import re

with open('config/settings.py', 'r') as f:
    content = f.read()

# Replace CHANNEL_LAYERS
old_channels = """CHANNEL_LAYERS = {
    "default": {
        "BACKEND": "channels_redis.core.RedisChannelLayer",
        "CONFIG": {
            "hosts": [env('REDIS_URL', default='redis://localhost:6379/0')],
        },
    },
}"""
new_channels = """REDIS_URL = env('REDIS_URL', default=None)
if REDIS_URL:
    CHANNEL_LAYERS = {
        "default": {
            "BACKEND": "channels_redis.core.RedisChannelLayer",
            "CONFIG": {
                "hosts": [REDIS_URL],
            },
        },
    }
else:
    CHANNEL_LAYERS = {
        "default": {
            "BACKEND": "channels.layers.InMemoryChannelLayer"
        }
    }"""
content = content.replace(old_channels, new_channels)

# Replace Celery defaults so they don't crash if REDIS_URL is None
old_celery1 = "CELERY_BROKER_URL = env('REDIS_URL', default='redis://localhost:6379/0')"
new_celery1 = "CELERY_BROKER_URL = env('REDIS_URL', default='memory://')"
old_celery2 = "CELERY_RESULT_BACKEND = env('REDIS_URL', default='redis://localhost:6379/0')"
new_celery2 = "CELERY_RESULT_BACKEND = env('REDIS_URL', default='cache+memory://')"
content = content.replace(old_celery1, new_celery1)
content = content.replace(old_celery2, new_celery2)

with open('config/settings.py', 'w') as f:
    f.write(content)