/*
 * Copyright (C) 2006 The Android Open Source Project
 *
 * 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.
 */
/*
 * Revised 5/19/2010 by GORGES
 * Now supports two-dimensional view scrolling
 * http://GORGES.us
 * Ported to Mono For Android/C# by Miha Markic, Righthand http://blog.rthand.com/
 */

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using Android.App;
using Android.Content;
using Android.OS;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using Android.Graphics;
using Android.Util;
using Java.Lang;
using Android.Views.Animations;

namespace AndroidApplication1
{
    /**
 * Layout container for a view hierarchy that can be scrolled by the user,
 * allowing it to be larger than the physical display.  A TwoDScrollView
 * is a {@link FrameLayout}, meaning you should place one child in it
 * containing the entire contents to scroll; this child may itself be a layout
 * manager with a complex hierarchy of objects.  A child that is often used
 * is a {@link LinearLayout} in a vertical orientation, presenting a vertical
 * array of top-level items that the user can scroll through.
 *
 * <p>The {@link TextView} class also
 * takes care of its own scrolling, so does not require a TwoDScrollView, but
 * using the two together is possible to achieve the effect of a text view
 * within a larger container.
 */
    /// <summary>
    /// Converted from Matt Clark's original sources at
    /// http://blog.gorges.us/2010/06/android-two-dimensional-scrollview/
    /// </summary>
    public class TwoDScrollView : FrameLayout
    {
        const int ANIMATED_SCROLL_GAP = 250;
        const float MAX_SCROLL_FACTOR = 0.5f;

        private long mLastScroll;

        Rect mTempRect = new Rect();
        private Scroller mScroller;

        /**
     * Flag to indicate that we are moving focus ourselves. This is so the
     * code that watches for focus changes initiated outside this TwoDScrollView
     * knows that it does not have to do anything.
     */
        private bool mTwoDScrollViewMovedFocus;

        /**
        * Position of the last motion event.
        */
        private float mLastMotionY;
        private float mLastMotionX;

        /**
        * True when the layout has changed but the traversal has not come through yet.
        * Ideally the view hierarchy would keep track of this for us.
        */
        private bool mIsLayoutDirty = true;

        /**
        * The child to give focus to in the event that a child has requested focus while the
        * layout is dirty. This prevents the scroll from being wrong if the child has not been
        * laid out before requesting focus.
        */
        private View mChildToScrollTo = null;

        /**
        * True if the user is currently dragging this TwoDScrollView around. This is
        * not the same as 'is being flinged', which can be checked by
        * mScroller.isFinished() (flinging begins when the user lifts his finger).
        */
        private bool mIsBeingDragged = false;

        /**
        * Determines speed during touch scrolling
        */
        private VelocityTracker mVelocityTracker;

        /**
        * Whether arrow scrolling is animated.
        */
        private int mTouchSlop;
        private int mMinimumVelocity;
        private int mMaximumVelocity;

        protected TwoDScrollView(IntPtr javaReference, JniHandleOwnership transfer)
            : base(javaReference, transfer)
        {
            InitTwoDScrollView();
        }
        public TwoDScrollView(Context context)
            : base(context)
        {
            InitTwoDScrollView();
        }
        public TwoDScrollView(Context context, IAttributeSet attrs)
            : base(context, attrs)
        {
            InitTwoDScrollView();
        }
        public TwoDScrollView(Context context, IAttributeSet attrs, int defStyle)
            : base(context, attrs, defStyle)
        {
            InitTwoDScrollView();
        }

        //protected override float GetTopFadingEdgeStrength()
        //{
        //    if (ChildCount == 0)
        //    {
        //        return 0.0f;
        //    }
        //    int length = VerticalFadingEdgeLength;
        //    if (ScrollY < length)
        //    {
        //        return ScrollY / (float)length;
        //    }
        //    return 1.0f;
        //}

        //protected override float GetBottomFadingEdgeStrength()
        //{
        //    if (ChildCount == 0)
        //    {
        //        return 0.0f;
        //    }
        //    int length = VerticalFadingEdgeLength;
        //    int bottomEdge = Height - PaddingBottom;
        //    int span = GetChildAt(0).Bottom - ScrollY - bottomEdge;
        //    if (span < length)
        //    {
        //        return span / (float)length;
        //    }
        //    return 1.0f;
        //}

        //protected override float GetLeftFadingEdgeStrength()
        //{
        //    if (ChildCount == 0)
        //    {
        //        return 0.0f;
        //    }
        //    int length = HorizontalFadingEdgeLength;
        //    if (ScrollX < length)
        //    {
        //        return ScrollX / (float)length;
        //    }
        //    return 1.0f;
        //}

        //protected override float GetRightFadingEdgeStrength()
        //{
        //    if (ChildCount == 0)
        //    {
        //        return 0.0f;
        //    }
        //    int length = HorizontalFadingEdgeLength;
        //    int rightEdge = Width - PaddingRight;
        //    int span = GetChildAt(0).Right - ScrollX - rightEdge;
        //    if (span < length)
        //    {
        //        return span / (float)length;
        //    }
        //    return 1.0f;
        //}

