//! Minimal privileged helper for hive-c0re.
//!
//! Runs as root. Exposes a narrow unix socket at `/run/hive/priv.sock`
//! that accepts `PrivRequest` JSON lines and executes only the
//! operations that genuinely require root. All coordination logic,
//! broker, HTTP, and scheduling stay in the unprivileged hive-c0re
//! process.
//!
//! **Security model**: every request is validated against a strict
//! container-name allowlist before any filesystem or process operation.
//! Only containers whose names match the hive convention (`h-*`,
//! the manager container, or known sibling service containers) are
//! accepted. Every variant maps to a single known operation — no
//! arbitrary command pass-through.
//!
//! **Socket activation**: when systemd passes the listener socket via
//! `LISTEN_FDS=1` + `LISTEN_PID=<self>`, the inherited fd 3 is used
//! instead of binding a fresh socket.

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

use anyhow::{Context as _, Result, bail};
use hive_sh4re::priv_proto::{AGENT_PREFIX, MANAGER_NAME, META_DIR, PRIV_SOCK, SIBLING_CONTAINERS, BindMount, PrivRequest, PrivResponse};
use tokio::io::{AsyncBufReadExt, AsyncWriteExt, BufReader};
use tokio::net::{UnixListener, UnixStream};
use tokio::process::Command;

/// Root of the per-agent unix-socket dirs on the host.
const SOCKET_DIR_ROOT: &str = "/run/hive-agent";

#[tokio::main]
async fn main() -> Result<()> {
    tracing_subscriber::fmt()
        .with_env_filter(
            tracing_subscriber::EnvFilter::try_from_default_env()
                .unwrap_or_else(|_| "info".into()),
        )
        .init();

    let listener = socket_listener()?;
    tracing::info!("hive-priv listening");

    loop {
        match listener.accept().await {
            Ok((stream, _)) => {
                tokio::spawn(handle(stream));
            }
            Err(e) => {
                tracing::error!(error = %e, "accept failed");
            }
        }
    }
}

fn socket_listener() -> Result<UnixListener> {
    // Socket activation: systemd passes the socket as fd 3 when
    // LISTEN_FDS >= 1 and LISTEN_PID matches our pid.
    let listen_fds: Option<i32> = std::env::var("LISTEN_FDS")
        .ok()
        .and_then(|s| s.parse().ok());
    let listen_pid: Option<u32> = std::env::var("LISTEN_PID")
        .ok()
        .and_then(|s| s.parse().ok());

    if let (Some(n), Some(p)) = (listen_fds, listen_pid) {
        if n >= 1 && p == std::process::id() {
            // SAFETY: systemd has passed us a ready UnixListener on fd 3.
            let std_listener = unsafe {
                use std::os::unix::io::FromRawFd;
                std::os::unix::net::UnixListener::from_raw_fd(3)
            };
            std_listener
                .set_nonblocking(true)
                .context("set socket non-blocking")?;
            let listener =
                tokio::net::UnixListener::from_std(std_listener).context("wrap systemd socket")?;
            tracing::info!("using systemd-activated socket");
            return Ok(listener);
        }
    }

    // Fallback: bind the socket ourselves.
    let path = Path::new(PRIV_SOCK);
    if let Some(parent) = path.parent() {
        std::fs::create_dir_all(parent)
            .with_context(|| format!("create {}", parent.display()))?;
    }
    let _ = std::fs::remove_file(path);
    let listener = UnixListener::bind(path).with_context(|| format!("bind {PRIV_SOCK}"))?;
    // Mode 0660: only the hive-core group can connect.
    use std::os::unix::fs::PermissionsExt as _;
    std::fs::set_permissions(path, std::fs::Permissions::from_mode(0o660))
        .context("chmod priv.sock")?;
    tracing::info!(path = PRIV_SOCK, "bound priv socket");
    Ok(listener)
}

async fn handle(stream: UnixStream) {
    let (reader, mut writer) = stream.into_split();
    let mut lines = BufReader::new(reader).lines();
    while let Ok(Some(line)) = lines.next_line().await {
        let resp = dispatch(&line).await;
        let mut json = serde_json::to_string(&resp).unwrap_or_else(|e| {
            format!("{{\"ok\":false,\"stdout\":\"\",\"stderr\":\"\",\"error\":\"serialise failed: {e}\"}}")
        });
        json.push('\n');
        if let Err(e) = writer.write_all(json.as_bytes()).await {
            tracing::warn!(error = %e, "write response failed");
            break;
        }
    }
}

async fn dispatch(line: &str) -> PrivResponse {
    match serde_json::from_str::<PrivRequest>(line) {
        Ok(req) => match exec(req).await {
            Ok((stdout, stderr)) => PrivResponse {
                ok: true,
                stdout,
                stderr,
                error: None,
            },
            Err(e) => PrivResponse {
                ok: false,
                stdout: String::new(),
                stderr: String::new(),
                error: Some(format!("{e:#}")),
            },
        },
        Err(e) => PrivResponse {
            ok: false,
            stdout: String::new(),
            stderr: String::new(),
            error: Some(format!("parse request: {e}")),
        },
    }
}

