//! `nixos-container` lifecycle + per-agent config flake generation.

use std::path::Path;

use anyhow::{Context, Result, bail};
use tokio::process::Command;

/// Sub-agent container prefix. `nixos-container` caps the total container name
/// at 11 chars (it gets encoded into network interface names), so the agent
/// name itself can be at most `MAX_AGENT_NAME` chars.
pub const AGENT_PREFIX: &str = "h-";
pub const MAX_AGENT_NAME: usize = 9;
/// Container name of the manager (a separate slot from sub-agents).
pub const MANAGER_NAME: &str = "hm1nd";

/// Mount point of the per-agent runtime directory inside the container.
pub const CONTAINER_RUNTIME_MOUNT: &str = "/run/hive";

const GIT_NAME: &str = "hive-c0re";
const GIT_EMAIL: &str = "hive-c0re@hyperhive";

pub fn container_name(name: &str) -> String {
    format!("{AGENT_PREFIX}{name}")
}

fn validate(name: &str) -> Result<()> {
    if name.is_empty() {
        bail!("agent name must not be empty");
    }
    if name.len() > MAX_AGENT_NAME {
        bail!(
            "agent name '{name}' is too long ({} chars); max {MAX_AGENT_NAME}",
            name.len()
        );
    }
    Ok(())
}

pub async fn spawn(
    name: &str,
    hyperhive_flake: &str,
    agent_dir: &Path,
    config_dir: &Path,
) -> Result<()> {
    validate(name)?;
    setup_config(config_dir, name, hyperhive_flake).await?;
    let container = container_name(name);
    let flake_ref = format!("{}#default", config_dir.display());
    run(&["create", &container, "--flake", &flake_ref]).await?;
    set_nspawn_flags(&container, agent_dir)?;
    run(&["start", &container]).await
}

pub async fn kill(name: &str) -> Result<()> {
    validate(name)?;
    let container = container_name(name);
    run(&["stop", &container]).await
}

pub async fn rebuild(
    name: &str,
    hyperhive_flake: &str,
    agent_dir: &Path,
    config_dir: &Path,
) -> Result<()> {
    validate(name)?;
    setup_config(config_dir, name, hyperhive_flake).await?;
    let container = container_name(name);
    let flake_ref = format!("{}#default", config_dir.display());
    set_nspawn_flags(&container, agent_dir)?;
    run(&["update", &container, "--flake", &flake_ref]).await?;
    // Restart so any nspawn-level changes (bind mounts, networking, etc.) apply.
    run(&["stop", &container]).await?;
    run(&["start", &container]).await
}

pub async fn list() -> Result<Vec<String>> {
    let out = Command::new("nixos-container")
        .arg("list")
        .output()
        .await
        .context("invoke nixos-container list")?;
    if !out.status.success() {
        bail!(
            "nixos-container list exited with status {}: {}",
            out.status,
            String::from_utf8_lossy(&out.stderr).trim()
        );
    }
    Ok(String::from_utf8_lossy(&out.stdout)
        .lines()
        .map(str::trim)
        .filter(|line| line.starts_with(AGENT_PREFIX) || *line == MANAGER_NAME)
        .map(str::to_owned)
        .collect())
}

/// Ensure `config_dir` exists as a git repo containing a per-agent flake. The
/// `flake.nix` is rewritten every call (so a new hyperhive store path
/// propagates on rebuild); `agent.nix` is written only the first time
/// (manager-editable thereafter).
pub async fn setup_config(config_dir: &Path, name: &str, hyperhive_flake: &str) -> Result<()> {
    std::fs::create_dir_all(config_dir)
        .with_context(|| format!("create {}", config_dir.display()))?;

    let flake_path = config_dir.join("flake.nix");
    let flake_body = format!(
        r#"{{
  description = "hyperhive sub-agent {name}";
  inputs.hyperhive.url = "{hyperhive_flake}";
  outputs =
    {{ hyperhive, ... }}:
    {{
      nixosConfigurations.default = hyperhive.nixosConfigurations.agent-base.extendModules {{
        modules = [ ./agent.nix ];
      }};
    }};
}}
"#,
    );
    std::fs::write(&flake_path, flake_body)
        .with_context(|| format!("write {}", flake_path.display()))?;

