/*
 * Copyright (C) 2013 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.
 */

package com.way.ui.swipeback;

import java.util.Arrays;

import android.annotation.SuppressLint;
import android.content.Context;
import android.support.v4.view.MotionEventCompat;
import android.support.v4.view.VelocityTrackerCompat;
import android.support.v4.view.ViewCompat;
import android.support.v4.widget.ScrollerCompat;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewGroup;
import android.view.animation.Interpolator;

/**
 * ViewDragHelper is a utility class for writing custom ViewGroups. It offers a
 * number of useful operations and state tracking for allowing a user to drag
 * and reposition views within their parent ViewGroup.
 */
@SuppressLint("NewApi")
public class ViewDragHelper {
	private static final String TAG = "ViewDragHelper";

	/**
	 * A null/invalid pointer ID.
	 */
	public static final int INVALID_POINTER = -1;

	/**
	 * A view is not currently being dragged or animating as a result of a
	 * fling/snap.
	 */
	public static final int STATE_IDLE = 0;

	/**
	 * A view is currently being dragged. The position is currently changing as
	 * a result of user input or simulated user input.
	 */
	public static final int STATE_DRAGGING = 1;

	/**
	 * A view is currently settling into place as a result of a fling or
	 * predefined non-interactive motion.
	 */
	public static final int STATE_SETTLING = 2;

	/**
	 * Edge flag indicating that the left edge should be affected.
	 */
	public static final int EDGE_LEFT = 1 << 0;

	/**
	 * Edge flag indicating that the right edge should be affected.
	 */
	public static final int EDGE_RIGHT = 1 << 1;

	/**
	 * Edge flag indicating that the top edge should be affected.
	 */
	public static final int EDGE_TOP = 1 << 2;

	/**
	 * Edge flag indicating that the bottom edge should be affected.
	 */
	public static final int EDGE_BOTTOM = 1 << 3;

	/**
	 * Edge flag set indicating all edges should be affected.
	 */
	public static final int EDGE_ALL = EDGE_LEFT | EDGE_TOP | EDGE_RIGHT
			| EDGE_BOTTOM;

	/**
	 * Indicates that a check should occur along the horizontal axis
	 */
	public static final int DIRECTION_HORIZONTAL = 1 << 0;

	/**
	 * Indicates that a check should occur along the vertical axis
	 */
	public static final int DIRECTION_VERTICAL = 1 << 1;

	/**
	 * Indicates that a check should occur along all axes
	 */
	public static final int DIRECTION_ALL = DIRECTION_HORIZONTAL
			| DIRECTION_VERTICAL;

	public static final int EDGE_SIZE = 20; // dp

	private static final int BASE_SETTLE_DURATION = 256; // ms

	private static final int MAX_SETTLE_DURATION = 600; // ms

	// Current drag state; idle, dragging or settling
	private int mDragState;

	// Distance to travel before a drag may begin
	private int mTouchSlop;

	// Last known position/pointer tracking
	private int mActivePointerId = INVALID_POINTER;

	private float[] mInitialMotionX;

	private float[] mInitialMotionY;

	private float[] mLastMotionX;

	private float[] mLastMotionY;

	private int[] mInitialEdgesTouched;

	private int[] mEdgeDragsInProgress;

	private int[] mEdgeDragsLocked;

	private int mPointersDown;

	private VelocityTracker mVelocityTracker;

	private float mMaxVelocity;

	private float mMinVelocity;

	private int mEdgeSize;

	private int mTrackingEdges;

	private ScrollerCompat mScroller;

	private final Callback mCallback;

	private View mCapturedView;

	private boolean mReleaseInProgress;

	private final ViewGroup mParentView;

	/**
	 * A Callback is used as a communication channel with the ViewDragHelper
	 * back to the parent view using it. <code>on*</code>methods are invoked on
	 * siginficant events and several accessor methods are expected to provide
	 * the ViewDragHelper with more information about the state of the parent
	 * view upon request. The callback also makes decisions governing the range
	 * and draggability of child views.
	 */
	public static abstract class Callback {
		/**
		 * Called when the drag state changes. See the <code>STATE_*</code>
		 * constants for more information.
		 * 
		 * @param state
		 *            The new drag state
		 * @see #STATE_IDLE
		 * @see #STATE_DRAGGING
		 * @see #STATE_SETTLING
		 */
		public void onViewDragStateChanged(int state) {
		}

