path: root/core-ui/src/main/kotlin/ca/allanwang/kau/ui/widgets/ElasticDragDismissFrameLayout.kt

/*
 * Copyright 2015 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package ca.allanwang.kau.ui.widgets

import android.app.Activity
import android.content.Context
import android.graphics.Color
import android.os.Build
import android.support.annotation.RequiresApi
import android.util.AttributeSet
import android.view.View
import android.widget.FrameLayout
import ca.allanwang.kau.ui.R
import ca.allanwang.kau.utils.*

/**
 * A [FrameLayout] which responds to nested scrolls to create drag-dismissable layouts.
 * Applies an elasticity factor to reduce movement as you approach the given dismiss distance.
 * Optionally also scales down content during drag.
 */
@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
class ElasticDragDismissFrameLayout @JvmOverloads constructor(
        context: Context, attrs: AttributeSet? = null, defStyleAttr: Int = 0, defStyleRes: Int = 0
) : FrameLayout(context, attrs, defStyleAttr, defStyleRes) {

    // configurable attribs
    var dragDismissDistance = context.dimen(R.dimen.kau_drag_dismiss_distance).dpToPx
    var dragDismissFraction = -1f
    var dragDismissScale = 1f
        set(value) {
            field = value
            shouldScale = value != 1f
        }
    private var shouldScale = false
    var dragElacticity = 0.8f

    // state
    private var totalDrag: Float = 0f
    private var draggingDown = false
    private var draggingUp = false

    private var callbacks: MutableList<ElasticDragDismissCallback> = mutableListOf()

    init {
        if (attrs != null) {
            val a = getContext().obtainStyledAttributes(attrs, R.styleable.ElasticDragDismissFrameLayout, 0, 0)
            dragDismissDistance = a.getDimensionPixelSize(R.styleable.ElasticDragDismissFrameLayout_dragDismissDistance, Int.MAX_VALUE).toFloat()
            dragDismissFraction = a.getFloat(R.styleable.ElasticDragDismissFrameLayout_dragDismissFraction, dragDismissFraction)
            dragDismissScale = a.getFloat(R.styleable.ElasticDragDismissFrameLayout_dragDismissScale, dragDismissScale)
            dragElacticity = a.getFloat(R.styleable.ElasticDragDismissFrameLayout_dragElasticity, dragElacticity)
            a.recycle()
        }
    }

    abstract class ElasticDragDismissCallback {

        /**
         * Called for each drag event.

         * @param elasticOffset       Indicating the drag offset with elasticity applied i.e. may
         * *                            exceed 1.
         * *
         * @param elasticOffsetPixels The elastically scaled drag distance in pixels.
         * *
         * @param rawOffset           Value from [0, 1] indicating the raw drag offset i.e.
         * *                            without elasticity applied. A value of 1 indicates that the
         * *                            dismiss distance has been reached.
         * *
         * @param rawOffsetPixels     The raw distance the user has dragged
         */
        internal open fun onDrag(elasticOffset: Float, elasticOffsetPixels: Float,
                                 rawOffset: Float, rawOffsetPixels: Float) {
        }

        /**
         * Called when dragging is released and has exceeded the threshold dismiss distance.
         */
        internal open fun onDragDismissed() {}

    }

    override fun onStartNestedScroll(child: View, target: View, nestedScrollAxes: Int): Boolean {
        return nestedScrollAxes and View.SCROLL_AXIS_VERTICAL != 0
    }

    override fun onNestedPreScroll(target: View, dx: Int, dy: Int, consumed: IntArray) {
        // if we're in a drag gesture and the user reverses up the we should take those events
        if (draggingDown && dy > 0 || draggingUp && dy < 0) {
            dragScale(dy)
            consumed[1] = dy
        }
    }

    override fun onNestedScroll(target: View, dxConsumed: Int, dyConsumed: Int,
                                dxUnconsumed: Int, dyUnconsumed: Int) {
        dragScale(dyUnconsumed)
    }

    override fun onStopNestedScroll(child: View) {
        if (Math.abs(totalDrag) >= dragDismissDistance) {
            dispatchDismissCallback()
        } else { // settle back to natural position
            animate()
                    .translationY(0f)
                    .scaleX(1f)
                    .scaleY(1f)
                    .setDuration(200L)
                    .setInterpolator(AnimHolder.fastOutSlowInInterpolator(context))
                    .setListener(null)
                    .start()
            totalDrag = 0f
            draggingUp = false
            draggingDown = draggingUp
            dispatchDragCallback(0f, 0f, 0f, 0f)
        }
    }

