/**

* Copyright (c) Rich Hickey. All rights reserved.

* The use and distribution terms for this software are covered by the

* Eclipse Public License 1.0 (http://opensource.org/licenses/eclipse-1.0.php)

* which can be found in the file epl-v10.html at the root of this distribution.

* By using this software in any fashion, you are agreeing to be bound by

* the terms of this license.

* You must not remove this notice, or any other, from this software.

**/

package clojure.lang;

/* Alex Miller, Dec 5, 2014 */

public class Cycle extends ASeq implements IReduce, IPending {

private static final long serialVersionUID = 4007270937279943908L;

private final ISeq all; // never null

private final ISeq prev;

private volatile ISeq _current; // lazily realized

private volatile ISeq _next; // cached

private Cycle(ISeq all, ISeq prev, ISeq current){

this.all = all;

this.prev = prev;

this._current = current;

}

private Cycle(IPersistentMap meta, ISeq all, ISeq prev, ISeq current, ISeq next){

super(meta);

this.all = all;

this.prev = prev;

this._current = current;

this._next = next;

}

public static ISeq create(ISeq vals){

if(vals == null)

return PersistentList.EMPTY;

return new Cycle(vals, null, vals);

}

// realization for use of current

private ISeq current() {

if(_current == null) {

ISeq current = prev.next();

_current = (current == null) ? all : current;

}

return _current;

}

public boolean isRealized() {

return _current != null;

}

public Object first(){

return current().first();

}

public ISeq next(){

if(_next == null)

_next = new Cycle(all, current(), null);

return _next;

}

public Cycle withMeta(IPersistentMap meta){

if(meta() == meta)

return this;

return new Cycle(meta, all, prev, _current, _next);

}

public Object reduce(IFn f){

ISeq s = current();

Object ret = s.first();

while(true) {

s = s.next();

if(s == null)

s = all;

ret = f.invoke(ret, s.first());

if(RT.isReduced(ret))

return ((IDeref)ret).deref();

}

}

public Object reduce(IFn f, Object start){

Object ret = start;

ISeq s = current();

while(true){

ret = f.invoke(ret, s.first());

if(RT.isReduced(ret))

return ((IDeref)ret).deref();

s = s.next();

if(s == null)

s = all;

}

}

public int hashCode(){

throw new UnsupportedOperationException();

}

public int hasheq(){

throw new UnsupportedOperationException();

}

}