import datetime
import pathlib
from typing import Union

from anaxi.file_persistence import read_yaml, write_yaml


class CheckpointManager:

    highest_synced_timestamp_field_key = "highest_synced_timestamp"

    def __init__(
        self,
        file_path: pathlib.Path,
        highest_synced_timestamp: Union[None, datetime.datetime],
    ):
        self.file_path = file_path
        self.highest_synced_timestamp = highest_synced_timestamp
        self.goal = None

    @classmethod
    def load_from_yml(cls, file_path: pathlib.Path) -> "CheckpointManager":
        contents = read_yaml(file_path)

        if CheckpointManager.highest_synced_timestamp_field_key not in contents.keys():
            raise ValueError(f"Invalid checkpoint state contents in file: {file_path}.")

        return CheckpointManager(
            file_path=file_path,
            highest_synced_timestamp=datetime.datetime.fromisoformat(
                contents[CheckpointManager.highest_synced_timestamp_field_key]
            ),
        )

    def update_yml(self):
        write_yaml(
            path=self.file_path,
            data={
                CheckpointManager.highest_synced_timestamp_field_key: self.highest_synced_timestamp.isoformat()
            },
        )

    def set_new_goal(self, goal_timestamp: datetime.datetime) -> None:
        self.goal = goal_timestamp

    def commit_goal(self):
        self.highest_synced_timestamp = self.goal
        self.update_yml()