//! `/var/lib/hyperhive/agent-sockets.json` writer. Sibling to
//! `agent_ports.rs`; same atomic `<path>.tmp` + `rename()` shape so
//! the gateway's nginx worker never reads a partial file. Manager
//! excluded from the map (manager UI routes via the dashboard
//! upstream, not per-agent `/agent/<name>/`).
//!
//! Full mechanism — per-agent subdir bind-mount, `hyperhive-socket-bound`
//! marker gate, gateway UDS upstream, transition vs `agent-ports.json`,
//! 10s poll loop: `docs/gateway.md::Per-agent unix-socket upstream`.

use std::collections::BTreeMap;
use std::path::{Path, PathBuf};

use anyhow::{Context, Result};

use crate::lifecycle::MANAGER_NAME;

const HOST_SOCKETS_PATH: &str = "/var/lib/hyperhive/agent-sockets.json";

/// Host-side parent directory holding per-agent socket subdirs. The
/// gateway container bind-mounts this whole tree (read-only) so it
/// can `proxy_pass` to any agent. Each agent's container bind-mounts
/// only its own `<name>/` subdir — agents can only access their own
/// sockets.
pub const AGENT_SOCKET_DIR: &str = "/run/hive-agent";

/// Socket filename inside each per-agent subdir. Fixed so the path
/// derives entirely from `(AGENT_SOCKET_DIR, name)` — no second
/// degree of freedom for callers to get wrong.
pub const SOCKET_FILENAME: &str = "web.sock";

/// Marker file the harness drops next to the socket after a
/// successful `bind_unix`. Presence = "this agent has opted in to
/// `hyperhive.web.useUnixSocket = true` and its harness has bound
/// the socket"; absence = "the harness is still on TCP, don't
/// publish the unix upstream for this agent yet". Without this gate
/// the gateway would `proxy_pass` to a non-existent socket for every
/// sub-agent that hasn't flipped the option yet.
///
/// Renamed from `.bound` (legacy) to match the `hyperhive-` prefix
/// convention for all harness-written state files (#838). `build_map`
/// checks both names during the transition window so existing containers
/// don't lose gateway routing before their next rebuild.
pub const READY_MARKER: &str = "hyperhive-socket-bound";
const READY_MARKER_LEGACY: &str = ".bound";

#[must_use]
pub fn host_sockets_path() -> PathBuf {
    PathBuf::from(HOST_SOCKETS_PATH)
}

/// Per-agent socket subdir on the host. Lifecycle pre-creates this
/// before container start so the bind-mount source exists; the
/// harness binds the socket inside it as `web.sock`.
#[must_use]
pub fn agent_dir_for(name: &str) -> PathBuf {
    Path::new(AGENT_SOCKET_DIR).join(name)
}

/// Compute the deterministic socket path for an agent. Pure function
/// of the agent name so the value matches whatever
/// [`agent_sockets::write`] writes for that agent, and whatever the
/// harness binds via `HIVE_WEB_SOCKET`.
#[must_use]
pub fn socket_path_for(name: &str) -> PathBuf {
    agent_dir_for(name).join(SOCKET_FILENAME)
}

/// Compute the agent-socket map for the given logical agent names.
/// Sub-agents only — manager is filtered out at the call boundary
/// for the same reason it's filtered from `agent_ports::build_map`
/// (manager UI is routed via the c0re dashboard upstream, not via
/// `/agent/<name>/`).
///
/// Also filters by `READY_MARKER` presence: only agents whose
/// harness has actually bound the unix socket (and dropped the
/// marker) appear in the map. Without this, the gateway would
/// `proxy_pass` to a non-existent socket for every sub-agent that
/// hasn't yet flipped `hyperhive.web.useUnixSocket = true`.
///
/// Accepts either the new `hyperhive-socket-bound` marker or the legacy
/// `.bound` marker so existing containers keep their gateway routing
/// through the transition window (before their next rebuild writes the
/// new marker name).
///
/// `BTreeMap` keeps the JSON output sorted by key so a re-emit
/// without churn produces byte-identical output — same idempotency
/// shape `agent_ports::write` relies on.
#[must_use]
pub fn build_map(names: &[String]) -> BTreeMap<String, PathBuf> {
    build_map_with(names, |name| {
        ready_marker_for(name).exists()
            || agent_dir_for(name).join(READY_MARKER_LEGACY).exists()
    })
}

/// Body of `build_map` with the ready-check parameterised. Tests
/// pass a predicate they control (no real filesystem access).
/// Production callers go through `build_map` which wires the
/// predicate to the on-disk `hyperhive-socket-bound` (or legacy
/// `.bound`) marker check.
fn build_map_with<F>(names: &[String], is_ready: F) -> BTreeMap<String, PathBuf>
where
    F: Fn(&str) -> bool,
{
    names
        .iter()
        .filter(|n| n.as_str() != MANAGER_NAME)
        .filter(|n| is_ready(n))
        .map(|n| (n.clone(), socket_path_for(n)))
        .collect()
}

