use crate::llm::providers::claude_code::{ClaudeCodeProvider, ClaudeCodeResult};
use crate::slog;
use pulldown_cmark::{Options, Parser, html};
use matrix_sdk::{
    Client,
    config::SyncSettings,
    event_handler::Ctx,
    room::Room,
    ruma::{
        OwnedEventId, OwnedRoomId, OwnedUserId,
        events::room::message::{
            MessageType, OriginalSyncRoomMessageEvent, Relation,
            RoomMessageEventContent, RoomMessageEventContentWithoutRelation,
        },
    },
};
use std::collections::{HashMap, HashSet};
use std::path::PathBuf;
use std::sync::Arc;
use std::sync::atomic::{AtomicBool, Ordering};
use tokio::sync::watch;
use tokio::sync::Mutex as TokioMutex;

use super::config::BotConfig;

// ---------------------------------------------------------------------------
// Conversation history types
// ---------------------------------------------------------------------------

/// Role of a participant in the conversation history.
#[derive(Clone, Debug, PartialEq)]
pub enum ConversationRole {
    /// A message sent by a Matrix room participant.
    User,
    /// A response generated by the bot / LLM.
    Assistant,
}

/// A single turn in the per-room conversation history.
#[derive(Clone, Debug)]
pub struct ConversationEntry {
    pub role: ConversationRole,
    /// Matrix user ID (e.g. `@alice:example.com`).  Empty for assistant turns.
    pub sender: String,
    pub content: String,
}

/// Per-room conversation history, keyed by room ID.
///
/// Wrapped in `Arc<TokioMutex<…>>` so it can be shared across concurrent
/// event-handler tasks without blocking the sync loop.
pub type ConversationHistory = Arc<TokioMutex<HashMap<OwnedRoomId, Vec<ConversationEntry>>>>;

// ---------------------------------------------------------------------------
// Bot context
// ---------------------------------------------------------------------------

/// Shared context injected into Matrix event handlers.
#[derive(Clone)]
pub struct BotContext {
    pub bot_user_id: OwnedUserId,
    /// All room IDs the bot listens in.
    pub target_room_ids: Vec<OwnedRoomId>,
    pub project_root: PathBuf,
    pub allowed_users: Vec<String>,
    /// Shared, per-room rolling conversation history.
    pub history: ConversationHistory,
    /// Maximum number of entries to keep per room before trimming the oldest.
    pub history_size: usize,
    /// Event IDs of messages the bot has sent.  Used to detect replies to the
    /// bot so it can continue a conversation thread without requiring an
    /// explicit `@mention` on every follow-up.
    pub bot_sent_event_ids: Arc<TokioMutex<HashSet<OwnedEventId>>>,
}

// ---------------------------------------------------------------------------
// Bot entry point
// ---------------------------------------------------------------------------

/// Connect to the Matrix homeserver, join all configured rooms, 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}");

    if config.allowed_users.is_empty() {
        return Err(
            "allowed_users is empty in bot.toml — refusing to start (fail-closed). \
             Add at least one Matrix user ID to allowed_users."
                .to_string(),
        );
    }

    slog!(
        "[matrix-bot] Allowed users: {:?}",
        config.allowed_users
    );

    // Parse and join all configured rooms.
    let mut target_room_ids: Vec<OwnedRoomId> = Vec::new();
    for room_id_str in config.effective_room_ids() {
        let room_id: OwnedRoomId = room_id_str
            .parse()
            .map_err(|_| format!("Invalid room ID '{room_id_str}'"))?;

        // Try to join 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(&room_id),
        )
        .await
        {
            Ok(Ok(_)) => slog!("[matrix-bot] Joined room {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)"),
        }

        target_room_ids.push(room_id);
    }

    if target_room_ids.is_empty() {
        return Err("No valid room IDs configured — cannot start".to_string());
    }

    slog!(
        "[matrix-bot] Listening in {} room(s): {:?}",
        target_room_ids.len(),
        target_room_ids
    );

    let ctx = BotContext {
        bot_user_id,
        target_room_ids,
        project_root,
        allowed_users: config.allowed_users,
        history: Arc::new(TokioMutex::new(HashMap::new())),
        history_size: config.history_size,
        bot_sent_event_ids: Arc::new(TokioMutex::new(HashSet::new())),
    };

