/*
 * Copyright 2010 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.view.client;

import com.google.gwt.view.client.SelectionModel.AbstractSelectionModel;

import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;

/**
 * A simple selection model that allows multiple objects to be selected.
 *
 * <p>
 * Note: This class is new and its interface subject to change.
 * </p>
 *
 * @param <T> the record data type
 */
public class MultiSelectionModel<T> extends AbstractSelectionModel<T> {

  // Ensure one value per key
  private final HashMap<Object, T> selectedSet = new HashMap<Object, T>();
  
  private final HashMap<T, Boolean> selectionChanges = new HashMap<T, Boolean>();

  /**
   * Get the set of selected items as a copy.
   *
   * @return the set of selected items
   */
  public Set<T> getSelectedSet() {
    resolveChanges();
    return new HashSet<T>(selectedSet.values());
  }

  public boolean isSelected(T object) {
    resolveChanges();
    return selectedSet.containsKey(getKey(object));
  }

  public void setSelected(T object, boolean selected) {
    selectionChanges.put(object, selected);
    scheduleSelectionChangeEvent();
  }
  
  @Override
  protected void fireSelectionChangeEvent() {
    if (isEventScheduled()) {
      setEventCancelled(true);
    }

    if (resolveChanges()) {
      SelectionChangeEvent.fire(this);
    }
  }

  private boolean resolveChanges() {
    if (selectionChanges.isEmpty()) {
      return false;
    }
  
    boolean changed = false;
    for (Map.Entry<T, Boolean> entry : selectionChanges.entrySet()) {
      T object = entry.getKey();
      boolean selected = entry.getValue();

      Object key = getKey(object);
      T oldValue = selectedSet.get(key);
      if (selected) {
        if (oldValue == null || !oldValue.equals(object)) {
          selectedSet.put(getKey(object), object);
          changed = true;
        }
      } else {
        if (oldValue != null) {
          selectedSet.remove(key);
          changed = true;
        }
      }
    }
    selectionChanges.clear();
    return changed;
  }
}