adding watermark to pdf using sharp.js & pdf-lib.js

watermark.ts

  async createWaterMark({
                          width,
                          height,
                          text,
                          fontSize,
                          fontColor,
                          opacity,
                        }: CreateWaterMarkDto) {
    const svg = `
      <svg width="${width}" height="${height}">
        <rect width="100%" height="100%" fill="transparent" />
        <text x="50%" y="50%"
              dominant-baseline="middle"
              text-anchor="middle"
              font-family="Arial,SimSun"
              font-size="${fontSize}"
              opacity="${opacity}"
              fill="${fontColor}">
          ${text}
        </text>
      </svg>
      `;
    return sharp(Buffer.from(svg)).png().toBuffer();
  }



  async addWaterMarkToPdf({
    buffer,
    watermarkImageBytes,
    watermarkOptions,
  }: AddWaterMarkToDocumentDto): Promise<Buffer> {
    const {
      opacity = 0.8,
      scale = 1,
    } = watermarkOptions;

    try {
      const pdfDoc = await PDFDocument.load(buffer);
      const pages = pdfDoc.getPages();

      const watermarkImage = await pdfDoc.embedPng(watermarkImageBytes);
      const { width: imgWidth, height: imgHeight } = watermarkImage.scale(scale);

      pages.forEach(page => {
        const { width, height } = page.getSize();
        const pageRotation = page.getRotation().angle;
        let x: number,
            y: number,
            rotation: number;
        switch (pageRotation) {
          case 0:
          default:
            x = 0;
            y = height - imgHeight;
            if (y < 0) y = 0;
            rotation = 0;
            break;
          case 90:
            x = width - imgHeight;  // wmHeight=20
            if (x < 0) x = 0;
            y = height;
            if (y > height) y = height;
            rotation = -90;
            break;
          case 180:
            x = width;
            y = imgHeight;
            if (x > width) x = width;
            if (y > height) y = height;
            rotation = -180;
            break;
          case 270:
            x = imgHeight;
            y = 0;
            rotation = -270;
            break;
        }
        page.drawImage(watermarkImage, {
          x,
          y,
          width: imgWidth,
          height: imgHeight,
          opacity,
          rotate: degrees(rotation),
        });
      });
      return Buffer.from(await pdfDoc.save());
    } catch (error) {
      const message = 'Error occurred while adding watermark to PDF';
      this.logger.error(message, error);
      throw new InternalServerErrorException(message);
    }
  }