    // 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(())
}

// ---------------------------------------------------------------------------
// Address-filtering helpers
// ---------------------------------------------------------------------------

/// Returns `true` if `body` contains a mention of the bot.
///
/// Two forms are recognised:
/// - The bot's full Matrix user ID (e.g. `@timmy:homeserver.local`)
/// - The bot's local part prefixed with `@` (e.g. `@timmy`)
///
/// A short mention (`@timmy`) is only counted when it is not immediately
/// followed by an alphanumeric character, hyphen, or underscore — this avoids
/// false-positives where a longer username (e.g. `@timmybot`) shares the same
/// prefix.
pub fn mentions_bot(body: &str, bot_user_id: &OwnedUserId) -> bool {
    let full_id = bot_user_id.as_str();
    if body.contains(full_id) {
        return true;
    }

    let short = format!("@{}", bot_user_id.localpart());
    let mut start = 0;
    while let Some(rel) = body[start..].find(short.as_str()) {
        let abs = start + rel;
        let after = abs + short.len();
        let next = body[after..].chars().next();
        let is_word_end =
            next.is_none_or(|c| !c.is_alphanumeric() && c != '-' && c != '_');
        if is_word_end {
            return true;
        }
        start = abs + 1;
    }
    false
}

/// Returns `true` if the message's `relates_to` field references an event that
/// the bot previously sent (i.e. the message is a reply or thread-reply to a
/// bot message).
async fn is_reply_to_bot(
    relates_to: Option<&Relation<RoomMessageEventContentWithoutRelation>>,
    bot_sent_event_ids: &TokioMutex<HashSet<OwnedEventId>>,
) -> bool {
    let candidate_ids: Vec<&OwnedEventId> = match relates_to {
        Some(Relation::Reply { in_reply_to }) => vec![&in_reply_to.event_id],
        Some(Relation::Thread(thread)) => {
            let mut ids = vec![&thread.event_id];
            if let Some(irti) = &thread.in_reply_to {
                ids.push(&irti.event_id);
            }
            ids
        }
        _ => return false,
    };
    let guard = bot_sent_event_ids.lock().await;
    candidate_ids.iter().any(|id| guard.contains(*id))
}

// ---------------------------------------------------------------------------
// Event handler
// ---------------------------------------------------------------------------

/// 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>,
) {
    let incoming_room_id = room.room_id().to_owned();

    slog!(
        "[matrix-bot] Event received: room={} sender={}",
        incoming_room_id,
        ev.sender,
    );

    // Only handle messages from rooms we are configured to listen in.
    if !ctx
        .target_room_ids
        .iter()
        .any(|r| r == &incoming_room_id)
    {
        slog!("[matrix-bot] Ignoring message from unconfigured room {incoming_room_id}");
        return;
    }

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

    // Only respond to users on the allowlist (fail-closed).
    if !ctx.allowed_users.iter().any(|u| u == ev.sender.as_str()) {
        slog!(
            "[matrix-bot] Ignoring message from unauthorised user: {}",
            ev.sender
        );
        return;
    }

    // Only handle plain text messages.
    let body = match &ev.content.msgtype {
        MessageType::Text(t) => t.body.clone(),
        _ => return,
    };

    // Only respond when the bot is directly addressed (mentioned by name/ID)
    // or when the message is a reply to one of the bot's own messages.
    if !mentions_bot(&body, &ctx.bot_user_id)
        && !is_reply_to_bot(
            ev.content.relates_to.as_ref(),
            &ctx.bot_sent_event_ids,
        )
        .await
    {
        slog!(
            "[matrix-bot] Ignoring unaddressed message from {}",
            ev.sender
        );
        return;
    }

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

    // 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, incoming_room_id, ctx, sender, user_message).await;
    });
}

// ---------------------------------------------------------------------------
// Message handler
// ---------------------------------------------------------------------------

