from typing import Optional


def system_content(self) -> Optional[str]:
    if self.type is MessageType.role_subscription_purchase:
        if not (data := self.role_subscription_data):
            return

        guild_name = f"**{self.guild.name}**" if self.guild else None
        if data.total_months_subscribed > 0:
            action = "renewed" if data.is_renewal else "joined"
            return (
                f"{self.author.name} {action} **{data.tier_name}** and has been a subscriber "
                f"of {guild_name} for {data.total_months_subscribed} "
                f"{'month' if data.total_months_subscribed == 1 else 'months'}!"
            )
        elif data.is_renewal:
            return f"{self.author.name} renewed **{data.tier_name}** in their {guild_name} membership!"
        else:
            return f"{self.author.name} joined **{data.tier_name}** as a subscriber of {guild_name}!"

    return None