/*! Scroller 2.2.0
 * © SpryMedia Ltd - datatables.net/license
 */

import jQuery from 'jquery';
import DataTable from 'datatables.net';

// Allow reassignment of the $ variable
let $ = jQuery;


/**
 * @summary     Scroller
 * @description Virtual rendering for DataTables
 * @version     2.2.0
 * @author      SpryMedia Ltd (www.sprymedia.co.uk)
 * @contact     www.sprymedia.co.uk/contact
 * @copyright   SpryMedia Ltd.
 *
 * This source file is free software, available under the following license:
 *   MIT license - http://datatables.net/license/mit
 *
 * This source file is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE. See the license files for details.
 *
 * For details please refer to: http://www.datatables.net
 */

/**
 * Scroller is a virtual rendering plug-in for DataTables which allows large
 * datasets to be drawn on screen every quickly. What the virtual rendering means
 * is that only the visible portion of the table (and a bit to either side to make
 * the scrolling smooth) is drawn, while the scrolling container gives the
 * visual impression that the whole table is visible. This is done by making use
 * of the pagination abilities of DataTables and moving the table around in the
 * scrolling container DataTables adds to the page. The scrolling container is
 * forced to the height it would be for the full table display using an extra
 * element.
 *
 * Note that rows in the table MUST all be the same height. Information in a cell
 * which expands on to multiple lines will cause some odd behaviour in the scrolling.
 *
 * Scroller is initialised by simply including the letter 'S' in the sDom for the
 * table you want to have this feature enabled on. Note that the 'S' must come
 * AFTER the 't' parameter in `dom`.
 *
 * Key features include:
 *   <ul class="limit_length">
 *     <li>Speed! The aim of Scroller for DataTables is to make rendering large data sets fast</li>
 *     <li>Full compatibility with deferred rendering in DataTables for maximum speed</li>
 *     <li>Display millions of rows</li>
 *     <li>Integration with state saving in DataTables (scrolling position is saved)</li>
 *     <li>Easy to use</li>
 *   </ul>
 *
 *  @class
 *  @constructor
 *  @global
 *  @param {object} dt DataTables settings object or API instance
 *  @param {object} [opts={}] Configuration object for Scroller. Options
 *    are defined by {@link Scroller.defaults}
 *
 *  @requires jQuery 1.7+
 *  @requires DataTables 1.10.0+
 *
 *  @example
 *    $(document).ready(function() {
 *        $('#example').DataTable( {
 *            "scrollY": "200px",
 *            "ajax": "media/dataset/large.txt",
 *            "scroller": true,
 *            "deferRender": true
 *        } );
 *    } );
 */
var Scroller = function (dt, opts) {
	/* Sanity check - you just know it will happen */
	if (!(this instanceof Scroller)) {
		alert("Scroller warning: Scroller must be initialised with the 'new' keyword.");
		return;
	}

	if (opts === undefined) {
		opts = {};
	}

	var dtApi = $.fn.dataTable.Api(dt);

	/**
	 * Settings object which contains customisable information for the Scroller instance
	 * @namespace
	 * @private
	 * @extends Scroller.defaults
	 */
	this.s = {
		/**
		 * DataTables settings object
		 *  @type     object
		 *  @default  Passed in as first parameter to constructor
		 */
		dt: dtApi.settings()[0],

		/**
		 * DataTables API instance
		 *  @type     DataTable.Api
		 */
		dtApi: dtApi,

		/**
		 * Pixel location of the top of the drawn table in the viewport
		 *  @type     int
		 *  @default  0
		 */
		tableTop: 0,

		/**
		 * Pixel location of the bottom of the drawn table in the viewport
		 *  @type     int
		 *  @default  0
		 */
		tableBottom: 0,

		/**
		 * Pixel location of the boundary for when the next data set should be loaded and drawn
		 * when scrolling up the way.
		 *  @type     int
		 *  @default  0
		 *  @private
		 */
		redrawTop: 0,

		/**
		 * Pixel location of the boundary for when the next data set should be loaded and drawn
		 * when scrolling down the way. Note that this is actually calculated as the offset from
		 * the top.
		 *  @type     int
		 *  @default  0
		 *  @private
		 */
		redrawBottom: 0,

		/**
		 * Auto row height or not indicator
		 *  @type     bool
		 *  @default  0
		 */
		autoHeight: true,

		/**
		 * Number of rows calculated as visible in the visible viewport
		 *  @type     int
		 *  @default  0
		 */
		viewportRows: 0,

		/**
		 * setTimeout reference for state saving, used when state saving is enabled in the DataTable
		 * and when the user scrolls the viewport in order to stop the cookie set taking too much
		 * CPU!
		 *  @type     int
		 *  @default  0
		 */
		stateTO: null,

		stateSaveThrottle: function () {},

		/**
		 * setTimeout reference for the redraw, used when server-side processing is enabled in the
		 * DataTables in order to prevent DoSing the server
		 *  @type     int
		 *  @default  null
		 */
		drawTO: null,

		heights: {
			jump: null,
			page: null,
			virtual: null,
			scroll: null,

			/**
			 * Height of rows in the table
			 *  @type     int
			 *  @default  0
			 */
			row: null,

