package collections;

import java.util.*;
import static collections.StaticTestData.*;

public class MergeCollections {
  static <T extends Comparable<? super T>>
  List<T> merge(Collection<? extends T> c1, Collection<? extends T> c2)
  {
    List<T> mergedList = new ArrayList<T>();

    Iterator<? extends T> itr1 = c1.iterator();
    Iterator<? extends T> itr2 = c2.iterator();

    T c1Element = getNextElement(itr1);
    T c2Element = getNextElement(itr2);

    // each iteration will take a task from one of the iterators;
    // continue until neither iterator has any further tasks
    while (c1Element != null || c2Element != null) {

      // use the current c1 element if either the current c2
      // element is null, or both are non-null and the c1 element
      // precedes the c2 element in the natural order
      boolean useC1Element = c2Element == null ||
              c1Element != null && c1Element.compareTo(c2Element) < 0;

      if (useC1Element) {
        mergedList.add(c1Element);
        c1Element = getNextElement(itr1);
      } else {
        mergedList.add(c2Element);
        c2Element = getNextElement(itr2);
      }
    }
    return mergedList;
  }
  static <E> E getNextElement(Iterator<E> itr) {
    if (itr.hasNext()){
      E nextElement = itr.next();
      if (nextElement == null) throw new NullPointerException();
      return nextElement;
    } else {
      return null;
    }
  }
  public static void main(String[] args) {
    Collection<Task> mergedTasks =
            MergeCollections.merge(mondayTasks, tuesdayTasks);
    assert mergedTasks.toString().equals(
            "[code db, code gui, code logic, phone Mike, phone Paul]");

  }
}