egroupware/etemplate/js/et2_dataview_view_grid.js

/**
 * eGroupWare eTemplate2 - Class which contains the "grid" base class
 *
 * @license http://opensource.org/licenses/gpl-license.php GPL - GNU General Public License
 * @package etemplate
 * @subpackage dataview
 * @link http://www.egroupware.org
 * @author Andreas Stöckel
 * @copyright Stylite 2011
 * @version $Id$
 */

"use strict";

/*egw:uses
	jquery.jquery;
	et2_core_common;

	et2_dataview_interfaces;
	et2_dataview_view_container;
	et2_dataview_view_spacer;
*/

/**
 * Determines how many pixels the view range of the gridview is extended inside
 * the scroll callback.
 */
var ET2_GRID_VIEW_EXT = 50;

/**
 * Determines the timeout after which the scroll-event is processed.
 */
var ET2_GRID_SCROLL_TIMEOUT = 50;

/**
 * Determines the timeout after which the invalidate-request gets processed.
 */
var ET2_GRID_INVALIDATE_TIMEOUT = 25;

/**
 * Determines how many elements are kept displayed outside of the current view
 * range until they get removed.
 */
var ET2_GRID_HOLD_COUNT = 50;

var et2_dataview_grid = et2_dataview_container.extend(et2_dataview_IViewRange, {

	/**
	 * Creates the grid.
	 *
	 * @param _parent is the parent grid class - if null, this means that this
	 * is the outer grid which manages the scrollarea. If not null, all other
	 * parameters are ignored and copied from the given grid instance.
	 * @param _avgHeight is the starting average height of the column rows.
	 */
	init: function (_parent, _egw, _rowProvider, _avgHeight) {

		// Call the inherited constructor
		this._super(_parent);

		// If the parent is given, copy all other parameters from it
		if (_parent != null)
		{
			this.egw = _parent.egw;
			this._orgAvgHeight = false;
			this._rowProvider = _parent._rowProvider;
		}
		else
		{
			// Otherwise copy the given parameters
			this.egw = _egw;
			this._orgAvgHeight = _avgHeight;
			this._rowProvider = _rowProvider;

			// As this grid instance has no parent, we need a scroll container
			this._scrollHeight = 0;
			this._scrollTimeout = null;
		}

		this._invalidateTimeout = null;

		this._invalidateCallback = null;
		this._invalidateContext = null;

		// _map contains a mapping between the grid indices and the elements
		// associated to it. The first element in the array always refers to the
		// element starting at index zero (being a spacer if the grid currently
		// displays another range).
		this._map = [];

		// _viewRange contains the current pixel-range of the grid which is
		// visible.
		this._viewRange = et2_range(0, 0);

		// Holds the maximum count of elements
		this._total = 0;

		// Holds data used for storing the current average height data
		this._avgHeight = false;
		this._avgCount = false;

		// Build the outer grid nodes
		this._createNodes();
	},

	destroy: function () {
		// Stop the scroll timeout
		if (this._scrollTimeout)
		{
			window.clearTimeout(this._scrollTimeout);
		}

		// Stop the invalidate timeout
		if (this._invalidateTimeout)
		{
			window.clearTimeout(this._invalidateTimeout);
		}

		// Destroy all containers
		this.setTotalCount(0);

		this._super();
	},

	clear: function () {
		// Store the old total count and rescue the current average height in
		// form of the "original average height"
		var oldTotalCount = this._total;
		this._orgAvgHeight = this.getAverageHeight();

		// Set the total count to zero
		this.setTotalCount(0);

		// Reset the total count value
		this.setTotalCount(oldTotalCount);
	},

	/**
	 * Throws all elements away which are outside the current view range
	 */
	cleanup: function () {
		// Update the pixel positions
		this._recalculateElementPosition();

		// Get the visible mapping indices and recalculate index and pixel
		// position of the containers.
		var mapVis = this._calculateVisibleMappingIndices();

		// Delete all invisible elements -- if anything changed, we have to
		// recalculate the pixel positions again
		this._cleanupOutOfRangeElements(mapVis, 0);
	},

	/**
	 * The insertRow function can be called to insert the given container(s) at
	 * the given row index. If there currently is another container at that
	 * given position, the new container(s) will be inserted above the old
	 * container. Yet the "total count" of the grid will be preserved by
	 * removing the correct count of elements from the next possible spacer. If
	 * no spacer is found, the last containers will be removed. This causes
	 * inserting new containers at the end of a grid to be immediately removed
	 * again.
	 *
	 * @param _index is the row index at which the given container(s) should be
	 * inserted.
	 * @param _container is eiter a single et2_dataview_container instance
	 * which should be inserted at the given position. Or an array of
	 * et2_dataview_container instances. If you want to remove the container
	 * don't do that manually by calling its "destroy" function but use the
	 * deleteRow function.
	 */
	insertRow: function (_index, _container) {
		// Calculate the map element the given index refers to
		var idx = this._calculateMapIndex(_index);

		if (idx !== false)
		{
			// Wrap the container inside an array
			if (_container instanceof et2_dataview_container)
			{
				_container = [_container];
			}