/// Execute a validated `PrivRequest`. Returns `(stdout, stderr)` on success.
async fn exec(req: PrivRequest) -> Result<(String, String)> {
    match req {
        PrivRequest::StartContainer { ref name } => {
            validate_container_name(name)?;
            container_run(&["start", &container_system_name(name)]).await
        }

        PrivRequest::StopContainer { ref name } => {
            validate_container_name(name)?;
            container_run(&["stop", &container_system_name(name)]).await
        }

        PrivRequest::KillContainer { ref name } => {
            validate_container_name(name)?;
            container_run(&["kill", &container_system_name(name)]).await
        }

        PrivRequest::UpdateContainer { ref name } => {
            validate_container_name(name)?;
            let flake_ref = agent_flake_ref(name);
            container_run(&["update", &container_system_name(name), "--flake", &flake_ref]).await
        }

        PrivRequest::CreateContainer { ref name } => {
            validate_container_name(name)?;
            let flake_ref = agent_flake_ref(name);
            container_run(&["create", &container_system_name(name), "--flake", &flake_ref]).await
        }

        PrivRequest::DestroyContainer { ref name } => {
            validate_container_name(name)?;
            container_run(&["destroy", &container_system_name(name)]).await
        }

        PrivRequest::ListContainers => container_run(&["list"]).await,

        PrivRequest::WriteNspawnFlags { ref container, ref binds } => {
            validate_container_system_name(container)?;
            for bind in binds {
                validate_bind_path(&bind.host_path)?;
                validate_bind_path(&bind.container_path)?;
            }
            write_nspawn_flags(container, binds)?;
            Ok((String::new(), String::new()))
        }

        PrivRequest::WriteResourceLimits {
            ref container,
            ref memory_max,
            ref cpu_quota,
        } => {
            validate_container_system_name(container)?;
            let dir = format!("/run/systemd/system/container@{container}.service.d");
            std::fs::create_dir_all(&dir).with_context(|| format!("create {dir}"))?;
            let path = format!("{dir}/hyperhive-limits.conf");
            let content = format!("[Service]\nMemoryMax={memory_max}\nCPUQuota={cpu_quota}\n");
            std::fs::write(&path, content).with_context(|| format!("write {path}"))?;
            Ok((String::new(), String::new()))
        }

        PrivRequest::RemoveServiceDropin { ref container } => {
            validate_container_system_name(container)?;
            let dir = format!("/run/systemd/system/container@{container}.service.d");
            if Path::new(&dir).exists() {
                std::fs::remove_dir_all(&dir)
                    .with_context(|| format!("remove {dir}"))?;
            }
            Ok((String::new(), String::new()))
        }

        PrivRequest::DaemonReload => {
            let out = Command::new("systemctl")
                .arg("daemon-reload")
                .output()
                .await
                .context("invoke systemctl daemon-reload")?;
            if !out.status.success() {
                bail!(
                    "systemctl daemon-reload failed ({}): {}",
                    out.status,
                    String::from_utf8_lossy(&out.stderr).trim()
                );
            }
            Ok((String::new(), String::new()))
        }

        PrivRequest::ReloadGatewayNginx => {
            let out = Command::new("systemd-run")
                .args(["--machine=hive-gateway", "--quiet", "--", "nginx", "-s", "reload"])
                .output()
                .await
                .context("invoke systemd-run for gateway nginx reload")?;
            if !out.status.success() {
                bail!(
                    "gateway nginx reload failed ({}): {}",
                    out.status,
                    String::from_utf8_lossy(&out.stderr).trim()
                );
            }
            Ok((String::new(), String::new()))
        }

        PrivRequest::ChownSocketDir { ref agent_name, uid, gid } => {
            validate_agent_name(agent_name)?;
            let path = socket_dir_path(agent_name);
            std::os::unix::fs::chown(&path, Some(uid), Some(gid))
                .with_context(|| format!("chown {} to {uid}:{gid}", path.display()))?;
            Ok((String::new(), String::new()))
        }

        PrivRequest::ChmodSocketDir { ref agent_name, mode } => {
            validate_agent_name(agent_name)?;
            let path = socket_dir_path(agent_name);
            use std::os::unix::fs::PermissionsExt as _;
            std::fs::set_permissions(&path, std::fs::Permissions::from_mode(mode))
                .with_context(|| format!("chmod {:o} {}", mode, path.display()))?;
            Ok((String::new(), String::new()))
        }
    }
}

/// Invoke `nixos-container` with the given args, log output to journald.
async fn container_run(args: &[&str]) -> Result<(String, String)> {
    let out = Command::new("nixos-container")
        .args(args)
        .output()
        .await
        .context("invoke nixos-container")?;
    let stdout = String::from_utf8_lossy(&out.stdout).into_owned();
    let stderr = String::from_utf8_lossy(&out.stderr).into_owned();
    for line in stdout.lines() {
        tracing::info!(target: "nixos-container", "{line}");
    }
    for line in stderr.lines() {
        tracing::warn!(target: "nixos-container", "{line}");
    }
    if !out.status.success() {
        bail!(
            "nixos-container {} failed ({}): {}",
            args.join(" "),
            out.status,
            stderr.trim()
        );
    }
    Ok((stdout, stderr))
}

