import java.util.HashMap;

public interface ExtraCredit {

  /** Finds the quality of match score, assuming that the upper left corner of 
    * the foreground photo is aligned to position (x, y) in the background photo, 
    * and that the two photos may be different sizes. The quality of match score 
    * is only averaged over the overlapping pixels.
    * @param foreground the foreground photo.
    * @param background the background photo.
    * @param x the x coordinate of the upper left of the foreground photo relative to the background.
    * @param y the y coordinate of the upper left of the foreground photo relative to the background.
    * @return the matching score.
    */
  public double getMatch(Photo foreground, Photo background, int x, int y);

  /** Finds the quality of match score between two photos, but the result 
    * is taken as the best possible score over all possible choices 
    * of (x, y) which overlap by at least n pixels. That is, the first 
    * version of getMatch() is used, but the value of the first version 
    * depends on the (x, y) offset which is chosen, so we want to pick 
    * the (x, y) which gives us the best possible score. The reason for 
    * the n is that you can sometimes get an easy perfect match by just 
    * matching a single pixel in the corner - we can avoid this by requiring 
    * that two photos overlap by at least n pixels if we want the score to 
    * count. 
    * @param foreground the foreground photo.
    * @param background the background photo.
    * @param n the minimum number of pixels overlap for a score to be considered.
    * @return the matching score.
    */ 
  public double getMatch(Photo foreground, Photo background, int n);
  
  /** Same as the normal version of getBestMatch(), except that it uses 
    * the extra-credit version of getMatch() with the given n value.
    * @param matches a hashmap which contains the set of foreground-to-background matchings which comprise the best result.
    * @param n the minimum number of pixels overlap for a score to be considered.
    * @return the matching of the best match.
    */
  public double getBestMatch(HashMap<String,String> matches, int n);
}