/**
 Class: Vector2D
 Description: A class for storing and manipulating 2D vectors
 Methods are included for adding and subtracting vectors, multiplying
 and dividing by a scalar, getting the magnitude, the direction, and
 collision detection (if it's a velocity).
 Created: 10/4/2006
 Last Modified: 10/22/2007
 By: Fred Green
 */
public class Vector2D
{
  private float x, y;

  /**
   Default constructor: Initialized vector to 0.
   */
  public Vector2D ()
  {
    reset();
  }

  /**
   Constructor: Initialize vector to x and y components.
   Example:
      Vector2D v = new Vector2D(3.2, -6.4);
   creates a vector with x-component 3.2 and y-component -6.4.
   */
  public Vector2D (float x, float y)
  {
    this.x = x;
    this.y = y;
  }

  /**
   Constructor: Initialize this vector to copy of argument.
   */
  public Vector2D (Vector2D toCopy)
  {
    this.x = toCopy.x;
    this.y = toCopy.y;
  }

  /**
   Method: reset()
   Sets this vector to 0.
   Example:
   Assuming v is a Vector2D object,
       v.reset();
   sets all components of v to 0.
   */
  public void reset ()
  {
    x = 0;
    y = 0;
  }

  /**
   Method: magnitude()
   Returns: the magnitude of this vector.
   Example:
      Vector2D v = new Vector2D(2, 2);
      float a = v.magnitude();
   will store the value sqrt(8) in a.
   */
  public float magnitude ()
  {
    return (float) Math.sqrt(x*x + y*y);
  }

  /**
   Method: getX()
   Returns: the x-component of this vector.
   Example:
      Vector2D v = new Vector2D(2, 3);
      float a = v.getX();
   will store the value 2 in a.
   */
  public float getX ()
  {
    return x;
  }

  /**
   Method: getY()
   Returns: The y-component of this vector.
   Example:
      Vector2D v = new Vector2D(2, 3);
      float a = v.getY();
   will store the value 3 in a.
   */
  public float getY()
  {
    return y;
  }

  /**
   Method: setX()
   Sets the x-component of this vector to the argument.
   Example:
      Vector2D v = new Vector2D(2, 3);
      v.setX(7);
      float a = v.getX();
   will store the value 7 in a.

   */
  public void setX (float x)
  {
    this.x = x;
  }

  /**
   Method: setY()
   Sets the y-component of this vector to the argument.
   */
  public void setY (float y)
  {
    this.y = y;
  }

  /**
   Method: plus()
   Returns: a Vector2D which is the sum of this vector with the argument.
   Example:
     Vector2D p = new Vector2D(3, 7);
     Vector2D v = new Vector2D(5, 2);
     Vector2D s = p.plus(v);
  stores a vector with components 8 and 9 in s.
   */
  public Vector2D plus (Vector2D w)
  {
    Vector2D sum = new Vector2D();

    sum.x = x + w.x;
    sum.y = y + w.y;

    return sum;
  }

  /**
   Method: minus()
   Returns: a Vector2D which is the difference of this vector with the argument.
   */
  public Vector2D minus (Vector2D w)
  {
    Vector2D diff = new Vector2D();

    diff.x = x - w.x;
    diff.y = y - w.y;

    return diff;
  }

  /**
   Method: times()
   Returns: a Vector 2D which is the product of this vector with the argument.
   Example:
      Vector2D v = new Vector2D(2, 3);
      Vector2D w = v.times(6);
   will store a vector with components 12 and 18 in w.
   */
  public Vector2D times (float n)
  {
    Vector2D product = new Vector2D();

    product.x = x*n;
    product.y = y*n;

    return product;
  }

  /**
   Method: multiplyBy()
   Sets this vector to its product with the argument.
   Example:
      Vector2D v = new Vector2D(2, 3);
      v.multiplyBy(6);
   will put the values 12 and 18 in v.
   */
  public void multiplyBy (float n)
  {
    x = x*n;
    y = y*n;
  }

  /**
   Method: dividedBy()
   Returns: a Vector2D which is this vector divided by the argument.
   Example:
      Vector2D v = new Vector2D(8, 10);
      Vector2D w = v.dividedBy(2);
   will store a vector with components 4 and 5 in w.
   */
  public Vector2D dividedBy (float n)
  {
    Vector2D quotient = new Vector2D();

    quotient.x = x/n;
    quotient.y = y/n;

    return quotient;
  }

  /**
   Method: divideBy()
   Sets this vector to its quotient with the argument.
   (Similar to multiplyBy(), but it divides instead of multiplies.)
   */
  public void divideBy (float n)
  {
    x = x/n;
    y = y/n;
  }

  /**
   Method: dotProduct()
   Returns: the dot product of this vector with the argument.
   */
  public float dotProduct (Vector2D w)
  {
    return x*w.x + y*w.y;
  }

  /**
   Method: direction()
   Returns: a unit Vector2D pointing in the same direction as this one.
   */
  public Vector2D direction ()
  {
    Vector2D quotient = new Vector2D (this);

    return quotient.dividedBy(magnitude());
  }
  
  /**
   Method: constrain()
   Contrains the x and y components to be within the limits set by the arguments.
   */
  public void constrain (float minX, float maxX, float minY, float maxY)
  {
    if (x <= minX)
     {
       x = minX;
     }
    if (x >= maxX)
    {
      x = maxX;
    }
    if (y <= minY)
    {
      y = minY;
    }
    if (y >= maxY)
    {
      y = maxY;
    }
  }
  
  /**
   Method: detectCollision()
   Detects a collision with the sides of the screen (or box) with dimensions width X height.
   The position, width, and height are also required arguments. This will only work if this
   vector is to be interpreted as a velocity, and if the collision is with horizontal or
   vertical edges.
   */
  public void detectCollision (Vector2D position, float objectWidth, float objectHeight, float width, float height)
  {
    if (position.getX() + objectWidth/2 >= width || position.getX() <= objectWidth/2)
      x *= -1;
    if (position.getY() + objectHeight/2 >= height || position.getY() <= objectHeight/2)
      y *= -1;
  }
  
  /**
   Method: toString()
   Returns: a string representation of the vector.
   */
  public String toString()
  {
    return "(" + x + "," + y + ")";
  }
}