//! Todo writer: pushes matrix *todos* (loose-ends v2) to the harness's
//! in-agent socket (`HIVE_AGENT_SOCKET`) when rooms have unread messages
//! or pending invites, so claude drives a turn to handle them. One JSON
//! line per op (`upsert_todo` / `clear_todo`), keyed by room id so
//! re-pushing an unchanged item is an idempotent no-op and resolving one
//! clears it. The harness owns the todo store locally and signals its own
//! turn loop — no hive-c0re round-trip.
//!
//! Todo summaries stay short: a SHORT TEASER, not the full message — the
//! agent then reads the unmarked event via the `read_room` MCP tool.
//! Truncation to ~100 chars keeps the summary focused.

use std::path::Path;

use anyhow::{Context, Result};
use tokio::io::AsyncWriteExt;
use tokio::net::UnixStream;

/// The harness-served in-agent socket (`HIVE_AGENT_SOCKET`) where todo ops
/// go — distinct from the host-served control socket used by [`send_wake`].
/// `None` when unset/empty, in which case todo sends are a best-effort
/// no-op (a standalone daemon without the harness socket).
fn agent_socket() -> Option<std::path::PathBuf> {
    std::env::var_os("HIVE_AGENT_SOCKET")
        .filter(|v| !v.is_empty())
        .map(std::path::PathBuf::from)
}

/// Upsert a matrix-subsystem *todo* (loose-ends v2) on the harness's
/// in-agent socket — the replacement for a direct wake. `key` is the room
/// id (the dedup key); the harness signals a turn iff the todo is new or
/// its `summary` changed. Best-effort: a no-op when `HIVE_AGENT_SOCKET`
/// isn't configured.
///
/// # Errors
///
/// Returns an error on socket connect failure, serialisation failure,
/// or I/O error writing to or reading from the socket.
pub async fn send_todo_upsert(key: &str, summary: impl AsRef<str>) -> Result<()> {
    let Some(socket) = agent_socket() else {
        return Ok(());
    };
    let payload = serde_json::json!({
        "cmd": "upsert_todo",
        "subsystem": "matrix",
        "key": key,
        "summary": summary.as_ref(),
    });
    send_line(&socket, &payload).await
}

/// Clear matrix-subsystem todos on the harness's in-agent socket. `key =
/// Some(room)` clears one room's todo (it was read); `all = true` wipes the
/// whole matrix set (cancel-and-recreate on daemon restart). Best-effort:
/// a no-op when `HIVE_AGENT_SOCKET` isn't configured.
///
/// # Errors
///
/// Returns an error on socket connect failure, serialisation failure,
/// or I/O error writing to or reading from the socket.
pub async fn send_todo_clear(key: Option<&str>, all: bool) -> Result<()> {
    let Some(socket) = agent_socket() else {
        return Ok(());
    };
    let payload = serde_json::json!({
        "cmd": "clear_todo",
        "subsystem": "matrix",
        "key": key,
        "all": all,
    });
    send_line(&socket, &payload).await
}

/// Write one JSON request line to the hyperhive control socket and drain
/// the response line (best-effort — the reply is not acted on, we just
/// read it so the server doesn't get ECONNRESET on its write-back).
/// Shared by [`send_wake`] and the todo senders.
///
/// # Errors
///
/// Returns an error on socket connect failure, serialisation failure,
/// or I/O error writing to or reading from the socket.
async fn send_line(socket: &Path, payload: &serde_json::Value) -> Result<()> {
    use tokio::io::AsyncBufReadExt;

    let line = format!("{}\n", serde_json::to_string(payload)?);
    let stream = UnixStream::connect(socket)
        .await
        .with_context(|| format!("connect hyperhive socket {}", socket.display()))?;
    let (read, mut write) = stream.into_split();
    write
        .write_all(line.as_bytes())
        .await
        .with_context(|| format!("write to {}", socket.display()))?;
    write
        .shutdown()
        .await
        .with_context(|| format!("shutdown write to {}", socket.display()))?;
    let mut reader = tokio::io::BufReader::new(read);
    let mut resp = String::new();
    let _ = reader.read_line(&mut resp).await;
    Ok(())
}

/// Format a wake-message body from a list of per-room unread summaries.
/// Single-room / single-message case collapses to the terse one-liner
/// format; multiple rooms expand to a bulleted list. Always appends a
/// read-hint line so the agent knows which tools to reach for.
#[must_use]
pub fn format_unread_summary(rooms: &[crate::protocol::RoomUnread]) -> String {
    use std::fmt::Write as _;
    if rooms.is_empty() {
        return String::new();
    }
    // Terse path: exactly one room, exactly one unread with body.
    if rooms.len() == 1 {
        let r = &rooms[0];
        if r.count == 1
            && let (Some(body), Some(sender)) = (&r.last_body, &r.last_sender)
        {
            return format!(
                "[matrix] {sender} in {label}: {body} — use read_room to view, mark_read to clear",
                label = r.label
            );
        }
        return format!(
            "[matrix] {} unread in {} — use read_room to view, mark_read to clear",
            r.count, r.label
        );
    }
    // Multi-room path.
    let mut out = String::from("[matrix] unread messages:");
    for r in rooms {
        if r.count == 1
            && let (Some(body), Some(sender)) = (&r.last_body, &r.last_sender)
        {
            let _ = write!(out, "\n- {}: {sender}: {body}", r.label);
            continue;
        }
        let _ = write!(out, "\n- {}: {} unread", r.label, r.count);
    }
    out.push_str("\nUse list_rooms + read_room to view, mark_read to clear.");
    out
}

/// Prepend an account marker to a wake `body` when the daemon serves
/// more than one matrix account. `tag` is `Some(name)` only in
/// multi-account mode; `None` returns `body` unchanged so single-account
/// wakes keep their exact format. Shape: `[acct:<name>] <body>`.
#[must_use]
pub fn tag_account(tag: Option<&str>, body: String) -> String {
    match tag {
        Some(name) => format!("[acct:{name}] {body}"),
        None => body,
    }
}

/// Truncate `s` to `max` Unicode chars, appending `…` when cut.
/// Char-based not byte-based so multi-byte content (most chat) doesn't
/// get cut mid-codepoint.
#[must_use]
pub fn truncate_chars(s: &str, max: usize) -> String {
    let mut end = s.len();
    for (count, (i, _)) in s.char_indices().enumerate() {
        if count == max {
            end = i;
            break;
        }
    }
    if end == s.len() {
        s.to_owned()
    } else {
        format!("{}…", &s[..end])
    }
}

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

    #[test]
    fn truncate_chars_handles_multibyte() {
        // `ü` is 2 bytes / 1 char. truncating to 3 chars on "üüüüüü"
        // should yield "üüü…" not "üü\xc3…" (mid-codepoint).
        let s = "üüüüüü";
        let t = truncate_chars(s, 3);
        assert_eq!(t, "üüü…");
    }

    #[test]
    fn truncate_chars_no_op_below_limit() {
        let s = "hi";
        assert_eq!(truncate_chars(s, 100), "hi");
    }

    #[test]
    fn tag_account_none_is_passthrough() {
        let body = "[matrix] @a:s in #x: hi".to_owned();
        assert_eq!(tag_account(None, body.clone()), body);
    }

    #[test]
    fn tag_account_some_prepends_marker() {
        let body = "[matrix] @a:s in #x: hi".to_owned();
        assert_eq!(
            tag_account(Some("ccc"), body),
            "[acct:ccc] [matrix] @a:s in #x: hi"
        );
    }
}