use std::path::Path;
use std::sync::Arc;

use anyhow::{Context, Result};
use hive_sh4re::{HostRequest, HostResponse};
use tokio::io::{AsyncBufReadExt, AsyncWriteExt, BufReader};
use tokio::net::{UnixListener, UnixStream};

use crate::actions;
use crate::coordinator::Coordinator;
use crate::lifecycle;

pub async fn serve(socket: &Path, coord: Arc<Coordinator>) -> Result<()> {
    // Prefer a socket passed by systemd socket-activation (LISTEN_FDS).
    // When running under a `.socket` unit, systemd has already created,
    // bound, and chmod-ed the socket for us — we just accept on it.
    // Fall back to the traditional bind path when not socket-activated
    // (direct invocation, dev, tests).
    let listener = {
        let mut listenfd = listenfd::ListenFd::from_env();
        if let Some(std_listener) = listenfd
            .take_unix_listener(0)
            .context("take socket-activated unix listener")?
        {
            std_listener.set_nonblocking(true)?;
            UnixListener::from_std(std_listener)
                .context("convert socket-activated listener to tokio")?
        } else {
            // Standalone: create parent dir, remove any stale socket, bind.
            if let Some(parent) = socket.parent() {
                std::fs::create_dir_all(parent)
                    .with_context(|| format!("create socket parent {}", parent.display()))?;
            }
            if socket.exists() {
                std::fs::remove_file(socket).context("remove stale socket")?;
            }
            UnixListener::bind(socket)
                .with_context(|| format!("bind admin socket {}", socket.display()))?
        }
    };
    tracing::info!(socket = %socket.display(), hyperhive_flake = %coord.hyperhive_flake, "hive-c0re admin listening");

    loop {
        let (stream, _) = listener.accept().await.context("accept connection")?;
        let coord = coord.clone();
        tokio::spawn(async move {
            if let Err(e) = handle(stream, coord).await {
                tracing::warn!(error = ?e, "connection failed");
            }
        });
    }
}

async fn handle(stream: UnixStream, 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::<HostRequest>(line.trim()) {
            Ok(req) => dispatch(&req, coord.clone()).await,
            Err(e) => HostResponse::error(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?;
    }
}

async fn dispatch(req: &HostRequest, coord: Arc<Coordinator>) -> HostResponse {
    let result: anyhow::Result<HostResponse> = async {
        Ok(match req {
            HostRequest::Spawn { name } => handle_spawn(&coord, name).await?,
            HostRequest::RequestSpawn { name } => {
                tracing::info!(%name, "request_spawn");
                let id =
                    coord
                        .approvals
                        .submit_kind(name, hive_sh4re::ApprovalKind::Spawn, "", None)?;
                tracing::info!(%id, %name, "spawn approval queued");
                HostResponse::success()
            }
            HostRequest::Kill { name } => handle_kill(&coord, name).await?,
            HostRequest::Restart { name } => {
                tracing::info!(%name, "restart");
                lifecycle::restart(name).await?;
                HostResponse::success()
            }
            HostRequest::RestartAll => handle_restart_all().await?,
            HostRequest::Destroy { name, purge } => {
                actions::destroy(&coord, name, *purge).await?;
                HostResponse::success()
            }
            HostRequest::Rebuild { name } => handle_rebuild(&coord, name).await?,
            HostRequest::List => HostResponse::list(lifecycle::list().await?),
            HostRequest::Pending => HostResponse::pending(coord.approvals.pending()?),
            HostRequest::Approve { id } => {
                actions::approve(coord.clone(), *id).await?;
                HostResponse::success()
            }
            HostRequest::Deny { id } => {
                actions::deny(&coord, *id, None).await?;
                HostResponse::success()
            }
            HostRequest::SetParent { child, new_parent } => {
                tracing::info!(%child, ?new_parent, "set_parent");
                // `reparent_with_notify` wraps `topology::set_parent`
                // with the three notification messages + the
                // ContainerView rescan. Idempotent same-parent calls
                // skip both the messages and the disk write per the
                // topology fast-path.
                coord
                    .reparent_with_notify(child, new_parent.as_deref())
                    .await
                    .map_err(anyhow::Error::msg)?;
                HostResponse::success()
            }
        })
    }
    .await;
    match result {
        Ok(r) => r,
        Err(e) => HostResponse::error(format!("{e:#}")),
    }
}

