from datetime import datetime


class Message:
    def __init__(self, author, text):
        self.author = author
        self.text = text
        self.timestamp = datetime.today()


class Topic:
    def __init__(self, title, collective=True):
        self.title = title
        self.collective = collective
        self.participants = []
        self.messages = []
        self.start_time = datetime.today()
        self.end_time = None

    @property
    def duration(self):
        if self.end_time:
            minutes = (self.end_time - self.start_time).seconds // 60
            seconds = (self.end_time - self.start_time).seconds % 60
        else:
            minutes = (datetime.today() - self.start_time).seconds // 60
            seconds = (datetime.today() - self.start_time).seconds % 60
        return f"{minutes}:{seconds:02d}"

    @property
    def individual(self):
        return not self.collective

    def add_message(self, sender, message):
        self.messages.append(Message(sender, message))
        if sender not in self.participants:
            self.participants.append(sender)

    def cancel_previous(self, author):
        messages = [message for message in self.messages if message.author == author]
        if len(messages) == 0:
            return
        message = messages[-1].text
        self.messages.remove(messages[-1])

        return message

    def get_messages(self, author=None):
        if self.collective:
            return self.messages
        return [message for message in self.messages if message.author == author]

    def has_participant(self, author):
        return author in self.get_participants()

    def get_participants(self):
        return set([message.author for message in self.messages])

    def close(self):
        self.end_time = datetime.today()