I/6123: The MergeTableCells command

src/commands/mergecellscommand.js

@@ -0,0 +1,241 @@
+/**
+ * @license Copyright (c) 2003-2020, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
+ */
+
+/**
+ * @module table/commands/mergecellscommand
+ */
+
+import Command from '@ckeditor/ckeditor5-core/src/command';
+import TableWalker from '../tablewalker';
+import { findAncestor, updateNumericAttribute } from './utils';
+import TableUtils from '../tableutils';
+import { getRowIndexes, getSelectedTableCells } from '../utils';
+
+/**
+ * The merge cells command.
+ *
+ * The command is registered by the {@link module:table/tableediting~TableEditing} as `'mergeTableCells'` editor command.
+ *
+ * For example, to merge selected table cells:
+ *
+ *		editor.execute( 'mergeTableCells' );
+ *
+ * @extends module:core/command~Command
+ */
+export default class MergeCellsCommand extends Command {
+	/**
+	 * @inheritDoc
+	 */
+	refresh() {
+		this.isEnabled = canMergeCells( this.editor.model.document.selection, this.editor.plugins.get( TableUtils ) );
+	}
+
+	/**
+	 * Executes the command.
+	 *
+	 * @fires execute
+	 */
+	execute() {
+		const model = this.editor.model;
+		const tableUtils = this.editor.plugins.get( TableUtils );
+
+		model.change( writer => {
+			const selectedTableCells = getSelectedTableCells( model.document.selection );
+
+			// All cells will be merge into the first one.
+			const firstTableCell = selectedTableCells.shift();
+
+			// This prevents the "model-selection-range-intersects" error, caused by removing row selected cells.
+			writer.setSelection( firstTableCell, 'on' );
+
+			// Update target cell dimensions.
+			const { mergeWidth, mergeHeight } = getMergeDimensions( firstTableCell, selectedTableCells, tableUtils );
+			updateNumericAttribute( 'colspan', mergeWidth, firstTableCell, writer );
+			updateNumericAttribute( 'rowspan', mergeHeight, firstTableCell, writer );
+
+			for ( const tableCell of selectedTableCells ) {
+				const tableRow = tableCell.parent;
+				mergeTableCells( tableCell, firstTableCell, writer );
+				removeRowIfEmpty( tableRow, writer );
+			}
+
+			writer.setSelection( firstTableCell, 'in' );
+		} );
+	}
+}
+
+// Properly removes the empty row from a table. Updates the `rowspan` attribute of cells that overlap the removed row.
+//
+// @param {module:engine/model/element~Element} row
+// @param {module:engine/model/writer~Writer} writer
+function removeRowIfEmpty( row, writer ) {
+	if ( row.childCount ) {
+		return;
+	}
+
+	const table = row.parent;
+	const removedRowIndex = table.getChildIndex( row );
+
+	for ( const { cell, row, rowspan } of new TableWalker( table, { endRow: removedRowIndex } ) ) {
+		const overlapsRemovedRow = row + rowspan - 1 >= removedRowIndex;
+
+		if ( overlapsRemovedRow ) {
+			updateNumericAttribute( 'rowspan', rowspan - 1, cell, writer );
+		}
+	}
+
+	writer.remove( row );
+}
+
+// Merges two table cells - will ensure that after merging cells with empty paragraphs the result table cell will only have one paragraph.
+// If one of the merged table cells is empty, the merged table cell will have contents of the non-empty table cell.
+// If both are empty, the merged table cell will have only one empty paragraph.
+//
+// @param {module:engine/model/element~Element} cellBeingMerged
+// @param {module:engine/model/element~Element} targetCell
+// @param {module:engine/model/writer~Writer} writer
+function mergeTableCells( cellBeingMerged, targetCell, writer ) {
+	if ( !isEmpty( cellBeingMerged ) ) {
+		if ( isEmpty( targetCell ) ) {
+			writer.remove( writer.createRangeIn( targetCell ) );
+		}
+
+		writer.move( writer.createRangeIn( cellBeingMerged ), writer.createPositionAt( targetCell, 'end' ) );
+	}
+
+	// Remove merged table cell.
+	writer.remove( cellBeingMerged );
+}
+
+// Checks if the passed table cell contains an empty paragraph.
+//
+// @param {module:engine/model/element~Element} tableCell
+// @returns {Boolean}
+function isEmpty( tableCell ) {
+	return tableCell.childCount == 1 && tableCell.getChild( 0 ).is( 'paragraph' ) && tableCell.getChild( 0 ).isEmpty;
+}
+
+// Checks if the selection contains mergeable cells.
+//
+// In a table below:
+//
+//   ┌───┬───┬───┬───┐
+//   │ a │ b │ c │ d │
+//   ├───┴───┼───┤   │