		/**
		 * Called when the captured view's position changes as the result of a
		 * drag or settle.
		 * 
		 * @param changedView
		 *            View whose position changed
		 * @param left
		 *            New X coordinate of the left edge of the view
		 * @param top
		 *            New Y coordinate of the top edge of the view
		 * @param dx
		 *            Change in X position from the last call
		 * @param dy
		 *            Change in Y position from the last call
		 */
		public void onViewPositionChanged(View changedView, int left, int top,
				int dx, int dy) {
		}

		/**
		 * Called when a child view is captured for dragging or settling. The ID
		 * of the pointer currently dragging the captured view is supplied. If
		 * activePointerId is identified as {@link #INVALID_POINTER} the capture
		 * is programmatic instead of pointer-initiated.
		 * 
		 * @param capturedChild
		 *            Child view that was captured
		 * @param activePointerId
		 *            Pointer id tracking the child capture
		 */
		public void onViewCaptured(View capturedChild, int activePointerId) {
		}

		/**
		 * Called when the child view is no longer being actively dragged. The
		 * fling velocity is also supplied, if relevant. The velocity values may
		 * be clamped to system minimums or maximums.
		 * <p>
		 * Calling code may decide to fling or otherwise release the view to let
		 * it settle into place. It should do so using
		 * {@link #settleCapturedViewAt(int, int)} or
		 * {@link #flingCapturedView(int, int, int, int)}. If the Callback
		 * invokes one of these methods, the ViewDragHelper will enter
		 * {@link #STATE_SETTLING} and the view capture will not fully end until
		 * it comes to a complete stop. If neither of these methods is invoked
		 * before <code>onViewReleased</code> returns, the view will stop in
		 * place and the ViewDragHelper will return to {@link #STATE_IDLE}.
		 * </p>
		 * 
		 * @param releasedChild
		 *            The captured child view now being released
		 * @param xvel
		 *            X velocity of the pointer as it left the screen in pixels
		 *            per second.
		 * @param yvel
		 *            Y velocity of the pointer as it left the screen in pixels
		 *            per second.
		 */
		public void onViewReleased(View releasedChild, float xvel, float yvel) {
		}

		/**
		 * Called when one of the subscribed edges in the parent view has been
		 * touched by the user while no child view is currently captured.
		 * 
		 * @param edgeFlags
		 *            A combination of edge flags describing the edge(s)
		 *            currently touched
		 * @param pointerId
		 *            ID of the pointer touching the described edge(s)
		 * @see #EDGE_LEFT
		 * @see #EDGE_TOP
		 * @see #EDGE_RIGHT
		 * @see #EDGE_BOTTOM
		 */
		public void onEdgeTouched(int edgeFlags, int pointerId) {
		}

		/**
		 * Called when the given edge may become locked. This can happen if an
		 * edge drag was preliminarily rejected before beginning, but after
		 * {@link #onEdgeTouched(int, int)} was called. This method should
		 * return true to lock this edge or false to leave it unlocked. The
		 * default behavior is to leave edges unlocked.
		 * 
		 * @param edgeFlags
		 *            A combination of edge flags describing the edge(s) locked
		 * @return true to lock the edge, false to leave it unlocked
		 */
		public boolean onEdgeLock(int edgeFlags) {
			return false;
		}

		/**
		 * Called when the user has started a deliberate drag away from one of
		 * the subscribed edges in the parent view while no child view is
		 * currently captured.
		 * 
		 * @param edgeFlags
		 *            A combination of edge flags describing the edge(s) dragged
		 * @param pointerId
		 *            ID of the pointer touching the described edge(s)
		 * @see #EDGE_LEFT
		 * @see #EDGE_TOP
		 * @see #EDGE_RIGHT
		 * @see #EDGE_BOTTOM
		 */
		public void onEdgeDragStarted(int edgeFlags, int pointerId) {
		}

		/**
		 * Called to determine the Z-order of child views.
		 * 
		 * @param index
		 *            the ordered position to query for
		 * @return index of the view that should be ordered at position
		 *         <code>index</code>
		 */
		public int getOrderedChildIndex(int index) {
			return index;
		}

