/*
 * Copyright (C) 2009 University of Washington
 * 
 * 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 org.commcare.android.util;


/**
 * Calculates the direction of a gesture/fling. Used by {@link GestureDetector}
 * 
 * @author Carl Hartung (carlhartung@gmail.com)
 */
public class GestureDirection {

    public enum UserGesture {
        SWIPE_RIGHT, SWIPE_LEFT, SWIPE_UP, SWIPE_DOWN, SWIPE_UNKNOWN
    }

    private final static int MAX_DISTANCE = 40;

    private float mStartX;
    private float mStartY;

    private float mEndX;
    private float mEndY;


    public GestureDirection(float x, float y) {
        mStartX = x;
        mStartY = y;
        mEndX = x;
        mEndY = y;
    }


    public void updateEndPoint(float x, float y) {
        mEndX = x;
        mEndY = y;
    }


    public float getStartX() {
        return mStartX;
    }


    public float getStartY() {
        return mStartY;
    }


    public UserGesture getDirection() {
        float dx = mEndX - mStartX;
        float dy = mEndY - mStartY;
        double distance = Math.hypot(dx, dy);

        if (distance < MAX_DISTANCE) {
            return UserGesture.SWIPE_UNKNOWN;
        }
        double angle = Math.acos(dx / distance);
        double limit = Math.PI / 6;
        if ((angle < limit || (angle > (Math.PI - limit)))) {
            if (dx > 0)
                return UserGesture.SWIPE_RIGHT;
            else
                return UserGesture.SWIPE_LEFT;

        }
        if ((angle > 2 * limit) && angle < 4 * limit) {
            if (dy > 0)
                return UserGesture.SWIPE_DOWN;
            else
                return UserGesture.SWIPE_UP;
        }
        return UserGesture.SWIPE_UNKNOWN;
    }
}