# Copyright 2015 The ChromiumOS Authors
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

"""Module used for run-time determination of toplogy information.

By Toplogy, we mean a specification of which external server dependencies are
located where. At the moment, this module provides a default key-value api via
the |topology| member, and a cidb-backed store to provide environment-specific
overrides of the default values.
"""

import collections

from chromite.lib import constants


BUILDBUCKET_HOST_KEY = "/buildbucket/host"
DATASTORE_WRITER_CREDS_KEY = "/datastore/creds_file"
SWARMING_PROXY_HOST_KEY = "/swarming_proxy/host"
CHROME_SWARMING_PROXY_HOST_KEY = "/chrome_swarming_proxy/host"
LUCI_LOGDOG_HOST_KEY = "/luci-logdog/host"
LUCI_MILO_HOST_KEY = "/luci-milo/host"
SHERIFFOMATIC_HOST_KEY = "/sheriffomatic/host"

TOPOLOGY_DEFAULTS = {
    SWARMING_PROXY_HOST_KEY: "fake_swarming_server",
    CHROME_SWARMING_PROXY_HOST_KEY: "fake_chrome_swarming_server",
    LUCI_LOGDOG_HOST_KEY: "luci-logdog.appspot.com",
    LUCI_MILO_HOST_KEY: "luci-milo.appspot.com",
    SHERIFFOMATIC_HOST_KEY: "sheriff-o-matic-staging.appspot.com",
}


class LockedDictAccessException(Exception):
    """Raised when attempting to access a locked dict."""


class LockedDefaultDict(collections.defaultdict):
    """collections.defaultdict which cannot be read from until unlocked."""

    def __init__(self):
        super().__init__()
        self._locked = True

    def get(self, key):
        if self._locked:
            raise LockedDictAccessException()
        return super().get(key)

    def unlock(self):
        self._locked = False


topology = LockedDefaultDict()
topology.update(TOPOLOGY_DEFAULTS)


def FetchTopology():
    """Update and unlock topology based on constant keyval store."""
    topology.update(constants.TOPOLOGY_DICT)
    topology.unlock()