//! `hivectl choom <agent>` — drop into an interactive Claude session inside
//! an agent container by exec-ing `machinectl shell` running claude as the
//! agent user, mirroring the harness's per-turn claude invocation.

#[cfg(unix)]
use std::os::unix::process::CommandExt as _;

use anyhow::{Result, bail};

use crate::util::agent_exists;

/// Drop into an interactive Claude session in the agent container.
///
/// Execs `machinectl shell <name>@h-<name>` running claude as the agent
/// user from its state dir, reproducing the harness's per-turn claude
/// invocation (flags, session selection, why it never collides with the
/// live harness session). See `docs/tools/hivectl.md` (Choom) for the
/// full rationale. Inherits the caller's PTY; requires root + a running
/// container.
pub(crate) fn choom(name: &str, resume_session: Option<&str>) -> Result<()> {
    if !agent_exists(name)? {
        bail!(
            "no such agent: '{name}' (no state dir under {}/)",
            hive_host_sock::AGENTS_ROOT
        );
    }
    let container = hive_host_sock::container_name(name);
    // Enter as the agent's unix user (== agent name) so claude reads the
    // right `$HOME/.claude`.
    let target = format!("{name}@{container}");
    let claude = "/run/current-system/sw/bin/claude";
    // Bind-mounted state dir; matches `hive-agent::paths::state_dir()`.
    let state_dir = format!("/agents/{name}/state");
    // Per-turn config the harness writes; matches `paths::config_dir()`.
    let cfg = "/run/hive-config";
    // `--resume <value>` passes through as `claude --resume <value>` —
    // the rejoin-by-id surface. (claude's `--continue` is a bare flag
    // that resumes the cwd's latest session — the harness's — and would
    // consume a trailing value as the first PROMPT; choom never uses
    // it.) The value is single-quoted into the shell script, so reject
    // an embedded single quote (the only char that breaks
    // single-quoting) to rule out injection — session ids never
    // contain one.
    let session_arg = match resume_session {
        Some(val) => {
            if val.contains('\'') {
                bail!("invalid --resume value '{val}': must not contain a single quote");
            }
            format!("set -- --resume '{val}';")
        }
        None => "set --;".to_string(),
    };
    // Build claude's argv as the harness does, each flag included only
    // when its file is present so a half-up container degrades to a bare
    // session. `name` is `[a-z0-9._-]` so there's nothing to quote.
    let inner = format!(
        "cd {state_dir} || exit 1; {session_arg} \
         [ -f {cfg}/claude-settings.json ] && set -- \"$@\" --settings {cfg}/claude-settings.json; \
         [ -f {cfg}/claude-mcp-config.json ] && set -- \"$@\" --mcp-config {cfg}/claude-mcp-config.json; \
         [ -f {cfg}/claude-system-prompt.md ] && set -- \"$@\" --system-prompt-file {cfg}/claude-system-prompt.md; \
         exec {claude} \"$@\""
    );
    let mut cmd = std::process::Command::new("machinectl");
    cmd.arg("shell")
        .arg(&target)
        .arg("/bin/sh")
        .arg("-lc")
        .arg(&inner);
    // exec() replaces the current process — we inherit stdin/stdout/stderr
    // (the caller's PTY) so the Claude session is fully interactive.
    // This call only returns on error.
    let err = cmd.exec();
    Err(anyhow::anyhow!("exec machinectl: {err}"))
}