class HitRecord
  def initialize(point, t, ray, out_normal, material)
    @point = point
    @t = t
    @front_face = ray.direction.dot(out_normal) < 0
    @normal = @front_face ? out_normal : -out_normal
    @material = material
  end

  attr_reader :point, :normal, :t, :front_face, :material
end

class Hittable
  def hit(ray, trange)
    nil
  end
end

class Hittables < Hittable
  def initialize
    clear
  end

  def clear
    @objects = []
  end

  def <<(object)
    @objects << object
  end

  def hit(ray, trange)
    rec = nil
    closest = trange.max

    @objects.each do |object|
      if trec = object.hit(ray, Interval.new(trange.min, closest))
        rec = trec
        closest = trec.t
      end
    end

    rec
  end
end

class Sphere < Hittable
  def initialize(centre, radius = 1, material)
    @centre = centre
    @radius = radius
    @material = material
  end

  attr_reader :centre, :radius

  def hit(ray, trange)
    oc = @centre - ray.origin
    a = ray.direction.mag_sqr
    h = ray.direction.dot(oc)
    c = oc.mag_sqr - @radius ** 2
    disc = h ** 2 - a * c
    
    return nil if disc < 0

    sqrtd = disc ** 0.5
    root = (h - sqrtd) / a
    if !trange.surround?(root)
      root = (h + sqrtd) / a
      if !trange.surround?(root)
        return nil
      end
    end

    t = root
    p = ray.at(t)
    o_n = (p - @centre) / @radius
    HitRecord.new(p, t, ray, o_n, @material)
  end
end