        /**
        * @return The maximum amount this scroll view will scroll in response to
        *   an arrow event.
        */
        public int getMaxScrollAmountVertical()
        {
            return (int)(MAX_SCROLL_FACTOR * Height);
        }

        public int getMaxScrollAmountHorizontal()
        {
            return (int)(MAX_SCROLL_FACTOR * Width);
        }

        private void InitTwoDScrollView()
        {
            mScroller = new Scroller(Context);
            Focusable = true;
            DescendantFocusability = Android.Views.DescendantFocusability.AfterDescendants;
            SetWillNotDraw(false);
            ViewConfiguration configuration = ViewConfiguration.Get(Context);
            mTouchSlop = configuration.ScaledTouchSlop;
            mMinimumVelocity = configuration.ScaledMinimumFlingVelocity;
            mMaximumVelocity = configuration.ScaledMaximumFlingVelocity;
        }

        public override void AddView(View child)
        {
            if (ChildCount > 0)
            {
                throw new IllegalStateException("TwoDScrollView can host only one direct child");
            }
            base.AddView(child);
        }

        public override void AddView(View child, int index)
        {
            if (ChildCount > 0)
            {
                throw new IllegalStateException("TwoDScrollView can host only one direct child");
            }
            base.AddView(child, index);
        }

        public override void AddView(View child, ViewGroup.LayoutParams p)
        {
            if (ChildCount > 0)
            {
                throw new IllegalStateException("TwoDScrollView can host only one direct child");
            }
            base.AddView(child, p);
        }

        public override void AddView(View child, int index, ViewGroup.LayoutParams p)
        {
            if (ChildCount > 0)
            {
                throw new IllegalStateException("TwoDScrollView can host only one direct child");
            }
            base.AddView(child, index, p);
        }

        /**
     * @return Returns true this TwoDScrollView can be scrolled
     */
        private bool CanScroll()
        {
            View child = GetChildAt(0);
            if (child != null)
            {
                int childHeight = child.Height;
                int childWidth = child.Width;
                return (Height < childHeight + PaddingTop + PaddingBottom) ||
                       (Width < childWidth + PaddingLeft + PaddingRight);
            }
            return false;
        }

        public override bool DispatchKeyEvent(KeyEvent e)
        {
            // Let the focused view and/or our descendants get the key first
            bool handled = base.DispatchKeyEvent(e);
            if (handled)
            {
                return true;
            }
            return ExecuteKeyEvent(e);
        }

        /**
     * You can call this function yourself to have the scroll view perform
     * scrolling from a key event, just as if the event had been dispatched to
     * it by the view hierarchy.
     *
     * @param event The key event to execute.
     * @return Return true if the event was handled, else false.
     */
        public bool ExecuteKeyEvent(KeyEvent e)
        {
            mTempRect.SetEmpty();
            if (!CanScroll())
            {
                if (IsFocused)
                {
                    View currentFocused = FindFocus();
                    if (currentFocused == this) currentFocused = null;
                    View nextFocused = FocusFinder.Instance.FindNextFocus(this, currentFocused, FocusSearchDirection.Down);
                    return nextFocused != null && nextFocused != this && nextFocused.RequestFocus(FocusSearchDirection.Down);
                }
                return false;
            }
            bool handled = false;
            if (e.Action == KeyEventActions.Down)
            {
                switch (e.KeyCode)
                {
                    case Keycode.DpadUp:
                        //if (!e.IsAltPressed) {
                        //  handled = ArrowScroll( View.FOCUS_UP, false);
                        //} else {
                        //  handled = DullScroll(View.FOCUS_UP, false);
                        //}
                        break;
                    case Keycode.DpadDown:
                        //if (!e.IsAltPressed) {
                        //  handled = arrowScroll(View.FOCUS_DOWN, false);
                        //} else {
                        //  handled = fullScroll(View.FOCUS_DOWN, false);
                        //}
                        break;
                    case Keycode.DpadLeft:
                        //if (!e.IsAltPressed) {
                        //  handled = arrowScroll(View.FOCUS_LEFT, true);
                        //} else {
                        //  handled = fullScroll(View.FOCUS_LEFT, true);
                        //}
                        break;
                    case Keycode.DpadRight:
                        //if (!e.IsAltPressed) {
                        //  handled = arrowScroll(View.FOCUS_RIGHT, true);
                        //} else {
                        //  handled = fullScroll(View.FOCUS_RIGHT, true);
                        //}
                        break;
                }
            }
            return handled;
        }