			// Fetch the average height
			var avg = this.getAverageHeight();

			// Call the internal _doInsertContainer function
			for (var i = 0; i < _container.length; i++)
			{
				this._doInsertContainer(_index, idx, _container[i], avg);
			}

			// Schedule an "invalidate" event
			this.invalidate();
		}
	},

	/**
	 * The deleteRow function can be used to remove the element at the given
	 * index.
	 *
	 * @param _index is the index from which should be deleted. If the given
	 * index is outside the so called "managedRange" nothing will happen, as the
	 * container has already been destroyed by the grid instance.
	 */
	deleteRow: function (_index) {
		// Calculate the map element the given index refers to
		var idx = this._calculateMapIndex(_index);

		if (idx !== false)
		{
			this._doDeleteContainer(idx, false);

			// Schedule an "invalidate" event
			this.invalidate();
		}
	},

	/**
	 * The given callback gets called whenever the scroll position changed or
	 * the visible element range changed. The element indices are passed to the
	 * function as et2_range.
	 */
	setInvalidateCallback: function (_callback, _context) {
		this._invalidateCallback = _callback;
		this._invalidateContext = _context;
	},

	/**
	 * The setDataCallback function is used to set the callback that will be
	 * called when the grid requires new data.
	 *
	 * @param _callback is the callback function which gets called when the grid
	 * needs some new rows.
	 * @param _context is the context in which the callback function gets
	 * called.
	 */
	setDataCallback: function (_callback, _context) {
		this._callback = _callback;
		this._context = _context;
	},

	/**
	 * The updateTotalCount function can be used to update the total count of
	 * rows that are displayed inside the grid. Changing the count always causes
	 * the spacer at the bottom (if it exists) to be 
	 *
	 * @param _count specifies how many entries the grid can show.
	 */
	setTotalCount: function (_count) {
		// Abort if the total count has not changed
		if (_count === this._total)
			return;

		// Calculate how many elements have to be removed/added
		var delta = Math.max(0, _count) - this._total;

		if (delta > 0)
		{
			this._appendEmptyRows(delta);
		}
		else
		{
			this._decreaseTotal(-delta);
		}

		this._total = Math.max(0, _count);

		// Schedule an invalidate
		this.invalidate();
	},

	/**
	 * Returns the current "total" count.
	 */
	getTotalCount: function () {
		return this._total;
	},

	/**
	 * The setViewRange function updates the range in which rows are shown.
	 */
	setViewRange: function (_range) {
		// Set the new view range
		this._viewRange = _range;

		// Immediately call the "invalidate" function
		this._doInvalidate();
	},

	/**
	 * Return the indices of the currently visible rows.
	 */
	getVisibleIndexRange: function (_viewRange) {

		function getElemIdx(_elem, _px)
		{
			if (_elem instanceof et2_dataview_spacer)
			{
				return _elem.getIndex()
					+ Math.floor((_px - _elem.getTop()) / this.getAverageHeight());
			}

			return _elem.getIndex();
		}

		var idxTop = 0;
		var idxBottom = 0;
		var vr;

		if (_viewRange)
		{
			vr = _viewRange;
		}
		else
		{
			// Calculate the "correct" view range by removing ET2_GRID_VIEW_EXT
			vr = et2_bounds(
					this._viewRange.top + ET2_GRID_VIEW_EXT,
					this._viewRange.bottom - ET2_GRID_VIEW_EXT);
		}

		// Get the elements at the top and the bottom of the view
		var topElem = null;
		var botElem = null;
		for (var i = 0; i < this._map.length; i++)
		{
			if (!topElem && this._map[i].getBottom() > vr.top)
			{
				topElem = this._map[i];
			}

			if (this._map[i].getTop() > vr.bottom)
			{
				botElem = this._map[i];
				break;
			}
		}

		if (!botElem)
		{
			botElem = this._map[this._map.length - 1];
		}

		if (topElem)
		{
			idxTop = getElemIdx.call(this, topElem, vr.top);
			idxBottom = getElemIdx.call(this, botElem, vr.bottom);
		}