		/**
		 * Return the magnitude of a draggable child view's horizontal range of
		 * motion in pixels. This method should return 0 for views that cannot
		 * move horizontally.
		 * 
		 * @param child
		 *            Child view to check
		 * @return range of horizontal motion in pixels
		 */
		public int getViewHorizontalDragRange(View child) {
			return 0;
		}

		/**
		 * Return the magnitude of a draggable child view's vertical range of
		 * motion in pixels. This method should return 0 for views that cannot
		 * move vertically.
		 * 
		 * @param child
		 *            Child view to check
		 * @return range of vertical motion in pixels
		 */
		public int getViewVerticalDragRange(View child) {
			return 0;
		}

		/**
		 * Called when the user's input indicates that they want to capture the
		 * given child view with the pointer indicated by pointerId. The
		 * callback should return true if the user is permitted to drag the
		 * given view with the indicated pointer.
		 * <p>
		 * ViewDragHelper may call this method multiple times for the same view
		 * even if the view is already captured; this indicates that a new
		 * pointer is trying to take control of the view.
		 * </p>
		 * <p>
		 * If this method returns true, a call to
		 * {@link #onViewCaptured(android.view.View, int)} will follow if the
		 * capture is successful.
		 * </p>
		 * 
		 * @param child
		 *            Child the user is attempting to capture
		 * @param pointerId
		 *            ID of the pointer attempting the capture
		 * @return true if capture should be allowed, false otherwise
		 */
		public abstract boolean tryCaptureView(View child, int pointerId);

		/**
		 * Restrict the motion of the dragged child view along the horizontal
		 * axis. The default implementation does not allow horizontal motion;
		 * the extending class must override this method and provide the desired
		 * clamping.
		 * 
		 * @param child
		 *            Child view being dragged
		 * @param left
		 *            Attempted motion along the X axis
		 * @param dx
		 *            Proposed change in position for left
		 * @return The new clamped position for left
		 */
		public int clampViewPositionHorizontal(View child, int left, int dx) {
			return 0;
		}

		/**
		 * Restrict the motion of the dragged child view along the vertical
		 * axis. The default implementation does not allow vertical motion; the
		 * extending class must override this method and provide the desired
		 * clamping.
		 * 
		 * @param child
		 *            Child view being dragged
		 * @param top
		 *            Attempted motion along the Y axis
		 * @param dy
		 *            Proposed change in position for top
		 * @return The new clamped position for top
		 */
		public int clampViewPositionVertical(View child, int top, int dy) {
			return 0;
		}
	}

	/**
	 * Interpolator defining the animation curve for mScroller
	 */
	private static final Interpolator sInterpolator = new Interpolator() {
		public float getInterpolation(float t) {
			t -= 1.0f;
			return t * t * t * t * t + 1.0f;
		}
	};

	private final Runnable mSetIdleRunnable = new Runnable() {
		public void run() {
			setDragState(STATE_IDLE);
		}
	};

	/**
	 * Factory method to create a new ViewDragHelper.
	 * 
	 * @param forParent
	 *            Parent view to monitor
	 * @param cb
	 *            Callback to provide information and receive events
	 * @return a new ViewDragHelper instance
	 */
	public static ViewDragHelper create(ViewGroup forParent, Callback cb) {
		return new ViewDragHelper(forParent.getContext(), forParent, cb);
	}

	/**
	 * Factory method to create a new ViewDragHelper.
	 * 
	 * @param forParent
	 *            Parent view to monitor
	 * @param sensitivity
	 *            Multiplier for how sensitive the helper should be about
	 *            detecting the start of a drag. Larger values are more
	 *            sensitive. 1.0f is normal.
	 * @param cb
	 *            Callback to provide information and receive events
	 * @return a new ViewDragHelper instance
	 */
	public static ViewDragHelper create(ViewGroup forParent, float sensitivity,
			Callback cb) {
		final ViewDragHelper helper = create(forParent, cb);
		helper.mTouchSlop = (int) (helper.mTouchSlop * (1 / sensitivity));
		return helper;
	}

