Merge pull request #89 from ckeditor/t/13

Feature: Implemented the table post–fixer which bulletproofs the feature in various complex use–cases (e.g. pasting and collaboration). Closes #13.

package.json

@@ -17,6 +17,7 @@
   "devDependencies": {
     "@ckeditor/ckeditor5-editor-classic": "^11.0.0",
     "@ckeditor/ckeditor5-paragraph": "^10.0.2",
+    "@ckeditor/ckeditor5-undo": "^10.0.1",
     "@ckeditor/ckeditor5-utils": "^10.2.0",
     "eslint": "^4.15.0",
     "eslint-config-ckeditor5": "^1.0.7",

src/converters/table-post-fixer.js

@@ -0,0 +1,378 @@
+/**
+ * @license Copyright (c) 2003-2018, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md.
+ */
+
+/**
+ * @module table/converters/table-post-fixer
+ */
+
+import Position from '@ckeditor/ckeditor5-engine/src/model/position';
+import { getParentTable, updateNumericAttribute } from './../commands/utils';
+import TableWalker from './../tablewalker';
+
+/**
+ * Injects a table post-fixer into the model.
+ *
+ * The role of the table post-fixer is to ensure that the table rows have the correct structure
+ * after a {@link module:engine/model/model~Model#change `change()`} block was executed.
+ *
+ * The correct structure means that:
+ *
+ * * All table rows have the same size.
+ * * None of a table cells that extend vertically beyond their section (either header or body).
+ *
+ * If the table structure is not correct, the post-fixer will automatically correct it in two steps:
+ *
+ * 1. It will clip table cells that extends beyond it section.
+ * 2. It will add empty table cells to those rows which are narrower then the widest table row.
+ *
+ * ## Clipping overlapping table cells
+ *
+ * Such situation may occur when pasting a table (or part of a table) to the editor from external sources.
+ *
+ * For example, see the following table which has the cell (FOO) with the rowspan attribute (2):
+ *
+ *		<table headingRows="1">
+ *			<tableRow>
+ *				<tableCell rowspan="2">FOO</tableCell>
+ *				<tableCell colspan="2">BAR</tableCell>
+ *			</tableRow>
+ *			<tableRow>
+ *				<tableCell>BAZ</tableCell>
+ *				<tableCell>XYZ</tableCell>
+ *			</tableRow>
+ *		</table>
+ *
+ * will be rendered in the view as:
+ *
+ *		<table>
+ *			<thead>
+ *				<tr>
+ *					<td rowspan="2">FOO</td>
+ *					<td colspan="2">BAR</td>
+ *				</tr>
+ *			</thead>
+ *			<tbody>
+ *				<tr>
+ *					<td>BAZ<td>
+ *					<td>XYZ<td>
+ *				</tr>
+ *			</tbody>
+ *		</table>
+ *
+ * In the above example the table will be rendered as a table with two rows - one in the header and second one in the body.
+ * The table cell (FOO) cannot span over multiple rows as it would expand from the header to the body section.
+ * The `rowspan` attribute must be changed to (1). The value (1) is a default value of the `rowspan` attribute
+ * so the `rowspan` attribute will be removed from the model.
+ *
+ * The table cell with BAZ contents will be in the first column of the table.
+ *
+ * ## Adding missing table cells
+ *
+ * The table post-fixer will insert empty table cells to equalize table rows sizes (number of columns).
+ * The size of a table row is calculated by counting column spans of table cells - both horizontal (from the same row) and
+ * vertical (from rows above).
+ *
+ * In the above example, the table row in the body section of the table is narrower then the row from the header - it has two cells
+ * with the default colspan (1). The header row has one cell with colspan (1) and second with colspan (2).
+ * The table cell (FOO) does not expand beyond the head section (and as such will be fixed in the first step of this post-fixer).
+ * The post-fixer will add a missing table cell to the row in the body section of the table.
+ *
+ * The table from the above example will be fixed and rendered to the view as below:
+ *
+ *		<table>
+ *			<thead>
+ *				<tr>
+ *					<td rowspan="2">FOO</td>
+ *					<td colspan="2">BAR</td>
+ *				</tr>
+ *			</thead>
+ *			<tbody>
+ *				<tr>
+ *					<td>BAZ<td>
+ *					<td>XYZ<td>
+ *				</tr>
+ *			</tbody>
+ *		</table>
+ *
+ * ## Collaboration & Undo - Expectations vs post-fixer results
+ *
