//! Transport-agnostic LLM turn driver shared by every chat transport that
//! forwards a non-command message to Claude Code (currently Discord and
//! WhatsApp). Formatting, chunking, and error-message differences between
//! transports are captured by the small [`TransportFormat`] trait; the
//! streaming/session/history plumbing lives once in [`run_llm_turn`].

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

use tokio::sync::Mutex as TokioMutex;

use crate::chat::ChatTransport;
use crate::chat::transport::matrix::{ConversationEntry, ConversationRole, RoomConversation};
use crate::http::context::PermissionDecision;
use crate::services::Services;
use crate::slog;

/// Per-transport formatting hooks needed to run a shared LLM turn.
pub trait TransportFormat: Send + Sync {
    /// Convert markdown into the transport's native formatting and split it
    /// into messages that respect the transport's size limit. Transports
    /// without a size limit (or that don't chunk) return a single-element
    /// vector.
    fn format_and_chunk(&self, markdown: &str) -> Vec<String>;

    /// Prefix used in `slog!` calls for this transport, e.g. `"[discord]"`.
    fn log_prefix(&self) -> &'static str;

    /// Convert an LLM error into a user-facing message.
    fn format_error(&self, err: &str) -> String;
}

/// Build the prompt for an LLM turn, prepending any pending CRDT
/// pipeline-transition events as a `<system-reminder>` block.
pub fn build_llm_prompt(persona: &str, bot_name: &str, user: &str, user_message: &str) -> String {
    let event_ctx = crate::llm_session::assemble_prompt_context(persona);
    format!(
        "{event_ctx}[Your name is {bot_name}. Refer to yourself as {bot_name}, not Claude.]\n\n{user}: {user_message}"
    )
}

/// Everything a shared LLM turn needs beyond formatting: transport handle,
/// routing/history key, display name, and shared services/history state.
pub struct LlmTurnContext<'a> {
    /// Chat transport used to send/post messages for this turn.
    pub transport: Arc<dyn ChatTransport>,
    /// Routing and history key (Discord channel id, WhatsApp phone number).
    pub key: &'a str,
    /// Display name stored in conversation history and used in the prompt.
    pub user: &'a str,
    /// Shared services bundle (project root, permissions, agents).
    pub services: &'a Arc<Services>,
    /// Per-key conversation history.
    pub history: &'a Arc<TokioMutex<HashMap<String, RoomConversation>>>,
    /// Maximum number of conversation entries to keep per key.
    pub history_size: usize,
    /// Persists conversation history to disk.
    pub save_history: fn(&std::path::Path, &HashMap<String, RoomConversation>),
}

/// Forward a message to Claude Code and stream the response back through the
/// transport, handling permission prompts and conversation history.
///
/// `F` is taken by value (and cloned into the posting task) rather than by
/// reference because the posting task is a `tokio::spawn`ed future, which
/// requires `'static` — the formatter types are zero-sized markers, so
/// cloning is free.
pub async fn run_llm_turn<F: TransportFormat + Clone + 'static>(
    ctx: LlmTurnContext<'_>,
    format: F,
    user_message: &str,
) {
    use crate::chat::util::drain_complete_paragraphs;
    use crate::llm::providers::claude_code::{ClaudeCodeProvider, ClaudeCodeResult};
    use std::sync::atomic::{AtomicBool, Ordering};
    use tokio::sync::watch;

    let prefix = format.log_prefix();

    // Look up existing session ID for this key.
    let resume_session_id: Option<String> = {
        let guard = ctx.history.lock().await;
        guard.get(ctx.key).and_then(|conv| conv.session_id.clone())
    };

    let bot_name = &ctx.services.bot_name;
    let persona = bot_name.to_lowercase();
    let prompt = build_llm_prompt(&persona, bot_name, ctx.user, user_message);

    let provider = ClaudeCodeProvider::new();
    let (_cancel_tx, mut cancel_rx) = watch::channel(false);

    // Channel for sending complete chunks to the 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 as they arrive.
    let post_transport = Arc::clone(&ctx.transport);
    let post_key = ctx.key.to_string();
    let post_format = format.clone();
    let post_task = tokio::spawn(async move {
        while let Some(chunk) = msg_rx.recv().await {
            for part in post_format.format_and_chunk(&chunk) {
                let _ = post_transport.send_message(&post_key, &part, "").await;
            }
        }
    });