	/**
	 * Apps should use ViewDragHelper.create() to get a new instance. This will
	 * allow VDH to use internal compatibility implementations for different
	 * platform versions.
	 * 
	 * @param context
	 *            Context to initialize config-dependent params from
	 * @param forParent
	 *            Parent view to monitor
	 */
	private ViewDragHelper(Context context, ViewGroup forParent, Callback cb) {
		if (forParent == null) {
			throw new IllegalArgumentException("Parent view may not be null");
		}
		if (cb == null) {
			throw new IllegalArgumentException("Callback may not be null");
		}

		mParentView = forParent;
		mCallback = cb;

		final ViewConfiguration vc = ViewConfiguration.get(context);
		final float density = context.getResources().getDisplayMetrics().density;
		mEdgeSize = (int) (EDGE_SIZE * density + 0.5f);

		mTouchSlop = vc.getScaledTouchSlop();
		mMaxVelocity = vc.getScaledMaximumFlingVelocity();
		mMinVelocity = vc.getScaledMinimumFlingVelocity();
		mScroller = ScrollerCompat.create(context, sInterpolator);
	}

	/**
	 * Set the minimum velocity that will be detected as having a magnitude
	 * greater than zero in pixels per second. Callback methods accepting a
	 * velocity will be clamped appropriately.
	 * 
	 * @param minVel
	 *            Minimum velocity to detect
	 */
	public void setMinVelocity(float minVel) {
		mMinVelocity = minVel;
	}

	/**
	 * Return the currently configured minimum velocity. Any flings with a
	 * magnitude less than this value in pixels per second. Callback methods
	 * accepting a velocity will receive zero as a velocity value if the real
	 * detected velocity was below this threshold.
	 * 
	 * @return the minimum velocity that will be detected
	 */
	public float getMinVelocity() {
		return mMinVelocity;
	}

	/**
	 * Retrieve the current drag state of this helper. This will return one of
	 * {@link #STATE_IDLE}, {@link #STATE_DRAGGING} or {@link #STATE_SETTLING}.
	 * 
	 * @return The current drag state
	 */
	public int getViewDragState() {
		return mDragState;
	}

	/**
	 * Enable edge tracking for the selected edges of the parent view. The
	 * callback's
	 * {@link com.way.ui.swipeback.ViewDragHelper.Callback#onEdgeTouched(int, int)}
	 * and
	 * {@link com.way.ui.swipeback.ViewDragHelper.Callback#onEdgeDragStarted(int, int)}
	 * methods will only be invoked for edges for which edge tracking has been
	 * enabled.
	 * 
	 * @param edgeFlags
	 *            Combination of edge flags describing the edges to watch
	 * @see #EDGE_LEFT
	 * @see #EDGE_TOP
	 * @see #EDGE_RIGHT
	 * @see #EDGE_BOTTOM
	 */
	public void setEdgeTrackingEnabled(int edgeFlags) {
		mTrackingEdges = edgeFlags;
	}

	/**
	 * Return the size of an edge. This is the range in pixels along the edges
	 * of this view that will actively detect edge touches or drags if edge
	 * tracking is enabled.
	 * 
	 * @return The size of an edge in pixels
	 * @see #setEdgeTrackingEnabled(int)
	 */
	public int getEdgeSize() {
		return mEdgeSize;
	}

	/**
	 * Set the size of an edge. This is the range in pixels along the edges of
	 * this view that will actively detect edge touches or drags if edge
	 * tracking is enabled.
	 * 
	 * @param size
	 *            The size of an edge in pixels
	 */
	public void setEdgeSize(int size) {
		mEdgeSize = size;
	}

	/**
	 * Capture a specific child view for dragging within the parent. The
	 * callback will be notified but
	 * {@link com.way.ui.swipeback.ViewDragHelper.Callback#tryCaptureView(android.view.View, int)}
	 * will not be asked permission to capture this view.
	 * 
	 * @param childView
	 *            Child view to capture
	 * @param activePointerId
	 *            ID of the pointer that is dragging the captured child view
	 */
	public void captureChildView(View childView, int activePointerId) {
		if (childView.getParent() != mParentView) {
			throw new IllegalArgumentException(
					"captureChildView: parameter must be a descendant "
							+ "of the ViewDragHelper's tracked parent view ("
							+ mParentView + ")");
		}

		mCapturedView = childView;
		mActivePointerId = activePointerId;
		mCallback.onViewCaptured(childView, activePointerId);
		setDragState(STATE_DRAGGING);
	}