			/**
			 * Pixel height of the viewport
			 *  @type     int
			 *  @default  0
			 */
			viewport: null,
			labelHeight: 0,
			xbar: 0
		},

		topRowFloat: 0,
		scrollDrawDiff: null,
		loaderVisible: false,
		forceReposition: false,
		baseRowTop: 0,
		baseScrollTop: 0,
		mousedown: false,
		lastScrollTop: 0
	};

	// @todo The defaults should extend a `c` property and the internal settings
	// only held in the `s` property. At the moment they are mixed
	this.s = $.extend(this.s, Scroller.oDefaults, opts);

	// Workaround for row height being read from height object (see above comment)
	this.s.heights.row = this.s.rowHeight;

	/**
	 * DOM elements used by the class instance
	 * @private
	 * @namespace
	 *
	 */
	this.dom = {
		force: document.createElement('div'),
		label: $('<div class="dts_label">0</div>'),
		scroller: null,
		table: null,
		loader: null
	};

	// Attach the instance to the DataTables instance so it can be accessed in
	// future. Don't initialise Scroller twice on the same table
	if (this.s.dt.oScroller) {
		return;
	}

	this.s.dt.oScroller = this;

	/* Let's do it */
	this.construct();
};

$.extend(Scroller.prototype, {
	/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
	 * Public methods - to be exposed via the DataTables API
	 */

	/**
	 * Calculate and store information about how many rows are to be displayed
	 * in the scrolling viewport, based on current dimensions in the browser's
	 * rendering. This can be particularly useful if the table is initially
	 * drawn in a hidden element - for example in a tab.
	 *  @param {bool} [redraw=true] Redraw the table automatically after the recalculation, with
	 *    the new dimensions forming the basis for the draw.
	 *  @returns {void}
	 */
	measure: function (redraw) {
		if (this.s.autoHeight) {
			this._calcRowHeight();
		}

		var heights = this.s.heights;

		if (heights.row) {
			heights.viewport = this._parseHeight($(this.dom.scroller).css('max-height'));

			this.s.viewportRows = parseInt(heights.viewport / heights.row, 10) + 1;
			this.s.dt._iDisplayLength = this.s.viewportRows * this.s.displayBuffer;
		}

		var label = this.dom.label.outerHeight();

		heights.xbar = this.dom.scroller.offsetHeight - this.dom.scroller.clientHeight;
		heights.labelHeight = label;

		if (redraw === undefined || redraw) {
			this.s.dt.oInstance.fnDraw(false);
		}
	},

	/**
	 * Get information about current displayed record range. This corresponds to
	 * the information usually displayed in the "Info" block of the table.
	 *
	 * @returns {object} info as an object:
	 *  {
	 *      start: {int}, // the 0-indexed record at the top of the viewport
	 *      end:   {int}, // the 0-indexed record at the bottom of the viewport
	 *  }
	 */
	pageInfo: function () {
		var dt = this.s.dt,
			iScrollTop = this.dom.scroller.scrollTop,
			iTotal = dt.fnRecordsDisplay(),
			iPossibleEnd = Math.ceil(
				this.pixelsToRow(iScrollTop + this.s.heights.viewport, false, this.s.ani)
			);

		return {
			start: Math.floor(this.pixelsToRow(iScrollTop, false, this.s.ani)),
			end: iTotal < iPossibleEnd ? iTotal - 1 : iPossibleEnd - 1
		};
	},

	/**
	 * Calculate the row number that will be found at the given pixel position
	 * (y-scroll).
	 *
	 * Please note that when the height of the full table exceeds 1 million
	 * pixels, Scroller switches into a non-linear mode for the scrollbar to fit
	 * all of the records into a finite area, but this function returns a linear
	 * value (relative to the last non-linear positioning).
	 *  @param {int} pixels Offset from top to calculate the row number of
	 *  @param {int} [intParse=true] If an integer value should be returned
	 *  @param {int} [virtual=false] Perform the calculations in the virtual domain
	 *  @returns {int} Row index
	 */
	pixelsToRow: function (pixels, intParse, virtual) {
		var diff = pixels - this.s.baseScrollTop;
		var row = virtual
			? (this._domain('physicalToVirtual', this.s.baseScrollTop) + diff) / this.s.heights.row
			: diff / this.s.heights.row + this.s.baseRowTop;

		return intParse || intParse === undefined ? parseInt(row, 10) : row;
	},

	/**
	 * Calculate the pixel position from the top of the scrolling container for
	 * a given row
	 *  @param {int} iRow Row number to calculate the position of
	 *  @returns {int} Pixels
	 */
	rowToPixels: function (rowIdx, intParse, virtual) {
		var pixels;
		var diff = rowIdx - this.s.baseRowTop;

		if (virtual) {
			pixels = this._domain('virtualToPhysical', this.s.baseScrollTop);
			pixels += diff * this.s.heights.row;
		}
		else {
			pixels = this.s.baseScrollTop;
			pixels += diff * this.s.heights.row;
		}

		return intParse || intParse === undefined ? parseInt(pixels, 10) : pixels;
	},

	/**
	 * Calculate the row number that will be found at the given pixel position (y-scroll)
	 *  @param {int} row Row index to scroll to
	 *  @param {bool} [animate=true] Animate the transition or not
	 *  @returns {void}
	 */
	scrollToRow: function (row, animate) {
		var that = this;
		var ani = false;
		var px = this.rowToPixels(row);