/// Build a context string from the room's conversation history to prepend to
/// the user's current message. Returns an empty string when history is empty.
fn build_context_prefix(
    history: &[ConversationEntry],
    current_sender: &str,
    current_message: &str,
) -> String {
    if history.is_empty() {
        return format!("{current_sender}: {current_message}");
    }

    let mut out = String::from("[Conversation history for this room]\n");
    for entry in history {
        match entry.role {
            ConversationRole::User => {
                out.push_str(&format!("User ({}): {}\n", entry.sender, entry.content));
            }
            ConversationRole::Assistant => {
                out.push_str(&format!("Assistant: {}\n", entry.content));
            }
        }
    }
    out.push('\n');
    out.push_str(&format!(
        "Current message from {current_sender}: {current_message}"
    ));
    out
}

async fn handle_message(
    room: Room,
    room_id: OwnedRoomId,
    ctx: BotContext,
    sender: String,
    user_message: String,
) {
    // Read current history for this room before calling the LLM.
    let history_snapshot: Vec<ConversationEntry> = {
        let guard = ctx.history.lock().await;
        guard.get(&room_id).cloned().unwrap_or_default()
    };

    // Build the prompt with conversation context.
    let prompt_with_context =
        build_context_prefix(&history_snapshot, &sender, &user_message);

    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 sent_ids = Arc::clone(&ctx.bot_sent_event_ids);
    let post_task = tokio::spawn(async move {
        while let Some(chunk) = msg_rx.recv().await {
            let html = markdown_to_html(&chunk);
            if let Ok(response) = post_room
                .send(RoomMessageEventContent::text_html(chunk, html))
                .await
            {
                sent_ids.lock().await.insert(response.event_id);
            }
        }
    });

    // 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(
            &prompt_with_context,
            &ctx.project_root.to_string_lossy(),
            None, // Each Matrix conversation turn is independent at the Claude Code session level.
            &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);

    let assistant_reply = match result {
        Ok(ClaudeCodeResult { messages, .. }) => {
            if !remaining.is_empty() {
                let _ = msg_tx.send(remaining.clone());
                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.clone());
                }
                last_text
            } else {
                remaining
            }
        }
        Err(e) => {
            slog!("[matrix-bot] LLM error: {e}");
            let err_msg = format!("Error processing your request: {e}");
            let _ = msg_tx.send(err_msg.clone());
            err_msg
        }
    };

    // 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;

    // Record this exchange in the per-room conversation history.
    if !assistant_reply.starts_with("Error processing") {
        let mut guard = ctx.history.lock().await;
        let entries = guard.entry(room_id).or_default();
        entries.push(ConversationEntry {
            role: ConversationRole::User,
            sender: sender.clone(),
            content: user_message,
        });
        entries.push(ConversationEntry {
            role: ConversationRole::Assistant,
            sender: String::new(),
            content: assistant_reply,
        });
        // Trim to the configured maximum, dropping the oldest entries first.
        if entries.len() > ctx.history_size {
            let excess = entries.len() - ctx.history_size;
            entries.drain(..excess);
        }
    }
}

// ---------------------------------------------------------------------------
// Markdown rendering helper
// ---------------------------------------------------------------------------

/// Convert a Markdown string to an HTML string using pulldown-cmark.
///
/// Enables the standard extension set (tables, footnotes, strikethrough,
/// tasklists) so that common Markdown constructs render correctly in Matrix
/// clients such as Element.
pub fn markdown_to_html(markdown: &str) -> String {
    let options = Options::ENABLE_TABLES
        | Options::ENABLE_FOOTNOTES
        | Options::ENABLE_STRIKETHROUGH
        | Options::ENABLE_TASKLISTS;
    let parser = Parser::new_ext(markdown, options);
    let mut html_output = String::new();
    html::push_html(&mut html_output, parser);
    html_output
}

// ---------------------------------------------------------------------------
// Paragraph buffering helper
// ---------------------------------------------------------------------------

/// Returns `true` when `text` ends while inside an open fenced code block.
///
/// A fenced code block opens and closes on lines that start with ` ``` `
/// (three or more backticks).  We count the fence markers and return `true`
/// when the count is odd (a fence was opened but not yet closed).
fn is_inside_code_fence(text: &str) -> bool {
    let mut in_fence = false;
    for line in text.lines() {
        if line.trim_start().starts_with("```") {
            in_fence = !in_fence;
        }
    }
    in_fence
}

