"""
automatically invoked app factory
"""
import logging
import os
from flask import Flask


def create_app():
    """
    overrides default settings with those found
    in the file read from env var SETTINGS_FILENAME

    :return: a new flask app instance
    """

    app = Flask(__name__)
    app.secret_key = "super secret session key"

    from inventory_provider.routes import default
    app.register_blueprint(default.routes, url_prefix='/')

    from inventory_provider.routes import data
    app.register_blueprint(data.routes, url_prefix='/data')

    from inventory_provider.routes import jobs
    app.register_blueprint(jobs.routes, url_prefix='/jobs')

    from inventory_provider.routes import opsdb
    app.register_blueprint(opsdb.routes, url_prefix='/opsdb')

    from inventory_provider.routes import classifier
    app.register_blueprint(classifier.routes, url_prefix='/classifier')

    from inventory_provider.routes import poller
    app.register_blueprint(poller.routes, url_prefix='/poller')

    if "SETTINGS_FILENAME" not in os.environ:
        assert False, \
            "environment variable SETTINGS_FILENAME' must be defined"

    logging.info("initializing Flask with config from: %r"
        % app.config["SETTINGS_FILENAME"])
    app.config.from_envvar("SETTINGS_FILENAME")

    assert "INVENTORY_PROVIDER_CONFIG_FILENAME" in app.config, (
        "INVENTORY_PROVIDER_CONFIG_FILENAME not defined in %s"
        % os.environ["SETTINGS_FILENAME"])

    assert os.path.isfile(app.config["INVENTORY_PROVIDER_CONFIG_FILENAME"]), (
        "config file '%s' not found" %
        app.config["INVENTORY_PROVIDER_CONFIG_FILENAME"])

    from inventory_provider import config
    with open(app.config["INVENTORY_PROVIDER_CONFIG_FILENAME"]) as f:
        # test the config file can be loaded
        logging.info("loading config from: %r"
            % app.config["INVENTORY_PROVIDER_CONFIG_FILENAME"])
        app.config["INVENTORY_PROVIDER_CONFIG"] = config.load(f)

    logging.info('Inventory Provider Flask app initialized')

    return app