import sys
import pygame
from settings import Settings
from ship import Ship
from bullet import Bullet
from pygame.sprite import Group


class AlienInvasion:
  """Overall class to manage game assets and behavior."""

  def __init__(self):
    pygame.init()
    self.clock = pygame.time.Clock()
    self.settings = Settings()
    self.screen = pygame.display.set_mode((0,0), pygame.FULLSCREEN)
    self.settings.screen_width = self.screen.get_rect().width
    self.settings.screen_height = self.screen.get_rect().height
    pygame.display.set_caption("Alien Invasion")
    self.bg_color = self.settings.bg_color
    self.ship = Ship(self)
    self.bullets = Group()

  def run_game(self):
    """Start the main loop for the game."""
    while True:
      # Check for events and update the game state.
      self._check_events()
      self.ship.update()
      self._update_bullets()
      # Redraw the screen during each pass through the loop.
      self._update_screen()
      self.clock.tick(60)

  def _check_events(self):
    """Respond to keypresses and mouse events."""
    for event in pygame.event.get():
      if event.type == pygame.QUIT:
        sys.exit()
      elif event.type == pygame.KEYDOWN:
        self._check_keydown_events(event)
      elif event.type == pygame.KEYUP:
        self._check_keyup_events(event)

  def _check_keydown_events(self, event):
    """Respond to key presses."""
    if event.key == pygame.K_RIGHT:
      self.ship.moving_right = True
    elif event.key == pygame.K_LEFT:
      self.ship.moving_left = True
    elif event.key == pygame.K_q:
      sys.exit()
    elif event.key == pygame.K_SPACE:
      self._fire_bullet()

  def _check_keyup_events(self, event):
    """Respond to key releases."""
    if event.key == pygame.K_RIGHT:
      self.ship.moving_right = False
    elif event.key == pygame.K_LEFT:
      self.ship.moving_left = False

  def _fire_bullet(self):
    """Fire a bullet if the limit is not reached."""
    if len(self.bullets) < self.settings.bullets_allowed:
      # Create a new bullet and add it to the bullets group.
      new_bullet = Bullet(self)
      self.bullets.add(new_bullet)

  def _update_bullets(self):
    """Update position of bullets and remove old bullets."""
    self.bullets.update()
    for bullet in self.bullets.copy():
      if bullet.rect.bottom <= 0:
        self.bullets.remove(bullet)

  def _update_screen(self):
    """Update images on the screen and flip to the new screen."""
    self.screen.fill(self.bg_color)
    for bullet in self.bullets.sprites():
      bullet.draw_bullet()
    self.ship.blitme()
    pygame.display.flip()

if __name__ == '__main__':
  # Make a game instance and run the game.
  ai = AlienInvasion()
  ai.run_game()