/*
 * Copyright 2008 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.gwt.gen2.table.client;

import com.google.gwt.user.client.*;
import com.google.gwt.user.client.ui.*;

import java.util.*;

/**
 * Creates a mapping from elements to their associated ui objects.
 *
 * @param <MappedType> the type that the element is mapped to
 */
public class ElementMapper<MappedType extends UIObject> {

    private static class FreeNode {
        int index;
        ElementMapper.FreeNode next;

        public FreeNode( int index, ElementMapper.FreeNode next ) {
            this.index = index;
            this.next = next;
        }
    }

    private static native void clearIndex( Element elem ) /*-{
        elem["__uiObjectID"] = null;
    }-*/;

    private static native int getIndex( Element elem ) /*-{
        var index = elem["__uiObjectID"];
        return (index == null) ? -1 : index;
    }-*/;

    private static native void setIndex( Element elem, int index ) /*-{
        elem["__uiObjectID"] = index;
    }-*/;

    private ElementMapper.FreeNode freeList = null;

    private final ArrayList<MappedType> uiObjectList = new ArrayList<MappedType>();

    /**
     * Returns the uiObject associated with the given element.
     *
     * @param elem uiObject's element
     *
     * @return the uiObject
     */
    public MappedType get( Element elem ) {
        int index = getIndex( elem );
        if ( index < 0 ) {
            return null;
        }
        return uiObjectList.get( index );
    }

    /**
     * Adds the MappedType.
     *
     * @param uiObject uiObject to add
     */
    public void put( MappedType uiObject ) {
        int index;
        if ( freeList == null ) {
            index = uiObjectList.size();
            uiObjectList.add( uiObject );
        } else {
            index = freeList.index;
            uiObjectList.set( index, uiObject );
            freeList = freeList.next;
        }
        setIndex( uiObject.getElement(), index );
    }

    /**
     * Remove the uiObject associated with the given element.
     *
     * @param elem the uiObject's element
     */
    public void removeByElement( Element elem ) {
        int index = getIndex( elem );
        removeImpl( elem, index );
    }

    /**
     * Creates an iterator of uiObjects.
     *
     * @return the iterator
     */
    public Iterator<MappedType> iterator() {

        return new Iterator() {
            int lastIndex = -1;
            int nextIndex = -1;

            {
                findNext();
            }

            public boolean hasNext() {
                return nextIndex < uiObjectList.size();
            }

            public Object next() {
                if ( !hasNext() ) {
                    throw new NoSuchElementException();
                }
                Object result = uiObjectList.get( nextIndex );
                lastIndex = nextIndex;
                findNext();
                return result;
            }

            public void remove() {
                if ( lastIndex < 0 ) {
                    throw new IllegalStateException();
                }
                Widget w = (Widget) uiObjectList.get( lastIndex );
                assert (w.getParent() instanceof HTMLTable);
                w.removeFromParent();
                lastIndex = -1;
            }

            private void findNext() {
                while ( ++nextIndex < uiObjectList.size() ) {
                    if ( uiObjectList.get( nextIndex ) != null ) {
                        return;
                    }
                }
            }
        };
    }

    private void removeImpl( Element elem, int index ) {
        clearIndex( elem );
        uiObjectList.set( index, null );
        freeList = new FreeNode( index, freeList );
    }
}