const workbook = this.createWorkbook();
const sheet = workbook.addWorksheet();

/**                                                                                                        
 * Omitted code related to filling in the rows/columns for brevity 
 */                                                                      

const buffer = await workbook.xlsx.writeBuffer();
const withLabel = await this.setSensitivityLabel(buffer);
return new Blob([withLabel]);

  /**
   * Low-level method to manually modify the contents of the .xlsx archive so that it has our company's 'Internal' sensitivity label.
   * This is a workaround for the fact that ExcelJS does not support adding sensitivity labels.
   *
   * Steps:
   * 1. Load the contents of the xlsx file into a JSZip object (an xlsx file is just a zip file that has a specific file structure).
   * 2. Add a LabelInfo.xml file to the archive which specifies our 'Internal' sensitivity label.
   * 3. Update the Content_Types.xml file to register the LabelInfo.xml file as the correct content type.
   * 4. Add a relationship to the _rels/.rels file to link the LabelInfo.xml with the 'classificationlabels' relationship type.
   * 5. Output a new buffer with our modifications that we can use to create a new Blob.
   */
  private async setSensitivityLabel(buffer: ExcelJS.Buffer): Promise<Uint8Array> {
    const zip = await JSZip.loadAsync(buffer);
    const labelInfoPath = 'docMetadata/LabelInfo.xml';
    const contentTypesPath = '[Content_Types].xml';
    const relsPath = '_rels/.rels';

    // Follow the steps in the walkthrough to find the values you need to use here
    const labelId = 'REPLACE_ME';
    const siteId = 'REPLACE_ME';

    // Create an xml that specifies our sensitivity label
    this.createSensitivityLabelXml(zip, labelInfoPath);

    // Mark our LabelInfo.xml file as a valid content type
    await this.updateContentTypesXml(zip, contentTypesPath, labelInfoPath);

    // Use our LabelInfo.xml file as the classification label for this workbook
    await this.updateRelationships(zip, relsPath, labelInfoPath);

    // Create a new buffer with our modifications
    return zip.generateAsync({ type: 'uint8array' });
  }

  /**
   * Creates the LabelInfo.xml file with the sensitivity label information to mark the file as 'Internal'.
   */
  private createSensitivityLabelXml(zip: JSZip, labelInfoPath: string): void {
    const xml = `<?xml version="1.0" encoding="utf-8" standalone="yes"?><clbl:labelList xmlns:clbl="http://schemas.microsoft.com/office/2020/mipLabelMetadata"><clbl:label id="{${labelId}}" enabled="1" method="Privileged" siteId="{${siteId}" contentBits="0" removed="0" /></clbl:labelList>`;
    zip.file(labelInfoPath, xml);
  }

  /**
   * Adds the LabelInfo.xml file to the Content_Types.xml file.
   * This marks the LabelInfo.xml file as a classificationslabel type and allows it to be used in relationships.
   */
  private async updateContentTypesXml(zip: JSZip, contentTypesPath: string, labelInfoPath: string): Promise<void> {
    const contentTypesXml = await zip.file(contentTypesPath)!.async('text');
    if (!contentTypesXml.includes('application/vnd.microsoft.label+xml')) {
      const updatedTypesXml = contentTypesXml.replace(
        '</Types>',
        `<Override PartName="/${labelInfoPath}" ContentType="application/vnd.ms-office.classificationlabels+xml"/></Types>`,
      );

      zip.file(contentTypesPath, updatedTypesXml);
    }
  }

  /**
   * Adds a relationship to the _rels/.rels file to link the LabelInfo.xml with the 'classificationlabels' relationship type.
   * This is necessary for Excel to use the LabelInfo.xml file to apply the sensitivity label.
   */
  private async updateRelationships(zip: JSZip, relsPath: string, labelInfoPath: string): Promise<void> {
    const relsFile = zip.file(relsPath);
    if (relsFile) {
      const relsXml = await relsFile.async('text');

      // Ensure there's no duplicate relationship
      if (!relsXml.includes('classificationlabels')) {
        const insertIndex = relsXml.lastIndexOf('</Relationships>');
        const relId = `rId${Math.floor(Math.random() * 10000) + 100}`; // Avoid collisions
        const newRel = `  <Relationship Id="${relId}" Type="http://schemas.microsoft.com/office/2020/02/relationships/classificationlabels" Target="${labelInfoPath}"/>\n`;

        const updatedXml = relsXml.slice(0, insertIndex) + newRel + relsXml.slice(insertIndex);
        zip.file(relsPath, updatedXml);
      }
    }
  }