//! Background loop that drains due reminders out of the broker and
//! delivers them as inbox messages. Mirrors the `events_vacuum` /
//! `crash_watch` shape — a single `spawn(coord)` entry point started
//! from `main.rs`.
//!
//! File-path semantics: a reminder may carry a `file_path` (the
//! agent-visible path inside its container). On delivery we:
//!
//! - Translate the container path (`/agents/<agent>/state/foo.md`) to
//!   the host path (`/var/lib/hyperhive/agents/<agent>/state/foo.md`)
//!   so hive-c0re can write to it from outside the container.
//! - Reject anything that isn't under the agent's own state subtree,
//!   contains `..` (path traversal), or has an empty relative tail.
//!   Falling outside the allowed prefix means the file write is
//!   skipped and the original message is delivered inline (with a
//!   noted warning) — the reminder still fires, just without the
//!   payload split.
//! - Defend against symlink escape: after `create_dir_all`, the
//!   parent dir is canonicalized and re-verified to live under the
//!   agent's host state root. Then we open the final file with
//!   `O_NOFOLLOW | O_CREAT | O_TRUNC` so an existing-symlink basename
//!   can't redirect the write either. Without this an agent could
//!   `ln -s /etc /agents/foo/state/escape` and bounce a write to an
//!   arbitrary host path.
//! - Write the reminder body to disk and deliver a short pointer
//!   message in its place, so the agent's inbox/wake-prompt stays
//!   small and the bulky payload can be read out of band.
//!
//! Atomicity of the inbox INSERT + `reminders.sent_at` UPDATE is handled
//! inside `Broker::deliver_reminder`; this module only computes the
//! body string before calling it.

use std::io::Write;
use std::os::unix::fs::OpenOptionsExt;
use std::path::{Path, PathBuf};
use std::sync::Arc;
use std::time::Duration;

use crate::coordinator::Coordinator;

/// Per-tick cap on reminders delivered. Anything over this stays due
/// in the table and gets picked up on the next tick — keeps a
/// 10k-deep backlog from flooding the broker (or hogging the broker
/// mutex) in one shot. 100/tick × 5s tick = sustained throughput cap
/// of ~20 reminders/sec; bump together if the loose-ends tracker
/// starts firing higher rates.
const REMINDER_BATCH_LIMIT: u64 = 100;

/// Poll interval. Trade-off between latency on a freshly due reminder
/// and CPU spent on empty sweeps; 5s matches the original inline
/// scheduler.
const POLL_INTERVAL: Duration = Duration::from_secs(5);

pub fn spawn(coord: Arc<Coordinator>) {
    let mut shutdown = coord.shutdown_rx();
    tokio::spawn(async move {
        loop {
            tick(&coord);
            tokio::select! {
                _ = tokio::time::sleep(POLL_INTERVAL) => {}
                _ = shutdown.changed() => {
                    tracing::info!("reminder scheduler: shutdown signal received");
                    break;
                }
            }
        }
    });
}

fn tick(coord: &Arc<Coordinator>) {
    let due = match coord.broker.get_due_reminders(REMINDER_BATCH_LIMIT) {
        Ok(rows) => rows,
        Err(e) => {
            tracing::warn!(error = ?e, "failed to query due reminders");
            return;
        }
    };
    for (agent, id, message, file_path) in due {
        let body = prepare_body(&agent, &message, file_path.as_deref());
        if let Err(e) = coord.broker.deliver_reminder(id, &agent, &body) {
            let reason = format!("{e:#}");
            tracing::warn!(
                reminder_id = id,
                %agent,
                error = %reason,
                "failed to deliver reminder"
            );
            // Persist the failure so the dashboard can surface it +
            // bump attempt_count. After MAX_REMINDER_ATTEMPTS the
            // row drops out of `get_due_reminders` and waits for
            // operator retry / cancel.
            if let Err(persist_err) = coord.broker.record_reminder_failure(id, &reason) {
                tracing::warn!(
                    reminder_id = id,
                    error = ?persist_err,
                    "failed to persist reminder failure"
                );
            }
        }
    }
}

