import unreachable from 'ts-unreachable'

type Shape =
  | { kind: 'square', size: number }
  | { kind: 'rectangle', width: number, height: number }
  | { kind: 'circle', radius: number }

function area (shape: Shape): number {
  if (shape.kind === 'square') {
    return shape.size ** 2
  }

  if (shape.kind === 'rectangle') {
    return shape.height * shape.width
  }

  if (shape.kind === 'circle') {
    return Math.PI * shape.radius ** 2
  }

  return unreachable(shape) // (1)
}