"""
Local filesystem–based credential persistence for Mail Intake.

---

## Summary

This module provides a file-backed implementation of the
``CredentialStore`` abstraction using Python's ``pickle`` module.

The pickle-based credential store is intended for local development,
single-node deployments, and controlled environments where credentials
do not need to be shared across processes or machines.

Due to the security and portability risks associated with pickle-based
serialization, this implementation is not suitable for distributed or
untrusted environments.
"""

import pickle
from typing import Optional, TypeVar

from mail_intake.credentials.store import CredentialStore

T = TypeVar("T")


class PickleCredentialStore(CredentialStore[T]):
    """
    Filesystem-backed credential store using pickle serialization.

    This store persists credentials as a pickled object on the local
    filesystem. It is a simple implementation intended primarily for
    development, testing, and single-process execution contexts.

    Notes:
        **Guarantees:**

            - Stores credentials on the local filesystem
            - Uses pickle for serialization and deserialization
            - Does not provide encryption, locking, or concurrency guarantees

        **Constraints:**
        
            - Credential lifecycle management, validation, and refresh logic are explicitly out of scope for this class
    """

    def __init__(self, path: str):
        """
        Initialize a pickle-backed credential store.

        Args:
            path (str):
                Filesystem path where credentials will be stored.
                The file will be created or overwritten as needed.
        """
        self.path = path

    def load(self) -> Optional[T]:
        """
        Load credentials from the local filesystem.

        Returns:
            Optional[T]:
                An instance of type ``T`` if credentials are present and
                successfully deserialized; otherwise ``None``.

        Notes:
            **Guarantees:**

                - If the credential file does not exist or cannot be successfully deserialized, this method returns ``None``
                - The store does not attempt to validate or interpret the returned credentials
        """
        try:
            with open(self.path, "rb") as fh:
                return pickle.load(fh)
        except Exception:
            return None

    def save(self, credentials: T) -> None:
        """
        Persist credentials to the local filesystem.

        Args:
            credentials (T):
                The credential object to persist.

        Notes:
            **Responsibilities:**

                - Any previously stored credentials at the configured path are overwritten
        """
        with open(self.path, "wb") as fh:
            pickle.dump(credentials, fh)

    def clear(self) -> None:
        """
        Remove persisted credentials from the local filesystem.

        Notes:
            **Lifecycle:**

                - This method deletes the credential file if it exists and should be treated as an idempotent operation
        """
        import os

        if os.path.exists(self.path):
            os.remove(self.path)