use std::{
    pin::pin,
    time::{Duration, Instant},
};

use actix_ws::AggregatedMessage;
use futures_util::{
    StreamExt as _,
    future::{Either, select},
};
use tokio::{sync::mpsc, time::interval};

use crate::{ChatServerHandle, ConnId};

/// How often heartbeat pings are sent
const HEARTBEAT_INTERVAL: Duration = Duration::from_secs(5);

/// How long before lack of client response causes a timeout
const CLIENT_TIMEOUT: Duration = Duration::from_secs(10);

/// Echo text & binary messages received from the client, respond to ping messages, and monitor
/// connection health to detect network issues and free up resources.
pub async fn chat_ws(
    chat_server: ChatServerHandle,
    mut session: actix_ws::Session,
    msg_stream: actix_ws::MessageStream,
) {
    log::info!("connected");

    let mut name = None;
    let mut last_heartbeat = Instant::now();
    let mut interval = interval(HEARTBEAT_INTERVAL);

    let (conn_tx, mut conn_rx) = mpsc::unbounded_channel();

    // unwrap: chat server is not dropped before the HTTP server
    let conn_id = chat_server.connect(conn_tx).await;

    let msg_stream = msg_stream
        .max_frame_size(128 * 1024)
        .aggregate_continuations()
        .max_continuation_size(2 * 1024 * 1024);

    let mut msg_stream = pin!(msg_stream);

    let close_reason = loop {
        // most of the futures we process need to be stack-pinned to work with select()

        let tick = pin!(interval.tick());
        let msg_rx = pin!(conn_rx.recv());

        // TODO: nested select is pretty gross for readability on the match
        let messages = pin!(select(msg_stream.next(), msg_rx));

        match select(messages, tick).await {
            // commands & messages received from client
            Either::Left((Either::Left((Some(Ok(msg)), _)), _)) => {
                log::debug!("msg: {msg:?}");

                match msg {
                    AggregatedMessage::Ping(bytes) => {
                        last_heartbeat = Instant::now();
                        // unwrap:
                        session.pong(&bytes).await.unwrap();
                    }

                    AggregatedMessage::Pong(_) => {
                        last_heartbeat = Instant::now();
                    }

                    AggregatedMessage::Text(text) => {
                        process_text_msg(&chat_server, &mut session, &text, conn_id, &mut name)
                            .await;
                    }

                    AggregatedMessage::Binary(_bin) => {
                        log::warn!("unexpected binary message");
                    }

                    AggregatedMessage::Close(reason) => break reason,
                }
            }

            // client WebSocket stream error
            Either::Left((Either::Left((Some(Err(err)), _)), _)) => {
                log::error!("{}", err);
                break None;
            }

            // client WebSocket stream ended
            Either::Left((Either::Left((None, _)), _)) => break None,

            // chat messages received from other room participants
            Either::Left((Either::Right((Some(chat_msg), _)), _)) => {
                session.text(chat_msg).await.unwrap();
            }

            // all connection's message senders were dropped
            Either::Left((Either::Right((None, _)), _)) => unreachable!(
                "all connection message senders were dropped; chat server may have panicked"
            ),

            // heartbeat internal tick
            Either::Right((_inst, _)) => {
                // if no heartbeat ping/pong received recently, close the connection
                if Instant::now().duration_since(last_heartbeat) > CLIENT_TIMEOUT {
                    log::info!(
                        "client has not sent heartbeat in over {CLIENT_TIMEOUT:?}; disconnecting"
                    );
                    break None;
                }

                // send heartbeat ping
                let _ = session.ping(b"").await;
            }
        };
    };

    chat_server.disconnect(conn_id);

    // attempt to close connection gracefully
    let _ = session.close(close_reason).await;
}

async fn process_text_msg(
    chat_server: &ChatServerHandle,
    session: &mut actix_ws::Session,
    text: &str,
    conn: ConnId,
    name: &mut Option<String>,
) {
    // strip leading and trailing whitespace (spaces, newlines, etc.)
    let msg = text.trim();

    // we check for /<cmd> type of messages
    if msg.starts_with('/') {
        let mut cmd_args = msg.splitn(2, ' ');

        // unwrap: we have guaranteed non-zero string length already
        match cmd_args.next().unwrap() {
            "/list" => {
                log::info!("conn {conn}: listing rooms");

                let rooms = chat_server.list_rooms().await;

                for room in rooms {
                    session.text(room).await.unwrap();
                }
            }

            "/join" => match cmd_args.next() {
                Some(room) => {
                    log::info!("conn {conn}: joining room {room}");

                    chat_server.join_room(conn, room).await;

                    session.text(format!("joined {room}")).await.unwrap();
                }

                None => {
                    session.text("!!! room name is required").await.unwrap();
                }
            },

            "/name" => match cmd_args.next() {
                Some(new_name) => {
                    log::info!("conn {conn}: setting name to: {new_name}");
                    name.replace(new_name.to_owned());
                }
                None => {
                    session.text("!!! name is required").await.unwrap();
                }
            },

            _ => {
                session
                    .text(format!("!!! unknown command: {msg}"))
                    .await
                    .unwrap();
            }
        }
    } else {
        // prefix message with our name, if assigned
        let msg = match name {
            Some(name) => format!("{name}: {msg}"),
            None => msg.to_owned(),
        };

        chat_server.send_message(conn, msg).await
    }
}