import json
import os.path



class File(object):
    "Holds controller state in the file"
    def __init__(self, filename=None):
        self.filename = filename

    def present(self):
        os.path.isfile(self.filename) 

    def load(self):
        if self.filename is None:
            raise ClassNotReadyException("Filename not set!")
        with open(self.filename) as input_file:
            self.data = json.load(input_file)

    def save(self):
        if self.filename is None:
            raise ClassNotReadyException("Filename not set!")
        if self.data is None:
            raise ClassNotReadyException("Data not loaded!")

        with open(self.filename, 'w') as out_file:
            json.dump(self.data, out_file)