import turtle
import random

WIDTH = 500
HEIGHT = 500
SNAKE_CELL_SIZE = 20
FOOD_SIZE = 10
SQUARE_SIZE = 20 # Default size of turtle "square" shape
DELAY = 200 # milliseconds

def move_snake():
    for index in range(len(segments) - 1, 0, -1):
        x = segments[index - 1].xcor()
        y = segments[index - 1].ycor()
        segments[index].goto(x, y)

    # Move segment 0 to where the head is
    if len(segments) > 0:
        x = head.xcor()
        y = head.ycor()
        segments[0].goto(x, y)

    if head.direction == "up":
        head.sety(head.ycor() + SNAKE_CELL_SIZE)
    elif head.direction == "right":
        head.setx(head.xcor() + SNAKE_CELL_SIZE)
    elif head.direction == "down":
        head.sety(head.ycor() - SNAKE_CELL_SIZE)
    elif head.direction == "left":
        head.setx(head.xcor() - SNAKE_CELL_SIZE)

def check_food_collision():
    if head.distance(food) < SNAKE_CELL_SIZE:
        x = random.randint(- WIDTH / 2 + FOOD_SIZE, WIDTH / 2 - FOOD_SIZE)
        y = random.randint(- HEIGHT / 2 + FOOD_SIZE, HEIGHT / 2 - FOOD_SIZE)
        food.goto(x, y)

        # Add new segment
        new_segment = turtle.Turtle()
        new_segment.shape("square")
        new_segment.color("cyan")
        new_segment.penup()
        segments.append(new_segment)


def go_up():
    if head.direction != "down":
        head.direction = "up"

def go_right():
    if head.direction != "left":
        head.direction = "right"

def go_down():
    if head.direction != "up":
        head.direction = "down"

def go_left():
    if head.direction != "right":
        head.direction = "left"

def play():
    move_snake()
    check_food_collision()
    screen.update()
    turtle.ontimer(play, DELAY)


# Set up screen
screen = turtle.Screen()
screen.title("Snake Game")
screen.bgcolor("pink")
screen.setup(500, 500)
screen.tracer(0)


# Event handlers
screen.listen()
screen.onkey(go_up, "Up")
screen.onkey(go_right, "Right")
screen.onkey(go_down, "Down")
screen.onkey(go_left, "Left")


# Snake head
head = turtle.Turtle()
head.speed(0)
head.shape("square")
head.color("black")
head.penup()
head.goto(100, 100)


# Food
food = turtle.Turtle()
food.shape("circle")
food.color("red")
food.shapesize(FOOD_SIZE / SQUARE_SIZE)
food.penup()

# Let's go!
segments = []
head.direction = "up"
play()
turtle.done()