/// Build the inbox body for a due reminder. When `file_path` is None
/// the body is the original message verbatim. When set, we attempt to
/// persist the message body to the requested file and return a short
/// pointer string instead. Failures (bad prefix, symlink escape,
/// write error, missing parent) fall back to inline delivery with a
/// noted warning so the reminder still fires.
fn prepare_body(agent: &str, message: &str, file_path: Option<&str>) -> String {
    let Some(req_path) = file_path else {
        return message.to_owned();
    };
    let host_path = match resolve_host_path(agent, req_path) {
        Ok(p) => p,
        Err(reason) => {
            tracing::warn!(%agent, %req_path, %reason, "reminder file_path rejected; delivering inline");
            return inline_fallback(req_path, &format!("rejected: {reason}"), message);
        }
    };
    match write_payload(agent, &host_path, message) {
        Ok(()) => {
            let bytes = message.len();
            // debug! not info! — under load this would dominate the log.
            tracing::debug!(%agent, path = %host_path.display(), bytes, "reminder body written to file");
            format!(
                "reminder body persisted to `{req_path}` ({bytes} bytes); read with your filesystem tools"
            )
        }
        Err(reason) => {
            tracing::warn!(%agent, path = %host_path.display(), %reason, "reminder file_path write failed; delivering inline");
            inline_fallback(req_path, &reason, message)
        }
    }
}

fn inline_fallback(req_path: &str, reason: &str, message: &str) -> String {
    format!("[reminder file_path '{req_path}' {reason}; delivering body inline]\n\n{message}")
}

/// Persist `message` to `host_path` with the symlink-escape defenses
/// described in the module docs. Returns `Ok(())` on success, or a
/// human-readable reason string on any failure (caller logs +
/// inline-falls-back). `pub` because `agent_server::handle_remind`
/// reuses it for the at-remind-time auto-file path.
pub fn write_payload(agent: &str, host_path: &Path, message: &str) -> Result<(), String> {
    let Some(parent) = host_path.parent() else {
        return Err("internal: host path has no parent".to_owned());
    };
    std::fs::create_dir_all(parent)
        .map_err(|e| format!("parent dir create failed: {e}"))?;
    // Resolve symlinks in the parent chain, then re-verify the
    // canonical form still lives under the agent's host state root —
    // catches `ln -s /etc state/escape` style attacks.
    let parent_canonical = parent
        .canonicalize()
        .map_err(|e| format!("parent canonicalize failed: {e}"))?;
    let agent_root = Coordinator::agent_notes_dir(agent)
        .canonicalize()
        .map_err(|e| format!("agent state root canonicalize failed: {e}"))?;
    if !parent_canonical.starts_with(&agent_root) {
        return Err(format!(
            "symlink escape: canonical parent `{}` outside agent root `{}`",
            parent_canonical.display(),
            agent_root.display()
        ));
    }
    let basename = host_path
        .file_name()
        .ok_or_else(|| "missing basename".to_owned())?;
    let target = parent_canonical.join(basename);
    // O_NOFOLLOW on the final component refuses to open if the
    // basename is itself an existing symlink. Combined with the
    // canonicalize-parent check above, no symlink anywhere in the
    // path can redirect the write.
    let mut file = std::fs::OpenOptions::new()
        .write(true)
        .create(true)
        .truncate(true)
        .custom_flags(libc::O_NOFOLLOW)
        .open(&target)
        .map_err(|e| format!("open failed: {e}"))?;
    file.write_all(message.as_bytes())
        .map_err(|e| format!("write failed: {e}"))?;
    Ok(())
}

