# Standard library imports.
import re

# Django imports.
from django.template import Context, loader

# Application imports.
import iptables


def generate_entity_iptables(entity):
    """
    Generates full iptables rules for the supplied entity. The generated rules
    can be fed directly to the iptables-restore utility.

    Arguments:

        entity - An Entity instance for which the iptables rules should be
        generated.

    Returns:

        String containing the iptables rules for entity.
    """

    # Fetch list of incoming communications.
    incoming = entity.incoming_communications()

    # Set-up the nat table.
    nat = iptables.Table("nat")
    for chain in ("PREROUTING", "INPUT", "OUTPUT", "POSTROUTING"):
        nat.add_chain(iptables.Chain(chain, "ACCEPT"))

    # Set-up the filter table INPUT chain.
    filter = iptables.Table("filter")
    input = iptables.Chain("INPUT", "DROP")

    input.add_rule(iptables.LoopbackRule())
    input.add_rule(iptables.RelatedRule())

    for communication in incoming:
        source = "%s/%s" % (communication.source.address, communication.source.netmask)
        destination = "%s/%s" % (communication.destination.address, communication.destination.netmask)
        input.add_rule(iptables.Rule(source, destination, communication.protocol, communication.port, communication.description))
    filter.add_chain(input)

    # Set-up empty chains.
    filter.add_chain(iptables.Chain("OUTPUT", "ACCEPT"))
    filter.add_chain(iptables.Chain("FORWARD", "DROP"))

    # Construct the iptables file using the two tables.
    content = "%s%s" % (filter, nat)

    return content