import CursoredLinkedList;
import Pair;

/**
 * A simple implementation of dictionaries, using a list of
 * key/value pairs.
 *
 * @author Samuel A. Rebelsky
 * @author Your Name Here
 */
public class AssociationList
  implements Dictionary
{
  // +--------+--------------------------------------------------
  // | Fields |
  // +--------+

  /** The pairs in the dictionary. */
  private CursoredLinkedList pairs;

  // +--------------+--------------------------------------------
  // | Constructors |
  // +--------------+

  /** Create a new association list. */
  public AssociationList() {
    this.pairs = new CursoredLinkedList();
    // Because the find method skips the starting node,
    // we make sure the association list begins with an
    // unused pair.  It should always have this pair at the
    // front.
    pairs.addToFront(new Pair("FRONT",""));
  } // AssociationList()

  // +---------+-------------------------------------------------
  // | Methods |
  // +---------+

  /**
   * Populate the association list with some sample pairs.
   * Intended primarily for testing.
   */
  public void populate() {
    pairs.addToEnd(new Pair("Joshua Vickery", "Undecided"));
    pairs.addToEnd(new Pair("Sierra Soleil", "Philosophy"));
    pairs.addToEnd(new Pair("Kate Ducey", "Theatre"));
    pairs.addToEnd(new Pair("Wanlin Liu", "Economics"));
  } // populate()

  /**
   * Get the value associated with a key.  See the interface
   * for more information.
   */
  public Object get(Object key)
    throws Exception
  {
    try {
      // Find the first pair with the appropriate key.
      pairs.front();
      pairs.find(new Pair(key, null));
      // If we got this far, find succeeded.
      return ((Pair) pairs.getCurrent()).getValue();
    }
    // Whoops!  Not found
    catch (Exception e) {
      throw new Exception(key.toString() + " not found");
    }
  } // get(Object)

  /**
   * Set the value associated with a particular key.  See the
   * interface for more information.
   */
  public void put(Object key, Object value) 
    throws Exception
  {
    // Delete any other pair with that key.
    try {
      // Find the first pair with the appropriate key.
      pairs.front();
      pairs.find(new Pair(key, null));
      // If we got this far, find succeeded, so delete the
      // now-useless element.
      pairs.delete();
    }
    // Whoops!  Not found.  But we don't care.
    catch (Exception e) {
      // Do nothing
    }
    // Put a new pair at the end.  
    pairs.addToEnd(new Pair(key,value));
  } // put(Object,Object)

  /**
   * Convert to a string.
   */
  public String toString() {
    String result = "";
    pairs.front(); 
    try {
      while (true) {
        Pair p = (Pair) pairs.getCurrent();
        result = result + p + " ";
        pairs.advance();
      }
    }
    catch (Exception e) {
      // Hit the end of the list.
    }
    return result;
  } // toString
} // AssociationList