        public override bool OnInterceptTouchEvent(MotionEvent ev)
        {
            /*
            * This method JUST determines whether we want to intercept the motion.
            * If we return true, onMotionEvent will be called and we do the actual
            * scrolling there.
            *
            * Shortcut the most recurring case: the user is in the dragging
            * state and he is moving his finger.  We want to intercept this
            * motion.
            */
            MotionEventActions action = ev.Action;
            if ((action == MotionEventActions.Move) && (mIsBeingDragged))
            {
                return true;
            }
            if (!CanScroll())
            {
                mIsBeingDragged = false;
                return false;
            }
            float y = ev.GetY();
            float x = ev.GetX();
            switch (action)
            {
                case MotionEventActions.Move:
                    /*
                    * mIsBeingDragged == false, otherwise the shortcut would have caught it. Check
                    * whether the user has moved far enough from his original down touch.
                    */
                    /*
                    * Locally do absolute value. mLastMotionY is set to the y value
                    * of the down event.
                    */
                    int yDiff = (int)System.Math.Abs(y - mLastMotionY);
                    int xDiff = (int)System.Math.Abs(x - mLastMotionX);
                    if (yDiff > mTouchSlop || xDiff > mTouchSlop)
                    {
                        mIsBeingDragged = true;
                    }
                    break;

                case MotionEventActions.Down:
                    /* Remember location of down touch */
                    mLastMotionY = y;
                    mLastMotionX = x;

                    /*
                    * If being flinged and user touches the screen, initiate drag;
                    * otherwise don't.  mScroller.isFinished should be false when
                    * being flinged.
                    */
                    mIsBeingDragged = !mScroller.IsFinished;
                    break;

                case MotionEventActions.Cancel:
                case MotionEventActions.Up:
                    /* Release the drag */
                    mIsBeingDragged = false;
                    break;
            }

            /*
            * The only time we want to intercept motion events is if we are in the
            * drag mode.
            */
            return mIsBeingDragged;
        }

        public override bool OnTouchEvent(MotionEvent ev)
        {

            if (ev.Action == MotionEventActions.Down && ev.EdgeFlags != 0)
            {
                // Don't handle edge touches immediately -- they may actually belong to one of our
                // descendants.
                return false;
            }

            if (!CanScroll())
            {
                return false;
            }

            if (mVelocityTracker == null)
            {
                mVelocityTracker = VelocityTracker.Obtain();
            }
            mVelocityTracker.AddMovement(ev);

            MotionEventActions action = ev.Action;
            float y = ev.GetY();
            float x = ev.GetX();

            switch (action)
            {
                case MotionEventActions.Down:
                    /*
                    * If being flinged and user touches, stop the fling. isFinished
                    * will be false if being flinged.
                    */
                    if (!mScroller.IsFinished)
                    {
                        mScroller.AbortAnimation();
                    }

                    // Remember where the motion event started
                    mLastMotionY = y;
                    mLastMotionX = x;
                    break;
                case MotionEventActions.Move:
                    // Scroll to follow the motion event
                    int deltaX = (int)(mLastMotionX - x);
                    int deltaY = (int)(mLastMotionY - y);
                    mLastMotionX = x;
                    mLastMotionY = y;

                    if (deltaX < 0)
                    {
                        if (ScrollX < 0)
                        {
                            deltaX = 0;
                        }
                    }
                    else if (deltaX > 0)
                    {
                        int rightEdge = Width - PaddingRight;
                        int availableToScroll = GetChildAt(0).Right - ScrollX - rightEdge;
                        if (availableToScroll > 0)
                        {
                            deltaX = System.Math.Min(availableToScroll, deltaX);
                        }
                        else
                        {
                            deltaX = 0;
                        }
                    }
                    if (deltaY < 0)
                    {
                        if (ScrollY < 0)
                        {
                            deltaY = 0;
                        }
                    }
                    else if (deltaY > 0)
                    {
                        int bottomEdge = Height - PaddingBottom;
                        int availableToScroll = GetChildAt(0).Bottom - ScrollY - bottomEdge;
                        if (availableToScroll > 0)
                        {
                            deltaY = System.Math.Min(availableToScroll, deltaY);
                        }
                        else
                        {
                            deltaY = 0;
                        }
                    }
                    if (deltaY != 0 || deltaX != 0)
                        ScrollBy(deltaX, deltaY);
                    break;
                case MotionEventActions.Up:
                    VelocityTracker velocityTracker = mVelocityTracker;
                    velocityTracker.ComputeCurrentVelocity(1000, mMaximumVelocity);
                    int initialXVelocity = (int)velocityTracker.XVelocity;
                    int initialYVelocity = (int)velocityTracker.YVelocity;
                    if ((System.Math.Abs(initialXVelocity) + System.Math.Abs(initialYVelocity) > mMinimumVelocity) && ChildCount > 0)
                    {
                        Fling(-initialXVelocity, -initialYVelocity);
                    }
                    if (mVelocityTracker != null)
                    {
                        mVelocityTracker.Recycle();
                        mVelocityTracker = null;
                    }
                    break;
            }
            return true;
        }

