AbstractPageableView.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.cyclop.web.components.iterablegrid;

import org.apache.wicket.markup.html.navigation.paging.IPageableItems;
import org.apache.wicket.markup.repeater.RefreshingView;
import org.apache.wicket.model.IModel;

import java.util.Collection;
import java.util.Iterator;
import java.util.NoSuchElementException;

// ####################################################################################################################
// This class has been copied from wicket 6.14.0
// Only minimal modifications has been made in order to simplify future updates to new wicket version, those are:
// - removed final from method setCurrentPage(long) - method can be overwritten now
// - removed final from method setItemsPerPage(long) - method can be overwritten now
// - AbstractPageableView is package protected
// ####################################################################################################################

/**
 * An abstract repeater view that provides paging functionality to its
 * subclasses.
 * <p>
 * The view is populated by overriding the
 * <code>getItemModels(int offset, int count)</code> method and providing an
 * iterator that returns models for items in the current page. The
 * AbstractPageableView builds the items that will be rendered by looping over
 * the models and calling the
 * <code>newItem(String id, int index, IModel model)</code> to generate the
 * child item container followed by <code>populateItem(Component item)</code> to
 * let the user populate the newly created item container with with custom
 * components.
 * </p>
 *
 * @param <T>
 *            Model object type
 * @author Igor Vaynberg (ivaynberg)
 * @see org.apache.wicket.markup.repeater.RefreshingView
 * @see org.apache.wicket.markup.html.navigation.paging.IPageable
 */
abstract class AbstractPageableView<T> extends RefreshingView<T> implements IPageableItems {
	/** */
	private static final long serialVersionUID = 1L;

	/**
	 * Keeps track of the number of items we show per page. The default is
	 * Integer.MAX_VALUE which effectively disables paging.
	 */
	private long itemsPerPage = Long.MAX_VALUE;

	/** Keeps track of the current page number. */
	private long currentPage;

	/**
	 * <code>cachedItemCount</code> is used to cache the call to
	 * <code>internalGetItemCount()</code> for the duration of the request
	 * because that call can potentially be expensive ( a select count query )
	 * and so we do not want to execute it multiple times.
	 */
	private transient long cachedItemCount;

	/**
	 * Constructor
	 *
	 * @param id
	 * @param model
	 * @see org.apache.wicket.Component#Component(String, IModel)
	 */
	public AbstractPageableView(String id, IModel<? extends Collection<? extends T>> model) {
		super(id, model);
		clearCachedItemCount();
	}

	/** @see org.apache.wicket.Component#Component(String) */
	public AbstractPageableView(String id) {
		super(id);
		clearCachedItemCount();
	}

	/**
	 * This method retrieves the subset of models for items in the current page
	 * and allows RefreshingView to generate items.
	 *
	 * @return iterator over models for items in the current page
	 */
	@Override
	protected Iterator<IModel<T>> getItemModels() {
		long offset = getFirstItemOffset();
		long size = getViewSize();

		Iterator<IModel<T>> models = getItemModels(offset, size);

		models = new CappedIteratorAdapter<T>(models, size);

		return models;
	}

	/** @see org.apache.wicket.markup.repeater.AbstractRepeater#onBeforeRender() */
	@Override
	protected void onBeforeRender() {
		clearCachedItemCount();
		super.onBeforeRender();
	}

	/**
	 * Returns an iterator over models for items in the current page
	 *
	 * @param offset
	 *            index of first item in this page
	 * @param size
	 *            number of items that will be shown in the current page
	 * @return an iterator over models for items in the current page
	 */
	protected abstract Iterator<IModel<T>> getItemModels(long offset, long size);

	// /////////////////////////////////////////////////////////////////////////
	// ITEM COUNT CACHE
	// /////////////////////////////////////////////////////////////////////////

	private void clearCachedItemCount() {
		cachedItemCount = -1;
	}

	private long getCachedItemCount() {
		if (cachedItemCount < 0) {
			throw new IllegalStateException("getItemCountCache() called when cache was not set");
		}
		return cachedItemCount;
	}

	private void setCachedItemCount(long itemCount) {
		cachedItemCount = itemCount;
	}

	private boolean isItemCountCached() {
		return cachedItemCount >= 0;
	}

	// /////////////////////////////////////////////////////////////////////////
	// PAGING
	// /////////////////////////////////////////////////////////////////////////

