//! Per-agent socket listener. Each socket file's existence on disk
//! authenticates the caller: connecting to `<.../agents/foo/mcp.sock>` means
//! you are `foo`.

use std::path::{Path, PathBuf};
use std::sync::Arc;

use anyhow::{Context, Result};
use hive_sh4re::{AgentRequest, AgentResponse, Message};
use tokio::io::{AsyncBufReadExt, AsyncWriteExt, BufReader};
use tokio::net::{UnixListener, UnixStream};
use tokio::task::JoinHandle;

use crate::coordinator::Coordinator;

pub struct AgentSocket {
    pub path: PathBuf,
    pub handle: JoinHandle<()>,
}

pub fn start(agent: &str, socket_path: &Path, coord: Arc<Coordinator>) -> Result<AgentSocket> {
    let agent = agent.to_owned();
    if let Some(parent) = socket_path.parent() {
        std::fs::create_dir_all(parent)
            .with_context(|| format!("create agent socket dir {}", parent.display()))?;
    }
    if socket_path.exists() {
        std::fs::remove_file(socket_path).context("remove stale agent socket")?;
    }
    let listener = UnixListener::bind(socket_path)
        .with_context(|| format!("bind agent socket {}", socket_path.display()))?;
    tracing::info!(%agent, socket = %socket_path.display(), "agent socket listening");

    let path = socket_path.to_path_buf();
    let handle = tokio::spawn(async move {
        loop {
            match listener.accept().await {
                Ok((stream, _)) => {
                    let agent = agent.clone();
                    let coord = coord.clone();
                    tokio::spawn(async move {
                        if let Err(e) = serve(stream, agent, coord).await {
                            tracing::warn!(error = ?e, "agent connection failed");
                        }
                    });
                }
                Err(e) => {
                    tracing::warn!(error = ?e, "agent listener accept failed; exiting");
                    return;
                }
            }
        }
    });
    Ok(AgentSocket { path, handle })
}

async fn serve(stream: UnixStream, agent: String, coord: Arc<Coordinator>) -> Result<()> {
    let (read, mut write) = stream.into_split();
    let mut reader = BufReader::new(read);
    let mut line = String::new();
    loop {
        line.clear();
        let n = reader.read_line(&mut line).await?;
        if n == 0 {
            return Ok(());
        }
        let resp = match serde_json::from_str::<AgentRequest>(line.trim()) {
            Ok(req) => dispatch(&req, &agent, &coord).await,
            Err(e) => AgentResponse::Err {
                message: format!("parse error: {e}"),
            },
        };
        let mut payload = serde_json::to_string(&resp)?;
        payload.push('\n');
        write.write_all(payload.as_bytes()).await?;
        write.flush().await?;
    }
}

/// Max long-poll window the caller can ask for; values above the
/// cap are clamped. 180s keeps us under typical TCP/proxy idle
/// limits while still letting agents park their turn until a
/// message arrives. Omitting `wait_seconds` (or passing `0`) means
/// "peek, don't wait" — claude can call recv whenever it wants a
/// cheap "is there anything pending?" check without blocking the
/// turn for 30 seconds. To actually park, the caller passes a
/// positive `wait_seconds`.
const RECV_LONG_POLL_MAX: std::time::Duration = std::time::Duration::from_secs(180);

fn recv_timeout(wait_seconds: Option<u64>) -> std::time::Duration {
    match wait_seconds {
        Some(s) => std::time::Duration::from_secs(s).min(RECV_LONG_POLL_MAX),
        None => std::time::Duration::ZERO,
    }
}

