use itertools::Itertools as _;

use super::{
    Id, Message,
    event::{Deleted, Event, Sent},
};
use crate::event::{Instant, Sequence};

#[derive(Clone, Debug, Eq, PartialEq)]
pub struct History {
    pub message: Message,
    pub deleted: Option<Instant>,
}

// State interface
impl History {
    pub fn id(&self) -> &Id {
        &self.message.id
    }

    // Snapshot of this message as it was when sent. (Note to the future: it's okay
    // if this returns a redacted or modified version of the message. If we
    // implement message editing by redacting the original body, then this should
    // return the edited message, not the original, even if that's not how it was
    // "as sent.")
    pub fn as_sent(&self) -> Message {
        self.message.clone()
    }

    pub fn as_of(&self, resume_point: Sequence) -> Option<Message> {
        self.events()
            .filter(Sequence::up_to(resume_point))
            .collect()
    }

    // Snapshot of this message as of all events recorded in this history.
    pub fn as_snapshot(&self) -> Option<Message> {
        self.events().collect()
    }
}

// Events interface
impl History {
    fn sent(&self) -> Event {
        Sent {
            message: self.message.clone(),
        }
        .into()
    }

    fn deleted(&self) -> Option<Event> {
        self.deleted.map(|instant| {
            Deleted {
                instant,
                id: self.message.id.clone(),
            }
            .into()
        })
    }

    pub fn events(&self) -> impl Iterator<Item = Event> + use<> {
        [self.sent()]
            .into_iter()
            .merge_by(self.deleted(), Sequence::merge)
    }
}