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Data model for Contract
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package org.seekay.contract.model.tools;

import java.util.*;


public class SetTools {

  /**
   * Private constructor for utility class
   */
  private SetTools() {
    throw new IllegalStateException("Utility classes should never be constructed");
  }

  /**
   * For multiple sets, only the elements contained in all will be returned
   *
   * @param sets
   * @param 
   * @return
   */
  public static  Set intersectingElements(Set... sets) {
    assert sets.length > 1;

    Set result = new HashSet();

    Set head = head(sets);
    List> tail = tail(sets);

    for (T t : head) {
      if (containedInAll(t, tail)) {
        result.add(t);
      }
    }

    return result;
  }

  /**
   * Returns the first element in a set
   *
   * @param set
   * @param 
   * @return
   */
  public static  T head(Set set) {
    return set.iterator().next();
  }

  /**
   * Returns the first set in a vararg of sets
   *
   * @param sets
   * @param 
   * @return
   */
  public static  Set head(Set... sets) {
    return Arrays.asList(sets).get(0);
  }

  /**
   * Returns all but the first element of a set
   *
   * @param set
   * @param 
   * @return
   */
  public static  Set tail(Set set) {
    Set result = new HashSet();
    Iterator iterator = set.iterator();
    iterator.next();
    while (iterator.hasNext()) {
      result.add(iterator.next());
    }

    return result;
  }

  /**
   * Converts a set of strings to an array of strings
   *
   * @param input
   * @return
   */
  public static String[] toArray(Set input) {
    if (input == null) {
      return new String[0];
    }
    String[] output = new String[input.size()];
    int i = 0;
    for (String inputString : input) {
      output[i] = inputString;
      i++;
    }
    return output;
  }

  /**
   * Converts an array of strings to a set of strings
   *
   * @param input
   * @return
   */
  public static Set toSet(String[] input) {
    Set output = new LinkedHashSet();
    if (input == null) {
      return output;
    }
    for (String inputString : input) {
      output.add(inputString);
    }
    return output;
  }

  /**
   * Converts a csv string to a set of strings
   *
   * @param csvTags
   * @return
   */
  public static Set toSet(String csvTags) {
    if (csvTags == null) {
      return new HashSet();
    }
    String[] tokens = csvTags.replaceAll(" ", "").split(",");
    return toSet(tokens);
  }

  private static  List> tail(Set... sets) {
    if (sets.length < 2) {
      throw new IllegalStateException("Matching configured incorrectly");
    }
    List> lists = Arrays.asList(sets);
    return lists.subList(1, lists.size());
  }

  private static  boolean containedInAll(T t, List> sets) {
    boolean found = true;
    for (Set set : sets) {
      if (!set.contains(t)) {
        found = false;
      }
    }
    return found;
  }


}