async fn dispatch(req: &AgentRequest, agent: &str, coord: &Arc<Coordinator>) -> AgentResponse {
    let broker = &coord.broker;
    match req {
        AgentRequest::Send { to, body } => handle_send(coord, agent, to, body),
        AgentRequest::Recv { wait_seconds } => match broker
            .recv_blocking(agent, recv_timeout(*wait_seconds))
            .await
        {
            Ok(Some(msg)) => AgentResponse::Message {
                from: msg.from,
                body: msg.body,
            },
            Ok(None) => AgentResponse::Empty,
            Err(e) => AgentResponse::Err {
                message: format!("{e:#}"),
            },
        },
        AgentRequest::Status => match broker.count_pending(agent) {
            Ok(unread) => AgentResponse::Status { unread },
            Err(e) => AgentResponse::Err {
                message: format!("{e:#}"),
            },
        },
        AgentRequest::OperatorMsg { body } => match broker.send(&Message {
            from: hive_sh4re::OPERATOR_RECIPIENT.to_owned(),
            to: agent.to_owned(),
            body: body.clone(),
        }) {
            Ok(()) => AgentResponse::Ok,
            Err(e) => AgentResponse::Err {
                message: format!("{e:#}"),
            },
        },
        AgentRequest::Wake { from, body } => match broker.send(&Message {
            from: from.clone(),
            to: agent.to_owned(),
            body: body.clone(),
        }) {
            Ok(()) => AgentResponse::Ok,
            Err(e) => AgentResponse::Err {
                message: format!("{e:#}"),
            },
        },
        AgentRequest::Recent { limit } => match broker.recent_for(agent, *limit) {
            Ok(rows) => AgentResponse::Recent { rows },
            Err(e) => AgentResponse::Err {
                message: format!("{e:#}"),
            },
        },
        AgentRequest::Ask {
            question,
            options,
            multi,
            ttl_seconds,
            to,
        } => crate::questions::handle_ask(
            coord,
            agent,
            question,
            options,
            *multi,
            *ttl_seconds,
            to.as_deref(),
        )
        .map_or_else(
            |message| AgentResponse::Err { message },
            |id| AgentResponse::QuestionQueued { id },
        ),
        AgentRequest::Answer { id, answer } => crate::questions::handle_answer(
            coord, agent, *id, answer,
        )
        .map_or_else(
            |message| AgentResponse::Err { message },
            |()| AgentResponse::Ok,
        ),
        AgentRequest::Remind {
            message,
            timing,
            file_path,
        } => handle_remind(coord, agent, message, timing, file_path.as_deref()),
    }
}

/// Common Send handler shared between dispatch arms. Applies the
/// 1 KiB body cap, then routes broadcast (`to == "*"`) vs unicast
/// through their respective broker calls. Pulled out of `dispatch`
/// to keep that function under the clippy too-many-lines limit; the
/// behaviour is identical to inlining.
fn handle_send(coord: &Arc<Coordinator>, agent: &str, to: &str, body: &str) -> AgentResponse {
    if let Err(message) = crate::limits::check_size("send", body) {
        return AgentResponse::Err { message };
    }
    if to == "*" {
        let errors = coord.broadcast_send(agent, body);
        return if errors.is_empty() {
            AgentResponse::Ok
        } else {
            AgentResponse::Err {
                message: format!("broadcast failed for agents: {}", errors.join(", ")),
            }
        };
    }
    match coord.broker.send(&Message {
        from: agent.to_owned(),
        to: to.to_owned(),
        body: body.to_owned(),
    }) {
        Ok(()) => AgentResponse::Ok,
        Err(e) => AgentResponse::Err {
            message: format!("{e:#}"),
        },
    }
}

fn handle_remind(
    coord: &Arc<Coordinator>,
    agent: &str,
    message: &str,
    timing: &hive_sh4re::ReminderTiming,
    file_path: Option<&str>,
) -> AgentResponse {
    match store_remind(coord, agent, message, timing, file_path) {
        Ok(()) => AgentResponse::Ok,
        Err(message) => AgentResponse::Err { message },
    }
}

/// Shared remind-storage path used by both the agent and the manager
/// dispatchers. Validates timing, applies the auto-file overflow
/// dance (see [`prepare_remind_storage`]), and writes the reminder
/// row. Returns `Ok(())` on success, or a caller-ready error string
/// the dispatcher wraps in `*Response::Err`.
pub(crate) fn store_remind(
    coord: &Arc<Coordinator>,
    agent: &str,
    message: &str,
    timing: &hive_sh4re::ReminderTiming,
    file_path: Option<&str>,
) -> Result<(), String> {
    let due_at = resolve_due_at(timing).map_err(|e| format!("invalid reminder timing: {e:#}"))?;
    let (stored_message, stored_path) = prepare_remind_storage(agent, message, file_path)?;
    let id = coord
        .broker
        .store_reminder(agent, &stored_message, stored_path.as_deref(), due_at)
        .map_err(|e| format!("failed to store reminder: {e:#}"))?;
    tracing::info!(%id, %agent, %due_at, "reminder scheduled");
    Ok(())
}