        /**
  * Finds the next focusable component that fits in this View's bounds
  * (excluding fading edges) pretending that this View's top is located at
  * the parameter top.
  *
  * @param topFocus           look for a candidate is the one at the top of the bounds
  *                           if topFocus is true, or at the bottom of the bounds if topFocus is
  *                           false
  * @param top                the top offset of the bounds in which a focusable must be
  *                           found (the fading edge is assumed to start at this position)
  * @param preferredFocusable the View that has highest priority and will be
  *                           returned if it is within my bounds (null is valid)
  * @return the next focusable component in the bounds or null if none can be
  *         found
  */
        private View findFocusableViewInMyBounds(bool topFocus, int top, bool leftFocus, int left, View preferredFocusable)
        {
            /*
            * The fading edge's transparent side should be considered for focus
            * since it's mostly visible, so we divide the actual fading edge length
            * by 2.
            */
            int verticalFadingEdgeLength = VerticalFadingEdgeLength / 2;
            int topWithoutFadingEdge = top + verticalFadingEdgeLength;
            int bottomWithoutFadingEdge = top + Height - verticalFadingEdgeLength;
            int horizontalFadingEdgeLength = HorizontalFadingEdgeLength / 2;
            int leftWithoutFadingEdge = left + horizontalFadingEdgeLength;
            int rightWithoutFadingEdge = left + Width - horizontalFadingEdgeLength;

            if ((preferredFocusable != null)
              && (preferredFocusable.Top < bottomWithoutFadingEdge)
              && (preferredFocusable.Bottom > topWithoutFadingEdge)
              && (preferredFocusable.Left < rightWithoutFadingEdge)
              && (preferredFocusable.Right > leftWithoutFadingEdge))
            {
                return preferredFocusable;
            }
            return FindFocusableViewInBounds(topFocus, topWithoutFadingEdge, bottomWithoutFadingEdge, leftFocus, leftWithoutFadingEdge, rightWithoutFadingEdge);
        }

        /**
 * Finds the next focusable component that fits in the specified bounds.
 * </p>
 *
 * @param topFocus look for a candidate is the one at the top of the bounds
 *                 if topFocus is true, or at the bottom of the bounds if topFocus is
 *                 false
 * @param top      the top offset of the bounds in which a focusable must be
 *                 found
 * @param bottom   the bottom offset of the bounds in which a focusable must
 *                 be found
 * @return the next focusable component in the bounds or null if none can
 *         be found
 */
        private View FindFocusableViewInBounds(bool topFocus, int top, int bottom, bool leftFocus, int left, int right)
        {
            IList<View> focusables = GetFocusables(FocusSearchDirection.Forward);
            View focusCandidate = null;

            /*
            * A fully contained focusable is one where its top is below the bound's
            * top, and its bottom is above the bound's bottom. A partially
            * contained focusable is one where some part of it is within the
            * bounds, but it also has some part that is not within bounds.  A fully contained
            * focusable is preferred to a partially contained focusable.
            */
            bool foundFullyContainedFocusable = false;

            int count = focusables.Count;
            for (int i = 0; i < count; i++)
            {
                View view = focusables[i];
                int viewTop = view.Top;
                int viewBottom = view.Bottom;
                int viewLeft = view.Left;
                int viewRight = view.Right;

                if (top < viewBottom && viewTop < bottom && left < viewRight && viewLeft < right)
                {
                    /*
                    * the focusable is in the target area, it is a candidate for
                    * focusing
                    */
                    bool viewIsFullyContained = (top < viewTop) && (viewBottom < bottom) && (left < viewLeft) && (viewRight < right);
                    if (focusCandidate == null)
                    {
                        /* No candidate, take this one */
                        focusCandidate = view;
                        foundFullyContainedFocusable = viewIsFullyContained;
                    }
                    else
                    {
                        bool viewIsCloserToVerticalBoundary =
                          (topFocus && viewTop < focusCandidate.Top) ||
                          (!topFocus && viewBottom > focusCandidate.Bottom);
                        bool viewIsCloserToHorizontalBoundary =
                          (leftFocus && viewLeft < focusCandidate.Left) ||
                          (!leftFocus && viewRight > focusCandidate.Right);
                        if (foundFullyContainedFocusable)
                        {
                            if (viewIsFullyContained && viewIsCloserToVerticalBoundary && viewIsCloserToHorizontalBoundary)
                            {
                                /*
                                 * We're dealing with only fully contained views, so
                                 * it has to be closer to the boundary to beat our
                                 * candidate
                                 */
                                focusCandidate = view;
                            }
                        }
                        else
                        {
                            if (viewIsFullyContained)
                            {
                                /* Any fully contained view beats a partially contained view */
                                focusCandidate = view;
                                foundFullyContainedFocusable = true;
                            }
                            else if (viewIsCloserToVerticalBoundary && viewIsCloserToHorizontalBoundary)
                            {
                                /*
                                 * Partially contained view beats another partially
                                 * contained view if it's closer
                                 */
                                focusCandidate = view;
                            }
                        }
                    }
                }
            }
            return focusCandidate;
        }