+ * The table post-fixer only ensures proper structure without deeper analysis of the nature of a change. As such, it might lead
+ * to a structure which was not intended by the user changes. In particular, it will also fix undo steps (in conjunction with collaboration)
+ * in which editor content might not return to the original state.
+ *
+ * This will usually happen when one or more users changes size of the table.
+ *
+ * As en example see a table below:
+ *
+ *		<table>
+ *			<tbody>
+ *				<tr>
+ *					<td>11</td>
+ *					<td>12</td>
+ *				</tr>
+ *				<tr>
+ *					<td>21<td>
+ *					<td>22<td>
+ *				</tr>
+ *			</tbody>
+ *		</table>
+ *
+ * and user actions:
+ *
+ * 1. Both user have table with two rows and two columns.
+ * 2. User A adds a column at the end of the table - this will insert empty table cells to two rows.
+ * 3. User B adds a row at the end of the table- this will insert a row with two empty table cells.
+ * 4. Both users will have a table as below:
+ *
+ *
+ *		<table>
+ *			<tbody>
+ *				<tr>
+ *					<td>11</td>
+ *					<td>12</td>
+ *					<td>(empty, inserted by A)</td>
+ *				</tr>
+ *				<tr>
+ *					<td>21</td>
+ *					<td>22</td>
+ *					<td>(empty, inserted by A)</td>
+ *				</tr>
+ *				<tr>
+ *					<td>(empty, inserted by B)</td>
+ *					<td>(empty, inserted by B)</td>
+ *				</tr>
+ *			</tbody>
+ *		</table>
+ *
+ * The last row is shorter then others so table post-fixer will add empty row to tha last row:
+ *
+ *		<table>
+ *			<tbody>
+ *				<tr>
+ *					<td>11</td>
+ *					<td>12</td>
+ *					<td>(empty, inserted by A)</td>
+ *				</tr>
+ *				<tr>
+ *					<td>21<td>
+ *					<td>22<td>
+ *					<td>(empty, inserted by A)</td>
+ *				</tr>
+ *				<tr>
+ *					<td>(empty, inserted by B)</td>
+ *					<td>(empty, inserted by B)</td>
+ *					<td>(empty, inserted by a post-fixer)</td>
+ *				</tr>
+ *			</tbody>
+ *		</table>
+ *
+ * Unfortunately undo doesn't know the nature of changes and depending which user will apply post-fixer changes undoing them might lead to
+ * broken table. If User B will undo inserting column to a table the undo engine will undo only operations of
+ * inserting empty cells to rows from initial table state (row 1 & 2) but the cell in post-fixed row will remain:
+ *
+ *		<table>
+ *			<tbody>
+ *				<tr>
+ *					<td>11</td>
+ *					<td>12</td>
+ *				</tr>
+ *				<tr>
+ *					<td>21</td>
+ *					<td>22</td>
+ *				</tr>
+ *				<tr>
+ *					<td>(empty, inserted by B)</td>
+ *					<td>(empty, inserted by B)</td>
+ *					<td>(empty, inserted by a post-fixer)</td>
+ *				</tr>
+ *			</tbody>
+ *		</table>
+ *
+ * After undo the table post-fixer will detect that two rows are shorter then other and will fix table to:
+ *
+ *		<table>
+ *			<tbody>
+ *				<tr>
+ *					<td>11</td>
+ *					<td>12</td>
+ *					<td>(empty, inserted by a post-fixer after undo)<td>
+ *				</tr>
+ *				<tr>
+ *					<td>21<td>
+ *					<td>22<td>
+ *					<td>(empty, inserted by a post-fixer after undo)<td>
+ *				</tr>
+ *				<tr>
+ *					<td>(empty, inserted by B)<td>
+ *					<td>(empty, inserted by B)<td>
+ *					<td>(empty, inserted by a post-fixer)<td>
+ *				</tr>
+ *			</tbody>
+ *		</table>
+ *
+ * @param {module:engine/model/model~Model} model
+ */
+export default function injectTablePostFixer( model ) {
+	model.document.registerPostFixer( writer => tablePostFixer( writer, model ) );
+}
+
+// The table post-fixer.
+//
+// @param {module:engine/model/writer~Writer} writer
+// @param {module:engine/model/model~Model} model
+function tablePostFixer( writer, model ) {
+	const changes = model.document.differ.getChanges();
+
+	let wasFixed = false;
+
+	// Do not analyze the same table more then once - may happen for multiple changes in the same table.
+	const analyzedTables = new Set();
+
+	for ( const entry of changes ) {
+		let table;
+
+		// Fix table on table insert.
+		if ( entry.name == 'table' && entry.type == 'insert' ) {
+			table = entry.position.nodeAfter;
+		}
+
+		// Fix table on adding/removing table cells and rows.
+		if ( entry.name == 'tableRow' || entry.name == 'tableCell' ) {
+			table = getParentTable( entry.position );
+		}
+