/// 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.
///
/// **Code-fence awareness:** a `\n\n` that occurs *inside* a fenced code
/// block (delimited by ` ``` ` lines) is **not** treated as a paragraph
/// boundary.  This prevents a blank line inside a code block from splitting
/// the fence across multiple Matrix messages, which would corrupt the
/// rendering of the second half.
pub fn drain_complete_paragraphs(buffer: &mut String) -> Vec<String> {
    let mut paragraphs = Vec::new();
    let mut search_from = 0;
    loop {
        let Some(pos) = buffer[search_from..].find("\n\n") else {
            break;
        };
        let abs_pos = search_from + pos;
        // Only split at this boundary when we are NOT inside a code fence.
        if is_inside_code_fence(&buffer[..abs_pos]) {
            // Skip past this \n\n and keep looking for the next boundary.
            search_from = abs_pos + 2;
        } else {
            let chunk = buffer[..abs_pos].trim().to_string();
            *buffer = buffer[abs_pos + 2..].to_string();
            search_from = 0;
            if !chunk.is_empty() {
                paragraphs.push(chunk);
            }
        }
    }
    paragraphs
}

// ---------------------------------------------------------------------------
// Tests
// ---------------------------------------------------------------------------

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

    // -- mentions_bot -------------------------------------------------------

    fn make_user_id(s: &str) -> OwnedUserId {
        s.parse().unwrap()
    }

    #[test]
    fn mentions_bot_by_full_id() {
        let uid = make_user_id("@timmy:homeserver.local");
        assert!(mentions_bot("hello @timmy:homeserver.local can you help?", &uid));
    }

    #[test]
    fn mentions_bot_by_localpart_at_start() {
        let uid = make_user_id("@timmy:homeserver.local");
        assert!(mentions_bot("@timmy please list open stories", &uid));
    }

    #[test]
    fn mentions_bot_by_localpart_mid_sentence() {
        let uid = make_user_id("@timmy:homeserver.local");
        assert!(mentions_bot("hey @timmy what's the status?", &uid));
    }

    #[test]
    fn mentions_bot_not_mentioned() {
        let uid = make_user_id("@timmy:homeserver.local");
        assert!(!mentions_bot("can someone help me with this PR?", &uid));
    }

    #[test]
    fn mentions_bot_no_false_positive_longer_username() {
        // "@timmybot" must NOT match "@timmy"
        let uid = make_user_id("@timmy:homeserver.local");
        assert!(!mentions_bot("hey @timmybot can you help?", &uid));
    }

    #[test]
    fn mentions_bot_at_end_of_string() {
        let uid = make_user_id("@timmy:homeserver.local");
        assert!(mentions_bot("shoutout to @timmy", &uid));
    }

    #[test]
    fn mentions_bot_followed_by_comma() {
        let uid = make_user_id("@timmy:homeserver.local");
        assert!(mentions_bot("@timmy, can you help?", &uid));
    }

    // -- is_reply_to_bot ----------------------------------------------------

    #[tokio::test]
    async fn is_reply_to_bot_direct_reply_match() {
        let sent: Arc<TokioMutex<HashSet<OwnedEventId>>> =
            Arc::new(TokioMutex::new(HashSet::new()));
        let event_id: OwnedEventId = "$abc123:example.com".parse().unwrap();
        sent.lock().await.insert(event_id.clone());

        let in_reply_to = matrix_sdk::ruma::events::relation::InReplyTo::new(event_id);
        let relates_to: Option<Relation<RoomMessageEventContentWithoutRelation>> =
            Some(Relation::Reply { in_reply_to });

        assert!(is_reply_to_bot(relates_to.as_ref(), &sent).await);
    }

    #[tokio::test]
    async fn is_reply_to_bot_direct_reply_no_match() {
        let sent: Arc<TokioMutex<HashSet<OwnedEventId>>> =
            Arc::new(TokioMutex::new(HashSet::new()));
        // sent is empty — this event was not sent by the bot

        let in_reply_to = matrix_sdk::ruma::events::relation::InReplyTo::new(
            "$other:example.com".parse::<OwnedEventId>().unwrap(),
        );
        let relates_to: Option<Relation<RoomMessageEventContentWithoutRelation>> =
            Some(Relation::Reply { in_reply_to });

        assert!(!is_reply_to_bot(relates_to.as_ref(), &sent).await);
    }

    #[tokio::test]
    async fn is_reply_to_bot_no_relation() {
        let sent: Arc<TokioMutex<HashSet<OwnedEventId>>> =
            Arc::new(TokioMutex::new(HashSet::new()));
        let relates_to: Option<Relation<RoomMessageEventContentWithoutRelation>> = None;
        assert!(!is_reply_to_bot(relates_to.as_ref(), &sent).await);
    }