        /**
  * <p>Handles scrolling in response to a "home/end" shortcut press. This
  * method will scroll the view to the top or bottom and give the focus
  * to the topmost/bottommost component in the new visible area. If no
  * component is a good candidate for focus, this scrollview reclaims the
  * focus.</p>
  *
  * @param direction the scroll direction: {@link android.view.View#FOCUS_UP}
  *                  to go the top of the view or
  *                  {@link android.view.View#FOCUS_DOWN} to go the bottom
  * @return true if the key event is consumed by this method, false otherwise
  */
        public bool FullScroll(FocusSearchDirection direction, bool horizontal)
        {
            if (!horizontal)
            {
                bool down = direction == FocusSearchDirection.Down;
                int height = Height;
                mTempRect.Top = 0;
                mTempRect.Bottom = height;
                if (down)
                {
                    int count = ChildCount;
                    if (count > 0)
                    {
                        View view = GetChildAt(count - 1);
                        mTempRect.Bottom = view.Bottom;
                        mTempRect.Top = mTempRect.Bottom - height;
                    }
                }
                return ScrollAndFocus(direction, mTempRect.Top, mTempRect.Bottom, 0, 0, 0);
            }
            else
            {
                bool right = direction == FocusSearchDirection.Down;
                int width = Width;
                mTempRect.Left = 0;
                mTempRect.Right = width;
                if (right)
                {
                    int count = ChildCount;
                    if (count > 0)
                    {
                        View view = GetChildAt(count - 1);
                        mTempRect.Right = view.Bottom;
                        mTempRect.Left = mTempRect.Right - width;
                    }
                }
                return ScrollAndFocus(0, 0, 0, direction, mTempRect.Top, mTempRect.Bottom);
            }
        }

        /**
  * <p>Scrolls the view to make the area defined by <code>top</code> and
  * <code>bottom</code> visible. This method attempts to give the focus
  * to a component visible in this area. If no component can be focused in
  * the new visible area, the focus is reclaimed by this scrollview.</p>
  *
  * @param direction the scroll direction: {@link android.view.View#FOCUS_UP}
  *                  to go upward
  *                  {@link android.view.View#FOCUS_DOWN} to downward
  * @param top       the top offset of the new area to be made visible
  * @param bottom    the bottom offset of the new area to be made visible
  * @return true if the key event is consumed by this method, false otherwise
  */
        private bool ScrollAndFocus(FocusSearchDirection directionY, int top, int bottom, FocusSearchDirection directionX, int left, int right)
        {
            bool handled = true;
            int height = Height;
            int containerTop = ScrollY;
            int containerBottom = containerTop + height;
            bool up = directionY == FocusSearchDirection.Up;
            int width = Width;
            int containerLeft = ScrollX;
            int containerRight = containerLeft + width;
            bool leftwards = directionX == FocusSearchDirection.Up;
            View newFocused = FindFocusableViewInBounds(up, top, bottom, leftwards, left, right);
            if (newFocused == null)
            {
                newFocused = this;
            }
            if ((top >= containerTop && bottom <= containerBottom) || (left >= containerLeft && right <= containerRight))
            {
                handled = false;
            }
            else
            {
                int deltaY = up ? (top - containerTop) : (bottom - containerBottom);
                int deltaX = leftwards ? (left - containerLeft) : (right - containerRight);
                DoScroll(deltaX, deltaY);
            }
            if (newFocused != FindFocus() && newFocused.RequestFocus(directionY))
            {
                mTwoDScrollViewMovedFocus = true;
                mTwoDScrollViewMovedFocus = false;
            }
            return handled;
        }

        /**
  * Handle scrolling in response to an up or down arrow click.
  *
  * @param direction The direction corresponding to the arrow key that was
  *                  pressed
  * @return True if we consumed the event, false otherwise
  */
        public bool arrowScroll(FocusSearchDirection direction, bool horizontal)
        {
            View currentFocused = FindFocus();
            if (currentFocused == this) currentFocused = null;
            View nextFocused = FocusFinder.Instance.FindNextFocus(this, currentFocused, direction);
            int maxJump = horizontal ? getMaxScrollAmountHorizontal() : getMaxScrollAmountVertical();

            if (!horizontal)
            {
                if (nextFocused != null)
                {
                    nextFocused.GetDrawingRect(mTempRect);
                    OffsetDescendantRectToMyCoords(nextFocused, mTempRect);
                    int scrollDelta = ComputeScrollDeltaToGetChildRectOnScreen(mTempRect);
                    DoScroll(0, scrollDelta);
                    nextFocused.RequestFocus(direction);
                }
                else
                {
                    // no new focus
                    int scrollDelta = maxJump;
                    if (direction == FocusSearchDirection.Up && ScrollY < scrollDelta)
                    {
                        scrollDelta = ScrollY;
                    }
                    else if (direction == FocusSearchDirection.Down)
                    {
                        if (ChildCount > 0)
                        {
                            int daBottom = GetChildAt(0).Bottom;
                            int screenBottom = ScrollY + Height;
                            if (daBottom - screenBottom < maxJump)
                            {
                                scrollDelta = daBottom - screenBottom;
                            }
                        }
                    }
                    if (scrollDelta == 0)
                    {
                        return false;
                    }
                    DoScroll(0, direction == FocusSearchDirection.Down ? scrollDelta : -scrollDelta);
                }
            }
            else
            {
                if (nextFocused != null)
                {
                    nextFocused.GetDrawingRect(mTempRect);
                    OffsetDescendantRectToMyCoords(nextFocused, mTempRect);
                    int scrollDelta = ComputeScrollDeltaToGetChildRectOnScreen(mTempRect);
                    DoScroll(scrollDelta, 0);
                    nextFocused.RequestFocus(direction);
                }
                else
                {
                    // no new focus
                    int scrollDelta = maxJump;
                    if (direction == FocusSearchDirection.Up && ScrollY < scrollDelta)
                    {
                        scrollDelta = ScrollY;
                    }
                    else if (direction == FocusSearchDirection.Down)
                    {
                        if (ChildCount > 0)
                        {
                            int daBottom = GetChildAt(0).Bottom;
                            int screenBottom = ScrollY + Height;
                            if (daBottom - screenBottom < maxJump)
                            {
                                scrollDelta = daBottom - screenBottom;
                            }
                        }
                    }
                    if (scrollDelta == 0)
                    {
                        return false;
                    }
                    DoScroll(direction == FocusSearchDirection.Down ? scrollDelta : -scrollDelta, 0);
                }
            }
            return true;
        }

