backup-tool/app/skeleton.py

"""Handles merging with the skeleton config."""
from typing import Dict


class InvalidKeyError(Exception):
    """Thrown when a config file contains an invalid key."""

    def __init__(self, key: str):
        """
        Create a new InvalidKeyError object with the given key.

        Args:
            key: the invalid key
        """
        self.message = "Invalid key: {}".format(key)

        super().__init__(key)


class MissingKeyError(Exception):
    """Thrown when a required key is missing from a config."""

    def __init__(self, key: str):
        """
        Create a new MissingKeyError object with the given key.

        Args:
            key: the invalid key
        """
        self.message = "Missing key: {}".format(key)

        super().__init__(key)


def merge(*dicts: [Dict]) -> Dict:
    """
    Merge multiple dicts into one.

    It reads the dicts from left to right, always preferring the "right"
    dictionary's values. Therefore, the dictionaries should be sorted from
    least important to most important (e.g. a default values skeleton should be
    to the left of a dict of selected values).

    Args:
        dicts: the dictionaries to merge

    Returns:
        a new dictionary representing the merged dictionaries

    Todo:
        * Make sure an infinite loop is not possible
    """
    # Base cases
    if len(dicts) == 0:
        return {}

    if len(dicts) == 1:
        return dicts[0]

    # We merge the first two dicts
    d1, d2 = dicts[0], dicts[1]

    output = d1.copy()

    for key, value in d2.items():
        if type(value) == dict:
            # Merge the two sub-dictionaries
            output[key] = (
                merge(output[key], value)
                if type(output.get(key)) == dict
                else value
            )

        else:
            output[key] = value

    return merge(output, *dicts[2:])


def merge_with_skeleton(data: Dict, skel: Dict) -> Dict:
    """
    Merge a dictionary with a skeleton containing default values.

    The skeleton not only defines what the default values are, but also
    enforces a certain shape. This allows us to define a config file using a
    dictionary and parse it.

    Args:
        data: dictionary containing the selected config values
        skel: dictionary containing the skeleton (aka the def)

    Todo:
        * Check if an infinite loop is possible
        * Split info less complex functions
    """
    # 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:
            # TODO make this error message more verbose
            raise TypeError("Invalid value type")

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

    return data