	/**
	 * @return The currently captured view, or null if no view has been
	 *         captured.
	 */
	public View getCapturedView() {
		return mCapturedView;
	}

	/**
	 * @return The ID of the pointer currently dragging the captured view, or
	 *         {@link #INVALID_POINTER}.
	 */
	public int getActivePointerId() {
		return mActivePointerId;
	}

	/**
	 * @return The minimum distance in pixels that the user must travel to
	 *         initiate a drag
	 */
	public int getTouchSlop() {
		return mTouchSlop;
	}

	/**
	 * The result of a call to this method is equivalent to
	 * {@link #processTouchEvent(android.view.MotionEvent)} receiving an
	 * ACTION_CANCEL event.
	 */
	public void cancel() {
		mActivePointerId = INVALID_POINTER;
		clearMotionHistory();

		if (mVelocityTracker != null) {
			mVelocityTracker.recycle();
			mVelocityTracker = null;
		}
	}

	/**
	 * {@link #cancel()}, but also abort all motion in progress and snap to the
	 * end of any animation.
	 */
	public void abort() {
		cancel();
		if (mDragState == STATE_SETTLING) {
			final int oldX = mScroller.getCurrX();
			final int oldY = mScroller.getCurrY();
			mScroller.abortAnimation();
			final int newX = mScroller.getCurrX();
			final int newY = mScroller.getCurrY();
			mCallback.onViewPositionChanged(mCapturedView, newX, newY, newX
					- oldX, newY - oldY);
		}
		setDragState(STATE_IDLE);
	}

	/**
	 * Animate the view <code>child</code> to the given (left, top) position. If
	 * this method returns true, the caller should invoke
	 * {@link #continueSettling(boolean)} on each subsequent frame to continue
	 * the motion until it returns false. If this method returns false there is
	 * no further work to do to complete the movement.
	 * <p>
	 * This operation does not count as a capture event, though
	 * {@link #getCapturedView()} will still report the sliding view while the
	 * slide is in progress.
	 * </p>
	 * 
	 * @param child
	 *            Child view to capture and animate
	 * @param finalLeft
	 *            Final left position of child
	 * @param finalTop
	 *            Final top position of child
	 * @return true if animation should continue through
	 *         {@link #continueSettling(boolean)} calls
	 */
	public boolean smoothSlideViewTo(View child, int finalLeft, int finalTop) {
		mCapturedView = child;
		mActivePointerId = INVALID_POINTER;

		return forceSettleCapturedViewAt(finalLeft, finalTop, 0, 0);
	}

	/**
	 * Settle the captured view at the given (left, top) position. The
	 * appropriate velocity from prior motion will be taken into account. If
	 * this method returns true, the caller should invoke
	 * {@link #continueSettling(boolean)} on each subsequent frame to continue
	 * the motion until it returns false. If this method returns false there is
	 * no further work to do to complete the movement.
	 * 
	 * @param finalLeft
	 *            Settled left edge position for the captured view
	 * @param finalTop
	 *            Settled top edge position for the captured view
	 * @return true if animation should continue through
	 *         {@link #continueSettling(boolean)} calls
	 */
	public boolean settleCapturedViewAt(int finalLeft, int finalTop) {
		if (!mReleaseInProgress) {
			throw new IllegalStateException(
					"Cannot settleCapturedViewAt outside of a call to "
							+ "Callback#onViewReleased");
		}

		return forceSettleCapturedViewAt(finalLeft, finalTop,
				(int) VelocityTrackerCompat.getXVelocity(mVelocityTracker,
						mActivePointerId),
				(int) VelocityTrackerCompat.getYVelocity(mVelocityTracker,
						mActivePointerId));
	}

