import pygame
import random

# Define some colors
BLACK    = (   0,   0,   0)
WHITE    = ( 255, 255, 255)
RED      = ( 255,   0,   0)

# This class represents the ball
# It derives from the "Sprite" class in Pygame
class Block(pygame.sprite.Sprite):

    # READ BEFORE USING:
    # This constructor lets you use any graphic:
    # my_sprite = Block("any_graphic.png")
    # But if you DON'T want any graphic, use the following instead:
    '''
    def __init__(self):
        super().__init__()

        self.image = pygame.image.load("my_graphic.png").convert()

        # Set background color to be transparent. Adjust to WHITE if your
        # background is WHITE.
        self.image.set_colorkey(BLACK)

        self.rect = self.image.get_rect()
    '''
    def __init__(self, filename):
        # Call the parent class (Sprite) constructor
        super().__init__()

        # Create an image of the block, and fill it with a color.
        # This could also be an image loaded from the disk.
        self.image = pygame.image.load(filename).convert()

        # Set background color to be transparent. Adjust to WHITE if your
        # background is WHITE.
        self.image.set_colorkey(BLACK)

        # Fetch the rectangle object that has the dimensions of the image
        # image.
        # Update the position of this object by setting the values
        # of rect.x and rect.y
        self.rect = self.image.get_rect()

# Initialize Pygame
pygame.init()

# Set the height and width of the screen
screen_width = 700
screen_height = 400
screen = pygame.display.set_mode([screen_width, screen_height])

# This is a list of 'sprites.' Each block in the program is
# added to this list. The list is managed by a class called 'Group.'
block_list = pygame.sprite.Group()

# This is a list of every sprite. All blocks and the player block as well.
all_sprites_list = pygame.sprite.Group()

for i in range(50):
    # This represents a block
    block = Block("alien.png")

    # Set a random location for the block
    block.rect.x = random.randrange(screen_width)
    block.rect.y = random.randrange(screen_height)

    # Add the block to the list of objects
    block_list.add(block)
    all_sprites_list.add(block)

# Create a RED player block
player = Block("ufo.png")
all_sprites_list.add(player)

# Hide the mouse cursor
pygame.mouse.set_visible(0)

#Loop until the user clicks the close button.
done = False

# Used to manage how fast the screen updates
clock = pygame.time.Clock()


# -------- Main Program Loop -----------
while not done:
    for event in pygame.event.get(): # User did something
        if event.type == pygame.QUIT: # If user clicked close
            done = True # Flag that we are done so we exit this loop

    # Clear the screen
    screen.fill(WHITE)

    # Get the current mouse position. This returns the position
    # as a list of two numbers.
    pos = pygame.mouse.get_pos()

    # Fetch the x and y out of the list,
       # just like we'd fetch letters out of a string.
    # Set the player object to the mouse location
    player.rect.x = pos[0]
    player.rect.y = pos[1]

    # See if the player block has collided with anything.
    blocks_hit_list = pygame.sprite.spritecollide(player, block_list, True)


    # Draw all the spites
    all_sprites_list.draw(screen)

    # Limit to 60 frames per second
    clock.tick(60)

    # Go ahead and update the screen with what we've drawn.
    pygame.display.flip()

pygame.quit()