use sqlx::sqlite::SqlitePool;

use super::{Channel, Snapshot};
use crate::{
    channel::repo::Provider as _, event::repo::Provider as _, message::repo::Provider as _,
};

pub struct Boot<'a> {
    db: &'a SqlitePool,
}

impl<'a> Boot<'a> {
    pub const fn new(db: &'a SqlitePool) -> Self {
        Self { db }
    }

    pub async fn snapshot(&self) -> Result<Snapshot, sqlx::Error> {
        let mut tx = self.db.begin().await?;
        let resume_point = tx.sequence().current().await?;
        let channels = tx.channels().all(resume_point.into()).await?;

        let channels = {
            let mut snapshots = Vec::with_capacity(channels.len());

            let channels = channels.into_iter().filter_map(|channel| {
                channel
                    .as_of(resume_point)
                    .map(|snapshot| (channel, snapshot))
            });

            for (channel, snapshot) in channels {
                let messages = tx
                    .messages()
                    .in_channel(&channel, resume_point.into())
                    .await?;

                let messages = messages
                    .into_iter()
                    .filter_map(|message| message.as_of(resume_point));

                snapshots.push(Channel::new(snapshot, messages));
            }

            snapshots
        };

        tx.commit().await?;

        Ok(Snapshot {
            resume_point,
            channels,
        })
    }
}