		// We need to know if the table will redraw or not before doing the
		// scroll. If it will not redraw, then we need to use the currently
		// displayed table, and scroll with the physical pixels. Otherwise, we
		// need to calculate the table's new position from the virtual
		// transform.
		var preRows = ((this.s.displayBuffer - 1) / 2) * this.s.viewportRows;
		var drawRow = row - preRows;
		if (drawRow < 0) {
			drawRow = 0;
		}

		if (
			(px > this.s.redrawBottom || px < this.s.redrawTop) &&
			this.s.dt._iDisplayStart !== drawRow
		) {
			ani = true;
			px = this._domain('virtualToPhysical', row * this.s.heights.row);

			// If we need records outside the current draw region, but the new
			// scrolling position is inside that (due to the non-linear nature
			// for larger numbers of records), we need to force position update.
			if (this.s.redrawTop < px && px < this.s.redrawBottom) {
				this.s.forceReposition = true;
				animate = false;
			}
		}

		if (animate === undefined || animate) {
			this.s.ani = ani;
			$(this.dom.scroller).animate(
				{
					scrollTop: px
				},
				function () {
					// This needs to happen after the animation has completed and
					// the final scroll event fired
					setTimeout(function () {
						that.s.ani = false;
					}, 250);
				}
			);
		}
		else {
			$(this.dom.scroller).scrollTop(px);
		}
	},

	/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
	 * Constructor
	 */

	/**
	 * Initialisation for Scroller
	 *  @returns {void}
	 *  @private
	 */
	construct: function () {
		var that = this;
		var dt = this.s.dtApi;

		/* Sanity check */
		if (!this.s.dt.oFeatures.bPaginate) {
			this.s.dt.oApi._fnLog(this.s.dt, 0, 'Pagination must be enabled for Scroller');
			return;
		}

		/* Insert a div element that we can use to force the DT scrolling container to
		 * the height that would be required if the whole table was being displayed
		 */
		this.dom.force.style.position = 'relative';
		this.dom.force.style.top = '0px';
		this.dom.force.style.left = '0px';
		this.dom.force.style.width = '1px';

		this.dom.scroller = $('div.' + this.s.dt.oClasses.sScrollBody, this.s.dt.nTableWrapper)[0];
		this.dom.scroller.appendChild(this.dom.force);
		this.dom.scroller.style.position = 'relative';

		this.dom.table = $('>table', this.dom.scroller)[0];
		this.dom.table.style.position = 'absolute';
		this.dom.table.style.top = '0px';
		this.dom.table.style.left = '0px';

		// Add class to 'announce' that we are a Scroller table
		$(dt.table().container()).addClass('dts DTS');

		// Add a 'loading' indicator
		if (this.s.loadingIndicator) {
			this.dom.loader = $(
				'<div class="dataTables_processing dts_loading">' +
					this.s.dt.oLanguage.sLoadingRecords +
					'</div>'
			).css('display', 'none');

			$(this.dom.scroller.parentNode).css('position', 'relative').append(this.dom.loader);
		}

		this.dom.label.appendTo(this.dom.scroller);

		/* Initial size calculations */
		if (this.s.heights.row && this.s.heights.row != 'auto') {
			this.s.autoHeight = false;
		}

		// Scrolling callback to see if a page change is needed
		this.s.ingnoreScroll = true;
		$(this.dom.scroller).on('scroll.dt-scroller', function (e) {
			that._scroll.call(that);
		});

		// In iOS we catch the touchstart event in case the user tries to scroll
		// while the display is already scrolling
		$(this.dom.scroller).on('touchstart.dt-scroller', function () {
			that._scroll.call(that);
		});

		$(this.dom.scroller)
			.on('mousedown.dt-scroller', function () {
				that.s.mousedown = true;
			})
			.on('mouseup.dt-scroller', function () {
				that.s.labelVisible = false;
				that.s.mousedown = false;
				that.dom.label.css('display', 'none');
			});

		// On resize, update the information element, since the number of rows shown might change
		$(window).on('resize.dt-scroller', function () {
			that.measure(false);
			that._info();
		});

