does anyone know how you could add collision detection to this code? [duplicate]

i would like when you cross their line the game closes and when the enemy hits your line the game restarts, any ideas on how to code that in? you don't have to rewrite the code just help me with some ideas on how i could add it in

here is the current code

import random 
import pygame, sys
from pygame.locals import *
import time

GREEN=(0,125,0)
BLUE=(0,0,125)

Yplayer = 225/2
Xplayer = 350

playerlinesavedata = []
playercurrent = []

Xplayerchange=0
Yplayerchange=0

Yenemy = 450
Xenemy = 300

enemylinesavedata = []
enemycurrent = []

Xenemychange=0
Yenemychange=0

windowX = 900
windowY = 600

pygame.init()
DISPLAY=pygame.display.set_mode((windowX,windowY),0,32)


def enemymovement():
    global Xplayer,Yplayer,Xenemy,Yenemy
    enemy1 = True
    enemydirection = random.randint(1,4)
    
    # enemy moves toward player
    if Xenemy > Xplayer: enemydirection = 1
    elif Xenemy < Xplayer: enemydirection = 2
    elif Yenemy > Yplayer: enemydirection = 3
    elif Yenemy < Yplayer: enemydirection = 4

    while enemy1 == True:    
        if enemydirection == 1:
            Xenemychange= -random.randint(1,2)
            Xenemy+=Xenemychange
            
        if enemydirection == 2:
            Xenemychange= random.randint(1,2)
            Xenemy+=Xenemychange
            
        if enemydirection == 3:            
            Yenemychange= -random.randint(1,2)
            Yenemy+=Yenemychange
            
        if enemydirection == 4:
            Yenemychange= random.randint(1,2)            
            Yenemy+=Yenemychange
            
        enemylinesavedata.append([Xenemy,Yenemy])
        enemy()
        break
            
def enemy():
    for XnY in enemylinesavedata:
        pygame.draw.rect(DISPLAY,BLUE, [XnY[0],XnY[1],5,5])

def player():
    for XnY in playerlinesavedata:
        pygame.draw.rect(DISPLAY,GREEN,[XnY[0],XnY[1],5,5])

def main():

    global Xplayer,Yplayer,Xenemy,Yenemy,Xplayerchange,Yplayerchange
    WHITE=(255,255,255)
    BLUE=(0,0,255)
    DISPLAY.fill(WHITE)

    
    pygame.display.update()
    while True:
        Yplayer+=Yplayerchange
        Xplayer+=Xplayerchange

        for event in pygame.event.get():
            if event.type==QUIT:
                pygame.quit()
                sys.exit()
            if event.type==KEYDOWN:
                if event.key==K_d:
                    Xplayerchange+=1
                    
                if event.key==K_a:
                    Xplayerchange-=1
                if event.key==K_w:
                    Yplayerchange-=1
                if event.key==K_s:
                    Yplayerchange+=1
            if event.type==KEYUP:
                if event.key==K_a or K_d:
                    Yplayerchange=0
                if event.key==K_w or K_s:
                    Xplayerchange=0


       
        playercurrent = []
        playercurrent.append(Xplayer)
        playercurrent.append(Yplayer)
        playerlinesavedata.append(playercurrent)
        
        Yplayer+=Yplayerchange
        Xplayer+=Xplayerchange

        enemymovement()

        Yplayer+=Yplayerchange
        Xplayer+=Xplayerchange
        
       
        DISPLAY.fill(WHITE)
        
        player()
        enemy()
        pygame.display.update()

main()

i am putting this text down here so i can post this question. if your still reading this them im sorry for the amount of code but i really want to get a game like this working