/**
 * @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 TableUtils from '../tableutils';
import { findAncestor, updateNumericAttribute } from './utils';
import { isSelectionRectangular, getSelectedTableCells } from '../utils/common';

/**
 * The merge cells command.
 *
 * The command is registered by {@link module:table/tableediting~TableEditing} as the `'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() {
		const selectedTableCells = getSelectedTableCells( this.editor.model.document.selection );
		this.isEnabled = isSelectionRectangular( selectedTableCells, 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 merged into the first one.
			const firstTableCell = selectedTableCells.shift();

			// Set the selection in cell that other cells are being merged to prevent model-selection-range-intersects error in undo.
			// See https://github.com/ckeditor/ckeditor5/issues/6634.
			// May be fixed by: https://github.com/ckeditor/ckeditor5/issues/6639.
			writer.setSelection( firstTableCell, 0 );

			// Update target cell dimensions.
			const { mergeWidth, mergeHeight } = getMergeDimensions( firstTableCell, selectedTableCells, tableUtils );
			updateNumericAttribute( 'colspan', mergeWidth, firstTableCell, writer );
			updateNumericAttribute( 'rowspan', mergeHeight, firstTableCell, writer );

			const emptyRowsIndexes = [];

			for ( const tableCell of selectedTableCells ) {
				const tableRow = tableCell.parent;

				mergeTableCells( tableCell, firstTableCell, writer );

				if ( !tableRow.childCount ) {
					emptyRowsIndexes.push( tableRow.index );
				}
			}

			if ( emptyRowsIndexes.length ) {
				const table = findAncestor( 'table', firstTableCell );

				emptyRowsIndexes.reverse().forEach( row => tableUtils.removeRows( table, { at: row, batch: writer.batch } ) );
			}

			writer.setSelection( firstTableCell, 'in' );
		} );
	}
}

// Merges two table cells. It will ensure that after merging cells with empty paragraphs the resulting 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;
}

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 );
}