		// Add a state saving parameter to the DT state saving so we can restore the exact
		// position of the scrolling.
		var initialStateSave = true;
		var loadedState = dt.state.loaded();

		dt.on('stateSaveParams.scroller', function (e, settings, data) {
			if (initialStateSave && loadedState) {
				data.scroller = loadedState.scroller;
				initialStateSave = false;

				if (data.scroller) {
					that.s.lastScrollTop = data.scroller.scrollTop;
				}
			}
			else {
				// Need to used the saved position on init
				data.scroller = {
					topRow: that.s.topRowFloat,
					baseScrollTop: that.s.baseScrollTop,
					baseRowTop: that.s.baseRowTop,
					scrollTop: that.s.lastScrollTop
				};
			}
		});

		dt.on('stateLoadParams.scroller', function (e, settings, data) {
			if (data.scroller !== undefined) {
				that.scrollToRow(data.scroller.topRow);
			}
		});

		if (loadedState && loadedState.scroller) {
			this.s.topRowFloat = loadedState.scroller.topRow;
			this.s.baseScrollTop = loadedState.scroller.baseScrollTop;
			this.s.baseRowTop = loadedState.scroller.baseRowTop;
		}

		this.measure(false);

		that.s.stateSaveThrottle = that.s.dt.oApi._fnThrottle(function () {
			that.s.dtApi.state.save();
		}, 500);

		dt.on('init.scroller', function () {
			that.measure(false);

			// Setting to `jump` will instruct _draw to calculate the scroll top
			// position
			that.s.scrollType = 'jump';
			that._draw();

			// Update the scroller when the DataTable is redrawn
			dt.on('draw.scroller', function () {
				that._draw();
			});
		});

		// Set height before the draw happens, allowing everything else to update
		// on draw complete without worry for roder.
		dt.on('preDraw.dt.scroller', function () {
			that._scrollForce();
		});

		// Destructor
		dt.on('destroy.scroller', function () {
			$(window).off('resize.dt-scroller');
			$(that.dom.scroller).off('.dt-scroller');
			$(that.s.dt.nTable).off('.scroller');

			$(that.s.dt.nTableWrapper).removeClass('DTS');
			$('div.DTS_Loading', that.dom.scroller.parentNode).remove();

			that.dom.table.style.position = '';
			that.dom.table.style.top = '';
			that.dom.table.style.left = '';
		});
	},

	/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
	 * Private methods
	 */

	/**
	 * Automatic calculation of table row height. This is just a little tricky here as using
	 * initialisation DataTables has tale the table out of the document, so we need to create
	 * a new table and insert it into the document, calculate the row height and then whip the
	 * table out.
	 *  @returns {void}
	 *  @private
	 */
	_calcRowHeight: function () {
		var dt = this.s.dt;
		var origTable = dt.nTable;
		var nTable = origTable.cloneNode(false);
		var tbody = $('<tbody/>').appendTo(nTable);
		var container = $(
			'<div class="' +
				dt.oClasses.sWrapper +
				' DTS">' +
				'<div class="' +
				dt.oClasses.sScrollWrapper +
				'">' +
				'<div class="' +
				dt.oClasses.sScrollBody +
				'"></div>' +
				'</div>' +
				'</div>'
		);

		// Want 3 rows in the sizing table so :first-child and :last-child
		// CSS styles don't come into play - take the size of the middle row
		$('tbody tr:lt(4)', origTable).clone().appendTo(tbody);
		var rowsCount = $('tr', tbody).length;

		if (rowsCount === 1) {
			tbody.prepend('<tr><td>&#160;</td></tr>');
			tbody.append('<tr><td>&#160;</td></tr>');
		}
		else {
			for (; rowsCount < 3; rowsCount++) {
				tbody.append('<tr><td>&#160;</td></tr>');
			}
		}

		$('div.' + dt.oClasses.sScrollBody, container).append(nTable);

		// If initialised using `dom`, use the holding element as the insert point
		var insertEl = this.s.dt.nHolding || origTable.parentNode;

		if (!$(insertEl).is(':visible')) {
			insertEl = 'body';
		}

		// Remove form element links as they might select over others (particularly radio and checkboxes)
		container.find('input').removeAttr('name');

		container.appendTo(insertEl);
		this.s.heights.row = $('tr', tbody).eq(1).outerHeight();

		container.remove();
	},

	/**
	 * Draw callback function which is fired when the DataTable is redrawn. The main function of
	 * this method is to position the drawn table correctly the scrolling container for the rows
	 * that is displays as a result of the scrolling position.
	 *  @returns {void}
	 *  @private
	 */
	_draw: function () {
		var that = this,
			heights = this.s.heights,
			iScrollTop = this.dom.scroller.scrollTop,
			iTableHeight = $(this.s.dt.nTable).height(),
			displayStart = this.s.dt._iDisplayStart,
			displayLen = this.s.dt._iDisplayLength,
			displayEnd = this.s.dt.fnRecordsDisplay(),
			viewportEndY = iScrollTop + heights.viewport;

		// Disable the scroll event listener while we are updating the DOM
		this.s.skip = true;

		// If paging is reset
		if (
			(this.s.dt.bSorted || this.s.dt.bFiltered) &&
			displayStart === 0 &&
			!this.s.dt._drawHold
		) {
			this.s.topRowFloat = 0;
		}

		iScrollTop =
			this.s.scrollType === 'jump'
				? this._domain('virtualToPhysical', this.s.topRowFloat * heights.row)
				: iScrollTop;

		// Store positional information so positional calculations can be based
		// upon the current table draw position
		this.s.baseScrollTop = iScrollTop;
		this.s.baseRowTop = this.s.topRowFloat;