        /**
  * Smooth scroll by a Y delta
  *
  * @param delta the number of pixels to scroll by on the Y axis
  */
        private void DoScroll(int deltaX, int deltaY)
        {
            if (deltaX != 0 || deltaY != 0)
            {
                SmoothScrollBy(deltaX, deltaY);
            }
        }

        /**
  * Like {@link View#scrollBy}, but scroll smoothly instead of immediately.
  *
  * @param dx the number of pixels to scroll by on the X axis
  * @param dy the number of pixels to scroll by on the Y axis
  */
        public void SmoothScrollBy(int dx, int dy)
        {
            long duration = AnimationUtils.CurrentAnimationTimeMillis() - mLastScroll;
            if (duration > ANIMATED_SCROLL_GAP)
            {
                mScroller.StartScroll(ScrollX, ScrollY, dx, dy);
                AwakenScrollBars(mScroller.Duration);
                Invalidate();
            }
            else
            {
                if (!mScroller.IsFinished)
                {
                    mScroller.AbortAnimation();
                }
                ScrollBy(dx, dy);
            }
            mLastScroll = AnimationUtils.CurrentAnimationTimeMillis();
        }

        /**
  * Like {@link #scrollTo}, but scroll smoothly instead of immediately.
  *
  * @param x the position where to scroll on the X axis
  * @param y the position where to scroll on the Y axis
  */
        public void SmoothScrollTo(int x, int y)
        {
            SmoothScrollBy(x - ScrollX, y - ScrollY);
        }

        /**
         * <p>The scroll range of a scroll view is the overall height of all of its
         * children.</p>
         */
        protected override int ComputeVerticalScrollRange()
        {
            int count = ChildCount;
            return count == 0 ? Height : (GetChildAt(0)).Bottom;
        }

        protected override int ComputeHorizontalScrollRange()
        {
            int count = ChildCount;
            return count == 0 ? Width : (GetChildAt(0)).Right;
        }

        protected override void MeasureChild(View child, int parentWidthMeasureSpec, int parentHeightMeasureSpec)
        {
            ViewGroup.LayoutParams lp = child.LayoutParameters;
            int childWidthMeasureSpec;
            int childHeightMeasureSpec;

            childWidthMeasureSpec = GetChildMeasureSpec(parentWidthMeasureSpec, PaddingLeft + PaddingRight, lp.Width);
            childHeightMeasureSpec = MeasureSpec.MakeMeasureSpec(0, MeasureSpecMode.Unspecified);

            child.Measure(childWidthMeasureSpec, childHeightMeasureSpec);
        }

        protected override void MeasureChildWithMargins(View child, int parentWidthMeasureSpec, int widthUsed, int parentHeightMeasureSpec, int heightUsed)
        {
            MarginLayoutParams lp = (MarginLayoutParams)child.LayoutParameters;
            int childWidthMeasureSpec = GetChildMeasureSpec(parentWidthMeasureSpec,
            PaddingLeft + PaddingRight + lp.LeftMargin + lp.RightMargin + widthUsed, lp.Width);
            int childHeightMeasureSpec = MeasureSpec.MakeMeasureSpec(lp.TopMargin + lp.BottomMargin, MeasureSpecMode.Unspecified);

            child.Measure(childWidthMeasureSpec, childHeightMeasureSpec);
        }

        public override void ComputeScroll()
        {
            if (mScroller.ComputeScrollOffset())
            {
                // This is called at drawing time by ViewGroup.  We don't want to
                // re-show the scrollbars at this point, which scrollTo will do,
                // so we replicate most of scrollTo here.
                //
                //         It's a little odd to call onScrollChanged from inside the drawing.
                //
                //         It is, except when you remember that computeScroll() is used to
                //         animate scrolling. So unless we want to defer the onScrollChanged()
                //         until the end of the animated scrolling, we don't really have a
                //         choice here.
                //
                //         I agree.  The alternative, which I think would be worse, is to post
                //         something and tell the subclasses later.  This is bad because there
                //         will be a window where mScrollX/Y is different from what the app
                //         thinks it is.
                //
                int oldX = ScrollX;
                int oldY = ScrollY;
                int x = mScroller.CurrX;
                int y = mScroller.CurrY;
                if (ChildCount > 0)
                {
                    View child = GetChildAt(0);
                    ScrollTo(Clamp(x, Width - PaddingRight - PaddingLeft, child.Width),
                    Clamp(y, Height - PaddingBottom - PaddingTop, child.Height));
                }
                else
                {
                    ScrollTo(x, y);
                }
                if (oldX != ScrollX || oldY != ScrollY)
                {
                    OnScrollChanged(ScrollX, ScrollY, oldX, oldY);
                }

