-- Gist accompanying https://alloca.space/blog/lua-lang.html
--
-- Build and Run
-- -------------
--
-- 1. Install https://love2d.org on your system
--
-- 2. Run with:
--
--    love .


-- Constants

SCREEN_WIDTH = 640
SCREEN_HEIGHT = 480
BALL_SPEED = 200
BALL_RADIUS = 50

-- Objects

local background = {
   ["color"] = {
      ["r"] = 0x08 / 255,
      ["g"] = 0x18 / 255,
      ["b"] = 0x29 / 255,
   }
}

local ball = {
   position = {
      ["x"] = SCREEN_WIDTH/3,
      ["y"] = SCREEN_HEIGHT/3,
   },
   direction = {
      ["x"] = 1,
      ["y"] = 1,
   },
   color = {
      ["r"] = 0xf9 / 255,
      ["g"] = 0x92 / 255,
      ["b"] = 0x26 / 255,
   },
   ["radius"] = BALL_RADIUS,
}

-- Main

function love.load()
   love.window.setMode(SCREEN_WIDTH, SCREEN_HEIGHT, {vsync=true,msaa=4})
end

function love.update()
   updateBall(ball)
end

function love.draw()
   love.graphics.clear(background.color.r, background.color.g, background.color.b, 255, true, true)

   love.graphics.setColor(ball.color.r, ball.color.g, ball.color.b)
   love.graphics.circle("fill", ball.position.x, ball.position.y, ball.radius)
end

-- Update

function updateBall(ball)
   applyKeys(ball)
   swingBall(ball)
end

function applyKeys(ball)
   if love.keyboard.isDown("d") then ball.direction.x = 1 end
   if love.keyboard.isDown("a") then ball.direction.x = -1 end
   if love.keyboard.isDown("s") then ball.direction.y = 1 end
   if love.keyboard.isDown("w") then ball.direction.y = -1 end
end

function swingBall(ball)
   local p, d = swing(ball.position.x, ball.direction.x, 0 + ball.radius, SCREEN_WIDTH - ball.radius)
   ball.position.x = p
   ball.direction.x = d

   local p, d = swing(ball.position.y, ball.direction.y, 0 + ball.radius, SCREEN_HEIGHT - ball.radius)
   ball.position.y = p
   ball.direction.y = d
end

function swing(position, direction, min, max)
   if (position <= min) then
      position = min
      direction = 1
   elseif (position >= max) then
      position = max
      direction = -1
   end

   local dt = love.timer.getDelta()
   position = position + (direction * BALL_SPEED * dt)
   return position, direction
end