    #[tokio::test]
    async fn is_reply_to_bot_thread_root_match() {
        let sent: Arc<TokioMutex<HashSet<OwnedEventId>>> =
            Arc::new(TokioMutex::new(HashSet::new()));
        let root_id: OwnedEventId = "$root123:example.com".parse().unwrap();
        sent.lock().await.insert(root_id.clone());

        // Thread reply where the thread root is the bot's message
        let thread = matrix_sdk::ruma::events::relation::Thread::plain(
            root_id,
            "$latest:example.com".parse::<OwnedEventId>().unwrap(),
        );
        let relates_to: Option<Relation<RoomMessageEventContentWithoutRelation>> =
            Some(Relation::Thread(thread));

        assert!(is_reply_to_bot(relates_to.as_ref(), &sent).await);
    }

    // -- markdown_to_html ---------------------------------------------------

    #[test]
    fn markdown_to_html_bold() {
        let html = markdown_to_html("**bold**");
        assert!(html.contains("<strong>bold</strong>"), "expected <strong>: {html}");
    }

    #[test]
    fn markdown_to_html_unordered_list() {
        let html = markdown_to_html("- item one\n- item two");
        assert!(html.contains("<ul>"), "expected <ul>: {html}");
        assert!(html.contains("<li>item one</li>"), "expected list item: {html}");
    }

    #[test]
    fn markdown_to_html_inline_code() {
        let html = markdown_to_html("`inline_code()`");
        assert!(html.contains("<code>inline_code()</code>"), "expected <code>: {html}");
    }

    #[test]
    fn markdown_to_html_code_block() {
        let html = markdown_to_html("```rust\nfn main() {}\n```");
        assert!(html.contains("<pre>"), "expected <pre>: {html}");
        assert!(html.contains("<code"), "expected <code> inside pre: {html}");
        assert!(html.contains("fn main() {}"), "expected code content: {html}");
    }

    #[test]
    fn markdown_to_html_plain_text_passthrough() {
        let html = markdown_to_html("Hello, world!");
        assert!(html.contains("Hello, world!"), "expected plain text passthrough: {html}");
    }

    // -- bot_context_is_clone -----------------------------------------------

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

    // -- drain_complete_paragraphs ------------------------------------------

    #[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  ");
    }

    // -- drain_complete_paragraphs: code-fence awareness -------------------

    #[test]
    fn drain_complete_paragraphs_code_fence_blank_line_not_split() {
        // A blank line inside a fenced code block must NOT trigger a split.
        // Before the fix the function would split at the blank line and the
        // second half would be sent without the opening fence, breaking rendering.
        let mut buf = "```rust\nfn foo() {\n    let x = 1;\n\n    let y = 2;\n}\n```\n\nNext paragraph."
            .to_string();
        let paras = drain_complete_paragraphs(&mut buf);
        assert_eq!(
            paras.len(),
            1,
            "code fence with blank line should not be split into multiple messages: {paras:?}"
        );
        assert!(
            paras[0].starts_with("```rust"),
            "first paragraph should be the code fence: {:?}",
            paras[0]
        );
        assert!(
            paras[0].contains("let y = 2;"),
            "code fence should contain content from both sides of the blank line: {:?}",
            paras[0]
        );
        assert_eq!(buf, "Next paragraph.");
    }

    #[test]
    fn drain_complete_paragraphs_text_before_and_after_fenced_block() {
        // Text paragraph, then a code block with an internal blank line, then more text.
        let mut buf =
            "Before\n\n```\ncode\n\nmore code\n```\n\nAfter".to_string();
        let paras = drain_complete_paragraphs(&mut buf);
        assert_eq!(paras.len(), 2, "expected two paragraphs: {paras:?}");
        assert_eq!(paras[0], "Before");
        assert!(
            paras[1].starts_with("```"),
            "second paragraph should be the code fence: {:?}",
            paras[1]
        );
        assert!(
            paras[1].contains("more code"),
            "code fence content must include the part after the blank line: {:?}",
            paras[1]
        );
        assert_eq!(buf, "After");
    }

    #[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.");
    }

    // -- build_context_prefix -----------------------------------------------

    #[test]
    fn build_context_prefix_empty_history() {
        let prefix = build_context_prefix(&[], "@alice:example.com", "Hello!");
        assert_eq!(prefix, "@alice:example.com: Hello!");
    }