+		// Fix table on any table's attribute change - including attributes of table cells.
+		if ( isTableAttributeEntry( entry ) ) {
+			table = getParentTable( entry.range.start );
+		}
+
+		if ( table && !analyzedTables.has( table ) ) {
+			// Step 1: correct rowspans of table cells if necessary.
+			// The wasFixed flag should be true if any of tables in batch was fixed - might be more then one.
+			wasFixed = fixTableCellsRowspan( table, writer ) || wasFixed;
+			// Step 2: fix table rows sizes.
+			wasFixed = fixTableRowsSizes( table, writer ) || wasFixed;
+
+			analyzedTables.add( table );
+		}
+	}
+
+	return wasFixed;
+}
+
+// Fixes the invalid value of the rowspan attribute because a table cell cannot vertically extend beyond the table section it belongs to.
+//
+// @param {module:engine/model/element~Element} table
+// @param {module:engine/model/writer~Writer} writer
+// @returns {Boolean} Returns true if table was fixed.
+function fixTableCellsRowspan( table, writer ) {
+	let wasFixed = false;
+
+	const cellsToTrim = findCellsToTrim( table );
+
+	if ( cellsToTrim.length ) {
+		wasFixed = true;
+
+		for ( const data of cellsToTrim ) {
+			updateNumericAttribute( 'rowspan', data.rowspan, data.cell, writer, 1 );
+		}
+	}
+
+	return wasFixed;
+}
+
+// Makes all table rows in a table the same size.
+//
+// @param {module:engine/model/element~Element} table
+// @param {module:engine/model/writer~Writer} writer
+// @returns {Boolean} Returns true if table was fixed.
+function fixTableRowsSizes( table, writer ) {
+	let wasFixed = false;
+
+	const rowsLengths = getRowsLengths( table );
+	const tableSize = rowsLengths[ 0 ];
+
+	const isValid = Object.values( rowsLengths ).every( length => length === tableSize );
+
+	if ( !isValid ) {
+		const maxColumns = Object.values( rowsLengths ).reduce( ( prev, current ) => current > prev ? current : prev, 0 );
+
+		for ( const [ rowIndex, size ] of Object.entries( rowsLengths ) ) {
+			const columnsToInsert = maxColumns - size;
+
+			if ( columnsToInsert ) {
+				for ( let i = 0; i < columnsToInsert; i++ ) {
+					writer.insertElement( 'tableCell', Position.createAt( table.getChild( rowIndex ), 'end' ) );
+				}
+
+				wasFixed = true;
+			}
+		}
+	}
+
+	return wasFixed;
+}
+
+// Searches for the table cells that extends beyond the table section to which they belong to. It will return an array of objects
+// that holds table cells to be trimmed and correct value of a rowspan attribute to set.
+//
+// @param {module:engine/model/element~Element} table
+// @returns {Array.<{{cell, rowspan}}>}
+function findCellsToTrim( table ) {
+	const headingRows = parseInt( table.getAttribute( 'headingRows' ) || 0 );
+	const maxRows = table.childCount;
+
+	const cellsToTrim = [];
+
+	for ( const { row, rowspan, cell } of new TableWalker( table ) ) {
+		// Skip cells that do not expand over its row.
+		if ( rowspan < 2 ) {
+			continue;
+		}
+
+		const isInHeader = row < headingRows;
+
+		// Row limit is either end of header section or whole table as table body is after the header.
+		const rowLimit = isInHeader ? headingRows : maxRows;
+
+		// If table cell expands over its limit reduce it height to proper value.
+		if ( row + rowspan > rowLimit ) {
+			const newRowspan = rowLimit - row;
+
+			cellsToTrim.push( { cell, rowspan: newRowspan } );
+		}
+	}
+
+	return cellsToTrim;
+}
+
+// Returns an object with lengths of rows assigned to the corresponding row index.
+//
+// @param {module:engine/model/element~Element} table
+// @returns {Object}
+function getRowsLengths( table ) {
+	const lengths = {};
+
+	for ( const { row } of new TableWalker( table, { includeSpanned: true } ) ) {
+		if ( !lengths[ row ] ) {
+			lengths[ row ] = 0;
+		}
+
+		lengths[ row ] += 1;
+	}
+
+	return lengths;
+}
+
+// Checks if the differ entry for an attribute change is one of table's attributes.
+//
+// @param entry
+// @returns {Boolean}
+function isTableAttributeEntry( entry ) {
+	const isAttributeType = entry.type === 'attribute';
+	const key = entry.attributeKey;
+
+	return isAttributeType && ( key === 'headingRows' || key === 'colspan' || key === 'rowspan' );
+}