Behavior for CoordinatorLayout that handles views fixed at the bottom

FixedBottomAwareScrollViewBehavior.kt

package com.github.edudobay.android

import android.content.Context
import android.support.design.widget.AppBarLayout
import android.support.design.widget.CoordinatorLayout
import android.support.v4.view.ViewCompat
import android.support.v7.widget.Toolbar
import android.util.AttributeSet
import android.view.Gravity
import android.view.View
import android.view.ViewGroup
import android.view.ViewGroup.LayoutParams.MATCH_PARENT


fun ViewGroup.children(start: Int = 0, end: Int = childCount): Sequence<View> =
        (start..end).asSequence().mapNotNull { i -> getChildAt(i) }

infix fun Int.andNot(other: Int): Int = and(other.inv())

fun Int.toggleBits(other: Int, enabled: Boolean = true) =
        if (enabled) this.or(other) else this.andNot(other)

/*
 * Converted to Kotlin by Eduardo Dobay (2016-12-05)
 * - Added: depend on views anchored to bottom, and subtract them from available height
 *
 * Original version by Maciej Karas
 * https://gist.github.com/MaciejKaras/02bff315f00b87d80467a470424f22c3
 */
@Suppress("unused")
class FixedBottomAwareScrollViewBehavior : AppBarLayout.ScrollingViewBehavior {

    constructor() : super()

    constructor(context: Context, attrs: AttributeSet) : super(context, attrs)

    override fun layoutDependsOn(parent: CoordinatorLayout, child: View, dependency: View): Boolean =
        isViewAnchoredToBottom(dependency) || super.layoutDependsOn(parent, child, dependency)

    fun isViewAnchoredToBottom(view: View) =
        (view.layoutParams as? CoordinatorLayout.LayoutParams)?.gravity == Gravity.BOTTOM

    override fun onMeasureChild(
            parent: CoordinatorLayout, child: View,
            parentWidthMeasureSpec: Int, widthUsed: Int,
            parentHeightMeasureSpec: Int, heightUsed: Int
    ): Boolean {
        val dependencies = parent.getDependencies(child)
        if (child.layoutParams.height == MATCH_PARENT && !dependencies.isEmpty()) {

            var availableHeight = View.MeasureSpec.getSize(parentHeightMeasureSpec)
            if (availableHeight == 0) {
                availableHeight = parent.height
            }

            // Subtract height of views anchored to bottom
            availableHeight -= dependencies.filter { isViewAnchoredToBottom(it) }.sumBy { it.measuredHeight }

            val availableHeightMeasureSpec = View.MeasureSpec.makeMeasureSpec(availableHeight, View.MeasureSpec.AT_MOST)

            val appBar = findFirstAppBarLayout(dependencies)
            if (appBar != null && ViewCompat.isLaidOut(appBar)) {
                val height = availableHeight - appBar.measuredHeight
                var newHeightMeasureSpec = View.MeasureSpec.makeMeasureSpec(height, View.MeasureSpec.AT_MOST)

                parent.onMeasureChild(child, parentWidthMeasureSpec, widthUsed, newHeightMeasureSpec, heightUsed)
                val childContentHeight = child.measuredHeight

                if (childContentHeight <= height) {
                    updateToolbar(parent, appBar, parentWidthMeasureSpec, widthUsed, availableHeightMeasureSpec, heightUsed, false)

                    newHeightMeasureSpec = View.MeasureSpec.makeMeasureSpec(height, View.MeasureSpec.EXACTLY)
                    parent.onMeasureChild(child, parentWidthMeasureSpec, widthUsed, newHeightMeasureSpec, heightUsed)

                    return true
                } else {
                    updateToolbar(parent, appBar, parentWidthMeasureSpec, widthUsed, availableHeightMeasureSpec, heightUsed, true)

                    return super.onMeasureChild(parent, child, parentWidthMeasureSpec, widthUsed, availableHeightMeasureSpec, heightUsed)
                }
            }
        }

        return super.onMeasureChild(parent, child, parentWidthMeasureSpec, widthUsed, parentHeightMeasureSpec, heightUsed)
    }

    private fun View.getContentHeight(): Int =
        (this as? ViewGroup)?.children()?.sumBy { it.measuredHeight } ?: measuredHeight

    private fun findFirstAppBarLayout(views: List<View>): AppBarLayout? =
        views.firstOrNull { view -> view is AppBarLayout } as? AppBarLayout

    private fun updateToolbar(
            parent: CoordinatorLayout, appBar: AppBarLayout,
            parentWidthMeasureSpec: Int, widthUsed: Int,
            parentHeightMeasureSpec: Int, heightUsed: Int,
            scroll: Boolean
    ) {
        toggleToolbarScroll(appBar, scroll)

        appBar.forceLayout()
        parent.onMeasureChild(appBar, parentWidthMeasureSpec, widthUsed, parentHeightMeasureSpec, heightUsed)
    }

    private fun toggleToolbarScroll(appBar: AppBarLayout, scroll: Boolean) {
        for (child in appBar.children().filter { child -> child is Toolbar }) {
            val params = child.layoutParams as AppBarLayout.LayoutParams
            params.scrollFlags = params.scrollFlags.toggleBits(AppBarLayout.LayoutParams.SCROLL_FLAG_SCROLL, scroll)
        }
    }
}