	/**
	 * Settle the captured view at the given (left, top) position.
	 * 
	 * @param finalLeft
	 *            Target left position for the captured view
	 * @param finalTop
	 *            Target top position for the captured view
	 * @param xvel
	 *            Horizontal velocity
	 * @param yvel
	 *            Vertical velocity
	 * @return true if animation should continue through
	 *         {@link #continueSettling(boolean)} calls
	 */
	private boolean forceSettleCapturedViewAt(int finalLeft, int finalTop,
			int xvel, int yvel) {
		final int startLeft = mCapturedView.getLeft();
		final int startTop = mCapturedView.getTop();
		final int dx = finalLeft - startLeft;
		final int dy = finalTop - startTop;

		if (dx == 0 && dy == 0) {
			// Nothing to do. Send callbacks, be done.
			mScroller.abortAnimation();
			setDragState(STATE_IDLE);
			return false;
		}

		final int duration = computeSettleDuration(mCapturedView, dx, dy, xvel,
				yvel);
		mScroller.startScroll(startLeft, startTop, dx, dy, duration);

		setDragState(STATE_SETTLING);
		return true;
	}

	private int computeSettleDuration(View child, int dx, int dy, int xvel,
			int yvel) {
		xvel = clampMag(xvel, (int) mMinVelocity, (int) mMaxVelocity);
		yvel = clampMag(yvel, (int) mMinVelocity, (int) mMaxVelocity);
		final int absDx = Math.abs(dx);
		final int absDy = Math.abs(dy);
		final int absXVel = Math.abs(xvel);
		final int absYVel = Math.abs(yvel);
		final int addedVel = absXVel + absYVel;
		final int addedDistance = absDx + absDy;

		final float xweight = xvel != 0 ? (float) absXVel / addedVel
				: (float) absDx / addedDistance;
		final float yweight = yvel != 0 ? (float) absYVel / addedVel
				: (float) absDy / addedDistance;

		int xduration = computeAxisDuration(dx, xvel,
				mCallback.getViewHorizontalDragRange(child));
		int yduration = computeAxisDuration(dy, yvel,
				mCallback.getViewVerticalDragRange(child));

		return (int) (xduration * xweight + yduration * yweight);
	}

	private int computeAxisDuration(int delta, int velocity, int motionRange) {
		if (delta == 0) {
			return 0;
		}

		final int width = mParentView.getWidth();
		final int halfWidth = width / 2;
		final float distanceRatio = Math.min(1f, (float) Math.abs(delta)
				/ width);
		final float distance = halfWidth + halfWidth
				* distanceInfluenceForSnapDuration(distanceRatio);

		int duration;
		velocity = Math.abs(velocity);
		if (velocity > 0) {
			duration = 4 * Math.round(1000 * Math.abs(distance / velocity));
		} else {
			final float range = (float) Math.abs(delta) / motionRange;
			duration = (int) ((range + 1) * BASE_SETTLE_DURATION);
		}
		return Math.min(duration, MAX_SETTLE_DURATION);
	}

	/**
	 * Clamp the magnitude of value for absMin and absMax. If the value is below
	 * the minimum, it will be clamped to zero. If the value is above the
	 * maximum, it will be clamped to the maximum.
	 * 
	 * @param value
	 *            Value to clamp
	 * @param absMin
	 *            Absolute value of the minimum significant value to return
	 * @param absMax
	 *            Absolute value of the maximum value to return
	 * @return The clamped value with the same sign as <code>value</code>
	 */
	private int clampMag(int value, int absMin, int absMax) {
		final int absValue = Math.abs(value);
		if (absValue < absMin)
			return 0;
		if (absValue > absMax)
			return value > 0 ? absMax : -absMax;
		return value;
	}

	/**
	 * Clamp the magnitude of value for absMin and absMax. If the value is below
	 * the minimum, it will be clamped to zero. If the value is above the
	 * maximum, it will be clamped to the maximum.
	 * 
	 * @param value
	 *            Value to clamp
	 * @param absMin
	 *            Absolute value of the minimum significant value to return
	 * @param absMax
	 *            Absolute value of the maximum value to return
	 * @return The clamped value with the same sign as <code>value</code>
	 */
	private float clampMag(float value, float absMin, float absMax) {
		final float absValue = Math.abs(value);
		if (absValue < absMin)
			return 0;
		if (absValue > absMax)
			return value > 0 ? absMax : -absMax;
		return value;
	}

	private float distanceInfluenceForSnapDuration(float f) {
		f -= 0.5f; // center the values about 0.
		f *= 0.3f * Math.PI / 2.0f;
		return (float) Math.sin(f);
	}