                // Keep on drawing until the animation has finished.
                PostInvalidate();
            }
        }

        /**
* Scrolls the view to the given child.
*
* @param child the View to scroll to
*/
        private void ScrollToChild(View child)
        {
            child.GetDrawingRect(mTempRect);
            /* Offset from child's local coordinates to TwoDScrollView coordinates */
            OffsetDescendantRectToMyCoords(child, mTempRect);
            int scrollDelta = ComputeScrollDeltaToGetChildRectOnScreen(mTempRect);
            if (scrollDelta != 0)
            {
                ScrollBy(0, scrollDelta);
            }
        }

        /**
         * If rect is off screen, scroll just enough to get it (or at least the
         * first screen size chunk of it) on screen.
         *
         * @param rect      The rectangle.
         * @param immediate True to scroll immediately without animation
         * @return true if scrolling was performed
         */
        private bool ScrollToChildRect(Rect rect, bool immediate)
        {
            int delta = ComputeScrollDeltaToGetChildRectOnScreen(rect);
            bool scroll = delta != 0;
            if (scroll)
            {
                if (immediate)
                {
                    ScrollBy(0, delta);
                }
                else
                {
                    SmoothScrollBy(0, delta);
                }
            }
            return scroll;
        }

        /**
         * Compute the amount to scroll in the Y direction in order to get
         * a rectangle completely on the screen (or, if taller than the screen,
         * at least the first screen size chunk of it).
         *
         * @param rect The rect.
         * @return The scroll delta.
         */
        protected int ComputeScrollDeltaToGetChildRectOnScreen(Rect rect)
        {
            if (ChildCount == 0) return 0;
            int height = Height;
            int screenTop = ScrollY;
            int screenBottom = screenTop + height;
            int fadingEdge = VerticalFadingEdgeLength;
            // leave room for top fading edge as long as rect isn't at very top
            if (rect.Top > 0)
            {
                screenTop += fadingEdge;
            }

            // leave room for bottom fading edge as long as rect isn't at very bottom
            if (rect.Bottom < GetChildAt(0).Height)
            {
                screenBottom -= fadingEdge;
            }
            int scrollYDelta = 0;
            if (rect.Bottom > screenBottom && rect.Top > screenTop)
            {
                // need to move down to get it in view: move down just enough so
                // that the entire rectangle is in view (or at least the first
                // screen size chunk).
                if (rect.Height() > height)
                {
                    // just enough to get screen size chunk on
                    scrollYDelta += (rect.Top - screenTop);
                }
                else
                {
                    // get entire rect at bottom of screen
                    scrollYDelta += (rect.Bottom - screenBottom);
                }

                // make sure we aren't scrolling beyond the end of our content
                int bottom = GetChildAt(0).Bottom;
                int distanceToBottom = bottom - screenBottom;
                scrollYDelta = System.Math.Min(scrollYDelta, distanceToBottom);

            }
            else if (rect.Top < screenTop && rect.Bottom < screenBottom)
            {
                // need to move up to get it in view: move up just enough so that
                // entire rectangle is in view (or at least the first screen
                // size chunk of it).

                if (rect.Height() > height)
                {
                    // screen size chunk
                    scrollYDelta -= (screenBottom - rect.Bottom);
                }
                else
                {
                    // entire rect at top
                    scrollYDelta -= (screenTop - rect.Top);
                }

                // make sure we aren't scrolling any further than the top our content
                scrollYDelta = System.Math.Max(scrollYDelta, -ScrollY);
            }
            return scrollYDelta;
        }

        public override void RequestChildFocus(View child, View focused)
        {
            if (!mTwoDScrollViewMovedFocus)
            {
                if (!mIsLayoutDirty)
                {
                    ScrollToChild(focused);
                }
                else
                {
                    // The child may not be laid out yet, we can't compute the scroll yet
                    mChildToScrollTo = focused;
                }
            }
            base.RequestChildFocus(child, focused);
        }

        /**
         * When looking for focus in children of a scroll view, need to be a little
         * more careful not to give focus to something that is scrolled off screen.
         *
         * This is more expensive than the default {@link android.view.ViewGroup}
         * implementation, otherwise this behavior might have been made the default.
         */
        protected bool OnRequestFocusInDescendants(FocusSearchDirection direction, Rect previouslyFocusedRect)
        {
            // convert from forward / backward notation to up / down / left / right
            // (ugh).
            if (direction == FocusSearchDirection.Forward)
            {
                direction = FocusSearchDirection.Down;
            }
            else if (direction == FocusSearchDirection.Backward)
            {
                direction = FocusSearchDirection.Up;
            }