		// Return the calculated index top and bottom
		return et2_bounds(idxTop, idxBottom);
	},

	/**
	 * Returns index range of all currently managed rows.
	 */
	getIndexRange: function () {
		var idxTop = false;
		var idxBottom = false;

		for (var i = 0; i < this._map.length; i++)
		{
			if (!(this._map[i] instanceof et2_dataview_spacer))
			{
				var idx = this._map[i].getIndex();

				if (idxTop === false)
				{
					idxTop = idx;
				}

				idxBottom = idx;
			}
		}

		return et2_bounds(idxTop, idxBottom);
	},

	/**
	 * Updates the scrollheight
	 */
	setScrollHeight: function (_height) {
		this._scrollHeight = _height;

		// Update the height of the outer container
		if (this.scrollarea)
		{
			this.scrollarea.height(_height);
		}

		// Update the viewing range
		this.setViewRange(et2_range(this._viewRange.top, this._scrollHeight));
	},

	/**
	 * Returns the average row height data, overrides the corresponding function
	 * of the et2_dataview_container.
	 */
	getAvgHeightData: function () {

		if (this._avgHeight === false)
		{
			var avgCount = 0;
			var avgSum = 0;

			for (var i = 0; i < this._map.length; i++)
			{
				var data = this._map[i].getAvgHeightData();

				if (data !== null)
				{
					avgSum += data.avgHeight * data.avgCount;
					avgCount += data.avgCount;
				}
			}

			// Calculate the average height
			if (avgCount > 0)
			{
				this._avgHeight = avgSum / avgCount;
				this._avgCount = avgCount;
			}
		}

		// Return the calculated average height if it is available
		if (this._avgHeight !== false)
		{
			return {
				"avgCount": this._avgCount,
				"avgHeight": this._avgHeight
			}
		}

		// Otherwise return the parent average height 
		if (this._parent)
		{
			return this._parent.getAvgHeightData();
		}

		// Otherwise return the original average height given in the constructor
		if (this._orgAvgHeight !== false)
		{
			return {
				"avgCount": 1,
				"avgHeight": this._orgAvgHeight
			}
		}
		else
		{
			return null;
		}
	},

	/**
	 * Returns the average row height in pixels.
	 */
	getAverageHeight: function () {
		var data = this.getAvgHeightData();
		return data ? data.avgHeight : 19;
	},

	/**
	 * Returns the row provider.
	 */
	getRowProvider: function () {
		return this._rowProvider;
	},

	/**
	 * Called whenever the size of this or another element in the container tree
	 * changes.
	 */
	invalidate: function() {
		// Clear the "_avgHeight"
		this._avgHeight = false;
		this._avgCount = false;

		// Clear any existing "invalidate" timeout
		if (this._invalidateTimeout)
		{
			window.clearTimeout(this._invalidateTimeout);
		}

		var self = this;
		this._invalidateTimeout = window.setTimeout(function() {
			self._invalidateTimeout = null;
			self._doInvalidate();
		}, ET2_GRID_INVALIDATE_TIMEOUT);

		// Call the inherited invalidate function, broadcast the invalidation
		// through the container tree.
		if (this._parent !== null)
		{
			this._super();
		}
	},

	/* ---- PRIVATE FUNCTIONS ---- */

/*	_inspectStructuralIntegrity: function() {
		var idx = 0;
		for (var i = 0; i < this._map.length; i++)
		{
			if (this._map[i].getIndex() != idx)
			{
				throw "Index missmatch!";
			}
			idx += this._map[i].getCount();
		}

		if (idx !== this._total)
		{
			throw "Total count missmatch!";
		}
	},*/

	/**
	 * Recalculates the position of the currently managed containers. This
	 * routine only updates the pixel position of the elements -- the index of
	 * the elements is guaranteed to be maintained correctly by all high level
	 * functions of the grid, as the index position is needed to be correct for
	 * the "deleteRow" and "insertRow" functions, and we cannot effort to call
	 * this calculation method after every change in the grid mapping.
	 */
	_recalculateElementPosition: function() {
		for (var i = 0; i < this._map.length; i++)
		{
			if (i == 0)
			{
				this._map[i].setTop(0);
			}
			else
			{
				this._map[i].setTop(this._map[i - 1].getBottom());
			}
		}
	},