	/**
	 * Settle the captured view based on standard free-moving fling behavior.
	 * The caller should invoke {@link #continueSettling(boolean)} on each
	 * subsequent frame to continue the motion until it returns false.
	 * 
	 * @param minLeft
	 *            Minimum X position for the view's left edge
	 * @param minTop
	 *            Minimum Y position for the view's top edge
	 * @param maxLeft
	 *            Maximum X position for the view's left edge
	 * @param maxTop
	 *            Maximum Y position for the view's top edge
	 */
	public void flingCapturedView(int minLeft, int minTop, int maxLeft,
			int maxTop) {
		if (!mReleaseInProgress) {
			throw new IllegalStateException(
					"Cannot flingCapturedView outside of a call to "
							+ "Callback#onViewReleased");
		}

		mScroller.fling(mCapturedView.getLeft(), mCapturedView.getTop(),
				(int) VelocityTrackerCompat.getXVelocity(mVelocityTracker,
						mActivePointerId), (int) VelocityTrackerCompat
						.getYVelocity(mVelocityTracker, mActivePointerId),
				minLeft, maxLeft, minTop, maxTop);

		setDragState(STATE_SETTLING);
	}

	/**
	 * Move the captured settling view by the appropriate amount for the current
	 * time. If <code>continueSettling</code> returns true, the caller should
	 * call it again on the next frame to continue.
	 * 
	 * @param deferCallbacks
	 *            true if state callbacks should be deferred via posted message.
	 *            Set this to true if you are calling this method from
	 *            {@link android.view.View#computeScroll()} or similar methods
	 *            invoked as part of layout or drawing.
	 * @return true if settle is still in progress
	 */
	public boolean continueSettling(boolean deferCallbacks) {
		if (mDragState == STATE_SETTLING) {
			boolean keepGoing = mScroller.computeScrollOffset();
			final int x = mScroller.getCurrX();
			final int y = mScroller.getCurrY();
			final int dx = x - mCapturedView.getLeft();
			final int dy = y - mCapturedView.getTop();

			if (dx != 0) {
				mCapturedView.offsetLeftAndRight(dx);
			}
			if (dy != 0) {
				mCapturedView.offsetTopAndBottom(dy);
			}

			if (dx != 0 || dy != 0) {
				mCallback.onViewPositionChanged(mCapturedView, x, y, dx, dy);
			}

			if (keepGoing && x == mScroller.getFinalX()
					&& y == mScroller.getFinalY()) {
				// Close enough. The interpolator/scroller might think we're
				// still moving
				// but the user sure doesn't.
				mScroller.abortAnimation();
				keepGoing = mScroller.isFinished();
			}

			if (!keepGoing) {
				if (deferCallbacks) {
					mParentView.post(mSetIdleRunnable);
				} else {
					setDragState(STATE_IDLE);
				}
			}
		}

		return mDragState == STATE_SETTLING;
	}

	/**
	 * Like all callback events this must happen on the UI thread, but release
	 * involves some extra semantics. During a release (mReleaseInProgress) is
	 * the only time it is valid to call {@link #settleCapturedViewAt(int, int)}
	 * or {@link #flingCapturedView(int, int, int, int)}.
	 */
	private void dispatchViewReleased(float xvel, float yvel) {
		mReleaseInProgress = true;
		mCallback.onViewReleased(mCapturedView, xvel, yvel);
		mReleaseInProgress = false;

		if (mDragState == STATE_DRAGGING) {
			// onViewReleased didn't call a method that would have changed this.
			// Go idle.
			setDragState(STATE_IDLE);
		}
	}

	private void clearMotionHistory() {
		if (mInitialMotionX == null) {
			return;
		}
		Arrays.fill(mInitialMotionX, 0);
		Arrays.fill(mInitialMotionY, 0);
		Arrays.fill(mLastMotionX, 0);
		Arrays.fill(mLastMotionY, 0);
		Arrays.fill(mInitialEdgesTouched, 0);
		Arrays.fill(mEdgeDragsInProgress, 0);
		Arrays.fill(mEdgeDragsLocked, 0);
		mPointersDown = 0;
	}

