoughtcrime.securesms.mms.GlideApp
-import kotlin.math.abs
+import kotlin.math.*
-import kotlin.math.roundToInt
-import kotlin.math.sqrt
 
-class ConversationActivityV2 : PassphraseRequiredActionBarActivity(), InputBarDelegate, InputBarRecordingViewDelegate {
+class ConversationActivityV2 : PassphraseRequiredActionBarActivity(), InputBarDelegate,
+    InputBarRecordingViewDelegate, ConversationRecyclerViewDelegate {
+    private val scrollButtonFullVisibilityThreshold by lazy { toPx(120.0f, resources) }
+    private val scrollButtonNoVisibilityThreshold by lazy { toPx(20.0f, resources) }
     private val screenWidth = Resources.getSystem().displayMetrics.widthPixels
     private var threadID: Long = -1
     private var actionMode: ActionMode? = null
@@ -102,6 +105,7 @@ class ConversationActivityV2 : PassphraseRequiredActionBarActivity(), InputBarDe
         conversationRecyclerView.adapter = adapter
         val layoutManager = LinearLayoutManager(this, LinearLayoutManager.VERTICAL, true)
         conversationRecyclerView.layoutManager = layoutManager
+        conversationRecyclerView.delegate = this
         // Workaround for the fact that CursorRecyclerViewAdapter doesn't auto-update automatically (even though it says it will)
         LoaderManager.getInstance(this).restartLoader(0, null, object : LoaderManager.LoaderCallbacks<Cursor> {
 
@@ -304,6 +308,13 @@ class ConversationActivityV2 : PassphraseRequiredActionBarActivity(), InputBarDe
         }
         animation.start()
     }
+
+    override fun handleConversationRecyclerViewBottomOffsetChanged(bottomOffset: Int) {
+        val rawAlpha = (bottomOffset.toFloat() - scrollButtonNoVisibilityThreshold) /
+            (scrollButtonFullVisibilityThreshold - scrollButtonNoVisibilityThreshold)
+        val alpha = max(min(rawAlpha, 1.0f), 0.0f)
+        Log.d("Test", "$alpha")
+    }
     // endregion
 
     // region Interaction

app/src/main/java/org/thoughtcrime/securesms/conversation/v2/ConversationRecyclerView.kt

@@ -2,17 +2,21 @@ package org.thoughtcrime.securesms.conversation.v2
 
 import android.content.Context
 import android.util.AttributeSet
+import android.util.Log
 import android.view.MotionEvent
 import android.view.VelocityTracker
 import androidx.recyclerview.widget.RecyclerView
+import kotlinx.android.synthetic.main.activity_conversation_v2.*
 import org.thoughtcrime.securesms.loki.utilities.disableClipping
 import org.thoughtcrime.securesms.loki.utilities.toPx
 import kotlin.math.abs
+import kotlin.math.max
 
 class ConversationRecyclerView : RecyclerView {
     private val maxLongPressVelocityY = toPx(10, resources)
     private val minSwipeVelocityX = toPx(10, resources)
     private var velocityTracker: VelocityTracker? = null
+    var delegate: ConversationRecyclerViewDelegate? = null
 
     constructor(context: Context) : super(context) { initialize() }
     constructor(context: Context, attrs: AttributeSet) : super(context, attrs) { initialize() }
@@ -20,6 +24,20 @@ class ConversationRecyclerView : RecyclerView {
 
     private fun initialize() {
         disableClipping()
+        addOnScrollListener(object : RecyclerView.OnScrollListener() {
+            private var maxScrollOffset = 0
+
+            override fun onScrollStateChanged(recyclerView: RecyclerView, newState: Int) {
+                // Do nothing
+            }
+
+            override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
+                val scrollOffset = recyclerView.computeVerticalScrollOffset()
+                maxScrollOffset = max(maxScrollOffset, scrollOffset)
+                val bottomOffset = (maxScrollOffset - scrollOffset)
+                delegate?.handleConversationRecyclerViewBottomOffsetChanged(bottomOffset)
+            }
+        })
     }
 
     override fun onInterceptTouchEvent(e: MotionEvent): Boolean {
@@ -48,4 +66,9 @@ class ConversationRecyclerView : RecyclerView {
         velocityTracker?.addMovement(e)
         return super.dispatchTouchEvent(e)
     }
+}
+
+interface ConversationRecyclerViewDelegate {
+
+    fun handleConversationRecyclerViewBottomOffsetChanged(bottomOffset: Int)
 }