+//   │ e     │ f │   │
+//   ├       ├───┼───┤
+//   │       │ g │ h │
+//   └───────┴───┴───┘
+//
+// Valid selections are these which create a solid rectangle (without gaps), such as:
+//   - a, b (two horizontal cells)
+//   - c, f (two vertical cells)
+//   - a, b, e (cell "e" spans over four cells)
+//   - c, d, f (cell d spans over a cell in the row below)
+//
+// While an invalid selection would be:
+//   - a, c (cell "b" not selected creates a gap)
+//   - f, g, h (cell "d" spans over a cell from row of "f" cell - thus creates a gap)
+//
+// @param {module:engine/model/selection~Selection} selection
+// @param {module:table/tableUtils~TableUtils} tableUtils
+// @returns {boolean}
+function canMergeCells( selection, tableUtils ) {
+	const selectedTableCells = getSelectedTableCells( selection );
+
+	if ( selectedTableCells.length < 2 || !areCellInTheSameTableSection( selectedTableCells ) ) {
+		return false;
+	}
+
+	// A valid selection is a fully occupied rectangle composed of table cells.
+	// Below we will calculate the area of a selected table cells and the area of valid selection.
+	// The area of a valid selection is defined by top-left and bottom-right cells.
+	const rows = new Set();
+	const columns = new Set();
+
+	let areaOfSelectedCells = 0;
+
+	for ( const tableCell of selectedTableCells ) {
+		const { row, column } = tableUtils.getCellLocation( tableCell );
+		const rowspan = parseInt( tableCell.getAttribute( 'rowspan' ) || 1 );
+		const colspan = parseInt( tableCell.getAttribute( 'colspan' ) || 1 );
+
+		// Record row & column indexes of current cell.
+		rows.add( row );
+		columns.add( column );
+
+		// For cells that spans over multiple rows add also the last row that this cell spans over.
+		if ( rowspan > 1 ) {
+			rows.add( row + rowspan - 1 );
+		}
+
+		// For cells that spans over multiple columns add also the last column that this cell spans over.
+		if ( colspan > 1 ) {
+			columns.add( column + colspan - 1 );
+		}
+
+		areaOfSelectedCells += ( rowspan * colspan );
+	}
+
+	// We can only merge table cells that are in adjacent rows...
+	const areaOfValidSelection = getBiggestRectangleArea( rows, columns );
+
+	return areaOfValidSelection == areaOfSelectedCells;
+}
+
+// Calculates the area of a maximum rectangle that can span over provided row & column indexes.
+//
+// @param {Array.<Number>} rows
+// @param {Array.<Number>} columns
+// @returns {Number}
+function getBiggestRectangleArea( rows, columns ) {
+	const rowsIndexes = Array.from( rows.values() );
+	const columnIndexes = Array.from( columns.values() );
+
+	const lastRow = Math.max( ...rowsIndexes );
+	const firstRow = Math.min( ...rowsIndexes );
+	const lastColumn = Math.max( ...columnIndexes );
+	const firstColumn = Math.min( ...columnIndexes );
+
+	return ( lastRow - firstRow + 1 ) * ( lastColumn - firstColumn + 1 );
+}
+
+function areCellInTheSameTableSection( tableCells ) {
+	const table = findAncestor( 'table', tableCells[ 0 ] );
+
+	const rowIndexes = getRowIndexes( tableCells );
+	const headingRows = parseInt( table.getAttribute( 'headingRows' ) || 0 );
+
+	const firstCellIsInBody = rowIndexes.first > headingRows - 1;
+	const lastCellIsInBody = rowIndexes.last > headingRows - 1;
+
+	return firstCellIsInBody === lastCellIsInBody;
+}
+
+function getMergeDimensions( firstTableCell, selectedTableCells, tableUtils ) {
+	let maxWidthOffset = 0;
+	let maxHeightOffset = 0;
+
+	for ( const tableCell of selectedTableCells ) {
+		const { row, column } = tableUtils.getCellLocation( tableCell );
+
+		maxWidthOffset = getMaxOffset( tableCell, column, maxWidthOffset, 'colspan' );
+		maxHeightOffset = getMaxOffset( tableCell, row, maxHeightOffset, 'rowspan' );
+	}
+
+	// Update table cell span attribute and merge set selection on a merged contents.
+	const { row: firstCellRow, column: firstCellColumn } = tableUtils.getCellLocation( firstTableCell );
+
+	const mergeWidth = maxWidthOffset - firstCellColumn;
+	const mergeHeight = maxHeightOffset - firstCellRow;
+
+	return { mergeWidth, mergeHeight };
+}
+
+function getMaxOffset( tableCell, start, currentMaxOffset, which ) {
+	const dimensionValue = parseInt( tableCell.getAttribute( which ) || 1 );
+
+	return Math.max( currentMaxOffset, start + dimensionValue );
+}

