:fix: handle rowSpan by convert between the virtual column index and the root index

src/file/table/table-row/table-row.ts

@@ -54,4 +54,44 @@ export class TableRow extends XmlComponent {
         // Offset because properties is also in root.
         this.root.splice(index + 1, 0, cell);
     }
+
+    public addCellToColumnIndex(cell: TableCell, columnIndex: number): void {
+        const rootIndex = this.columnIndexToRootIndex(columnIndex, true);
+        this.addCellToIndex(cell, rootIndex - 1);
+    }
+
+    public rootIndexToColumnIndex(rootIndex: number): number {
+        // convert the root index to the virtual column index
+        if (rootIndex < 1 || rootIndex >= this.root.length) {
+            throw new Error(`cell 'rootIndex' should between 1 to ${this.root.length - 1}`);
+        }
+        let colIdx = 0;
+        // Offset because properties is also in root.
+        for (let rootIdx = 1; rootIdx < rootIndex; rootIdx++) {
+            const cell = this.root[rootIdx] as TableCell;
+            colIdx += cell.options.columnSpan || 1;
+        }
+        return colIdx;
+    }
+
+    public columnIndexToRootIndex(columnIndex: number, allowEndNewCell: boolean = false): number {
+        // convert the virtual column index to the root index
+        // `allowEndNewCell` for get index to inert new cell
+        if (columnIndex < 0) {
+            throw new Error(`cell 'columnIndex' should not less than zero`);
+        }
+        let colIdx = 0;
+        // Offset because properties is also in root.
+        let rootIdx = 1;
+        const endRootIndex = allowEndNewCell ? this.root.length : this.root.length - 1;
+        while (colIdx <= columnIndex) {
+            if (rootIdx > endRootIndex) {
+                throw new Error(`cell 'columnIndex' should not great than ${colIdx - 1}`);
+            }
+            const cell = this.root[rootIdx] as TableCell;
+            rootIdx += 1;
+            colIdx += (cell && cell.options.columnSpan) || 1;
+        }
+        return rootIdx - 1;
+    }
 }