    #[test]
    fn build_context_prefix_includes_history_entries() {
        let history = vec![
            ConversationEntry {
                role: ConversationRole::User,
                sender: "@alice:example.com".to_string(),
                content: "What is story 42?".to_string(),
            },
            ConversationEntry {
                role: ConversationRole::Assistant,
                sender: String::new(),
                content: "Story 42 is about…".to_string(),
            },
        ];
        let prefix = build_context_prefix(&history, "@bob:example.com", "Tell me more.");
        assert!(prefix.contains("[Conversation history for this room]"));
        assert!(prefix.contains("User (@alice:example.com): What is story 42?"));
        assert!(prefix.contains("Assistant: Story 42 is about…"));
        assert!(prefix.contains("Current message from @bob:example.com: Tell me more."));
    }

    #[test]
    fn build_context_prefix_attributes_multiple_users() {
        let history = vec![
            ConversationEntry {
                role: ConversationRole::User,
                sender: "@alice:example.com".to_string(),
                content: "First question".to_string(),
            },
            ConversationEntry {
                role: ConversationRole::Assistant,
                sender: String::new(),
                content: "First answer".to_string(),
            },
            ConversationEntry {
                role: ConversationRole::User,
                sender: "@bob:example.com".to_string(),
                content: "Follow-up".to_string(),
            },
            ConversationEntry {
                role: ConversationRole::Assistant,
                sender: String::new(),
                content: "Second answer".to_string(),
            },
        ];
        let prefix = build_context_prefix(&history, "@alice:example.com", "Another question");
        assert!(prefix.contains("User (@alice:example.com): First question"));
        assert!(prefix.contains("User (@bob:example.com): Follow-up"));
    }

    // -- conversation history trimming --------------------------------------

    #[tokio::test]
    async fn history_trims_to_configured_size() {
        let history: ConversationHistory =
            Arc::new(TokioMutex::new(HashMap::new()));
        let room_id: OwnedRoomId = "!test:example.com".parse().unwrap();
        let history_size = 4usize; // keep at most 4 entries

        // Add 6 entries (3 user + 3 assistant turns).
        {
            let mut guard = history.lock().await;
            let entries = guard.entry(room_id.clone()).or_default();
            for i in 0..3usize {
                entries.push(ConversationEntry {
                    role: ConversationRole::User,
                    sender: "@user:example.com".to_string(),
                    content: format!("msg {i}"),
                });
                entries.push(ConversationEntry {
                    role: ConversationRole::Assistant,
                    sender: String::new(),
                    content: format!("reply {i}"),
                });
                if entries.len() > history_size {
                    let excess = entries.len() - history_size;
                    entries.drain(..excess);
                }
            }
        }

        let guard = history.lock().await;
        let entries = guard.get(&room_id).unwrap();
        assert_eq!(
            entries.len(),
            history_size,
            "history must be trimmed to history_size"
        );
        // The oldest entries (msg 0 / reply 0) should have been dropped.
        assert!(
            entries.iter().all(|e| !e.content.contains("msg 0")),
            "oldest entries must be dropped"
        );
    }

    #[tokio::test]
    async fn each_room_has_independent_history() {
        let history: ConversationHistory =
            Arc::new(TokioMutex::new(HashMap::new()));
        let room_a: OwnedRoomId = "!room_a:example.com".parse().unwrap();
        let room_b: OwnedRoomId = "!room_b:example.com".parse().unwrap();

        {
            let mut guard = history.lock().await;
            guard.entry(room_a.clone()).or_default().push(ConversationEntry {
                role: ConversationRole::User,
                sender: "@alice:example.com".to_string(),
                content: "Room A message".to_string(),
            });
            guard.entry(room_b.clone()).or_default().push(ConversationEntry {
                role: ConversationRole::User,
                sender: "@bob:example.com".to_string(),
                content: "Room B message".to_string(),
            });
        }

        let guard = history.lock().await;
        let entries_a = guard.get(&room_a).unwrap();
        let entries_b = guard.get(&room_b).unwrap();
        assert_eq!(entries_a.len(), 1);
        assert_eq!(entries_b.len(), 1);
        assert_eq!(entries_a[0].content, "Room A message");
        assert_eq!(entries_b[0].content, "Room B message");
    }
}