/// Path to the `hyperhive-socket-bound` marker file the harness writes
/// after a successful `bind_unix`. Lives next to `web.sock` in the
/// per-agent subdir so it's covered by the same bind-mount and same
/// per-agent isolation as the socket itself.
#[must_use]
pub fn ready_marker_for(name: &str) -> PathBuf {
    agent_dir_for(name).join(READY_MARKER)
}

/// Render the map as pretty-printed JSON. Pretty so a human peek at
/// `cat /var/lib/hyperhive/agent-sockets.json` shows one row per agent
/// — keeps the file readable without a separate jq step (mirrors
/// `agent_ports::render`).
fn render(map: &BTreeMap<String, PathBuf>) -> String {
    // Serialize as strings (PathBuf → JSON string via the Display
    // impl). BTreeMap → serde_json::to_string_pretty preserves key
    // order, so the output is deterministic across calls with the
    // same agent set.
    let stringly: BTreeMap<&String, String> = map
        .iter()
        .map(|(k, v)| (k, v.display().to_string()))
        .collect();
    serde_json::to_string_pretty(&stringly)
        .expect("BTreeMap<&String, String> is always serialisable")
}

/// Atomically write the JSON for `names` to
/// `/var/lib/hyperhive/agent-sockets.json`. Writes via a sibling
/// `<path>.tmp` + rename so a crashing process never leaves a
/// partial file behind that the gateway worker would fail to parse.
///
/// Idempotent — if the rendered content matches what's already on
/// disk, the write + rename are skipped so the file's mtime stays
/// stable and inotify watchers in the gateway (or any future
/// watchers) don't fire spurious reload events. Mirrors the
/// `agent_ports::write` shape — keep them in lockstep.
pub fn write(names: &[String]) -> Result<()> {
    let map = build_map(names);
    let body = render(&map);
    let path = host_sockets_path();
    if std::fs::read_to_string(&path).ok().as_deref() == Some(&body) {
        return Ok(());
    }
    if let Some(parent) = path.parent() {
        std::fs::create_dir_all(parent)
            .with_context(|| format!("create {}", parent.display()))?;
    }
    let tmp = path.with_extension("json.tmp");
    std::fs::write(&tmp, &body)
        .with_context(|| format!("write {}", tmp.display()))?;
    std::fs::rename(&tmp, &path).with_context(|| {
        format!(
            "rename {} -> {} (atomic publish)",
            tmp.display(),
            path.display()
        )
    })?;
    Ok(())
}

/// Spawn the marker poll task. Periodically re-runs `write` so the
/// JSON map picks up newly-bound sockets (an agent flipping
/// `hyperhive.web.useUnixSocket = true`, rebuilding, then having its
/// harness drop a fresh `.bound` marker) without needing an explicit
/// hook on container start. `write` is idempotent (skips the rename
/// when content unchanged) so the steady-state cost is one directory
/// stat per agent per poll interval.
///
/// Mirrors the spawn-loop shape used by `crash_watch`,
/// `reminder_scheduler`, etc. — the existing background-task
/// convention in `main.rs`.
pub fn spawn_poll() {
    tokio::spawn(async move {
        let mut interval = tokio::time::interval(std::time::Duration::from_secs(10));
        // First tick fires immediately; that's fine — meta::sync_agents
        // also writes on boot, this just catches up the window before
        // the next agent restart.
        loop {
            interval.tick().await;
            match crate::lifecycle::agents_for_meta_listing().await {
                Ok(agents) => {
                    let names: Vec<String> = agents.into_iter().map(|a| a.name).collect();
                    if let Err(e) = write(&names) {
                        tracing::debug!(error = ?e, "agent_sockets poll write failed");
                    }
                    // Regenerate the gateway nginx include whenever
                    // socket readiness changes — the upstream
                    // selection (UDS vs TCP) depends on .bound markers
                    // which change independently of topology. Write is
                    // idempotent; skips rename when nothing changed.
                    if let Err(e) = crate::gateway_nginx::write(&names) {
                        tracing::debug!(error = ?e, "gateway_nginx poll write failed");
                    }
                }
                Err(e) => {
                    tracing::debug!(error = ?e, "agent_sockets poll: failed to list agents");
                }
            }
        }
    });
}

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

    #[test]
    fn socket_path_for_uses_subdir_layout() {
        // Per-agent subdir + fixed socket filename — see module-level
        // "Per-agent subdir layout" for why this isn't a flat
        // `<name>.sock`. Pin both ends so a future move (e.g. to
        // `/run/hyperhive/sockets/`) requires updating both the
        // constant and the consumers.
        let p = socket_path_for("iris");
        assert_eq!(p, Path::new("/run/hive-agent/iris/web.sock"));
    }