    override fun onSizeChanged(w: Int, h: Int, oldw: Int, oldh: Int) {
        super.onSizeChanged(w, h, oldw, oldh)
        if (dragDismissFraction > 0f) {
            dragDismissDistance = h * dragDismissFraction
        }
    }

    fun addListener(listener: ElasticDragDismissCallback) {
        callbacks.add(listener)
    }

    fun removeListener(listener: ElasticDragDismissCallback) {
        callbacks.remove(listener)
    }

    private fun dragScale(scroll: Int) {
        if (scroll == 0) return

        totalDrag += scroll.toFloat()

        // track the direction & set the pivot point for scaling
        // don't double track i.e. if start dragging down and then reverse, keep tracking as
        // dragging down until they reach the 'natural' position
        if (scroll < 0 && !draggingUp && !draggingDown) {
            draggingDown = true
            if (shouldScale) pivotY = height.toFloat()
        } else if (scroll > 0 && !draggingDown && !draggingUp) {
            draggingUp = true
            if (shouldScale) pivotY = 0f
        }
        // how far have we dragged relative to the distance to perform a dismiss
        // (0–1 where 1 = dismiss distance). Decreasing logarithmically as we approach the limit
        var dragFraction = Math.log10((1 + Math.abs(totalDrag) / dragDismissDistance).toDouble()).toFloat()

        // calculate the desired translation given the drag fraction
        var dragTo = dragFraction * dragDismissDistance * dragElacticity

        if (draggingUp) {
            // as we use the absolute magnitude when calculating the drag fraction, need to
            // re-apply the drag direction
            dragTo *= -1f
        }
        translationY = dragTo

        if (shouldScale) {
            val scale = 1 - (1 - dragDismissScale) * dragFraction
            scaleX = scale
            scaleY = scale
        }

        // if we've reversed direction and gone past the settle point then clear the flags to
        // allow the list to get the scroll events & reset any transforms
        if (draggingDown && totalDrag >= 0 || draggingUp && totalDrag <= 0) {
            dragFraction = 0f
            dragTo = dragFraction
            totalDrag = dragTo
            draggingUp = false
            draggingDown = draggingUp
            translationY = 0f
            scaleX = 1f
            scaleY = 1f
        }
        dispatchDragCallback(dragFraction, dragTo,
                Math.min(1f, Math.abs(totalDrag) / dragDismissDistance), totalDrag)
    }

    private fun dispatchDragCallback(elasticOffset: Float, elasticOffsetPixels: Float,
                                     rawOffset: Float, rawOffsetPixels: Float) {
        callbacks.forEach {
            it.onDrag(elasticOffset, elasticOffsetPixels,
                    rawOffset, rawOffsetPixels)
        }
    }

    private fun dispatchDismissCallback() {
        callbacks.forEach { it.onDragDismissed() }
    }

    /**
     * An [ElasticDragDismissCallback] which fades system chrome (i.e. status bar and
     * navigation bar) whilst elastic drags are performed and
     * [finishes][Activity.finishAfterTransition] the activity when drag dismissed.
     */
    open class SystemChromeFader(private val activity: Activity) : ElasticDragDismissCallback() {
        private val statusBarAlpha: Int = Color.alpha(activity.statusBarColor)
        private val navBarAlpha: Int = Color.alpha(activity.navigationBarColor)
        private val fadeNavBar: Boolean = activity.isNavBarOnBottom

        public override fun onDrag(elasticOffset: Float, elasticOffsetPixels: Float,
                                   rawOffset: Float, rawOffsetPixels: Float) {
            if (elasticOffsetPixels > 0) {
                // dragging downward, fade the status bar in proportion
                activity.statusBarColor = activity.statusBarColor.withAlpha(((1f - rawOffset) * statusBarAlpha).toInt())
            } else if (elasticOffsetPixels == 0f) {
                // reset
                activity.statusBarColor = activity.statusBarColor.withAlpha(statusBarAlpha)
                activity.navigationBarColor = activity.navigationBarColor.withAlpha(navBarAlpha)
            } else if (fadeNavBar) {
                // dragging upward, fade the navigation bar in proportion
                activity.navigationBarColor = activity.navigationBarColor.withAlpha(((1f - rawOffset) * navBarAlpha).toInt())
            }
        }

        public override fun onDragDismissed() {
            activity.finishAfterTransition()
        }
    }

}