import java.util.List;
import java.io.IOException;

/**
 * BackendInterface - CS400 Project 1: iSongify
 */
public interface BackendInterface {

    //public BackendPlaceholder(IterableSortedCollection<SongInterface> tree);

    /**
     * Loads data from the .csv file referenced by filename.
     * @param filename is the name of the csv file to load data from
     * @throws IOException when there is trouble finding/reading file
     */
    public void readData(String filename) throws IOException;

    /**
     * Retrieves a list of song titles for songs that have a Danceability
     * within the specified range (sorted by Danceability in ascending order).
     * If a minEnergy filter has been set using filterEnergeticSongs(), then 
     * only songs with an energy rating greater than or equal to this minEnergy
     * should be included in the list that is returned by this method.
     *
     * Note that either this danceability range, or the resulting unfiltered 
     * list of songs should be saved for later use by the other methods 
     * defined in this class.
     *
     * @param low is the minimum Danceability of songs in the returned list
     * @param hight is the maximum Danceability of songs in the returned list
     * @return List of titles for all songs in specified range 
     */
    public List<String> getRange(int low, int high);

    /**
     * Filters the list of songs returned by future calls of getRange() and 
     * fiveFastest() to only include energetic songs.  If getRange() was 
     * previously called, then this method will return a list of song titles
     * (sorted in ascending order by Danceability) that only includes songs on
     * with the specified minEnergy or higher.  If getRange() was not 
     * previously called, then this method should return an empty list.
     *
     * Note that this minEnergy threshold should be saved for later use by the 
     * other methods defined in this class.
     *
     * @param minEnergy is the minimum energy of songs that are returned
     * @return List of song titles, empty if getRange was not previously called
     */
    public List<String> filterEnergeticSongs(int minEnergy);

    /**
     * This method makes use of the attribute range specified by the most
     * recent call to getRange().  If a minEnergy threshold has been set by
     * filterEnergeticSongs() then that will also be utilized by this method.
     * Of those songs that match these criteria, the five fastest will be 
     * returned by this method as a List of Strings in increasing order of 
     * danceability.  Each string contains the speed in BPM followed by a 
     * colon, a space, and then the song's title.
     * If fewer than five such songs exist, return all of them.
     *
     * @return List of five fastest song titles and their respective speeds
     * @throws IllegalStateException when getRange() was not previously called.
     */
    public List<String> fiveFastest();
}