if isCollision(enemyX[i], enemyY[i], bulletX, bulletY):
            bulletY = PLAYER_START_Y
            bullet_state = "ready"
            score_value += 1
            enemyX[i] = random.randint(0, SCREEN_WIDTH - 64)
            enemyY[i] = random.randint(ENEMY_START_Y_MIN, ENEMY_START_Y_MAX)

        enemy(enemyX[i], enemyY[i], i)

    # Bullet Movement
    if bulletY <= 0:
        bulletY = PLAYER_START_Y
        bullet_state = "ready"
    elif bullet_state == "fire":
        fire_bullet(bulletX, bulletY)
        bulletY -= bulletY_change

    player(playerX, playerY)
    show_score(textX, textY)
    pygame.display.update()