use crate::http::context::AppContext;
use crate::http::workflow::{PipelineState, load_pipeline_state};
use crate::io::watcher::WatcherEvent;
use crate::llm::chat;
use crate::llm::types::Message;
use futures::{SinkExt, StreamExt};
use poem::handler;
use poem::web::Data;
use poem::web::websocket::{Message as WsMessage, WebSocket};
use serde::{Deserialize, Serialize};
use std::sync::Arc;
use tokio::sync::mpsc;

#[derive(Deserialize)]
#[serde(tag = "type", rename_all = "snake_case")]
/// WebSocket request messages sent by the client.
///
/// - `chat` starts a streaming chat session.
/// - `cancel` stops the active session.
enum WsRequest {
    Chat {
        messages: Vec<Message>,
        config: chat::ProviderConfig,
    },
    Cancel,
}

#[derive(Serialize)]
#[serde(tag = "type", rename_all = "snake_case")]
/// WebSocket response messages sent by the server.
///
/// - `token` streams partial model output.
/// - `update` pushes the updated message history.
/// - `error` reports a request or processing failure.
/// - `work_item_changed` notifies that a `.story_kit/work/` file changed.
enum WsResponse {
    Token {
        content: String,
    },
    Update {
        messages: Vec<Message>,
    },
    /// Session ID for Claude Code conversation resumption.
    SessionId {
        session_id: String,
    },
    Error {
        message: String,
    },
    /// Filesystem watcher notification: a work-pipeline file was created or
    /// modified and auto-committed. The frontend can use this to refresh its
    /// story/bug list without polling.
    WorkItemChanged {
        stage: String,
        item_id: String,
        action: String,
        commit_msg: String,
    },
    /// Full pipeline state pushed on connect and after every watcher event.
    PipelineState {
        upcoming: Vec<crate::http::workflow::UpcomingStory>,
        current: Vec<crate::http::workflow::UpcomingStory>,
        qa: Vec<crate::http::workflow::UpcomingStory>,
        merge: Vec<crate::http::workflow::UpcomingStory>,
    },
}

impl From<WatcherEvent> for WsResponse {
    fn from(e: WatcherEvent) -> Self {
        WsResponse::WorkItemChanged {
            stage: e.stage,
            item_id: e.item_id,
            action: e.action,
            commit_msg: e.commit_msg,
        }
    }
}

impl From<PipelineState> for WsResponse {
    fn from(s: PipelineState) -> Self {
        WsResponse::PipelineState {
            upcoming: s.upcoming,
            current: s.current,
            qa: s.qa,
            merge: s.merge,
        }
    }
}

#[handler]
/// WebSocket endpoint for streaming chat responses, cancellation, and
/// filesystem watcher notifications.
///
/// Accepts JSON `WsRequest` messages and streams `WsResponse` messages.
pub async fn ws_handler(ws: WebSocket, ctx: Data<&Arc<AppContext>>) -> impl poem::IntoResponse {
    let ctx = ctx.0.clone();
    ws.on_upgrade(move |socket| async move {
        let (mut sink, mut stream) = socket.split();
        let (tx, mut rx) = mpsc::unbounded_channel::<WsResponse>();

        let forward = tokio::spawn(async move {
            while let Some(msg) = rx.recv().await {
                if let Ok(text) = serde_json::to_string(&msg)
                    && sink.send(WsMessage::Text(text)).await.is_err()
                {
                    break;
                }
            }
        });

        // Push initial pipeline state to the client on connect.
        if let Ok(state) = load_pipeline_state(ctx.as_ref()) {
            let _ = tx.send(state.into());
        }

        // Subscribe to filesystem watcher events and forward them to the client.
        // After each watcher event, also push the updated pipeline state.
        let tx_watcher = tx.clone();
        let ctx_watcher = ctx.clone();
        let mut watcher_rx = ctx.watcher_tx.subscribe();
        tokio::spawn(async move {
            loop {
                match watcher_rx.recv().await {
                    Ok(evt) => {
                        if tx_watcher.send(evt.into()).is_err() {
                            break;
                        }
                        // Push refreshed pipeline state after the change.
                        if let Ok(state) = load_pipeline_state(ctx_watcher.as_ref())
                            && tx_watcher.send(state.into()).is_err()
                        {
                            break;
                        }
                    }
                    // Lagged: skip missed events, keep going.
                    Err(tokio::sync::broadcast::error::RecvError::Lagged(_)) => continue,
                    Err(tokio::sync::broadcast::error::RecvError::Closed) => break,
                }
            }
        });

        while let Some(Ok(msg)) = stream.next().await {
            if let WsMessage::Text(text) = msg {
                let parsed: Result<WsRequest, _> = serde_json::from_str(&text);
                match parsed {
                    Ok(WsRequest::Chat { messages, config }) => {
                        let tx_updates = tx.clone();
                        let tx_tokens = tx.clone();
                        let ctx_clone = ctx.clone();

                        let result = chat::chat(
                            messages,
                            config,
                            &ctx_clone.state,
                            ctx_clone.store.as_ref(),
                            |history| {
                                let _ = tx_updates.send(WsResponse::Update {
                                    messages: history.to_vec(),
                                });
                            },
                            |token| {
                                let _ = tx_tokens.send(WsResponse::Token {
                                    content: token.to_string(),
                                });
                            },
                        )
                        .await;

                        match result {
                            Ok(chat_result) => {
                                if let Some(sid) = chat_result.session_id {
                                    let _ = tx.send(WsResponse::SessionId { session_id: sid });
                                }
                            }
                            Err(err) => {
                                let _ = tx.send(WsResponse::Error { message: err });
                            }
                        }
                    }
                    Ok(WsRequest::Cancel) => {
                        let _ = chat::cancel_chat(&ctx.state);
                    }
                    Err(err) => {
                        let _ = tx.send(WsResponse::Error {
                            message: format!("Invalid request: {err}"),
                        });
                    }
                }
            }
        }

        drop(tx);
        let _ = forward.await;
    })
}