-- Enemys Test01
-- Last updated: <2017/11/24 02:54:51 +0900>

function love.load()
  -- init

  -- set filter
  love.graphics.setDefaultFilter("nearest", "nearest")

  scr_w = 640
  scr_h = 480
  canvas = love.graphics.newCanvas(scr_w, scr_h)

  -- get window width and height
  wdw_w, wdw_h = love.graphics.getDimensions()
  scr_scale = math.min((wdw_w / scr_w), (wdw_h / scr_h))
  scr_ofsx = (wdw_w - (scr_w * scr_scale)) / 2
  scr_ofsy = (wdw_h - (scr_h * scr_scale)) / 2

  -- load image
  bgimg = love.graphics.newImage("bg_640x480_02.png")
  enemy_img = love.graphics.newImage("enemy02.png")

  -- define enemy class
  Enemy = {}
  Enemy.new = function(x, y, dx, dy, xw, ang, angspd, img)
    local obj = {}
    obj.activate = true
    obj.x = x
    obj.y = y
    obj.dx = dx
    obj.dy = dy
    obj.bx = x
    obj.by = y
    obj.xw = xw
    obj.angle = ang
    obj.angspd = angspd
    obj.img = img
    obj.img_w = img:getWidth()
    obj.img_h = img:getHeight()
    setmetatable(obj, {__index = Enemy})
    return obj
  end

  Enemy.update = function(self, dt)
    if not self.activate then return end

    self.bx = self.bx + self.dx * dt
    self.y = self.y + self.dy * dt
    self.x = self.bx + self.xw * math.sin(math.rad(self.angle))
    self.angle = (self.angle + self.angspd * dt) % 360.0
    if self.y - self.img_h > scr_h then self.activate = false end
  end

  Enemy.draw = function(self)
    if not self.activate then return end

    local x = self.x - self.img_w / 2
    local y = self.y - self.img_h / 2
    local ang = math.rad(self.angle)
    local scale = 1.0
    local ox = self.img_w / 2
    local oy = self.img_h / 2
    love.graphics.draw(self.img, x, y, ang, scale, scale, ox, oy)
  end

  -- work
  enemys = {}
  born_timer = 0.0
  math.randomseed(0)

  -- framerate steady
  min_dt = 1 / 60
  next_time = love.timer.getTime()
end

function love.update(dt)
  -- update
  next_time = next_time + min_dt
  if dt > 1.0 then return end

  born_timer = born_timer + dt
  if born_timer >= 0.3 then
    -- enemy born
    born_timer = born_timer - 0.3
    x = math.random(scr_w)
    y = -32
    dx = 0
    dy = 40 + math.random(80)
    xw = 50
    ang = math.random(360)
    angspd = 240
    obj = Enemy.new(x, y, dx, dy, xw, ang, angspd, enemy_img)
    table.insert(enemys, obj)
  end

  -- move enemys
  for i, spr in ipairs(enemys) do
    spr:update(dt)
  end

  -- remove enemy
  local elen = #enemys
  for i=elen,1,-1 do
    if not enemys[i].activate then
      table.remove(enemys, i)
    end
  end
end

function love.draw()
  -- set canvas
  love.graphics.setCanvas(canvas)

  -- draw BG
  love.graphics.setColor(255, 255, 255)
  love.graphics.draw(bgimg, 0, 0)

  -- draw objects
  love.graphics.setColor(255, 255, 255)
  for i, spr in ipairs(enemys) do
    spr:draw()
  end

  -- unset canvas
  love.graphics.setCanvas()

  -- draw canvas to window
  love.graphics.setColor(255, 255, 255)
  love.graphics.draw(canvas, scr_ofsx, scr_ofsy, 0, scr_scale, scr_scale)

  love.graphics.print("FPS: "..tostring(love.timer.getFPS()), 10, 10)
  love.graphics.print("env: "..tostring(love.system.getOS()), 10, 40)
  love.graphics.print("enemys: "..tostring(#enemys), 10, 60)

  if love.system.getOS() == "Windows" then
    -- wait
    local cur_time = love.timer.getTime()
    if next_time <= cur_time then
      next_time = cur_time
    else
      love.timer.sleep(next_time - cur_time)
    end
  end
end

function love.keypressed(key, isrepeat)
  -- ESC to exit
  if key == "escape" then
    love.event.quit()
  end
end