use crate::llm::providers::claude_code::{ClaudeCodeProvider, ClaudeCodeResult};
use crate::slog;
use matrix_sdk::{
    Client,
    config::SyncSettings,
    event_handler::Ctx,
    room::Room,
    ruma::{
        OwnedRoomId, OwnedUserId,
        events::room::message::{
            MessageType, OriginalSyncRoomMessageEvent, RoomMessageEventContent,
        },
    },
};
use std::path::PathBuf;
use std::sync::Arc;
use std::sync::atomic::{AtomicBool, Ordering};
use tokio::sync::watch;

use super::config::BotConfig;

/// Shared context injected into Matrix event handlers.
#[derive(Clone)]
pub struct BotContext {
    pub bot_user_id: OwnedUserId,
    pub target_room_id: OwnedRoomId,
    pub project_root: PathBuf,
}

/// Connect to the Matrix homeserver, join the configured room, and start
/// listening for messages. Runs the full Matrix sync loop — call from a
/// `tokio::spawn` task so it doesn't block the main thread.
pub async fn run_bot(config: BotConfig, project_root: PathBuf) -> Result<(), String> {
    let store_path = project_root.join(".story_kit").join("matrix_store");
    let client = Client::builder()
        .homeserver_url(&config.homeserver)
        .sqlite_store(&store_path, None)
        .build()
        .await
        .map_err(|e| format!("Failed to build Matrix client: {e}"))?;

    // Login
    client
        .matrix_auth()
        .login_username(&config.username, &config.password)
        .initial_device_display_name("Story Kit Bot")
        .await
        .map_err(|e| format!("Matrix login failed: {e}"))?;

    let bot_user_id = client
        .user_id()
        .ok_or_else(|| "No user ID after login".to_string())?
        .to_owned();

    slog!("[matrix-bot] Logged in as {bot_user_id}");

    // Parse and join the configured room
    let target_room_id: OwnedRoomId = config
        .room_id
        .parse()
        .map_err(|_| format!("Invalid room ID '{}'", config.room_id))?;

    // Try to join the room with a timeout. Conduit sometimes hangs or
    // returns errors on join if the bot is already a member.
    match tokio::time::timeout(
        std::time::Duration::from_secs(10),
        client.join_room_by_id(&target_room_id),
    )
    .await
    {
        Ok(Ok(_)) => slog!("[matrix-bot] Joined room {target_room_id}"),
        Ok(Err(e)) => slog!("[matrix-bot] Join room error (may already be a member): {e}"),
        Err(_) => slog!("[matrix-bot] Join room timed out (may already be a member)"),
    }

    let ctx = BotContext {
        bot_user_id,
        target_room_id,
        project_root,
    };

    // Register event handler and inject shared context
    client.add_event_handler_context(ctx);
    client.add_event_handler(on_room_message);

    slog!("[matrix-bot] Starting Matrix sync loop");

    // This blocks until the connection is terminated or an error occurs.
    client
        .sync(SyncSettings::default())
        .await
        .map_err(|e| format!("Matrix sync error: {e}"))?;

    Ok(())
}

/// Matrix event handler for room messages. Each invocation spawns an
/// independent task so the sync loop is not blocked by LLM calls.
async fn on_room_message(
    ev: OriginalSyncRoomMessageEvent,
    room: Room,
    Ctx(ctx): Ctx<BotContext>,
) {
    slog!(
        "[matrix-bot] Event received: room={} sender={} target={}",
        room.room_id(),
        ev.sender,
        ctx.target_room_id
    );

    // Only handle messages in the configured room
    if room.room_id() != &*ctx.target_room_id {
        slog!("[matrix-bot] Ignoring message from wrong room");
        return;
    }

    // Ignore the bot's own messages to prevent echo loops
    if ev.sender == ctx.bot_user_id {
        return;
    }

    // Only handle plain text messages
    let MessageType::Text(text_content) = ev.content.msgtype else {
        return;
    };

    let user_message = text_content.body.clone();
    slog!("[matrix-bot] Message from {}: {user_message}", ev.sender);

    // Spawn a separate task so the Matrix sync loop is not blocked while we
    // wait for the LLM response (which can take several seconds).
    tokio::spawn(async move {
        handle_message(room, ctx, user_message).await;
    });
}

/// Drain all complete paragraphs from `buffer` and return them.
///
/// A paragraph boundary is a double newline (`\n\n`). Each drained paragraph
/// is trimmed of surrounding whitespace; empty paragraphs are discarded.
/// The buffer is left with only the remaining incomplete text.
pub fn drain_complete_paragraphs(buffer: &mut String) -> Vec<String> {
    let mut paragraphs = Vec::new();
    while let Some(pos) = buffer.find("\n\n") {
        let chunk = buffer[..pos].trim().to_string();
        *buffer = buffer[pos + 2..].to_string();
        if !chunk.is_empty() {
            paragraphs.push(chunk);
        }
    }
    paragraphs
}

async fn handle_message(room: Room, ctx: BotContext, user_message: String) {
    let provider = ClaudeCodeProvider::new();
    let (cancel_tx, mut cancel_rx) = watch::channel(false);
    // Keep the sender alive for the duration of the call.
    let _cancel_tx = cancel_tx;

    // Channel for sending complete paragraphs to the Matrix posting task.
    let (msg_tx, mut msg_rx) = tokio::sync::mpsc::unbounded_channel::<String>();
    let msg_tx_for_callback = msg_tx.clone();