	/**
	 * The "_calculateVisibleMappingIndices" function calculates the indices of
	 * the _map array, which refer to containers that are currently (partially)
	 * visible. This function is used internally by "_doInvalidate".
	 */
	_calculateVisibleMappingIndices: function() {
		// First update the "top" and "bottom", and "index" values of all
		// managed elements, and at the same time calculate the mapping indices
		// of the elements which are inside the current view range.
		var mapVis = {"top": false, "bottom": false};

		for (var i = 0; i < this._map.length; i++)
		{
			// Update the top of the "map visible index" -- set it to the first
			// element index, where the bottom line is beneath the top line
			// of the view range.
			if (mapVis.top === false
				&& this._map[i].getBottom() > this._viewRange.top)
			{
				mapVis.top = i;
			}

			// Update the bottom of the "map visible index" -- set it to the
			// first element index, where the top line is beneath the bottom
			// line of the view range.
			if (mapVis.bottom === false
				&& this._map[i].getTop() > this._viewRange.bottom)
			{
				mapVis.bottom = i;
				break;
			}
		}

		return mapVis;
	},

	/**
	 * Deletes all elements which are "out of the view range". This function is
	 * internally used by "_doInvalidate". How many elements that are out of the
	 * view range get preserved fully depends on the _holdCount parameter
	 * variable.
	 *
	 * @param _mapVis contains the _map indices of the just visible containers.
	 * @param _holdCount contains the number of elements that should be kept,
	 * if not given, this parameter defaults to ET2_GRID_HOLD_COUNT
	 */
	_cleanupOutOfRangeElements: function(_mapVis, _holdCount) {

		// Iterates over the map from and to the given indices and pushes all
		// elements onto the given array, which are more than _holdCount
		// elements remote from the start.
		function searchElements(_arr, _start, _stop, _dir)
		{
			var dist = 0;
			for (var i = _start; _dir > 0 ? i <= _stop : i >= _stop; i += _dir)
			{
				if (dist > _holdCount)
				{
					_arr.push(i);
				}
				else
				{
					dist += this._map[i].getCount();
				}
			}
		}

		// Set _holdCount to ET2_GRID_HOLD_COUNT if the parameters is not given
		_holdCount = typeof _holdCount === "undefined" ? ET2_GRID_HOLD_COUNT :
				_holdCount;

		// Collect all elements that will be deleted at the top and at the
		// bottom of the grid
		var deleteTop = [];
		var deleteBottom = [];

		if (_mapVis.top !== false)
		{
			searchElements.call(this, deleteTop, _mapVis.top, 0, -1);
		}

		if (_mapVis.bottom !== false)
		{
			searchElements.call(this, deleteBottom, _mapVis.bottom,
				this._map.length - 1, 1);
		}

		// The offset variable specifies how many elements have been deleted
		// from the map -- this variable is needed as deleting elements from the
		// map shifts the map indices. We iterate in oposite direction over the
		// elements, as this allows the _doDeleteContainer/ container function
		// to extend the (possibly) existing spacer at the top of the grid
		var offs = 0;
		for (var i = deleteTop.length - 1; i >= 0; i--)
		{
			// Delete the container and calculate the new offset
			var mapLength = this._map.length;
			this._doDeleteContainer(deleteTop[i] - offs, true);
			offs += mapLength - this._map.length;
		}

		for (var i = deleteBottom.length - 1; i >= 0; i--)
		{
			this._doDeleteContainer(deleteBottom[i] - offs, true);
		}

		return deleteBottom.length + deleteTop.length > 0;
	},

	/**
	 * The _updateContainers function is used internally by "_doInvalidate" in
	 * order to call the "setViewRange" function of all containers the implement
	 * that interfaces (needed for nested grids), and to request new elements
	 * for all currently visible spacers.
	 */
	_updateContainers: function() {
		for (var i = 0; i < this._map.length; i++)
		{
			var container = this._map[i];

			// Check which type the container object has
			var isSpacer = container instanceof et2_dataview_spacer;
			var hasIViewRange = !isSpacer
					&& container.implements(et2_dataview_IViewRange);

			// If the container has one of those special types, calculate the
			// view range and use that to update the view range of the element
			// or to request new elements for the spacer
			if (isSpacer || hasIViewRange)
			{
				// Calculate the relative view range and check whether
				// the element is really visible
				var elemRange = container.getRange();

				// Abort if the element is not inside the visible range
				if (!et2_rangeIntersect(this._viewRange, elemRange))
				{
					continue;
				}

				if (hasIViewRange)
				{
					// Update the view range of the container
					container.setViewRange(et2_bounds(
							this._viewRange.top - elemRange.top,
							this._viewRange.bottom - elemRange.top));
				}
				else // This container is a spacer
				{
					// Obtain the average element height
					var avg = container._rowHeight;

					// Get the visible container range (vcr)
					var vcr_top = Math.max(this._viewRange.top, elemRange.top);
					var vcr_bot = Math.min(this._viewRange.bottom, elemRange.bottom);

