use chrono::TimeDelta;
use itertools::Itertools;
use sqlx::sqlite::SqlitePool;

use crate::{
    channel::{repo::Provider as _, Channel},
    clock::DateTime,
    event::{broadcaster::Broadcaster, repo::Provider as _, Sequence},
};

pub struct Channels<'a> {
    db: &'a SqlitePool,
    events: &'a Broadcaster,
}

impl<'a> Channels<'a> {
    pub const fn new(db: &'a SqlitePool, events: &'a Broadcaster) -> Self {
        Self { db, events }
    }

    pub async fn create(&self, name: &str, created_at: &DateTime) -> Result<Channel, CreateError> {
        let mut tx = self.db.begin().await?;
        let created = tx.sequence().next(created_at).await?;
        let channel = tx
            .channels()
            .create(name, &created)
            .await
            .map_err(|err| CreateError::from_duplicate_name(err, name))?;
        tx.commit().await?;

        for event in channel.events() {
            self.events.broadcast(event);
        }

        Ok(channel.snapshot())
    }

    pub async fn all(&self, resume_point: Option<Sequence>) -> Result<Vec<Channel>, InternalError> {
        let mut tx = self.db.begin().await?;
        let channels = tx.channels().all(resume_point).await?;
        tx.commit().await?;

        let channels = channels
            .into_iter()
            .filter_map(|channel| {
                channel
                    .events()
                    .filter(Sequence::up_to(resume_point))
                    .collect()
            })
            .collect();

        Ok(channels)
    }

    pub async fn expire(&self, relative_to: &DateTime) -> Result<(), sqlx::Error> {
        // Somewhat arbitrarily, expire after 90 days.
        let expire_at = relative_to.to_owned() - TimeDelta::days(90);

        let mut tx = self.db.begin().await?;
        let expired = tx.channels().expired(&expire_at).await?;

        let mut events = Vec::with_capacity(expired.len());
        for channel in expired {
            let deleted = tx.sequence().next(relative_to).await?;
            let channel = tx.channels().delete(&channel, &deleted).await?;
            events.push(
                channel
                    .events()
                    .filter(Sequence::start_from(deleted.sequence)),
            );
        }

        tx.commit().await?;

        for event in events
            .into_iter()
            .kmerge_by(|a, b| a.instant.sequence < b.instant.sequence)
        {
            self.events.broadcast(event);
        }

        Ok(())
    }
}

#[derive(Debug, thiserror::Error)]
pub enum CreateError {
    #[error("channel named {0} already exists")]
    DuplicateName(String),
    #[error(transparent)]
    DatabaseError(#[from] sqlx::Error),
}

impl CreateError {
    fn from_duplicate_name(error: sqlx::Error, name: &str) -> Self {
        if let Some(error) = error.as_database_error() {
            if error.is_unique_violation() {
                return Self::DuplicateName(name.into());
            }
        }

        Self::from(error)
    }
}

#[derive(Debug, thiserror::Error)]
pub enum InternalError {
    #[error(transparent)]
    DatabaseError(#[from] sqlx::Error),
}