		// Position the table in the virtual scroller
		var tableTop = iScrollTop - (this.s.topRowFloat - displayStart) * heights.row;
		if (displayStart === 0) {
			tableTop = 0;
		}
		else if (displayStart + displayLen >= displayEnd) {
			tableTop = heights.scroll - iTableHeight;
		}
		else {
			var iTableBottomY = tableTop + iTableHeight;
			if (iTableBottomY < viewportEndY) {
				// The last row of the data is above the end of the viewport.
				// This means the background is visible, which is not what the user expects.
				var newTableTop = viewportEndY - iTableHeight;
				var diffPx = newTableTop - tableTop;
				this.s.baseScrollTop += diffPx + 1; // Update start row number in footer.
				tableTop = newTableTop; // Move table so last line of data is at the bottom of the viewport.
			}
		}

		this.dom.table.style.top = tableTop + 'px';

		/* Cache some information for the scroller */
		this.s.tableTop = tableTop;
		this.s.tableBottom = iTableHeight + this.s.tableTop;

		// Calculate the boundaries for where a redraw will be triggered by the
		// scroll event listener
		var boundaryPx = (iScrollTop - this.s.tableTop) * this.s.boundaryScale;
		this.s.redrawTop = iScrollTop - boundaryPx;
		this.s.redrawBottom =
			iScrollTop + boundaryPx > heights.scroll - heights.viewport - heights.row
				? heights.scroll - heights.viewport - heights.row
				: iScrollTop + boundaryPx;

		this.s.skip = false;

		if (that.s.ingnoreScroll) {
			// Restore the scrolling position that was saved by DataTable's state
			// saving Note that this is done on the second draw when data is Ajax
			// sourced, and the first draw when DOM soured
			if (
				this.s.dt.oFeatures.bStateSave &&
				this.s.dt.oLoadedState !== null &&
				typeof this.s.dt.oLoadedState.scroller != 'undefined'
			) {
				// A quirk of DataTables is that the draw callback will occur on an
				// empty set if Ajax sourced, but not if server-side processing.
				var ajaxSourced =
					(this.s.dt.sAjaxSource || that.s.dt.ajax) && !this.s.dt.oFeatures.bServerSide
						? true
						: false;

				if (
					(ajaxSourced && this.s.dt.iDraw >= 2) ||
					(!ajaxSourced && this.s.dt.iDraw >= 1)
				) {
					setTimeout(function () {
						$(that.dom.scroller).scrollTop(that.s.dt.oLoadedState.scroller.scrollTop);

						// In order to prevent layout thrashing we need another
						// small delay
						setTimeout(function () {
							that.s.ingnoreScroll = false;
						}, 0);
					}, 0);
				}
			}
			else {
				that.s.ingnoreScroll = false;
			}
		}

		// Because of the order of the DT callbacks, the info update will
		// take precedence over the one we want here. So a 'thread' break is
		// needed.  Only add the thread break if bInfo is set
		if (this.s.dt.oFeatures.bInfo) {
			setTimeout(function () {
				that._info.call(that);
			}, 0);
		}

		$(this.s.dt.nTable).triggerHandler('position.dts.dt', tableTop);

		// Hide the loading indicator
		if (this.dom.loader && this.s.loaderVisible) {
			this.dom.loader.css('display', 'none');
			this.s.loaderVisible = false;
		}
	},

	/**
	 * Convert from one domain to another. The physical domain is the actual
	 * pixel count on the screen, while the virtual is if we had browsers which
	 * had scrolling containers of infinite height (i.e. the absolute value)
	 *
	 *  @param {string} dir Domain transform direction, `virtualToPhysical` or
	 *    `physicalToVirtual`
	 *  @returns {number} Calculated transform
	 *  @private
	 */
	_domain: function (dir, val) {
		var heights = this.s.heights;
		var diff;
		var magic = 10000; // the point at which the non-linear calculations start to happen

		// If the virtual and physical height match, then we use a linear
		// transform between the two, allowing the scrollbar to be linear
		if (heights.virtual === heights.scroll) {
			return val;
		}

		// In the first 10k pixels and the last 10k pixels, we want the scrolling
		// to be linear. After that it can be non-linear. It would be unusual for
		// anyone to mouse wheel through that much.
		if (val < magic) {
			return val;
		}
		else if (dir === 'virtualToPhysical' && val >= heights.virtual - magic) {
			diff = heights.virtual - val;
			return heights.scroll - diff;
		}
		else if (dir === 'physicalToVirtual' && val >= heights.scroll - magic) {
			diff = heights.scroll - val;
			return heights.virtual - diff;
		}