					// Calculate the indices of the elements which will be
					// requested
					var cidx = container.getIndex();
					var ccnt = container.getCount();

					// Calculate the start index -- prevent vtop from getting
					// negative (and so idxStart being smaller than cidx) and
					// ensure that idxStart is not larger than the maximum
					// container index.
					var vtop = Math.max(0, vcr_top);
					var idxStart = Math.floor(
							Math.min(cidx + ccnt - 1, 
								cidx + (vtop - elemRange.top) / avg));

					// Calculate the end index -- prevent vtop from getting
					// negative (and so idxEnd being smaller than cidx) and
					// ensure that idxEnd is not larger than the maximum
					// container index.
					var vbot = Math.max(0, vcr_bot);
					var idxEnd = Math.ceil(
							Math.min(cidx + ccnt - 1, 
								cidx + (vbot - elemRange.top) / avg));

					// Call the data callback
					if (this._callback)
					{
						var self = this;
						window.setTimeout(function() {
							self._callback.call(self._context, idxStart, idxEnd);
						}, 0);
					}
				}
			}
		}
	},

	/**
	 * Invalidate iterates over the "mapping" array. It calculates which
	 * containers have to be removed and where new containers should be added.
	 */
	_doInvalidate: function() {
		// Update the pixel positions
		this._recalculateElementPosition();

		// Call the callback
		if (this._invalidateCallback)
		{
			var range = this.getVisibleIndexRange(
				et2_range(this.scrollarea.scrollTop(), this._scrollHeight));
			this._invalidateCallback.call(this._invalidateContext, range);
		}

		// Get the visible mapping indices and recalculate index and pixel
		// position of the containers.
		var mapVis = this._calculateVisibleMappingIndices();

		// Delete all invisible elements -- if anything changed, we have to
		// recalculate the pixel positions again
		if (this._cleanupOutOfRangeElements(mapVis))
		{
			this._recalculateElementPosition();
		}

		// Update the view range of all visible elements that implement the
		// corresponding interface and request elements for all visible spacers
		this._updateContainers();
	},

	/**
	 * Translates the given grid index into the element index of the map. If the
	 * given index is completely out of the range, "false" is returned.
	 */
	_calculateMapIndex: function(_index) {

		var top = 0;
		var bot = this._map.length - 1;

		while (top <= bot)
		{
			var idx = Math.floor((top + bot) / 2);
			var elem = this._map[idx];

			var realIdx = elem.getIndex();
			var realCnt = elem.getCount();

			if (_index >= realIdx && _index < realIdx + realCnt)
			{
				return idx;
			}
			else if (_index < realIdx)
			{
				bot = idx - 1;
			}
			else
			{
				top = idx + 1;
			}
		}

		return false;
	},

	_insertContainerAtSpacer: function(_index, _mapIndex, _mapElem, _container,
			_avg) {
		// Set the index of the new container
		_container.setIndex(_index);

		// Calculate at which position the spacer has to be splitted
		var splitIdx = _index - _mapElem.getIndex();

		// Get the count of elements that remain at the top of the splitter
		var cntTop = splitIdx;

		// Get the count of elements that remain at the bottom of the splitter
		// -- it has to be one element less than before
		var cntBottom = _mapElem.getCount() - splitIdx - 1;

		// Split the containers if cntTop and cntBottom are larger than zero
		if (cntTop > 0 && cntBottom > 0)
		{
			// Set the new count of the currently existing container, preserving
			// its height as it was
			_mapElem.setCount(cntTop);

			// Add the new element after the old container
			_container.insertIntoTree(_mapElem.getLastNode());

			// Create a new spacer and add it after the newly inserted container
			var newSpacer = new et2_dataview_spacer(this,
					this._rowProvider);
			newSpacer.setCount(cntBottom, _avg);
			newSpacer.setIndex(_index + 1);
			newSpacer.insertIntoTree(_container.getLastNode());

			// Insert the container and the new spacer into the map
			this._map.splice(_mapIndex + 1, 0, _container, newSpacer);
		}
		else if (cntTop === 0 && cntBottom > 0)
		{
			// Simply adjust the size of the old spacer and insert the new
			// container in front of it
			_container.insertIntoTree(_mapElem.getFirstNode(), true);
			_mapElem.setIndex(_index + 1);
			_mapElem.setCount(cntBottom, _avg);

			this._map.splice(_mapIndex, 0, _container);
		}
		else if (cntTop > 0 && cntBottom === 0)
		{
			// Simply add the new container to the end of the old container and
			// adjust the count of the old spacer to the remaining count.
			_container.insertIntoTree(_mapElem.getLastNode());
			_mapElem.setCount(cntTop);

