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

use super::{Body, History, Id, Message, history, repo::Provider as _};
use crate::{
    clock::DateTime,
    conversation::{self, repo::Provider as _},
    db,
    db::NotFound as _,
    error::failed::{Failed, ResultExt as _},
    event::{Broadcaster, Sequence, repo::Provider as _},
    login::Login,
    user::{self, repo::Provider as _},
};

pub struct Messages {
    db: SqlitePool,
    events: Broadcaster,
}

impl Messages {
    pub const fn new(db: SqlitePool, events: Broadcaster) -> Self {
        Self { db, events }
    }

    pub async fn send(
        &self,
        conversation: &conversation::Id,
        sender: &Login,
        sent_at: &DateTime,
        body: &Body,
    ) -> Result<Message, SendError> {
        let conversation_not_found = || SendError::ConversationNotFound(conversation.clone());
        let conversation_deleted = || SendError::ConversationDeleted(conversation.clone());
        let sender_not_found = || SendError::SenderNotFound(sender.id.clone().into());
        let sender_deleted = || SendError::SenderDeleted(sender.id.clone().into());

        let mut tx = self.db.begin().await.fail(db::failed::BEGIN)?;
        let conversation = tx
            .conversations()
            .by_id(conversation)
            .await
            .optional()
            .fail("Failed to load conversation")?
            .ok_or_else(conversation_not_found)?;
        let sender = tx
            .users()
            .by_login(sender)
            .await
            .optional()
            .fail("Failed to load sending user")?
            .ok_or_else(sender_not_found)?;

        // Ordering: don't bother allocating a sequence number before we know the channel might
        // exist.
        let sent = tx
            .sequence()
            .next(sent_at)
            .await
            .fail("Failed to find event sequence number")?;
        let conversation = conversation.as_of(sent).ok_or_else(conversation_deleted)?;
        let sender = sender.as_of(sent).ok_or_else(sender_deleted)?;
        let message = History::begin(&conversation, &sender, body, sent);

        // This filter technically includes every event in the history, but it's easier to follow if
        // the various event-manipulating app methods are consistent, and it's harmless to have an
        // always-satisfied filter.
        let events = message.events().filter(Sequence::start_from(sent));
        tx.messages()
            .record_events(events.clone())
            .await
            .fail("Failed to store events")?;

        tx.commit().await.fail(db::failed::COMMIT)?;

        self.events.broadcast_from(events);

        Ok(message.as_sent())
    }

    pub async fn delete(
        &self,
        deleted_by: &Login,
        message: &Id,
        deleted_at: &DateTime,
    ) -> Result<(), DeleteError> {
        let message_not_found = || DeleteError::MessageNotFound(message.clone());
        let not_sender = || DeleteError::NotSender(deleted_by.id.clone().into());

        let mut tx = self.db.begin().await.fail(db::failed::BEGIN)?;

        let message = tx
            .messages()
            .by_id(message)
            .await
            .optional()
            .fail("Failed to load message")?
            .ok_or_else(message_not_found)?;
        if message.sender() == &deleted_by.id {
            let deleted_at = tx
                .sequence()
                .next(deleted_at)
                .await
                .fail("Failed to find event sequence number")?;
            let message = message.delete(deleted_at)?;

            let events = message.events().filter(Sequence::start_from(deleted_at));
            tx.messages()
                .record_events(events.clone())
                .await
                .fail("Failed to store events")?;
            tx.commit().await.fail(db::failed::COMMIT)?;

            self.events.broadcast_from(events);

            Ok(())
        } else {
            Err(not_sender())
        }
    }

    pub async fn expire(&self, relative_to: &DateTime) -> Result<(), sqlx::Error> {
        // Somewhat arbitrarily, expire after 30 days.
        let expire_at = relative_to.to_owned() - TimeDelta::days(30);

        let mut tx = self.db.begin().await?;

        let expired = tx.messages().expired(&expire_at).await?;
        let mut events = Vec::with_capacity(expired.len());
        for message in expired {
            let deleted = tx.sequence().next(relative_to).await?;
            match message.delete(deleted) {
                Ok(message) => {
                    let message_events = message
                        .events()
                        .filter(Sequence::start_from(deleted.sequence));
                    tx.messages().record_events(message_events.clone()).await?;

                    events.push(message_events);
                }
                Err(history::DeleteError::Deleted(_)) => {}
            }
        }

        tx.commit().await?;

        self.events
            .broadcast_from(events.into_iter().kmerge_by(Sequence::merge));

        Ok(())
    }

    pub async fn purge(&self, relative_to: &DateTime) -> Result<(), sqlx::Error> {
        // Somewhat arbitrarily, purge after 6 hours.
        let purge_at = relative_to.to_owned() - TimeDelta::hours(6);

        let mut tx = self.db.begin().await?;
        tx.messages().purge(&purge_at).await?;
        tx.commit().await?;

        Ok(())
    }
}

#[derive(Debug, thiserror::Error)]
pub enum SendError {
    #[error("conversation {0} not found")]
    ConversationNotFound(conversation::Id),
    #[error("conversation {0} deleted")]
    ConversationDeleted(conversation::Id),
    #[error("user {0} not found")]
    SenderNotFound(user::Id),
    #[error("user {0} deleted")]
    SenderDeleted(user::Id),
    #[error(transparent)]
    Failed(#[from] Failed),
}

#[derive(Debug, thiserror::Error)]
pub enum DeleteError {
    #[error("message {0} not found")]
    MessageNotFound(Id),
    #[error("user {0} not the message's sender")]
    NotSender(user::Id),
    #[error("message {0} deleted")]
    Deleted(Id),
    #[error(transparent)]
    Failed(#[from] Failed),
}

impl From<history::DeleteError> for DeleteError {
    fn from(error: history::DeleteError) -> Self {
        match error {
            history::DeleteError::Deleted(message) => Self::Deleted(message.id().clone()),
        }
    }
}