export interface PdfPoint { x: number; y: number }
export interface ScreenPoint { x: number; y: number }

export interface PdfRect { x: number; y: number; width: number; height: number }
export interface ScreenRect { x: number; y: number; width: number; height: number }

export interface ViewportParams {
  scale: number;          // CSS zoom level (1.0 = 100%)
  rotation: number;       // 0, 90, 180, 270 (clockwise)
  canonicalWidth: number; // Unrotated CropBox width in PDF points
  canonicalHeight: number;// Unrotated CropBox height in PDF points
  dpr?: number;           // Backing-store density; never part of CSS geometry
}

export function pdfToScreen(p: PdfPoint, vp: ViewportParams): ScreenPoint {
  // Screen points are CSS pixels. Device-pixel-ratio only controls the PDF.js
  // backing canvas; including it here would make Fabric objects overflow the
  // CSS overlay on retina displays.
  const s = vp.scale;
  const { rotation, canonicalWidth: W, canonicalHeight: H } = vp;
  const { x, y } = p;
  
  const rot = ((rotation % 360) + 360) % 360;

  switch (rot) {
    case 0:   return { x: x * s, y: y * s };
    case 90:  return { x: (H - y) * s, y: x * s };
    case 180: return { x: (W - x) * s, y: (H - y) * s };
    case 270: return { x: y * s, y: (W - x) * s };
    default:  throw new Error(`Invalid rotation: ${rotation}`);
  }
}

export function screenToPdf(p: ScreenPoint, vp: ViewportParams): PdfPoint {
  const s = vp.scale;
  const { rotation, canonicalWidth: W, canonicalHeight: H } = vp;
  const sx = p.x / s;
  const sy = p.y / s;

  const rot = ((rotation % 360) + 360) % 360;

  switch (rot) {
    case 0:   return { x: sx, y: sy };
    case 90:  return { x: sy, y: H - sx };
    case 180: return { x: W - sx, y: H - sy };
    case 270: return { x: W - sy, y: sx };
    default:  throw new Error(`Invalid rotation: ${rotation}`);
  }
}

export function pdfRectToScreen(r: PdfRect, vp: ViewportParams): ScreenRect {
  const p1 = pdfToScreen({ x: r.x, y: r.y }, vp);
  const p2 = pdfToScreen({ x: r.x + r.width, y: r.y + r.height }, vp);

  return {
    x: Math.min(p1.x, p2.x),
    y: Math.min(p1.y, p2.y),
    width: Math.abs(p2.x - p1.x),
    height: Math.abs(p2.y - p1.y)
  };
}

export function screenRectToPdf(r: ScreenRect, vp: ViewportParams): PdfRect {
  const p1 = screenToPdf({ x: r.x, y: r.y }, vp);
  const p2 = screenToPdf({ x: r.x + r.width, y: r.y + r.height }, vp);

  return {
    x: Math.min(p1.x, p2.x),
    y: Math.min(p1.y, p2.y),
    width: Math.abs(p2.x - p1.x),
    height: Math.abs(p2.y - p1.y)
  };
}