use itertools::Itertools as _;

use super::{
    event::{Created, Deleted, Event},
    Channel, Id,
};
use crate::event::{Instant, ResumePoint, Sequence};

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

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

    // Snapshot of this channel as it was when created. (Note to the future: it's
    // okay if this returns a redacted or modified version of the channel. If we
    // implement renames by redacting the original name, then this should return the
    // renamed channel, not the original, even if that's not how it was "as
    // created.")
    pub fn as_created(&self) -> Channel {
        self.channel.clone()
    }

    pub fn as_of(&self, resume_point: impl Into<ResumePoint>) -> Option<Channel> {
        self.events()
            .filter(Sequence::up_to(resume_point.into()))
            .collect()
    }

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

// Event factories
impl History {
    pub fn events(&self) -> impl Iterator<Item = Event> {
        [self.created()]
            .into_iter()
            .merge_by(self.deleted(), Sequence::merge)
    }

    fn created(&self) -> Event {
        Created {
            instant: self.created,
            channel: self.channel.clone(),
        }
        .into()
    }

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