src/commands/removerowcommand.js

@@ -11,7 +11,7 @@ import Command from '@ckeditor/ckeditor5-core/src/command';
 
 import TableWalker from '../tablewalker';
 import { findAncestor, updateNumericAttribute } from './utils';
-import { getSelectionAffectedTableCells } from '../utils';
+import { getRowIndexes, getSelectionAffectedTableCells } from '../utils';
 
 /**
  * The remove row command.
@@ -138,16 +138,6 @@ export default class RemoveRowCommand extends Command {
 	}
 }
 
-// Returns a helper object with first and last row index contained in given `referenceCells`.
-function getRowIndexes( referenceCells ) {
-	const allIndexesSorted = referenceCells.map( cell => cell.parent.index ).sort();
-
-	return {
-		first: allIndexesSorted[ 0 ],
-		last: allIndexesSorted[ allIndexesSorted.length - 1 ]
-	};
-}
-
 // Returns a cell that should be focused before removing the row, belonging to the same column as the currently focused cell.
 // * If the row was not the last one, the cell to focus will be in the row that followed it (before removal).
 // * If the row was the last one, the cell to focus will be in the row that preceded it (before removal).

src/tableediting.js

@@ -28,6 +28,7 @@ import RemoveRowCommand from './commands/removerowcommand';
 import RemoveColumnCommand from './commands/removecolumncommand';
 import SetHeaderRowCommand from './commands/setheaderrowcommand';
 import SetHeaderColumnCommand from './commands/setheadercolumncommand';
+import MergeCellsCommand from './commands/mergecellscommand';
 import { getTableCellsContainingSelection } from './utils';
 import TableUtils from '../src/tableutils';
 
@@ -131,6 +132,8 @@ export default class TableEditing extends Plugin {
 		editor.commands.add( 'splitTableCellVertically', new SplitCellCommand( editor, { direction: 'vertically' } ) );
 		editor.commands.add( 'splitTableCellHorizontally', new SplitCellCommand( editor, { direction: 'horizontally' } ) );
 
+		editor.commands.add( 'mergeTableCells', new MergeCellsCommand( editor ) );
+
 		editor.commands.add( 'mergeTableCellRight', new MergeCellCommand( editor, { direction: 'right' } ) );
 		editor.commands.add( 'mergeTableCellLeft', new MergeCellCommand( editor, { direction: 'left' } ) );
 		editor.commands.add( 'mergeTableCellDown', new MergeCellCommand( editor, { direction: 'down' } ) );

src/tableui.js

@@ -187,6 +187,14 @@ export default class TableUI extends Plugin {
 					}
 				},
 				{ type: 'separator' },
+				{
+					type: 'button',
+					model: {
+						commandName: 'mergeTableCells',
+						label: t( 'Merge cells' )
+					}
+				},
+				{ type: 'separator' },
 				{
 					type: 'button',
 					model: {

src/utils.js

@@ -137,6 +137,27 @@ export function getSelectionAffectedTableCells( selection ) {
 	return getTableCellsContainingSelection( selection );
 }
 
+/**
+ * Returns a helper object with `first` and `last` row index contained in given `tableCells`.
+ *
+ *		const selectedTableCells = getSelectedTableCells( editor.model.document.selection );
+ *
+ *		const { first, last } = getRowIndexes( selectedTableCells );
+ *
+ *		console.log( `Selected rows ${ first } to ${ last }` );
+ *
+ * @package {Array.<module:engine/model/element~Element>}
+ * @returns {Object} Returns an object with `first` and `last` table row indexes.
+ */
+export function getRowIndexes( tableCells ) {
+	const allIndexesSorted = tableCells.map( cell => cell.parent.index ).sort();
+
+	return {
+		first: allIndexesSorted[ 0 ],
+		last: allIndexesSorted[ allIndexesSorted.length - 1 ]
+	};
+}
+
 function sortRanges( rangesIterator ) {
 	return Array.from( rangesIterator ).sort( compareRangeOrder );
 }