bookhoard/web/src/reader/pdf/pdf-rotation.ts

// Handle rotated/landscape pages in PDFs
// Procedural implementation (no OOP)

interface PDFRotationState {
  rotations: Map<number, number>;
}

function createPDFRotation(): PDFRotationState {
  return {
    rotations: new Map(),
  };
}

async function loadPDFPageRotations(
  state: PDFRotationState,
  doc: any,
): Promise<PDFRotationState> {
  const rotations = new Map<number, number>();

  for (let pageNum = 1; pageNum <= doc.numPages; pageNum++) {
    const page = await doc.getPage(pageNum);
    const viewport = page.getViewport({ scale: 1 });
    const rotation = viewport.rotation;

    if (rotation !== 0) {
      rotations.set(pageNum, rotation);
    }
  }

  return { ...state, rotations };
}

function getPDFPageRotation(
  state: PDFRotationState,
  pageNumber: number,
): number {
  return state.rotations.get(pageNumber) || 0;
}

function hasPDFPageRotation(
  state: PDFRotationState,
  pageNumber: number,
): boolean {
  return state.rotations.has(pageNumber);
}

function applyPDFRotation(
  state: PDFRotationState,
  canvas: HTMLCanvasElement,
  pageNumber: number,
): void {
  const rotation = getPDFPageRotation(state, pageNumber);

  if (rotation === 0) return;

  const ctx = canvas.getContext("2d");
  if (!ctx) return;

  ctx.save();
  ctx.translate(canvas.width / 2, canvas.height / 2);
  ctx.rotate((rotation * Math.PI) / 180);
  ctx.translate(-canvas.width / 2, -canvas.height / 2);
  ctx.restore();
}

function getPDFAdjustedViewport(
  state: PDFRotationState,
  pageNumber: number,
  viewport: any,
): any {
  const rotation = getPDFPageRotation(state, pageNumber);

  if (rotation === 0 || rotation === 180) {
    return viewport;
  }

  return {
    ...viewport,
    width: viewport.height,
    height: viewport.width,
  };
}