export const PROOF_WATERMARK_TEXT = 'MUSTER – nicht verkaufsfähig';

const WATERMARK_COLOR = '#808080';
const WATERMARK_OPACITY = 0.5;
const WATERMARK_FONT = 'Helvetica-Bold';
// The text runs along the label's diagonal; this share of it is covered.
const DIAGONAL_COVERAGE = 0.8;
// Never taller than this share of the label's height.
const MAX_HEIGHT_SHARE = 0.5;
const MEASURE_SIZE_PT = 10;

/**
 * Draws the proof stamp "MUSTER – nicht verkaufsfähig" over one label: grey,
 * half opaque, rotated along the label's diagonal and centred. Called once
 * per label, after its content. The graphics state is restored, so nothing
 * leaks into the next label.
 */
export function drawProofWatermark(
  doc: PDFKit.PDFDocument,
  originX: number,
  originY: number,
  widthPt: number,
  heightPt: number,
): void {
  const centerX = originX + widthPt / 2;
  const centerY = originY + heightPt / 2;
  const angleDeg = (Math.atan2(heightPt, widthPt) * 180) / Math.PI;

  doc.save();
  doc.font(WATERMARK_FONT).fontSize(MEASURE_SIZE_PT);
  const widthAtMeasureSize = doc.widthOfString(PROOF_WATERMARK_TEXT);
  const targetWidth = Math.hypot(widthPt, heightPt) * DIAGONAL_COVERAGE;
  const fontSize = Math.min(
    (MEASURE_SIZE_PT * targetWidth) / widthAtMeasureSize,
    heightPt * MAX_HEIGHT_SHARE,
  );
  const textWidth = (widthAtMeasureSize * fontSize) / MEASURE_SIZE_PT;

  doc.fillColor(WATERMARK_COLOR).fillOpacity(WATERMARK_OPACITY);
  doc.rotate(-angleDeg, { origin: [centerX, centerY] });
  doc.fontSize(fontSize);
  doc.text(
    PROOF_WATERMARK_TEXT,
    centerX - textWidth / 2,
    centerY - fontSize / 2,
    { lineBreak: false },
  );
  doc.restore();
}