#!/usr/bin/env python3

import pickle
from typing import Any, Mapping

import file_utils


class PersistentState(object):
    """
    An object that behaves like a persistent hash map; it can be
    accessed to store key-value pairs but also saved to disk and read
    back from disk easily.

    """
    def __init__(self, filename: str, *, max_age_sec: int = None):
        self.filename = filename
        if file_utils.does_file_exist(self.filename):
            if max_age_sec is not None:
                age = file_utils.get_file_mtime_age_seconds(self.filename)
                if age < max_age_sec:
                    self.state = self.load()
                else:
                    self.state = {}
            else:
                self.state = self.load()
        else:
            self.state = {}

    def __getitem__(self, key: str) -> Any:
        return self.state.get(key, "")

    def __setitem__(self, key: str, value: Any):
        self.state[key] = value

    def __delitem__(self, key: str):
        del self.state[key]

    def __iter__(self):
        return iter(self.state)

    def __len__(self):
        return len(self.state)

    def save(self) -> None:
        with open(self.filename, 'wb') as f:
            pickle.dump(self.state, f, pickle.HIGHEST_PROTOCOL)

    def load(self) -> Mapping[str, Any]:
        with open(self.filename, 'rb') as f:
            return(pickle.load(f))