			this._map.splice(_mapIndex + 1, 0, _container);
		}
		else // if (cntTop === 0 && cntBottom === 0)
		{
			// Append the new container to the current container and then
			// destroy the old container
			_container.insertIntoTree(_mapElem.getLastNode());
			_mapElem.free();

			this._map.splice(_mapIndex, 1, _container);
		}
	},

	_insertContainerAtElement: function(_index, _mapIndex, _mapElem, _container,
			_avg) {
		// In a first step, simply insert the element at the specified position,
		// in front of the element _mapElem.
		_container.setIndex(_index);
		_container.insertIntoTree(_mapElem.getFirstNode(), true);
		this._map.splice(_mapIndex, 0, _container);

		// Search for the next spacer and increment the indices of all other
		// elements until there
		var _newIndex = _index + 1;
		for (var i = _mapIndex + 1; i < this._map.length; i++)
		{
			// Update the index of the element
			this._map[i].setIndex(_newIndex++);

			// We've found a spacer -- decrement its element count and abort
			if (this._map[i] instanceof et2_dataview_spacer)
			{
				this._decrementSpacerCount(i, _avg);
				return;
			}
		}

		// We've found no spacer so far, remove the last element from the map in
		// order to obtain the "totalCount" (especially the last element is no
		// spacer, so the following code cannot remove a spacer)
		this._map.pop().free();
	},

	/**
	 * Inserts the given container at the given index.
	 */
	_doInsertContainer: function(_index, _mapIndex, _container, _avg) {
		// Check whether the given element at the map index is a spacer. If
		// yes, we have to split the spacer at that position.
		var mapElem = this._map[_mapIndex];

		if (mapElem instanceof et2_dataview_spacer)
		{
			this._insertContainerAtSpacer(_index, _mapIndex, mapElem,
				_container, _avg);
		}
		else
		{
			this._insertContainerAtElement(_index, _mapIndex, mapElem,
				_container, _avg);
		}

//		this._inspectStructuralIntegrity();
	},

	/**
	 * Replaces the container at the given index with a spacer. The function
	 * tries to extend any spacer lying above or below the given _mapIndex.
	 * This code does not destroy the given container, but maintains its map
	 * index.
	 *
	 * @param _mapIndex is the index of _mapElem in the _map array.
	 * @param _mapElem is the container which should be replaced.
	 */
	_replaceContainerWithSpacer: function(_mapIndex, _mapElem) {
		// Check whether a spacer can be extended above or below the given
		// _mapIndex
		var spacerAbove = null;
		var spacerBelow = null;

		if (_mapIndex > 0
		    && this._map[_mapIndex - 1] instanceof et2_dataview_spacer)
		{
			spacerAbove = this._map[_mapIndex - 1];
		}

		if (_mapIndex < this._map.length - 1
		    && this._map[_mapIndex + 1] instanceof et2_dataview_spacer)
		{
			spacerBelow = this._map[_mapIndex + 1];
		}

		if (!spacerAbove && !spacerBelow)
		{
			// No spacer can be extended -- simply create a new one
			var spacer = new et2_dataview_spacer(this, this._rowProvider);
			spacer.setIndex(_mapElem.getIndex());
			spacer.addAvgHeight(_mapElem.getHeight());
			spacer.setCount(1, _mapElem.getHeight());

			// Insert the new spacer at the correct place into the DOM tree and
			// the mapping
			spacer.insertIntoTree(_mapElem.getLastNode());
			this._map.splice(_mapIndex + 1, 0, spacer);
		}
		else if (spacerAbove && spacerBelow)
		{
			// We're going to consolidate the upper and the lower spacer. To do
			// that we'll calculate a new count of elements and a new average
			// height, so that the upper container can get the height of all
			// three elements together
			var totalHeight = spacerAbove.getHeight() + spacerBelow.getHeight()
					+ _mapElem.getHeight();
			var totalCount = spacerAbove.getCount() + spacerBelow.getCount()
					+ 1;
			var newAvg = totalHeight / totalCount;

			// Update the upper spacer
			spacerAbove.addAvgHeight(_mapElem.getHeight());
			spacerAbove.setCount(totalCount, newAvg);

			// Delete the lower spacer and remove it from the mapping
			spacerBelow.free();
			this._map.splice(_mapIndex + 1, 1);
		}
		else
		{
			// One of the two spacers is available
			var spacer = spacerAbove || spacerBelow;

			// Calculate the new count and the new average height of that spacer
			var totalCount = spacer.getCount() + 1;
			var totalHeight = spacer.getHeight() + _mapElem.getHeight();
			var newAvg = totalHeight / totalCount;

