import os.path

def make(seen_file):
    if seen_file:
        return SerializedSet(seen_file)
    else:
        return DummySerializedSet()

class ISerializedSet(object):
    def put(self, name):
        raise NotImplementedError

class SerializedSet(ISerializedSet):
    """This set also records itself to a file, so that it
    is persisted over multiple sessions."""
    def __init__(self, file):
        self.set = set()
        if os.path.isfile(file):
            for line in open(file, "r"):
                self.set.add(line.rstrip())
        self.file = open(file, "a")
    def __contains__(self, name):
        return name in self.set
    def add(self, name):
        self.set.add(name)
        self.file.write(name + "\n")
        self.file.flush()

class DummySerializedSet(ISerializedSet):
    """Dummy object that doesn't actually cache anything and
    claims that everything needs to be done"""
    def __contains__(self, name):
        return False
    def add(self, name):
        pass