//! Domain of dialogs – conversations between two participants.
//!
//! Dialogs are different from rooms in that they are always between two participants.
//! There are no admins or other roles in dialogs, both participants have equal rights.

use std::collections::HashMap;
use std::sync::Arc;

use chrono::{DateTime, Utc};
use tokio::sync::RwLock as AsyncRwLock;

use crate::player::{PlayerId, PlayerRegistry, Updates};
use crate::prelude::*;
use crate::repo::Storage;

/// Id of a conversation between two players.
///
/// Dialogs are identified by the pair of participants' ids. The order of ids does not matter.
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub struct DialogId(PlayerId, PlayerId);
impl DialogId {
    pub fn new(a: PlayerId, b: PlayerId) -> DialogId {
        if a.as_inner() < b.as_inner() {
            DialogId(a, b)
        } else {
            DialogId(b, a)
        }
    }

    pub fn as_inner(&self) -> (&PlayerId, &PlayerId) {
        (&self.0, &self.1)
    }

    pub fn into_inner(self) -> (PlayerId, PlayerId) {
        (self.0, self.1)
    }
}

struct Dialog {
    storage_id: u32,
    player_storage_id_1: u32,
    player_storage_id_2: u32,
    message_count: u32,
}

struct DialogRegistryInner {
    dialogs: HashMap<DialogId, AsyncRwLock<Dialog>>,
    players: Option<PlayerRegistry>,
    storage: Storage,
}

#[derive(Clone)]
pub struct DialogRegistry(Arc<AsyncRwLock<DialogRegistryInner>>);

impl DialogRegistry {
    pub async fn send_message(
        &self,
        from: PlayerId,
        to: PlayerId,
        body: Str,
        created_at: &DateTime<Utc>,
    ) -> Result<()> {
        let mut guard = self.0.read().await;
        let id = DialogId::new(from.clone(), to.clone());
        let dialog = guard.dialogs.get(&id);
        if let Some(d) = dialog {
            let mut d = d.write().await;
            guard.storage.increment_dialog_message_count(d.storage_id).await?;
            d.message_count += 1;
        } else {
            drop(guard);
            let mut guard2 = self.0.write().await;
            // double check in case concurrent access has loaded this dialog
            if let Some(d) = guard2.dialogs.get(&id) {
                let mut d = d.write().await;
                guard2.storage.increment_dialog_message_count(d.storage_id).await?;
                d.message_count += 1;
            } else {
                let (p1, p2) = id.as_inner();
                tracing::info!("Dialog {id:?} not found locally, trying to load from storage");
                let stored_dialog = match guard2.storage.retrieve_dialog(p1.as_inner(), p2.as_inner()).await? {
                    Some(t) => t,
                    None => {
                        tracing::info!("Dialog {id:?} does not exist, creating a new one in storage");
                        guard2.storage.initialize_dialog(p1.as_inner(), p2.as_inner(), created_at).await?
                    }
                };
                tracing::info!("Dialog {id:?} loaded");
                guard2.storage.increment_dialog_message_count(stored_dialog.id).await?;
                let dialog = Dialog {
                    storage_id: stored_dialog.id,
                    player_storage_id_1: stored_dialog.participant_1,
                    player_storage_id_2: stored_dialog.participant_2,
                    message_count: stored_dialog.message_count + 1,
                };
                guard2.dialogs.insert(id.clone(), AsyncRwLock::new(dialog));
            }
            guard = guard2.downgrade();
        }
        // TODO send message to the other player and persist it
        let Some(players) = &guard.players else {
            tracing::error!("No player registry present");
            return Ok(());
        };
        let Some(player) = players.get_player(&to).await else {
            tracing::debug!("Player {to:?} not active, not sending message");
            return Ok(());
        };
        let update = Updates::NewDialogMessage {
            sender: from.clone(),
            receiver: to.clone(),
            body: body.clone(),
            created_at: created_at.clone(),
        };
        player.update(update).await;
        return Ok(());
    }
}

impl DialogRegistry {
    pub fn new(storage: Storage) -> DialogRegistry {
        DialogRegistry(Arc::new(AsyncRwLock::new(DialogRegistryInner {
            dialogs: HashMap::new(),
            players: None,
            storage,
        })))
    }

    pub async fn set_players(&self, players: PlayerRegistry) {
        let mut guard = self.0.write().await;
        guard.players = Some(players);
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_dialog_id_new() {
        let a = PlayerId::from("a").unwrap();
        let b = PlayerId::from("b").unwrap();
        let id1 = DialogId::new(a.clone(), b.clone());
        let id2 = DialogId::new(a.clone(), b.clone());
        // Dialog ids are invariant with respect to the order of participants
        assert_eq!(id1, id2);
        assert_eq!(id1.as_inner(), (&a, &b));
        assert_eq!(id2.as_inner(), (&a, &b));
    }
}