/// Create + start the container for `name`, rolling back socket
/// registration and notifying the manager on failure.
async fn handle_spawn(coord: &Arc<Coordinator>, name: &str) -> Result<HostResponse> {
    tracing::info!(%name, "spawn");
    let agent_dir = coord.ensure_runtime(name)?;
    let hive = coord.hive_env();
    let paths = Coordinator::agent_paths(name, agent_dir);
    match lifecycle::spawn(name, &hive, &paths).await {
        Ok(()) => {
            coord.notify_manager(&hive_sh4re::HelperEvent::Spawned {
                agent: name.to_owned(),
                ok: true,
                note: None,
                sha: None,
            });
        }
        Err(e) => {
            // Roll back socket registration if container creation failed.
            coord.unregister_agent(name);
            coord.notify_manager(&hive_sh4re::HelperEvent::Spawned {
                agent: name.to_owned(),
                ok: false,
                note: Some(format!("{e:#}")),
                sha: None,
            });
            return Err(e);
        }
    }
    Ok(HostResponse::success())
}

/// Kill `name`'s container, unregister its socket, notify the manager.
async fn handle_kill(coord: &Arc<Coordinator>, name: &str) -> Result<HostResponse> {
    tracing::info!(%name, "kill");
    lifecycle::kill(name).await?;
    coord.unregister_agent(name);
    coord.notify_manager(&hive_sh4re::HelperEvent::Killed {
        agent: name.to_owned(),
    });
    Ok(HostResponse::success())
}

/// Restart every container, aggregating per-agent failures into one
/// response rather than aborting on the first error.
async fn handle_restart_all() -> Result<HostResponse> {
    tracing::info!("restart-all");
    let agents = lifecycle::list().await?;
    let mut ok_agents: Vec<String> = Vec::new();
    let mut errors: Vec<String> = Vec::new();
    for agent in &agents {
        if let Err(e) = lifecycle::restart(agent).await {
            tracing::warn!(%agent, error = ?e, "restart-all: failed to restart agent");
            errors.push(format!("{agent}: {e:#}"));
        } else {
            ok_agents.push(agent.clone());
        }
    }
    if errors.is_empty() {
        Ok(HostResponse::list(ok_agents))
    } else {
        Ok(HostResponse {
            ok: false,
            error: Some(errors.join("; ")),
            agents: Some(ok_agents),
            approvals: None,
        })
    }
}

/// Rebuild `name`'s container, notifying the manager of the outcome
/// (success or failure) and kicking the agent's next turn on success.
async fn handle_rebuild(coord: &Arc<Coordinator>, name: &str) -> Result<HostResponse> {
    tracing::info!(%name, "rebuild");
    let agent_dir = coord.ensure_runtime(name)?;
    let hive = coord.hive_env();
    let paths = Coordinator::agent_paths(name, agent_dir);
    let result = lifecycle::rebuild(name, &hive, &paths, &|_| (), &|_| ()).await;
    // Mirror auto_update::rebuild_agent — the manager wants to know
    // about every rebuild attempt regardless of which surface triggered
    // it, especially failures (build error → manager can adjust the
    // agent's agent.nix). Without this the admin-socket CLI was a
    // notify-gap.
    match &result {
        Ok(()) => {
            coord.notify_manager(&hive_sh4re::HelperEvent::Rebuilt {
                agent: name.to_owned(),
                ok: true,
                note: None,
                sha: None,
                tag: None,
            });
            // Wake the agent's next turn with the "you were rebuilt"
            // hint. Same pattern as auto_update::rebuild_agent and the
            // dashboard rebuild path — this is the CLI's equivalent.
            coord.kick_agent(name, "container rebuilt");
        }
        Err(e) => coord.notify_manager(&hive_sh4re::HelperEvent::Rebuilt {
            agent: name.to_owned(),
            ok: false,
            note: Some(format!("{e:#}")),
            sha: None,
            tag: None,
        }),
    }
    result?;
    Ok(HostResponse::success())
}