/// Container-visible state prefix the caller's `file_path` must live
/// under. Sub-agents see their state at `/agents/<name>/state/`;
/// the manager keeps the legacy `/state/` mount (see
/// `lifecycle::set_nspawn_flags`). Auto-file paths use the same
/// prefix so the round-trip is symmetric.
#[must_use]
pub fn container_state_prefix(agent: &str) -> String {
    if agent == hive_sh4re::MANAGER_AGENT {
        "/state/".to_owned()
    } else {
        format!("/agents/{agent}/state/")
    }
}

/// Map an agent-visible container path to the matching host path,
/// validating that it lives under the agent's own state subtree, has
/// a non-empty relative tail, and doesn't try to traverse out via
/// `..`. Returns the host `PathBuf` on success, or a human-readable
/// reason string on rejection. `pub` so `agent_server::handle_remind`
/// can reuse it for the at-remind-time auto-file path.
pub fn resolve_host_path(agent: &str, req_path: &str) -> Result<PathBuf, String> {
    let prefix = container_state_prefix(agent);
    let Some(rel) = req_path.strip_prefix(&prefix) else {
        return Err(format!(
            "must be absolute and under `{prefix}` (got `{req_path}`)"
        ));
    };
    if rel.is_empty() {
        return Err("file_path must include a filename, not just the state dir".to_owned());
    }
    let rel_path = Path::new(rel);
    for comp in rel_path.components() {
        match comp {
            std::path::Component::Normal(_) => {}
            other => {
                return Err(format!(
                    "path component `{other:?}` not allowed (no traversal / absolute / root)"
                ));
            }
        }
    }
    Ok(Coordinator::agent_notes_dir(agent).join(rel_path))
}

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

    #[test]
    fn rejects_paths_outside_agent_state() {
        assert!(resolve_host_path("foo", "/etc/passwd").is_err());
        assert!(resolve_host_path("foo", "/agents/bar/state/x.md").is_err());
        assert!(resolve_host_path("foo", "relative.md").is_err());
    }

    #[test]
    fn rejects_traversal() {
        assert!(resolve_host_path("foo", "/agents/foo/state/../../etc/passwd").is_err());
        assert!(resolve_host_path("foo", "/agents/foo/state/./x.md").is_err());
    }

    #[test]
    fn rejects_empty_relative_tail() {
        // Trailing slash → empty tail. Used to fall through to
        // create_dir_all + write-to-dir → confusing inline fallback;
        // explicit reject gives a cleaner log.
        let err = resolve_host_path("foo", "/agents/foo/state/").unwrap_err();
        assert!(err.contains("must include a filename"), "got: {err}");
    }

    #[test]
    fn accepts_well_formed_path() {
        let p = resolve_host_path("foo", "/agents/foo/state/reminders/123.md").unwrap();
        assert_eq!(
            p,
            PathBuf::from("/var/lib/hyperhive/agents/foo/state/reminders/123.md")
        );
    }

    #[test]
    fn manager_uses_legacy_state_prefix() {
        // The manager container mounts its state at `/state/` (legacy),
        // not `/agents/manager/state/`. Same host path; different
        // container-visible path. resolve_host_path needs to know.
        assert_eq!(container_state_prefix("manager"), "/state/");
        let p = resolve_host_path("manager", "/state/reminders/x.md").unwrap();
        assert_eq!(
            p,
            PathBuf::from("/var/lib/hyperhive/agents/manager/state/reminders/x.md")
        );
        // And the sub-agent prefix must NOT be accepted for the manager.
        assert!(resolve_host_path("manager", "/agents/manager/state/x.md").is_err());
    }

    #[test]
    fn prepare_body_passthrough_when_no_file_path() {
        let s = prepare_body("foo", "hello world", None);
        assert_eq!(s, "hello world");
    }

    #[test]
    fn prepare_body_falls_back_inline_on_bad_path() {
        let s = prepare_body("foo", "payload", Some("/etc/passwd"));
        assert!(s.starts_with("[reminder file_path '/etc/passwd' rejected:"));
        assert!(s.contains("payload"));
    }
}