	private void clearMotionHistory(int pointerId) {
		if (mInitialMotionX == null) {
			return;
		}
		mInitialMotionX[pointerId] = 0;
		mInitialMotionY[pointerId] = 0;
		mLastMotionX[pointerId] = 0;
		mLastMotionY[pointerId] = 0;
		mInitialEdgesTouched[pointerId] = 0;
		mEdgeDragsInProgress[pointerId] = 0;
		mEdgeDragsLocked[pointerId] = 0;
		mPointersDown &= ~(1 << pointerId);
	}

	private void ensureMotionHistorySizeForId(int pointerId) {
		if (mInitialMotionX == null || mInitialMotionX.length <= pointerId) {
			float[] imx = new float[pointerId + 1];
			float[] imy = new float[pointerId + 1];
			float[] lmx = new float[pointerId + 1];
			float[] lmy = new float[pointerId + 1];
			int[] iit = new int[pointerId + 1];
			int[] edip = new int[pointerId + 1];
			int[] edl = new int[pointerId + 1];

			if (mInitialMotionX != null) {
				System.arraycopy(mInitialMotionX, 0, imx, 0,
						mInitialMotionX.length);
				System.arraycopy(mInitialMotionY, 0, imy, 0,
						mInitialMotionY.length);
				System.arraycopy(mLastMotionX, 0, lmx, 0, mLastMotionX.length);
				System.arraycopy(mLastMotionY, 0, lmy, 0, mLastMotionY.length);
				System.arraycopy(mInitialEdgesTouched, 0, iit, 0,
						mInitialEdgesTouched.length);
				System.arraycopy(mEdgeDragsInProgress, 0, edip, 0,
						mEdgeDragsInProgress.length);
				System.arraycopy(mEdgeDragsLocked, 0, edl, 0,
						mEdgeDragsLocked.length);
			}

			mInitialMotionX = imx;
			mInitialMotionY = imy;
			mLastMotionX = lmx;
			mLastMotionY = lmy;
			mInitialEdgesTouched = iit;
			mEdgeDragsInProgress = edip;
			mEdgeDragsLocked = edl;
		}
	}

	private void saveInitialMotion(float x, float y, int pointerId) {
		ensureMotionHistorySizeForId(pointerId);
		mInitialMotionX[pointerId] = mLastMotionX[pointerId] = x;
		mInitialMotionY[pointerId] = mLastMotionY[pointerId] = y;
		mInitialEdgesTouched[pointerId] = getEdgesTouched((int) x, (int) y);
		mPointersDown |= 1 << pointerId;
	}

	private void saveLastMotion(MotionEvent ev) {
		final int pointerCount = MotionEventCompat.getPointerCount(ev);
		for (int i = 0; i < pointerCount; i++) {
			final int pointerId = MotionEventCompat.getPointerId(ev, i);
			final float x = MotionEventCompat.getX(ev, i);
			final float y = MotionEventCompat.getY(ev, i);
			mLastMotionX[pointerId] = x;
			mLastMotionY[pointerId] = y;
		}
	}

	/**
	 * Check if the given pointer ID represents a pointer that is currently down
	 * (to the best of the ViewDragHelper's knowledge).
	 * <p>
	 * The state used to report this information is populated by the methods
	 * {@link #shouldInterceptTouchEvent(android.view.MotionEvent)} or
	 * {@link #processTouchEvent(android.view.MotionEvent)}. If one of these
	 * methods has not been called for all relevant MotionEvents to track, the
	 * information reported by this method may be stale or incorrect.
	 * </p>
	 * 
	 * @param pointerId
	 *            pointer ID to check; corresponds to IDs provided by
	 *            MotionEvent
	 * @return true if the pointer with the given ID is still down
	 */
	public boolean isPointerDown(int pointerId) {
		return (mPointersDown & 1 << pointerId) != 0;
	}

	void setDragState(int state) {
		if (mDragState != state) {
			mDragState = state;
			mCallback.onViewDragStateChanged(state);
			if (state == STATE_IDLE) {
				mCapturedView = null;
			}
		}
	}

	/**
	 * Attempt to capture the view with the given pointer ID. The callback will
	 * be involved. This will put us into the "dragging" state. If we've already
