local class = require'r.class'
local Pos = require'r.pos'

-- in screen units

-- zoom is screen pixels per world unit
local Camera = class()
function Camera.make(cls,pos,zoom)
	pos = pos or Pos:make(0,0)
	zoom = zoom or 1
	return setmetatable({pos=pos,zoom=zoom},cls)
end
local function screen_offset()
	-- in screen units, not in world units !
	local W,H = love.graphics.getDimensions()
	return Pos:make(W/2,H/2)
end
function Camera.apply_trans(self)
	local so = screen_offset()

	-- centre (0,0) in the middle of the screen
	love.graphics.translate(so.x,so.y)

	-- apply camera transformations
	love.graphics.scale(self.zoom)
	love.graphics.translate(-self.pos.x,-self.pos.y)
end

function Camera.screen_to_world(self,pos)
	local so = screen_offset()
	return (pos-so)/self.zoom + self.pos
end
function Camera.world_to_screen(self,pos)
	local so = screen_offset()
	return (pos-self.pos) * self.zoom + so
end

function Camera.extents(self)
	local W,H = love.graphics.getDimensions()
	-- returns top left and bottom right pos's in world coords
	return self:screen_to_world(Pos:make(0,0)),
			self:screen_to_world(Pos:make(W,H))
end


return Camera