/// Decide what we actually store in the reminders row, applying the
/// same byte cap as the rest of the wire protocol
/// ([`crate::limits::MESSAGE_MAX_BYTES`]). Three outcomes:
///
/// 1. Body within the cap → stored verbatim, with whatever `file_path`
///    the caller passed (None or Some). The scheduler honours
///    `file_path` at delivery time as before.
/// 2. Body over the cap, no caller `file_path` → auto-generate a path
///    under `/agents/<agent>/state/reminders/auto-<ts>.md`, write the
///    body to disk now, store a short pointer hint as the message and
///    clear `file_path` (so the scheduler doesn't re-write at
///    delivery and overwrite the body with the hint).
/// 3. Body over the cap, caller provided `file_path` → honour the
///    caller's path: write the body to it now, store the same hint
///    and clear `file_path` for the same reason as (2).
///
/// Returns `(stored_message, stored_file_path)` on success, or a
/// caller-ready error string on auto-save failure (which is the only
/// way a Remind request can be refused for size — the agent never has
/// to think about the cap).
fn prepare_remind_storage(
    agent: &str,
    message: &str,
    file_path: Option<&str>,
) -> Result<(String, Option<String>), String> {
    if message.len() <= crate::limits::MESSAGE_MAX_BYTES {
        return Ok((message.to_owned(), file_path.map(str::to_owned)));
    }
    let req_path = match file_path {
        Some(p) => p.to_owned(),
        None => auto_reminder_path(agent),
    };
    let host_path = crate::reminder_scheduler::resolve_host_path(agent, &req_path)
        .map_err(|reason| format!("auto-save path `{req_path}` rejected: {reason}"))?;
    crate::reminder_scheduler::write_payload(agent, &host_path, message)
        .map_err(|reason| format!("auto-save of large reminder body to `{req_path}` failed: {reason}"))?;
    let hint = format!(
        "[reminder body of {} bytes auto-saved to `{req_path}`; read with your filesystem tools]",
        message.len()
    );
    Ok((hint, None))
}

/// Generate a per-agent path for an auto-saved reminder body. Uses
/// `unix_nanos` plus the agent name to keep collisions infinitesimal
/// across the agent's own state subtree (we're not stamping a hostname
/// since hive-c0re is single-host).
fn auto_reminder_path(agent: &str) -> String {
    let ts_ns = std::time::SystemTime::now()
        .duration_since(std::time::UNIX_EPOCH)
        .map(|d| d.as_nanos())
        .unwrap_or(0);
    format!("/agents/{agent}/state/reminders/auto-{ts_ns}.md")
}

/// Resolve the `due_at` unix timestamp for a Remind request. Returns
/// distinct error messages for each failure mode (overflow on
/// `InSeconds`, pre-epoch clock, `i64` cast wrap) so the caller can tell
/// what went wrong without inspecting the chain.
fn resolve_due_at(timing: &hive_sh4re::ReminderTiming) -> anyhow::Result<i64> {
    use hive_sh4re::ReminderTiming;
    match timing {
        ReminderTiming::InSeconds { seconds } => {
            let now = std::time::SystemTime::now();
            let future = now
                .checked_add(std::time::Duration::from_secs(*seconds))
                .ok_or_else(|| {
                    anyhow::anyhow!("InSeconds overflow: {seconds}s exceeds system time range")
                })?;
            let duration = future
                .duration_since(std::time::UNIX_EPOCH)
                .map_err(|e| anyhow::anyhow!("system time before UNIX_EPOCH: {e}"))?;
            i64::try_from(duration.as_secs())
                .map_err(|e| anyhow::anyhow!("unix timestamp exceeds i64 range: {e}"))
        }
        ReminderTiming::At { unix_timestamp } => Ok(*unix_timestamp),
    }
}

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

    #[test]
    fn auto_reminder_path_format() {
        let p = auto_reminder_path("damocles");
        assert!(p.starts_with("/agents/damocles/state/reminders/auto-"));
        assert!(p.ends_with(".md"));
    }

    #[test]
    fn prepare_remind_storage_passthrough_under_cap() {
        let (msg, fp) = prepare_remind_storage("foo", "small body", None).unwrap();
        assert_eq!(msg, "small body");
        assert_eq!(fp, None);
    }

    #[test]
    fn prepare_remind_storage_passthrough_with_caller_file_path() {
        let (msg, fp) =
            prepare_remind_storage("foo", "small", Some("/agents/foo/state/x.md")).unwrap();
        assert_eq!(msg, "small");
        assert_eq!(fp.as_deref(), Some("/agents/foo/state/x.md"));
    }
}