define([
	'dojo/_base/lang',
	'dojo/_base/declare',
	'dojo/_base/array',
	'dojo/dom-class',
	'dojo/on',
	'dojo/query',
	'dojo/dnd/Source'
], function (lang, declare, arrayUtil, domClass, on, query, DndSource) {
	var dndTypeRx = /(\d+)(?:-(\d+))?$/; // used to determine subrow from dndType

	// The following 2 functions are used by onDropInternal logic for
	// retrieving/modifying a given subRow.  The `match` variable in each is
	// expected to be the result of executing dndTypeRx on a subRow ID.

	function getMatchingSubRow(grid, match) {
		var hasColumnSets = match[2],
			rowOrSet = grid[hasColumnSets ? 'columnSets' : 'subRows'][match[1]];

		return hasColumnSets ? rowOrSet[match[2]] : rowOrSet;
	}

	function setMatchingSubRow(grid, match, subRow) {
		if (match[2]) {
			grid.columnSets[match[1]][match[2]] = subRow;
		}
		else {
			grid.subRows[match[1]] = subRow;
		}
	}

	// Builds a prefix for a dndtype value based on a grid id.
	function makeDndTypePrefix(gridId) {
		return 'dgrid-' + gridId + '-';
	}

	// Removes the grid id prefix from a dndtype value.  This allows the grid id to contain
	// a dash-number suffix.  This works only if a column is dropped on the grid from which it
	// originated.  Otherwise, a dash-number suffix will cause the regex to match on the wrong values.
	function stripIdPrefix(gridId, dndtype) {
		return dndtype.slice(makeDndTypePrefix(gridId).length);
	}

	var ColumnDndSource = declare(DndSource, {
		// summary:
		//		Custom dojo/dnd source extension configured specifically for
		//		dgrid column reordering.

		copyState: function () {
			return false; // never copy
		},

		checkAcceptance: function (source) {
			return source === this; // self-accept only
		},

		_legalMouseDown: function (evt) {
			// Overridden to prevent blocking ColumnResizer resize handles.
			return evt.target.className.indexOf('dgrid-resize-handle') > -1 ? false :
				this.inherited(arguments);
		},

		onDropInternal: function (nodes) {
			var grid = this.grid,
				match = dndTypeRx.exec(stripIdPrefix(grid.id, nodes[0].getAttribute('dndType'))),
				structureProperty = match[2] ? 'columnSets' : 'subRows',
				oldSubRow = getMatchingSubRow(grid, match),
				columns = grid.columns;

			// First, allow original DnD logic to place node in new location.
			this.inherited(arguments);

			if (!match) {
				return;
			}

			// Then, iterate through the header cells in their new order,
			// to populate a new row array to assign as a new sub-row to the grid.
			// (Wait until the next turn to avoid errors in Opera.)
			setTimeout(function () {
				var newSubRow = arrayUtil.map(nodes[0].parentNode.childNodes, function (col) {
						return columns[col.columnId];
					}),
					eventObject;

				setMatchingSubRow(grid, match, newSubRow);

				eventObject = {
					grid: grid,
					subRow: newSubRow,
					column: columns[nodes[0].columnId],
					bubbles: true,
					cancelable: true,
					// Set parentType to indicate this is the result of user interaction.
					parentType: 'dnd'
				};
				// Set columnSets or subRows depending on which the grid is using.
				eventObject[structureProperty] = grid[structureProperty];

				// Emit a custom event which passes the new structure.
				// Allow calling preventDefault() to cancel the reorder operation.
				if (on.emit(grid.domNode, 'dgrid-columnreorder', eventObject)) {
					// Event was not canceled - force processing of modified structure.
					grid.set(structureProperty, grid[structureProperty]);
				}
				else {
					// Event was canceled - revert the structure and re-render the header
					// (since the inherited logic invoked above will have shifted cells).
					setMatchingSubRow(grid, match, oldSubRow);
					grid.renderHeader();
					// After re-rendering the header, re-apply the sort arrow if needed.
					if (grid.sort.length) {
						grid.updateSortArrow(grid.sort);
					}
				}
			}, 0);
		}
	});

	var ColumnReorder = declare(null, {
		// summary:
		//		Extension allowing reordering of columns in a grid via drag'n'drop.
		//		Reordering of columns within the same subrow or columnset is also
		//		supported; between different ones is not.

		// columnDndConstructor: Function
		//		Constructor to call for instantiating DnD sources within the grid's
		//		header.
		columnDndConstructor: ColumnDndSource,

		_initSubRowDnd: function (subRow, dndType) {
			// summary:
			//		Initializes a dojo/dnd source for one subrow of a grid;
			//		this could be its only subrow, one of several, or a subrow within a
			//		columnset.

			var dndParent, c, len, col, th;

			for (c = 0, len = subRow.length; c < len; c++) {
				col = subRow[c];
				if (col.reorderable === false) {
					continue;
				}

				th = col.headerNode;
				// Add dojoDndItem class, and a dndType unique to this subrow.
				domClass.add(th, 'dojoDndItem');
				th.setAttribute('dndType', dndType);

				if (!dndParent) {
					dndParent = th.parentNode;
				}
			}

			if (dndParent) {
				this._columnDndSources.push(new this.columnDndConstructor(dndParent, {
					horizontal: true,
					grid: this
				}));
			}
			// (If dndParent wasn't set, no columns are draggable)
		},

		renderHeader: function () {
			var dndTypePrefix = makeDndTypePrefix(this.id),
				csLength, cs;

			this.inherited(arguments);

			// After header is rendered, set up a dnd source on each of its subrows.

			this._columnDndSources = [];

			if (this.columnSets) {
				// Iterate columnsets->subrows->columns.
				for (cs = 0, csLength = this.columnSets.length; cs < csLength; cs++) {
					arrayUtil.forEach(this.columnSets[cs], function (subRow, sr) {
						this._initSubRowDnd(subRow, dndTypePrefix + cs + '-' + sr);
					}, this);
				}
			}
			else {
				// Iterate subrows->columns.
				arrayUtil.forEach(this.subRows, function (subRow, sr) {
					this._initSubRowDnd(subRow, dndTypePrefix + sr);
				}, this);
			}
		},

		_destroyColumns: function () {
			if (this._columnDndSources) {
				// Destroy old dnd sources.
				arrayUtil.forEach(this._columnDndSources, function (source) {
					source.destroy();
				});
			}

			this.inherited(arguments);
		}
	});

	ColumnReorder.ColumnDndSource = ColumnDndSource;
	return ColumnReorder;
});