import yaml
import sys
from . import network, container


class YamlTopology:
    """ Parse a YAML description of a network topology. The networks' links and domains
    are contained in the `links` and `domains` attributes, but their `create` methods
    are not called. """

    class InvalidConfiguration(Exception):
        def __init__(self, reason):
            self.reason = reason

        def __str__(self):
            return "Bad topology configuration: {}".format(self.reason)

    def __init__(self, path, conn):
        self.path = path
        self.conn = conn

        self.domains = None
        self.links = None

        self._parse()

    def _parse(self):
        with open(self.path, "r") as handle:
            topology = yaml.safe_load(handle)

        if "links" not in topology:
            raise self.InvalidConfiguration("links definition is mandatory")

        link_descr = topology["links"]
        self.links = []

        dom_descr = {}
        for link_conf in link_descr:
            if "domains" not in link_conf:
                raise self.InvalidConfiguration(
                    "a 'domains' attribute is mandatory for each link"
                )

            cur_link = network.Network(self.conn)
            self.links.append(cur_link)

            for dom in link_conf["domains"]:
                if dom not in dom_descr:
                    dom_descr[dom] = {"links": []}
                dom_descr[dom]["links"].append(cur_link)

        for dom_conf_name in topology.get("domains", {}):
            if dom_conf_name not in dom_descr:
                # Domain does not participate in any link: warn and ignore
                print(
                    (
                        "WARNING: domain {} does not participate in any link. "
                        "Ignored."
                    ).format(dom_conf_name),
                    file=sys.stderr,
                )
                continue

            dom_conf = topology["domains"][dom_conf_name]
            dom_descr[dom_conf_name]["enable_v4"] = dom_conf.get("enable_v4", True)

        sorted_dom_names = sorted(list(dom_descr.keys()))

        self.domains = [
            container.Container(
                self.conn,
                dom_descr[dom]["links"],
                enable_v4=dom_descr[dom].get("enable_v4", True),
            )
            for dom in sorted_dom_names
        ]