		// Otherwise, we want a non-linear scrollbar to take account of the
		// redrawing regions at the start and end of the table, otherwise these
		// can stutter badly - on large tables 30px (for example) scroll might
		// be hundreds of rows, so the table would be redrawing every few px at
		// the start and end. Use a simple linear eq. to stop this, effectively
		// causing a kink in the scrolling ratio. It does mean the scrollbar is
		// non-linear, but with such massive data sets, the scrollbar is going
		// to be a best guess anyway
		var m = (heights.virtual - magic - magic) / (heights.scroll - magic - magic);
		var c = magic - m * magic;

		return dir === 'virtualToPhysical' ? (val - c) / m : m * val + c;
	},

	/**
	 * Update any information elements that are controlled by the DataTable based on the scrolling
	 * viewport and what rows are visible in it. This function basically acts in the same way as
	 * _fnUpdateInfo in DataTables, and effectively replaces that function.
	 *  @returns {void}
	 *  @private
	 */
	_info: function () {
		if (!this.s.dt.oFeatures.bInfo) {
			return;
		}

		var dt = this.s.dt,
			language = dt.oLanguage,
			iScrollTop = this.dom.scroller.scrollTop,
			iStart = Math.floor(this.pixelsToRow(iScrollTop, false, this.s.ani) + 1),
			iMax = dt.fnRecordsTotal(),
			iTotal = dt.fnRecordsDisplay(),
			iPossibleEnd = Math.ceil(
				this.pixelsToRow(iScrollTop + this.s.heights.viewport, false, this.s.ani)
			),
			iEnd = iTotal < iPossibleEnd ? iTotal : iPossibleEnd,
			sStart = dt.fnFormatNumber(iStart),
			sEnd = dt.fnFormatNumber(iEnd),
			sMax = dt.fnFormatNumber(iMax),
			sTotal = dt.fnFormatNumber(iTotal),
			sOut;

		if (dt.fnRecordsDisplay() === 0 && dt.fnRecordsDisplay() == dt.fnRecordsTotal()) {
			/* Empty record set */
			sOut = language.sInfoEmpty + language.sInfoPostFix;
		}
		else if (dt.fnRecordsDisplay() === 0) {
			/* Empty record set after filtering */
			sOut =
				language.sInfoEmpty +
				' ' +
				language.sInfoFiltered.replace('_MAX_', sMax) +
				language.sInfoPostFix;
		}
		else if (dt.fnRecordsDisplay() == dt.fnRecordsTotal()) {
			/* Normal record set */
			sOut =
				language.sInfo
					.replace('_START_', sStart)
					.replace('_END_', sEnd)
					.replace('_MAX_', sMax)
					.replace('_TOTAL_', sTotal) + language.sInfoPostFix;
		}
		else {
			/* Record set after filtering */
			sOut =
				language.sInfo
					.replace('_START_', sStart)
					.replace('_END_', sEnd)
					.replace('_MAX_', sMax)
					.replace('_TOTAL_', sTotal) +
				' ' +
				language.sInfoFiltered.replace('_MAX_', dt.fnFormatNumber(dt.fnRecordsTotal())) +
				language.sInfoPostFix;
		}

		var callback = language.fnInfoCallback;
		if (callback) {
			sOut = callback.call(dt.oInstance, dt, iStart, iEnd, iMax, iTotal, sOut);
		}

		var n = dt.aanFeatures.i;
		if (typeof n != 'undefined') {
			for (var i = 0, iLen = n.length; i < iLen; i++) {
				$(n[i]).html(sOut);
			}
		}

		// DT doesn't actually (yet) trigger this event, but it will in future
		$(dt.nTable).triggerHandler('info.dt');
	},

	/**
	 * Parse CSS height property string as number
	 *
	 * An attempt is made to parse the string as a number. Currently supported units are 'px',
	 * 'vh', and 'rem'. 'em' is partially supported; it works as long as the parent element's
	 * font size matches the body element. Zero is returned for unrecognized strings.
	 *  @param {string} cssHeight CSS height property string
	 *  @returns {number} height
	 *  @private
	 */
	_parseHeight: function (cssHeight) {
		var height;
		var matches = /^([+-]?(?:\d+(?:\.\d+)?|\.\d+))(px|em|rem|vh)$/.exec(cssHeight);

		if (matches === null) {
			return 0;
		}

		var value = parseFloat(matches[1]);
		var unit = matches[2];

		if (unit === 'px') {
			height = value;
		}
		else if (unit === 'vh') {
			height = (value / 100) * $(window).height();
		}
		else if (unit === 'rem') {
			height = value * parseFloat($(':root').css('font-size'));
		}
		else if (unit === 'em') {
			height = value * parseFloat($('body').css('font-size'));
		}

		return height ? height : 0;
	},

	/**
	 * Scrolling function - fired whenever the scrolling position is changed.
	 * This method needs to use the stored values to see if the table should be
	 * redrawn as we are moving towards the end of the information that is
	 * currently drawn or not. If needed, then it will redraw the table based on
	 * the new position.
	 *  @returns {void}
	 *  @private
	 */
	_scroll: function () {
		var that = this,
			heights = this.s.heights,
			iScrollTop = this.dom.scroller.scrollTop,
			iTopRow;

		if (this.s.skip) {
			return;
		}

		if (this.s.ingnoreScroll) {
			return;
		}

		if (iScrollTop === this.s.lastScrollTop) {
			return;
		}

		/* If the table has been sorted or filtered, then we use the redraw that
		 * DataTables as done, rather than performing our own
		 */
		if (this.s.dt.bFiltered || this.s.dt.bSorted) {
			this.s.lastScrollTop = 0;
			return;
		}