	/** @return maximum number of items that will be shown per page */
	@Override
	public long getItemsPerPage() {
		return itemsPerPage;
	}

	/**
	 * Sets the maximum number of items to show per page. The current page will
	 * also be set to zero
	 *
	 * @param items
	 */
	public void setItemsPerPage(long items) {
		if (items < 1) {
			throw new IllegalArgumentException("Argument [itemsPerPage] cannot be less than 1");
		}

		if (itemsPerPage != items) {
			if (isVersioned()) {
				addStateChange();
			}
		}

		itemsPerPage = items;

		// because items per page can effect the total number of pages we always
		// reset the current page back to zero
		setCurrentPage(0);
	}

	/** @return total item count */
	protected abstract long internalGetItemCount();

	/**
	 * Get the row count.
	 *
	 * @return total item count, but 0 if not visible in the hierarchy
	 * @see #getItemCount()
	 */
	public final long getRowCount() {
		if (!isVisibleInHierarchy()) {
			return 0;
		}

		return getItemCount();
	}

	/**
	 * Get the item count. Since dataprovider.readSize() could potentially be
	 * expensive, the item count is cached.
	 *
	 * @return the item count
	 * @see #getRowCount()
	 */
	@Override
	public final long getItemCount() {
		if (isItemCountCached()) {
			return getCachedItemCount();
		}

		long count = internalGetItemCount();

		setCachedItemCount(count);
		return count;
	}

	/** @see org.apache.wicket.markup.html.navigation.paging.IPageable#getCurrentPage() */
	@Override
	public final long getCurrentPage() {
		long page = currentPage;

		/*
		 * trim current page if its out of bounds this can happen if items are
		 * added/deleted between requests
		 */

		if (page > 0 && page >= getPageCount()) {
			page = Math.max(getPageCount() - 1, 0);
			currentPage = page;
			return page;
		}

		return page;
	}

	/** @see org.apache.wicket.markup.html.navigation.paging.IPageable#setCurrentPage(long) */
	@Override
	public void setCurrentPage(long page) {
		if (currentPage != page) {
			if (isVersioned()) {
				addStateChange();

			}
		}
		currentPage = page;
	}

	/** @see org.apache.wicket.markup.html.navigation.paging.IPageable#getPageCount() */
	@Override
	public final long getPageCount() {
		long total = getRowCount();
		long itemsPerPage = getItemsPerPage();
		long count = total / itemsPerPage;

		if (itemsPerPage * count < total) {
			count++;
		}

		return count;

	}

	/** @return the index of the first visible item in the view */
	public long getFirstItemOffset() {
		return getCurrentPage() * getItemsPerPage();
	}

	/** @return the number of items visible */
	public long getViewSize() {
		return Math.min(getItemsPerPage(), getRowCount() - getFirstItemOffset());
	}

	// /////////////////////////////////////////////////////////////////////////
	// HELPER CLASSES
	// /////////////////////////////////////////////////////////////////////////

	/** @see org.apache.wicket.Component#onDetach() */
	@Override
	protected void onDetach() {
		clearCachedItemCount();
		super.onDetach();
	}

	private void readObject(java.io.ObjectInputStream s) throws java.io.IOException, ClassNotFoundException {
		// Read in all fields
		s.defaultReadObject();
		clearCachedItemCount();
	}

	/**
	 * Iterator adapter that makes sure only the specified max number of items
	 * can be accessed from its delegate.
	 *
	 * @param <T>
	 *            Model object type
	 */
	private static class CappedIteratorAdapter<T> implements Iterator<IModel<T>> {
		private final long max;

		private final Iterator<IModel<T>> delegate;

		private long index;

		/**
		 * Constructor
		 *
		 * @param delegate
		 *            delegate iterator
		 * @param max
		 *            maximum number of items that can be accessed.
		 */
		public CappedIteratorAdapter(Iterator<IModel<T>> delegate, long max) {
			this.delegate = delegate;
			this.max = max;
		}

		/** @see Iterator#remove() */
		@Override
		public void remove() {
			throw new UnsupportedOperationException();
		}

		/** @see Iterator#hasNext() */
		@Override
		public boolean hasNext() {
			return (index < max) && delegate.hasNext();
		}

		/** @see Iterator#next() */
		@Override
		public IModel<T> next() {
			if (index >= max) {
				throw new NoSuchElementException();
			}
			index++;
			return delegate.next();
		}

	}
}