    // Spawn a task to post messages to Matrix as they arrive so we don't
    // block the LLM stream while waiting for Matrix send round-trips.
    let post_room = room.clone();
    let post_task = tokio::spawn(async move {
        while let Some(chunk) = msg_rx.recv().await {
            let _ = post_room
                .send(RoomMessageEventContent::text_plain(chunk))
                .await;
        }
    });

    // Shared state between the sync token callback and the async outer scope.
    let buffer = Arc::new(std::sync::Mutex::new(String::new()));
    let buffer_for_callback = Arc::clone(&buffer);
    let sent_any_chunk = Arc::new(AtomicBool::new(false));
    let sent_any_chunk_for_callback = Arc::clone(&sent_any_chunk);

    let result = provider
        .chat_stream(
            &user_message,
            &ctx.project_root.to_string_lossy(),
            None, // No session resumption for now (see story 182)
            &mut cancel_rx,
            move |token| {
                let mut buf = buffer_for_callback.lock().unwrap();
                buf.push_str(token);
                // Flush complete paragraphs as they arrive.
                let paragraphs = drain_complete_paragraphs(&mut buf);
                for chunk in paragraphs {
                    sent_any_chunk_for_callback.store(true, Ordering::Relaxed);
                    let _ = msg_tx_for_callback.send(chunk);
                }
            },
            |_thinking| {}, // Discard thinking tokens
            |_activity| {}, // Discard activity signals
        )
        .await;

    // Flush any remaining text that didn't end with a paragraph boundary.
    let remaining = buffer.lock().unwrap().trim().to_string();
    let did_send_any = sent_any_chunk.load(Ordering::Relaxed);

    match result {
        Ok(ClaudeCodeResult { messages, .. }) => {
            if !remaining.is_empty() {
                let _ = msg_tx.send(remaining);
            } else if !did_send_any {
                // Nothing was streamed at all (e.g. only tool calls with no
                // final text) — fall back to the last assistant message from
                // the structured result.
                let last_text = messages
                    .iter()
                    .rev()
                    .find(|m| m.role == crate::llm::types::Role::Assistant && !m.content.is_empty())
                    .map(|m| m.content.clone())
                    .unwrap_or_default();
                if !last_text.is_empty() {
                    let _ = msg_tx.send(last_text);
                }
            }
        }
        Err(e) => {
            slog!("[matrix-bot] LLM error: {e}");
            // Discard any partial buffered text and send the error as one message.
            let _ = msg_tx.send(format!("Error processing your request: {e}"));
        }
    }

    // Drop the sender to signal the posting task that no more messages will
    // arrive, then wait for all pending Matrix sends to complete.
    drop(msg_tx);
    let _ = post_task.await;
}

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

    #[test]
    fn bot_context_is_clone() {
        // BotContext must be Clone for the Matrix event handler injection.
        fn assert_clone<T: Clone>() {}
        assert_clone::<BotContext>();
    }

    #[test]
    fn drain_complete_paragraphs_no_boundary_returns_empty() {
        let mut buf = "Hello World".to_string();
        let paras = drain_complete_paragraphs(&mut buf);
        assert!(paras.is_empty());
        assert_eq!(buf, "Hello World");
    }

    #[test]
    fn drain_complete_paragraphs_single_boundary() {
        let mut buf = "Paragraph one.\n\nParagraph two.".to_string();
        let paras = drain_complete_paragraphs(&mut buf);
        assert_eq!(paras, vec!["Paragraph one."]);
        assert_eq!(buf, "Paragraph two.");
    }

    #[test]
    fn drain_complete_paragraphs_multiple_boundaries() {
        let mut buf = "A\n\nB\n\nC".to_string();
        let paras = drain_complete_paragraphs(&mut buf);
        assert_eq!(paras, vec!["A", "B"]);
        assert_eq!(buf, "C");
    }

    #[test]
    fn drain_complete_paragraphs_trailing_boundary() {
        let mut buf = "A\n\nB\n\n".to_string();
        let paras = drain_complete_paragraphs(&mut buf);
        assert_eq!(paras, vec!["A", "B"]);
        assert_eq!(buf, "");
    }

    #[test]
    fn drain_complete_paragraphs_empty_input() {
        let mut buf = String::new();
        let paras = drain_complete_paragraphs(&mut buf);
        assert!(paras.is_empty());
        assert_eq!(buf, "");
    }

    #[test]
    fn drain_complete_paragraphs_skips_empty_chunks() {
        // Consecutive double-newlines produce no empty paragraphs.
        let mut buf = "\n\n\n\nHello".to_string();
        let paras = drain_complete_paragraphs(&mut buf);
        assert!(paras.is_empty());
        assert_eq!(buf, "Hello");
    }

    #[test]
    fn drain_complete_paragraphs_trims_whitespace() {
        let mut buf = "  Hello  \n\n  World  ".to_string();
        let paras = drain_complete_paragraphs(&mut buf);
        assert_eq!(paras, vec!["Hello"]);
        assert_eq!(buf, "  World  ");
    }

    #[test]
    fn drain_complete_paragraphs_incremental_simulation() {
        // Simulate tokens arriving one character at a time.
        let mut buf = String::new();
        let mut all_paragraphs = Vec::new();

        for ch in "First para.\n\nSecond para.\n\nThird.".chars() {
            buf.push(ch);
            all_paragraphs.extend(drain_complete_paragraphs(&mut buf));
        }

        assert_eq!(all_paragraphs, vec!["First para.", "Second para."]);
        assert_eq!(buf, "Third.");
    }
}