    // Shared buffer between the sync token callback and the async 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 project_root_str = ctx.services.project_root.to_string_lossy().to_string();
    let chat_fut = provider.chat_stream(
        &prompt,
        &project_root_str,
        resume_session_id.as_deref(),
        None,
        None,
        &mut cancel_rx,
        move |token| {
            let mut buf = buffer_for_callback.lock().unwrap();
            buf.push_str(token);
            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| {},
        |_activity| {},
    );
    tokio::pin!(chat_fut);

    // Register as a permission responder for the duration of this chat turn.
    let (_perm_guard, mut perm_rx) = ctx.services.permission_registry.register();

    let result = loop {
        tokio::select! {
            r = &mut chat_fut => break r,

            Some(perm_fwd) = perm_rx.recv() => {
                let prompt_msg = format!(
                    "**Permission Request**\n\nTool: `{}`\n```json\n{}\n```\n\nReply **yes** to approve or **no** to deny.",
                    perm_fwd.tool_name,
                    serde_json::to_string_pretty(&perm_fwd.tool_input)
                        .unwrap_or_else(|_| perm_fwd.tool_input.to_string()),
                );
                for part in format.format_and_chunk(&prompt_msg) {
                    let _ = ctx.transport.send_message(ctx.key, &part, "").await;
                }

                // Keyed by request_id (not just key) so a second
                // concurrent request doesn't drop the first's sender.
                ctx.services
                    .pending_perm_replies
                    .insert(ctx.key.to_string(), perm_fwd.request_id.clone(), perm_fwd.response_tx)
                    .await;

                // Spawn a timeout task: auto-deny if the user does not respond.
                let pending = Arc::clone(&ctx.services.pending_perm_replies);
                let timeout_key = ctx.key.to_string();
                let timeout_request_id = perm_fwd.request_id.clone();
                let timeout_transport = Arc::clone(&ctx.transport);
                let timeout_secs = ctx.services.permission_timeout_secs;
                tokio::spawn(async move {
                    tokio::time::sleep(std::time::Duration::from_secs(timeout_secs)).await;
                    if let Some(tx) = pending.remove_by_request_id(&timeout_key, &timeout_request_id).await {
                        let _ = tx.send(PermissionDecision::Deny);
                        let msg = "Permission request timed out — denied (fail-closed).";
                        let _ = timeout_transport.send_message(&timeout_key, msg, "").await;
                    }
                });
            }
        }
    };

    // Flush remaining text.
    let remaining = buffer.lock().unwrap().trim().to_string();
    let did_send_any = sent_any_chunk.load(Ordering::Relaxed);

    let (assistant_reply, new_session_id) = match result {
        Ok(ClaudeCodeResult {
            messages,
            session_id,
            ..
        }) => {
            let reply = if !remaining.is_empty() {
                let _ = msg_tx.send(remaining.clone());
                remaining
            } else if !did_send_any {
                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.clone());
                }
                last_text
            } else {
                remaining
            };
            slog!("{prefix} session_id from chat_stream: {:?}", session_id);
            (reply, session_id)
        }
        Err(e) => {
            slog!("{prefix} LLM error: {e}");
            let err_msg = format.format_error(&e);
            let _ = msg_tx.send(err_msg.clone());
            (err_msg, None)
        }
    };

    // Signal the posting task to finish and wait for it.
    drop(msg_tx);
    let _ = post_task.await;

    // Record this exchange in conversation history.
    if !assistant_reply.starts_with("Error processing") {
        let mut guard = ctx.history.lock().await;
        let conv = guard.entry(ctx.key.to_string()).or_default();

        if new_session_id.is_some() {
            conv.session_id = new_session_id;
        }

        conv.entries.push(ConversationEntry {
            role: ConversationRole::User,
            sender: ctx.user.to_string(),
            content: user_message.to_string(),
        });
        conv.entries.push(ConversationEntry {
            role: ConversationRole::Assistant,
            sender: String::new(),
            content: assistant_reply,
        });

        // Trim to configured maximum.
        if conv.entries.len() > ctx.history_size {
            let excess = conv.entries.len() - ctx.history_size;
            conv.entries.drain(..excess);
        }

        (ctx.save_history)(&ctx.services.project_root, &guard);
    }
}