resize image and keep aspect ratio

get-new-image-size-by-aspect-ratio.ts

type OneRequiredOneOptional =
  | {desiredWidth: number; desiredHeight?: number}
  | {desiredWidth?: number; desiredHeight: number};

interface CommonProps {
  widthReadFromImage: number;
  heightReadFromImage: number;
}

type FullProps = CommonProps & OneRequiredOneOptional;

export const getNewImageSizeByAspectRatio = ({
  widthReadFromImage,
  heightReadFromImage,
  desiredWidth,
  desiredHeight,
}: FullProps) => {
  let ratio = 1;

  if (desiredWidth && desiredHeight) {
    ratio = Math.min(
      desiredWidth / widthReadFromImage,
      desiredHeight / heightReadFromImage,
    );
  } else if (desiredWidth) {
    ratio = desiredWidth / widthReadFromImage;
  } else if (desiredHeight) {
    ratio = desiredHeight / heightReadFromImage;
  }

  return {
    finalWidth: widthReadFromImage * ratio,
    finalHeight: heightReadFromImage * ratio,
  };
};