pdf-lib/src/api/rotations.ts

Create and modify PDF files with JavaScript

import { assertIs, error } from 'src/utils';

export enum RotationTypes {
  Degrees = 'degrees',
  Radians = 'radians',
}

export interface Radians {
  type: RotationTypes.Radians;
  angle: number;
}

export interface Degrees {
  type: RotationTypes.Degrees;
  angle: number;
}

export type Rotation = Radians | Degrees;

export const radians = (radianAngle: number): Radians => {
  assertIs(radianAngle, 'radianAngle', ['number']);
  return { type: RotationTypes.Radians, angle: radianAngle };
};

export const degrees = (degreeAngle: number): Degrees => {
  assertIs(degreeAngle, 'degreeAngle', ['number']);
  return { type: RotationTypes.Degrees, angle: degreeAngle };
};

const { Radians, Degrees } = RotationTypes;

export const degreesToRadians = (degree: number) => (degree * Math.PI) / 180;
export const radiansToDegrees = (radian: number) => (radian * 180) / Math.PI;

// prettier-ignore
export const toRadians = (rotation: Rotation) => 
    rotation.type === Radians ? rotation.angle
  : rotation.type === Degrees ? degreesToRadians(rotation.angle)
  : error(`Invalid rotation: ${JSON.stringify(rotation)}`);

// prettier-ignore
export const toDegrees = (rotation: Rotation) => 
    rotation.type === Radians ? radiansToDegrees(rotation.angle)
  : rotation.type === Degrees ? rotation.angle
  : error(`Invalid rotation: ${JSON.stringify(rotation)}`);

export const reduceRotation = (degreeAngle = 0) => {
  const quadrants = (degreeAngle / 90) % 4;
  if (quadrants === 0) return 0;
  if (quadrants === 1) return 90;
  if (quadrants === 2) return 180;
  if (quadrants === 3) return 270;
  return 0; // `degreeAngle` is not a multiple of 90
};

export const adjustDimsForRotation = (
  dims: { width: number; height: number },
  degreeAngle = 0,
) => {
  const rotation = reduceRotation(degreeAngle);
  return rotation === 90 || rotation === 270
    ? { width: dims.height, height: dims.width }
    : { width: dims.width, height: dims.height };
};

export const rotateRectangle = (
  rectangle: {
    x: number;
    y: number;
    width: number;
    height: number;
  },
  borderWidth = 0,
  degreeAngle = 0,
) => {
  const { x, y, width: w, height: h } = rectangle;

  const r = reduceRotation(degreeAngle);
  const b = borderWidth / 2;

  // prettier-ignore
  if (r === 0) return { x: x - b, y: y - b, width: w, height: h };
  else if (r === 90) return { x: x - h + b, y: y - b, width: h, height: w };
  else if (r === 180) return { x: x - w + b, y: y - h + b, width: w, height: h };
  else if (r === 270) return { x: x - b, y: y - w + b, width: h, height: w };
  else return { x: x - b, y: y - b, width: w, height: h };
};