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Collections library of the Staccato-Commons project, focused on providing new abstractions that mix object oriented and functional programming style for dealing with iterable objects.

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/*
 Copyright (c) 2011, The Staccato-Commons Team

 This program is free software; you can redistribute it and/or modify
 it under the terms of the GNU Lesser General Public License as published by
 the Free Software Foundation; version 3 of the License.

 This program is distributed in the hope that it will be useful,
 but WITHOUT ANY WARRANTY; without even the implied warranty of
 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 GNU Lesser General Public License for more details.
 */
package net.sf.staccatocommons.collections.stream.internal.algorithms;

import java.util.NoSuchElementException;

import net.sf.staccatocommons.defs.Thunk;
import net.sf.staccatocommons.defs.partial.EmptyAware;
import net.sf.staccatocommons.iterators.thriter.AdvanceThriterator;
import net.sf.staccatocommons.iterators.thriter.Thriterator;
import net.sf.staccatocommons.lang.thunk.Thunks;
import net.sf.staccatocommons.restrictions.check.NonNull;
import net.sf.staccatocommons.restrictions.processing.EnforceRestrictions;

import org.apache.commons.lang.StringUtils;

/**
 * A basic implementation of a single FIFO linked list, with lazy elements
 * 
 * @author flbulgarelli
 * 
 */
public class SingleLinkedDelayedQueue implements Iterable, EmptyAware {

  private final Cell head = new Cell(Thunks. undefined());
  private Cell last = head;

  /**
   * Adds an element at the end of the queue
   * 
   * @param element
   */
  @EnforceRestrictions
  public void add(@NonNull Thunk element) {
    Cell prev = last;
    last = new Cell(element);
    prev.next = last;
  }

  @Override
  public Thriterator iterator() {
    return new Iter(head);
  }

  private static final class Cell {
    private final Thunk element;
    private Cell next;

    public Cell(Thunk element) {
      this.element = element;
    }

    boolean hasNext() {
      return next != null;
    }
  }

  @Override
  public boolean isEmpty() {
    return !head.hasNext();
  }

  @Override
  public String toString() {
    return "[" + StringUtils.join(iterator(), ",") + "]";
  }

  private static final class Iter extends AdvanceThriterator {

    private Cell current;

    public Iter(Cell current) {
      this.current = current;
    }

    public boolean hasNext() {
      return current.hasNext();
    }

    public void advanceNext() throws NoSuchElementException {
      current = current.next;
    }

    public A current() {
      return delayedCurrent().value();
    }

    @Override
    public Thunk delayedCurrent() {
      return current.element;
    }

  }

}