package org.apidesign.effectivelist

 /** 

  * Implementation of add and remove efficient list. It has just one

  * restriction - its items need to carry additional information to help

  * the list to be effective. All items must extend trait {@link Listable}:

  * <pre>

  * <b>case class</b> Person(name : String) <b>extends</b> Listable[Person]

  * </pre>

  */

 final class List[T <: Listable[T]] {

   private var item : T = _

   private final var EMPTY : T = _

   final def get(index : Int) : T = {

     var pos : T = item;

     for (i <- 1 to index) {

       pos = pos.next;

       if (pos == item) {

         throw new IndexOutOfBoundsException()

       }

     }

     return pos

   }

   final def size() : Int = {

     if (item == EMPTY) {

       return 0

     }

     var size = 0

     var pos : T = item

     do {

       size = size + 1

       pos = pos.next

     } while (pos != item)

     return size

   }

   final def add(toAdd : T) : Boolean = {

     if (toAdd.prev != EMPTY) {

       return false

     }

     if (item == null) {

       item = toAdd

       toAdd.next = toAdd

       toAdd.prev = toAdd

       return true

     } else {

       toAdd.prev = item.prev

       item.prev.next = toAdd

       item.prev = toAdd

       toAdd.next = item

       return true

     }

   }

   final def remove(toRemove : T) : Boolean = {

     if (toRemove.prev == EMPTY) {

       return false

     } else {

       toRemove.prev.next = toRemove.next

       toRemove.next.prev = toRemove.prev;

       if (item.next == item) {

         item = EMPTY

       }

       if (item == toRemove) {

         item = toRemove.next

       }

       toRemove.next = EMPTY

       toRemove.prev = EMPTY

       return true

     }

   }

 }