    #[test]
    fn agent_dir_for_is_socket_parent() {
        // `agent_dir_for` is what lifecycle bind-mounts per agent;
        // `socket_path_for` lives inside it. Keep them in lockstep so
        // a divergence (e.g. typo in one constant) surfaces here
        // rather than as a confusing nspawn bind-source-not-found at
        // container start.
        let dir = agent_dir_for("iris");
        let sock = socket_path_for("iris");
        assert_eq!(sock.parent(), Some(dir.as_path()));
    }

    #[test]
    fn build_map_filters_manager() {
        // Use `MANAGER_NAME` in the input so the assert actually
        // exercises the filter path — a literal `"hm1nd"` would pass
        // trivially if the constant ever changed and the filter
        // silently became a no-op. All-ready predicate bypasses the
        // marker check so we exercise the manager filter in isolation.
        let names: Vec<String> = ["iris", MANAGER_NAME, "argus"]
            .iter()
            .map(|s| (*s).to_owned())
            .collect();
        let map = build_map_with(&names, |_| true);
        assert!(!map.contains_key(MANAGER_NAME));
        assert!(map.contains_key("iris"));
        assert!(map.contains_key("argus"));
    }

    #[test]
    fn build_map_uses_socket_path_for() {
        // Map values agree with the helper so callers can use either
        // (build_map for the bulk write, socket_path_for for one-off
        // lookups) without divergence.
        let names = vec!["iris".to_owned()];
        let map = build_map_with(&names, |_| true);
        assert_eq!(map.get("iris"), Some(&socket_path_for("iris")));
    }

    #[test]
    fn build_map_handles_empty_input() {
        let map = build_map_with::<fn(&str) -> bool>(&[], |_| true);
        assert!(map.is_empty());
    }

    #[test]
    fn build_map_dedupes_via_btreemap_key_collision() {
        // Duplicate inputs collapse via the map; no callsite passes
        // dups today, but guarding the invariant here means a future
        // bug doesn't surface as a corrupt JSON doc (two `"iris":`
        // keys). Mirrors agent_ports test.
        let names = vec!["iris".to_owned(), "iris".to_owned()];
        let map = build_map_with(&names, |_| true);
        assert_eq!(map.len(), 1);
    }

    #[test]
    fn build_map_filters_by_ready_predicate() {
        // Only ready agents (with `hyperhive-socket-bound` marker) get
        // published. Pin the behaviour so a future refactor that drops
        // the filter surfaces here, not as a 502-spew in the gateway.
        let names: Vec<String> = ["iris", "argus", "atlas"]
            .iter()
            .map(|s| (*s).to_owned())
            .collect();
        // Pretend only `atlas` has flipped + bound — the gate makes
        // sure only opted-in agents get a UDS upstream.
        let map = build_map_with(&names, |name| name == "atlas");
        assert!(map.contains_key("atlas"));
        assert!(!map.contains_key("iris"));
        assert!(!map.contains_key("argus"));
    }

    #[test]
    fn ready_marker_path_is_sibling_of_socket() {
        // Marker lives in the same per-agent subdir as the socket so
        // the same bind-mount covers both; harness writes both inside
        // the container, host (and gateway via shared bind-mount)
        // sees both at the deterministic path.
        let marker = ready_marker_for("iris");
        let socket = socket_path_for("iris");
        assert_eq!(marker.parent(), socket.parent());
        assert_eq!(marker, Path::new("/run/hive-agent/iris/hyperhive-socket-bound"));
    }

    #[test]
    fn render_is_pretty_and_sorted() {
        let mut map = BTreeMap::new();
        map.insert("zeta".to_owned(), PathBuf::from("/run/hive-agent/zeta/web.sock"));
        map.insert("alpha".to_owned(), PathBuf::from("/run/hive-agent/alpha/web.sock"));
        let body = render(&map);
        // Pretty-print = newlines between keys + indentation.
        assert!(body.contains('\n'));
        // BTreeMap sorts → alpha before zeta in output.
        let alpha_pos = body.find("alpha").expect("alpha in output");
        let zeta_pos = body.find("zeta").expect("zeta in output");
        assert!(
            alpha_pos < zeta_pos,
            "sorted order broken:\n{body}"
        );
    }

    #[test]
    fn render_emits_paths_as_strings() {
        // PathBuf-valued map serialises as plain JSON strings (not
        // some {"inner": "..."} wrapper). Pin the shape so the
        // gateway-side reader can deserialise into String values
        // without nested struct logic.
        let mut map = BTreeMap::new();
        map.insert("iris".to_owned(), PathBuf::from("/run/hive-agent/iris/web.sock"));
        let body = render(&map);
        assert!(body.contains("\"iris\""));
        assert!(body.contains("\"/run/hive-agent/iris/web.sock\""));
    }
}