/// Return the system container name for a logical agent name.
/// Manager (`MANAGER_NAME`) passes through; sub-agents get `h-` prefix.
fn container_system_name(name: &str) -> String {
    if name == MANAGER_NAME {
        name.to_owned()
    } else {
        format!("{AGENT_PREFIX}{name}")
    }
}

/// Path of the per-agent unix-socket dir on the host.
fn socket_dir_path(agent_name: &str) -> PathBuf {
    PathBuf::from(format!("{SOCKET_DIR_ROOT}/{agent_name}"))
}

/// Validate a logical agent name (the name hive-c0re uses internally,
/// before the `h-` container prefix is applied).
fn validate_agent_name(name: &str) -> Result<()> {
    if name == MANAGER_NAME {
        return Ok(());
    }
    validate_name_chars(name)?;
    Ok(())
}

/// Validate a logical agent name and check it maps to a hive-managed container.
fn validate_container_name(name: &str) -> Result<()> {
    if name == MANAGER_NAME {
        return Ok(());
    }
    if SIBLING_CONTAINERS.contains(&name) {
        return Ok(());
    }
    validate_name_chars(name)?;
    Ok(())
}

/// Validate a system-level container name (already has `h-` prefix for
/// sub-agents, or is the manager name / sibling service name).
fn validate_container_system_name(name: &str) -> Result<()> {
    if name == MANAGER_NAME {
        return Ok(());
    }
    if SIBLING_CONTAINERS.contains(&name) {
        return Ok(());
    }
    if let Some(suffix) = name.strip_prefix(AGENT_PREFIX) {
        validate_name_chars(suffix)?;
        return Ok(());
    }
    bail!("container name {name:?} is not managed by hive");
}

fn validate_name_chars(name: &str) -> Result<()> {
    if name.is_empty()
        || !name
            .chars()
            .all(|c| c.is_ascii_lowercase() || c.is_ascii_digit() || c == '-')
    {
        bail!("invalid name {name:?}: must be non-empty lowercase ascii + digits + hyphens");
    }
    Ok(())
}

/// Derive the meta-flake ref for an agent by name.
fn agent_flake_ref(name: &str) -> String {
    format!("{META_DIR}#{name}")
}

/// Validate a bind-mount path: must be absolute, non-empty, and contain
/// no newlines, null bytes, or double-quotes (which would break the
/// `EXTRA_NSPAWN_FLAGS="..."` conf line format).
fn validate_bind_path(path: &str) -> Result<()> {
    if path.is_empty()
        || !path.starts_with('/')
        || path.bytes().any(|b| b == 0 || b == b'\n' || b == b'"' || b == b':')
    {
        bail!(
            "invalid bind path {path:?}: must be an absolute path with no colons, newlines, null bytes, or double-quotes"
        );
    }
    Ok(())
}

/// Update `/etc/nixos-containers/<container>.conf`: strips network-isolation
/// vars (`PRIVATE_NETWORK`, `HOST_ADDRESS*`, `LOCAL_ADDRESS*`, `HOST_BRIDGE`,
/// `EXTRA_NSPAWN_FLAGS`), forces `PRIVATE_NETWORK=0` and blank network vars,
/// then appends `EXTRA_NSPAWN_FLAGS="<flags>"`.
fn write_nspawn_flags(container: &str, binds: &[BindMount]) -> Result<()> {
    let path = format!("/etc/nixos-containers/{container}.conf");
    let original = std::fs::read_to_string(&path)
        .with_context(|| format!("read {path}"))?;
    let mut lines: Vec<&str> = original
        .lines()
        .filter(|line| {
            let t = line.trim_start();
            !t.starts_with("EXTRA_NSPAWN_FLAGS=")
                && !t.starts_with("PRIVATE_NETWORK=")
                && !t.starts_with("HOST_ADDRESS=")
                && !t.starts_with("LOCAL_ADDRESS=")
                && !t.starts_with("HOST_ADDRESS6=")
                && !t.starts_with("LOCAL_ADDRESS6=")
                && !t.starts_with("HOST_BRIDGE=")
        })
        .collect();
    let mut out = lines.join("\n");
    if !out.is_empty() {
        out.push('\n');
    }
    out.push_str("PRIVATE_NETWORK=0\n");
    out.push_str("HOST_ADDRESS=\n");
    out.push_str("LOCAL_ADDRESS=\n");
    out.push_str("HOST_ADDRESS6=\n");
    out.push_str("LOCAL_ADDRESS6=\n");
    out.push_str("HOST_BRIDGE=\n");
    let flags: Vec<String> = binds.iter().map(|b| {
        let flag = if b.read_only { "--bind-ro" } else { "--bind" };
        format!("{flag}={}:{}", b.host_path, b.container_path)
    }).collect();
    let flags_joined = flags.join(" ");
    out.push_str(&format!("EXTRA_NSPAWN_FLAGS=\"{flags_joined}\"\n"));
    std::fs::write(&path, out).with_context(|| format!("write {path}"))
}