import yaml
from pathlib import Path
from specs import Spec
from typing import List, Dict


class InvalidKeyError(Exception):
    def __init__(self, key):
        message = "Invalid key: {}".format(key)

        super().__init__(key)


class MissingKeyError(Exception):
    def __init__(self, key):
        message = "Missing key: {}".format(key)

        super().__init__(key)


def parse_specs_file(path: Path) -> List[Spec]:
    """
    Parse a YAML file defining backup specs.

    Args:
        path: path to the specs file

    Returns:
        A list of specs
    """

    # Skeleton of a spec config
    # If a value is None, this means it doesn't have a default value and must be
    # defined
    spec_skel = {
        "source": None,
        "destination": None,
        "limit": None,
        "volume": False,
        "notify": {
            "title": "Backup Notification",
            "events": ["failure"]
        }
    }

    # Read YAML file
    with open(path, "r") as yaml_file:
        data = yaml.load(yaml_file, Loader=yaml.Loader)

    # Check specs section exists
    if "specs" not in data:
        raise MissingKeyError("specs")

    # Allow for default notify settings
    if "notify" in data:
        spec_skel["notify"] = data["notify"]

    specs = []
    # Check format for each spec
    for key in data["specs"]:
        specs.append(Spec.from_dict(key, combine_with_skeleton(
            data["specs"][key], spec_skel)
        ))

    return specs


def combine_with_skeleton(data: Dict, skel: Dict) -> Dict:
    """
    Compare a dict with a given skeleton dict, and fill in default values where
    needed.
    """

    # First, check for illegal keys
    for key in data:
        if key not in skel:
            raise InvalidKeyError(key)

    # Then, check the default values
    for key, value in skel.items():
        if key not in data:
            # Raise error if there's not default value
            if value is None:
                raise MissingKeyError(key)

            # Replace with default value
            data[key] = value

        # Error if value is not same type as default value
        elif type(data[key]) != type(value) and value is not None:
            raise TypeError("Invalid value type")

        # Recurse into dicts
        elif type(value) == dict:
            data[key] = combine_with_skeleton(data[key], value)

    return data


# Test cases
if __name__ == "__main__":
    d1 = {
        "a": 5
    }
    s1 = {
        "a": 7,
        "b": 2
    }
    r1 = {
        "a": 5,
        "b": 2
    }

    assert combine_with_skeleton(d1, s1) == r1