export interface Box {
  width: number;
  height: number;
}

export function box(width: number, height: number): Box {
  return { width, height };
}

export function constrain(subject: Box, container: Box): Box {
  if (subject.width < container.width && subject.height < container.height) {
    return subject;
  }

  const subjectAspectRatio = subject.width / subject.height;
  const containerAspectRatio = container.width / container.height;

  if (subjectAspectRatio < containerAspectRatio) {
    // ┌────┐
    // │    │ subject
    // └────┘
    // ┏━━━━━━━━━━━━┓
    // ┃            ┃ container
    // ┗━━━━━━━━━━━━┛
    const shrinkFactor = container.height / subject.height;
    return box(Math.ceil(subject.width * shrinkFactor), Math.ceil(subject.height * shrinkFactor));
  } else {
    // ┌───────────┐
    // │           │ subject
    // └───────────┘
    // ┏━━━━┓
    // ┃    ┃ container
    // ┗━━━━┛
    const shrinkFactor = container.width / subject.width;
    return box(Math.ceil(subject.width * shrinkFactor), Math.ceil(subject.height * shrinkFactor));
  }
}