    let agent_path = config_dir.join("agent.nix");
    if !agent_path.exists() {
        let initial = format!(
            "{{ ... }}:\n{{\n  # Per-agent overrides for {name}. The manager edits this\n  # file (and commits) to customise the agent's NixOS config.\n}}\n",
        );
        std::fs::write(&agent_path, initial)
            .with_context(|| format!("write {}", agent_path.display()))?;
    }

    if !config_dir.join(".git").exists() {
        git(config_dir, &["init", "--initial-branch=main"]).await?;
    }
    git(config_dir, &["add", "-A"]).await?;
    let clean = git_status(config_dir, &["diff", "--cached", "--quiet"]).await?;
    if !clean {
        git(
            config_dir,
            &[
                "-c",
                &format!("user.name={GIT_NAME}"),
                "-c",
                &format!("user.email={GIT_EMAIL}"),
                "commit",
                "-m",
                "hive-c0re sync",
            ],
        )
        .await?;
    }
    Ok(())
}

/// Verify `commit_ref` exists in the config repo, advance `main` to it, and
/// reset the working tree. Caller is responsible for the subsequent rebuild.
pub async fn apply_commit(config_dir: &Path, commit_ref: &str) -> Result<()> {
    let st = Command::new("git")
        .current_dir(config_dir)
        .args(["cat-file", "-e", commit_ref])
        .status()
        .await
        .with_context(|| format!("git cat-file in {}", config_dir.display()))?;
    if !st.success() {
        bail!(
            "commit {commit_ref} not found in {}",
            config_dir.display()
        );
    }
    git(config_dir, &["update-ref", "refs/heads/main", commit_ref]).await?;
    git(config_dir, &["reset", "--hard", commit_ref]).await?;
    Ok(())
}

async fn git(dir: &Path, args: &[&str]) -> Result<()> {
    let out = Command::new("git")
        .current_dir(dir)
        .args(args)
        .output()
        .await
        .with_context(|| format!("git {} in {}", args.join(" "), dir.display()))?;
    if !out.status.success() {
        bail!(
            "git {} failed ({}): {}",
            args.join(" "),
            out.status,
            String::from_utf8_lossy(&out.stderr).trim()
        );
    }
    Ok(())
}

/// Returns true if the command exits 0.
async fn git_status(dir: &Path, args: &[&str]) -> Result<bool> {
    let st = Command::new("git")
        .current_dir(dir)
        .args(args)
        .status()
        .await
        .with_context(|| format!("git {} in {}", args.join(" "), dir.display()))?;
    Ok(st.success())
}

/// Idempotently rewrite the `EXTRA_NSPAWN_FLAGS` line in
/// `/etc/nixos-containers/<container>.conf`. The start script expands this
/// variable unquoted into the `systemd-nspawn` command.
fn set_nspawn_flags(container: &str, agent_dir: &Path) -> Result<()> {
    let path = format!("/etc/nixos-containers/{container}.conf");
    let original = std::fs::read_to_string(&path).with_context(|| format!("read {path}"))?;
    let flag = format!(
        "EXTRA_NSPAWN_FLAGS=\"--bind={}:{CONTAINER_RUNTIME_MOUNT}\"",
        agent_dir.display()
    );
    let mut lines: Vec<String> = original
        .lines()
        .filter(|line| !line.trim_start().starts_with("EXTRA_NSPAWN_FLAGS="))
        .map(str::to_owned)
        .collect();
    lines.push(flag);
    let mut content = lines.join("\n");
    content.push('\n');
    std::fs::write(&path, content).with_context(|| format!("write {path}"))?;
    tracing::info!(%path, "set EXTRA_NSPAWN_FLAGS");
    Ok(())
}

async fn run(args: &[&str]) -> Result<()> {
    let out = Command::new("nixos-container")
        .args(args)
        .output()
        .await
        .with_context(|| format!("invoke nixos-container {}", args.join(" ")))?;
    let stdout = String::from_utf8_lossy(&out.stdout);
    let stderr = String::from_utf8_lossy(&out.stderr);
    if !stdout.trim().is_empty() {
        tracing::info!(target: "nixos-container", "{}", stdout.trim());
    }
    if !stderr.trim().is_empty() {
        tracing::warn!(target: "nixos-container", "{}", stderr.trim());
    }
    if !out.status.success() {
        bail!(
            "nixos-container {} failed ({}): {}",
            args.join(" "),
            out.status,
            stderr.trim()
        );
    }
    Ok(())
}