import java.util.Collection;

public interface PhotoLoader {
  
  /**  Load image data from the named text file. Throws an exception if there 
    *  was a problem opening the file (does not exist, etc), or if it's badly 
    *  formatted (lines which are different length). Each line in the file 
    *  represents one row of pixels, and each character represents a single 
    *  pixel. Specifically, a ' ' (blank space) represents a white pixel, 
    *  a '.' (period) represents a gray pixel, and any other character 
    *  (for example a 'x') represents a black pixel.
    *  @param photoname the filename of the photo, which is also the name used to identify the photo.
    *  @return the loaded photo object.
    */
  public Photo getPhoto(String photoname) throws Exception;
  
  /** Load all of the background photos which are listed in the specified file.
    * @param filename the file to use for the list of background photos.
    */
  public void loadBGManifest(String filename) throws Exception;
  
  /** Load all of the foreground photos which are listed in the specified file.
    * @param filename the file to use for the list of foreground photos.
    */
  public void loadFGManifest(String filename) throws Exception;
  
  /** Get a list of all background photos which have been loaded.
    * @return a list of photos.
    */
  public Collection<? extends Photo> getBGPhotos();

  /** Get a list of all foreground photos which have been loaded.
    * @return a list of photos.
    */
  public Collection<? extends Photo> getFGPhotos();
}