            View nextFocus = previouslyFocusedRect == null ?
            FocusFinder.Instance.FindNextFocus(this, null, direction) :
            FocusFinder.Instance.FindNextFocusFromRect(this,
            previouslyFocusedRect, direction);

            if (nextFocus == null)
            {
                return false;
            }

            return nextFocus.RequestFocus(direction, previouslyFocusedRect);
        }

        public override bool RequestChildRectangleOnScreen(View child, Rect rectangle, bool immediate)
        {
            // offset into coordinate space of this scroll view
            rectangle.Offset(child.Left - child.ScrollX, child.Top - child.ScrollY);
            return ScrollToChildRect(rectangle, immediate);
        }

        public override void RequestLayout()
        {
            mIsLayoutDirty = true;
            base.RequestLayout();
        }


        protected override void OnLayout(bool changed, int l, int t, int r, int b)
        {
            base.OnLayout(changed, l, t, r, b);
            mIsLayoutDirty = false;
            // Give a child focus if it needs it
            if (mChildToScrollTo != null && IsViewDescendantOf(mChildToScrollTo, this))
            {
                ScrollToChild(mChildToScrollTo);
            }
            mChildToScrollTo = null;

            // Calling this with the present values causes it to re-clam them
            ScrollTo(ScrollX, ScrollY);
        }

        protected override void OnSizeChanged(int w, int h, int oldw, int oldh)
        {
            base.OnSizeChanged(w, h, oldw, oldh);

            View currentFocused = FindFocus();
            if (null == currentFocused || this == currentFocused)
                return;

            // If the currently-focused view was visible on the screen when the
            // screen was at the old height, then scroll the screen to make that
            // view visible with the new screen height.
            currentFocused.GetDrawingRect(mTempRect);
            OffsetDescendantRectToMyCoords(currentFocused, mTempRect);
            int scrollDeltaX = ComputeScrollDeltaToGetChildRectOnScreen(mTempRect);
            int scrollDeltaY = ComputeScrollDeltaToGetChildRectOnScreen(mTempRect);
            DoScroll(scrollDeltaX, scrollDeltaY);
        }

        /**
         * Return true if child is an descendant of parent, (or equal to the parent).
         */
        private bool IsViewDescendantOf(View child, View parent)
        {
            if (child == parent)
            {
                return true;
            }

            IViewParent theParent = child.Parent;
            return (theParent is ViewGroup) && IsViewDescendantOf((View)theParent, parent);
        }

        /**
         * Fling the scroll view
         *
         * @param velocityY The initial velocity in the Y direction. Positive
         *                  numbers mean that the finger/curor is moving down the screen,
         *                  which means we want to scroll towards the top.
         */
        public void Fling(int velocityX, int velocityY)
        {
            if (ChildCount > 0)
            {
                int height = Height - PaddingBottom - PaddingTop;
                int bottom = GetChildAt(0).Height;
                int width = Width - PaddingRight - PaddingLeft;
                int right = GetChildAt(0).Width;

                mScroller.Fling(ScrollX, ScrollY, velocityX, velocityY, 0, right - width, 0, bottom - height);

                bool movingDown = velocityY > 0;
                bool movingRight = velocityX > 0;

                View newFocused = findFocusableViewInMyBounds(movingRight, mScroller.FinalX, movingDown, mScroller.FinalY, FindFocus());
                if (newFocused == null)
                {
                    newFocused = this;
                }

                if (newFocused != FindFocus() && newFocused.RequestFocus(movingDown ? FocusSearchDirection.Down : FocusSearchDirection.Up))
                {
                    mTwoDScrollViewMovedFocus = true;
                    mTwoDScrollViewMovedFocus = false;
                }

                AwakenScrollBars(mScroller.Duration);
                Invalidate();
            }
        }

        /**
         * {@inheritDoc}
         *
         * <p>This version also clamps the scrolling to the bounds of our child.
         */
        public override void ScrollTo(int x, int y)
        {
            // we rely on the fact the View.scrollBy calls scrollTo.
            if (ChildCount > 0)
            {
                View child = GetChildAt(0);
                x = Clamp(x, Width - PaddingRight - PaddingLeft, child.Width);
                y = Clamp(y, Height - PaddingBottom - PaddingTop, child.Height);
                if (x != ScrollX || y != ScrollY)
                {
                    base.ScrollTo(x, y);
                }
            }
        }

        private int Clamp(int n, int my, int child)
        {
            if (my >= child || n < 0)
            {
                /* my >= child is this case:
                 *                    |--------------- me ---------------|
                 *     |------ child ------|
                 * or
                 *     |--------------- me ---------------|
                 *            |------ child ------|
                 * or
                 *     |--------------- me ---------------|
                 *                                  |------ child ------|
                 *
                 * n < 0 is this case:
                 *     |------ me ------|
                 *                    |-------- child --------|
                 *     |-- mScrollX --|
                 */
                return 0;
            }
            if ((my + n) > child)
            {
                /* this case:
                 *                    |------ me ------|
                 *     |------ child ------|
                 *     |-- mScrollX --|
                 */
                return child - my;
            }
            return n;
        }

    }
}