local geom = {}

local function class(tbl)
   setmetatable(tbl, tbl)
   return tbl
end

-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--
-- point
--
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

geom.point = class{
   __call = function(this, x, y)
      local pt = {}
      pt.x = x
      pt.y = y
      setmetatable(pt, {__index=this})
      return pt
   end,

   distance_to = function(self, pt)
      local d_x = self.x - pt.x
      local d_y = self.y - pt.y
      return math.sqrt(d_x*d_x + d_y*d_y)
   end,
}


-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--
-- square
--
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

geom.square = class{
   __call = function(this, center, span)
      local square = {}
      square.center = center
      square.span = span
      square.x = this.axis_range(center.x, span/2)
      square.y = this.axis_range(center.y, span/2)
      setmetatable(square, {__index=this})
      return square
   end,

   axis_range = function(c, r) return {min=c-r, max=c+r} end,

   -- returns true if a point is inside of the square
   -- and false otherwise
   -- (x/y mininum exclusive, maximum inclusive)
   contains = function(self, point)
      local x_overlap =
	 (point.x > self.x.min) and (point.x <= self.x.max)
      local y_overlap =
	 (point.y > self.y.min) and (point.y <= self.y.max)

      if x_overlap and y_overlap then
	 return true
      end
      return false
   end,

   -- return an array of four squares covering the same
   -- area as their parent
   divide = function(self)
      local this = getmetatable(self).__index
      
      local x = self.center.x
      local y = self.center.y
      local d = self.span / 4
      
      return {
	 this(geom.point(x-d, y-d), d*2),
	 this(geom.point(x+d, y-d), d*2),
	 this(geom.point(x-d, y+d), d*2),
	 this(geom.point(x+d, y+d), d*2),
      }
   end
}

return geom