from collections import UserDict
from dataclasses import dataclass, field
from typing import Dict

from . import SyncId
from .model import Model


@dataclass(frozen=True)
class ModelStore(UserDict):
    """Dict of sync ID keys and `Model` values.

    The dict keys must be the sync ID of `Model` values.
    If a non-existent key is accessed, a corresponding `Model` will be
    created, put into the interal `data` dict and returned.
    """

    data: Dict[SyncId, Model] = field(default_factory=dict)


    def __missing__(self, key: SyncId) -> Model:
        """When accessing a non-existent model, create and return it."""

        model          = Model(sync_id=key)
        self.data[key] = model
        return model


    def __str__(self) -> str:
        """Provide a nice overview of stored models when `print()` called."""

        return "%s(\n    %s\n)" % (
            type(self).__name__,
            "\n    ".join(sorted(str(v) for v in self.values())),
        )