			// Set the new container height
			spacer.setIndex(Math.min(spacer.getIndex(), _mapElem.getIndex()));
			spacer.addAvgHeight(_mapElem.getHeight());
			spacer.setCount(totalCount, newAvg);
		}
	},

	/**
	 * Checks whether there is another spacer below the given map index and if
	 * yes, consolidates the two.
	 */
	_consolidateSpacers: function(_mapIndex) {
		if (_mapIndex < this._map.length - 1
		    && this._map[_mapIndex] instanceof et2_dataview_spacer
		    && this._map[_mapIndex + 1] instanceof et2_dataview_spacer)
		{
			var spacerAbove = this._map[_mapIndex];
			var spacerBelow = this._map[_mapIndex + 1];

			// Calculate the new height/count of both containers
			var totalHeight = spacerAbove.getHeight() + spacerBelow.getHeight();
			var totalCount = spacerAbove.getCount() + spacerBelow.getCount();
			var newAvg = totalCount / totalHeight;

			// Extend the new spacer
			spacerAbove.setCount(totalCount, newAvg);

			// Delete the old spacer
			spacerBelow.free();
			this._map.splice(_mapIndex + 1, 1);
		}
	},

	/**
	 * Decrements the count of the spacer at the given _mapIndex by one. If the
	 * given spacer has no more elements, it will be removed from the mapping.
	 * Note that this function does not update the indices of the following
	 * elements, this function is only used internally by the
	 * _insertContainerAtElement function and the _doDeleteContainer function
	 * where appropriate adjustments to the map data structure are done.
	 *
	 * @param _mapIndex is the index of the spacer in the "map" data structure.
	 * @param _avg is the new average height of the container, may be
	 * "undefined" in which case the height of the spacer rows is kept as it
	 * was.
	 */
	_decrementSpacerCount: function(_mapIndex, _avg) {
		var cnt = this._map[_mapIndex].getCount() - 1;
		if (cnt > 0)
		{
			this._map[_mapIndex].setCount(cnt, _avg);
		}
		else
		{
			this._map[_mapIndex].free();
			this._map.splice(_mapIndex, 1);
		}
	},

	/**
	 * Deletes the container at the given index.
	 */
	_doDeleteContainer: function(_mapIndex, _replaceWithSpacer) {
		// _replaceWithSpacer defaults to false
		_replaceWithSpacer = _replaceWithSpacer ? _replaceWithSpacer : false;

		// Fetch the element at the given map index
		var mapElem = this._map[_mapIndex];

		// Indicates whether an element has really been removed -- if yes, the
		// bottom spacer will be extended
		var removedElement = false;

		// Check whether the map element is a spacer -- if yes, we have to do
		// some special treatment
		if (mapElem instanceof et2_dataview_spacer)
		{
			// Do nothing if the "_replaceWithSpacer" flag is true as the
			// element already is a spacer
			if (!_replaceWithSpacer)
			{
				this._decrementSpacerCount(_mapIndex);
				removedElement = true;
			}
		}
		else
		{
			if (_replaceWithSpacer)
			{
				this._replaceContainerWithSpacer(_mapIndex, mapElem);
			}
			else
			{
				removedElement = true;
			}

			// Remove the complete (current) container, decrement the _mapIndex
			this._map[_mapIndex].free();
			this._map.splice(_mapIndex, 1);
			_mapIndex--;

			// The delete operation may have created two joining spacers -- this
			// is highly suboptimal, so we'll consolidate those two spacers
			this._consolidateSpacers(_mapIndex);
		}

		// Update the indices of all elements after the current one, if we've
		// really removed an element
		if (removedElement)
		{
			for (var i = _mapIndex + 1; i < this._map.length; i++)
			{
				this._map[i].setIndex(this._map[i].getIndex() - 1);
			}

			// Extend the last spacer as we have to maintain the spacer count
			this._appendEmptyRows(1);
		}

//		this._inspectStructuralIntegrity();
	},

	/**
	 * The appendEmptyRows function is used internally to append empty rows to
	 * the end of the table. This functionality is needed in order to maintain
	 * the "total count" in the _doDeleteContainer function and to increase the
	 * "total count" in the "setCount" function.
	 *
	 * @param _count specifies the count of empty rows that will be added to the
	 * end of the table.
	 */
	_appendEmptyRows: function(_count) {
		// Special case -- the last element in the "_map" is no spacer -- this
		// means, that the "managedRange" is currently at the bottom of the list
		// -- so we have to insert a new spacer
		var spacer = null;
		var lastIndex = this._map.length - 1;
		if (this._map.length === 0 ||
			!(this._map[lastIndex] instanceof et2_dataview_spacer))
		{
			// Create a new spacer
			spacer = new et2_dataview_spacer(this, this._rowProvider);