		/* Update the table's information display for what is now in the viewport */
		this._info();

		/* We don't want to state save on every scroll event - that's heavy
		 * handed, so use a timeout to update the state saving only when the
		 * scrolling has finished
		 */
		clearTimeout(this.s.stateTO);
		this.s.stateTO = setTimeout(function () {
			that.s.dtApi.state.save();
		}, 250);

		this.s.scrollType =
			Math.abs(iScrollTop - this.s.lastScrollTop) > heights.viewport ? 'jump' : 'cont';

		this.s.topRowFloat =
			this.s.scrollType === 'cont'
				? this.pixelsToRow(iScrollTop, false, false)
				: this._domain('physicalToVirtual', iScrollTop) / heights.row;

		if (this.s.topRowFloat < 0) {
			this.s.topRowFloat = 0;
		}

		/* Check if the scroll point is outside the trigger boundary which would required
		 * a DataTables redraw
		 */
		if (
			this.s.forceReposition ||
			iScrollTop < this.s.redrawTop ||
			iScrollTop > this.s.redrawBottom
		) {
			var preRows = Math.ceil(((this.s.displayBuffer - 1) / 2) * this.s.viewportRows);

			iTopRow = parseInt(this.s.topRowFloat, 10) - preRows;
			this.s.forceReposition = false;

			if (iTopRow <= 0) {
				/* At the start of the table */
				iTopRow = 0;
			}
			else if (iTopRow + this.s.dt._iDisplayLength > this.s.dt.fnRecordsDisplay()) {
				/* At the end of the table */
				iTopRow = this.s.dt.fnRecordsDisplay() - this.s.dt._iDisplayLength;
				if (iTopRow < 0) {
					iTopRow = 0;
				}
			}
			else if (iTopRow % 2 !== 0) {
				// For the row-striping classes (odd/even) we want only to start
				// on evens otherwise the stripes will change between draws and
				// look rubbish
				iTopRow++;
			}

			// Store calcuated value, in case the following condition is not met, but so
			// that the draw function will still use it.
			this.s.targetTop = iTopRow;

			if (iTopRow != this.s.dt._iDisplayStart) {
				/* Cache the new table position for quick lookups */
				this.s.tableTop = $(this.s.dt.nTable).offset().top;
				this.s.tableBottom = $(this.s.dt.nTable).height() + this.s.tableTop;

				var draw = function () {
					that.s.dt._iDisplayStart = that.s.targetTop;
					that.s.dt.oApi._fnDraw(that.s.dt);
				};

				/* Do the DataTables redraw based on the calculated start point - note that when
				 * using server-side processing we introduce a small delay to not DoS the server...
				 */
				if (this.s.dt.oFeatures.bServerSide) {
					this.s.forceReposition = true;

					clearTimeout(this.s.drawTO);
					this.s.drawTO = setTimeout(draw, this.s.serverWait);
				}
				else {
					draw();
				}

				if (this.dom.loader && !this.s.loaderVisible) {
					this.dom.loader.css('display', 'block');
					this.s.loaderVisible = true;
				}
			}
		}
		else {
			this.s.topRowFloat = this.pixelsToRow(iScrollTop, false, true);
		}

		this.s.lastScrollTop = iScrollTop;
		this.s.stateSaveThrottle();

		if (this.s.scrollType === 'jump' && this.s.mousedown) {
			this.s.labelVisible = true;
		}
		if (this.s.labelVisible) {
			var labelFactor =
				(heights.viewport - heights.labelHeight - heights.xbar) / heights.scroll;

			this.dom.label
				.html(this.s.dt.fnFormatNumber(parseInt(this.s.topRowFloat, 10) + 1))
				.css('top', iScrollTop + iScrollTop * labelFactor)
				.css('display', 'block');
		}
	},

	/**
	 * Force the scrolling container to have height beyond that of just the
	 * table that has been drawn so the user can scroll the whole data set.
	 *
	 * Note that if the calculated required scrolling height exceeds a maximum
	 * value (1 million pixels - hard-coded) the forcing element will be set
	 * only to that maximum value and virtual / physical domain transforms will
	 * be used to allow Scroller to display tables of any number of records.
	 *  @returns {void}
	 *  @private
	 */
	_scrollForce: function () {
		var heights = this.s.heights;
		var max = 1000000;

		heights.virtual = heights.row * this.s.dt.fnRecordsDisplay();
		heights.scroll = heights.virtual;

		if (heights.scroll > max) {
			heights.scroll = max;
		}

		// Minimum height so there is always a row visible (the 'no rows found'
		// if reduced to zero filtering)
		this.dom.force.style.height =
			heights.scroll > this.s.heights.row ? heights.scroll + 'px' : this.s.heights.row + 'px';
	}
});

/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 * Statics
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