			// Insert the spacer -- we have a special case if there currently is
			// no element inside the mapping
			if (this._map.length === 0)
			{
				// Add a dummy element to the grid
				var dummy = $j(document.createElement("tr"));
				this.innerTbody.append(dummy);

				// Append the spacer to the grid
				spacer.setIndex(0);
				spacer.insertIntoTree(dummy, false);

				// Remove the dummy element
				dummy.remove();
			}
			else
			{
				// Insert the new spacer after the last element
				spacer.setIndex(this._map[lastIndex].getIndex() + 1);
				spacer.insertIntoTree(this._map[lastIndex].getLastNode());
			}

			// Add the new spacer to the mapping
			this._map.push(spacer);
		}
		else
		{
			// Get the spacer at the bottom of the mapping
			spacer = this._map[lastIndex];
		}

		// Update the spacer count
		spacer.setCount(_count + spacer.getCount(), this.getAverageHeight());
	},

	/**
	 * The _decreaseTotal function is used to decrease the total row count in
	 * the grid. It tries to remove the given count of rows from the spacer
	 * located at the bottom of the grid, if this is not possible, it starts
	 * removing complete rows.
	 *
	 * @param _delta specifies how many rows should be removed.
	 */
	_decreaseTotal: function(_delta) {
		// Iterate over the current mapping, starting at the bottom and delete
		// rows. _delta is decreased for each removed row. Abort when delta is
		// zero or the map is empty
		while (_delta > 0 && this._map.length > 0)
		{
			var cont = this._map[this._map.length - 1];

			// Remove as many containers as possible from spacers
			if (cont instanceof et2_dataview_spacer)
			{
				var diff = cont.getCount() - _delta;

				if (diff > 0)
				{
					// We're done as the spacer still has entries left
					_delta = 0;
					cont.setCount(diff, this.getAverageHeight());
					break;
				}
				else
				{
					// Decrease _delta by the count of rows the spacer had
					_delta -= diff + _delta;
				}
			}
			else
			{
				// We're going to remove a single row: remove it
				_delta -= 1;
			}

			// Destroy the container if there are no rows left
			cont.free();
			this._map.pop();
		}

		// Check whether _delta is really zero
		if (_delta > 0)
		{
			this.egw.debug('error', "Error while decreasing the total count - requested to remove more rows than available.");
		}
	},

	/**
	 * Creates the grid DOM-Nodes
	 */
	_createNodes: function() {

		this.tr = $j(document.createElement("tr"));

		this.outerCell = $j(document.createElement("td"))
			.addClass("frame")
			.attr("colspan", this._rowProvider.getColumnCount()
					+ (this._parent ? 0 : 1))
			.appendTo(this.tr);

		// Create the scrollarea div if this is the outer grid
		this.scrollarea = null;
		if (this._parent == null)
		{
			this.scrollarea = $j(document.createElement("div"))
				.addClass("egwGridView_scrollarea")
				.scroll(this, function(e) {

						// Clear any older scroll timeout
						if (e.data._scrollTimeout)
						{
							window.clearTimeout(e.data._scrollTimeout);
						}

						// Clear any existing "invalidate" timeout (as the
						// "setViewRange" function triggered by the scroll event
						// forces an "invalidate").
						if (e.data._invalidateTimeout)
						{
							window.clearTimeout(e.data._invalidateTimeout);
							e.data._invalidateTimeout = null;
						}

						// Set a new timeout which calls the setViewArea
						// function
						e.data._scrollTimeout = window.setTimeout(function() {
							var newRange = et2_range(
								e.data.scrollarea.scrollTop() - ET2_GRID_VIEW_EXT,
								e.data._scrollHeight + ET2_GRID_VIEW_EXT * 2
							);

							if (!et2_rangeEqual(newRange, e.data._viewRange))
							{
								e.data.setViewRange(newRange);
							}
						}, ET2_GRID_SCROLL_TIMEOUT);
					})
				.height(this._scrollHeight)
				.appendTo(this.outerCell);
		}

		// Create the inner table
		var table = $j(document.createElement("table"))
			.addClass("egwGridView_grid")
			.appendTo(this.scrollarea ? this.scrollarea : this.outerCell);

		this.innerTbody = $j(document.createElement("tbody"))
			.appendTo(table);

		// Set the tr as container element
		this.appendNode(this.tr[0]);
	}

});