/**
 * Scroller default settings for initialisation
 *  @namespace
 *  @name Scroller.defaults
 *  @static
 */
Scroller.defaults = {
	/**
	 * Scroller uses the boundary scaling factor to decide when to redraw the table - which it
	 * typically does before you reach the end of the currently loaded data set (in order to
	 * allow the data to look continuous to a user scrolling through the data). If given as 0
	 * then the table will be redrawn whenever the viewport is scrolled, while 1 would not
	 * redraw the table until the currently loaded data has all been shown. You will want
	 * something in the middle - the default factor of 0.5 is usually suitable.
	 *  @type     float
	 *  @default  0.5
	 *  @static
	 */
	boundaryScale: 0.5,

	/**
	 * The display buffer is what Scroller uses to calculate how many rows it should pre-fetch
	 * for scrolling. Scroller automatically adjusts DataTables' display length to pre-fetch
	 * rows that will be shown in "near scrolling" (i.e. just beyond the current display area).
	 * The value is based upon the number of rows that can be displayed in the viewport (i.e.
	 * a value of 1), and will apply the display range to records before before and after the
	 * current viewport - i.e. a factor of 3 will allow Scroller to pre-fetch 1 viewport's worth
	 * of rows before the current viewport, the current viewport's rows and 1 viewport's worth
	 * of rows after the current viewport. Adjusting this value can be useful for ensuring
	 * smooth scrolling based on your data set.
	 *  @type     int
	 *  @default  7
	 *  @static
	 */
	displayBuffer: 9,

	/**
	 * Show (or not) the loading element in the background of the table. Note that you should
	 * include the dataTables.scroller.css file for this to be displayed correctly.
	 *  @type     boolean
	 *  @default  false
	 *  @static
	 */
	loadingIndicator: false,

	/**
	 * Scroller will attempt to automatically calculate the height of rows for it's internal
	 * calculations. However the height that is used can be overridden using this parameter.
	 *  @type     int|string
	 *  @default  auto
	 *  @static
	 */
	rowHeight: 'auto',

	/**
	 * When using server-side processing, Scroller will wait a small amount of time to allow
	 * the scrolling to finish before requesting more data from the server. This prevents
	 * you from DoSing your own server! The wait time can be configured by this parameter.
	 *  @type     int
	 *  @default  200
	 *  @static
	 */
	serverWait: 200
};

Scroller.oDefaults = Scroller.defaults;

/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 * Constants
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

/**
 * Scroller version
 *  @type      String
 *  @default   See code
 *  @name      Scroller.version
 *  @static
 */
Scroller.version = '2.2.0';

/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 * Initialisation
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

// Attach a listener to the document which listens for DataTables initialisation
// events so we can automatically initialise
$(document).on('preInit.dt.dtscroller', function (e, settings) {
	if (e.namespace !== 'dt') {
		return;
	}

	var init = settings.oInit.scroller;
	var defaults = DataTable.defaults.scroller;

	if (init || defaults) {
		var opts = $.extend({}, init, defaults);

		if (init !== false) {
			new Scroller(settings, opts);
		}
	}
});

// Attach Scroller to DataTables so it can be accessed as an 'extra'
$.fn.dataTable.Scroller = Scroller;
$.fn.DataTable.Scroller = Scroller;

// DataTables 1.10 API method aliases
var Api = $.fn.dataTable.Api;

Api.register('scroller()', function () {
	return this;
});

// Undocumented and deprecated - is it actually useful at all?
Api.register('scroller().rowToPixels()', function (rowIdx, intParse, virtual) {
	var ctx = this.context;

	if (ctx.length && ctx[0].oScroller) {
		return ctx[0].oScroller.rowToPixels(rowIdx, intParse, virtual);
	}
	// undefined
});

// Undocumented and deprecated - is it actually useful at all?
Api.register('scroller().pixelsToRow()', function (pixels, intParse, virtual) {
	var ctx = this.context;

	if (ctx.length && ctx[0].oScroller) {
		return ctx[0].oScroller.pixelsToRow(pixels, intParse, virtual);
	}
	// undefined
});

// `scroller().scrollToRow()` is undocumented and deprecated. Use `scroller.toPosition()
Api.register(['scroller().scrollToRow()', 'scroller.toPosition()'], function (idx, ani) {
	this.iterator('table', function (ctx) {
		if (ctx.oScroller) {
			ctx.oScroller.scrollToRow(idx, ani);
		}
	});

	return this;
});

Api.register('row().scrollTo()', function (ani) {
	var that = this;

	this.iterator('row', function (ctx, rowIdx) {
		if (ctx.oScroller) {
			var displayIdx = that
				.rows({ order: 'applied', search: 'applied' })
				.indexes()
				.indexOf(rowIdx);

			ctx.oScroller.scrollToRow(displayIdx, ani);
		}
	});

	return this;
});

Api.register('scroller.measure()', function (redraw) {
	this.iterator('table', function (ctx) {
		if (ctx.oScroller) {
			ctx.oScroller.measure(redraw);
		}
	});

	return this;
});

Api.register('scroller.page()', function () {
	var ctx = this.context;

	if (ctx.length && ctx[0].oScroller) {
		return ctx[0].oScroller.pageInfo();
	}
	// undefined
});


export default DataTable;
