//! Operations that are exposed through more than one surface (the host admin
//! socket *and* the dashboard's POST endpoints). Each function takes a
//! `&Coordinator` and the request parameters; callers stitch the response
//! shape they want (HTTP redirect vs JSON).

use std::sync::Arc;

use anyhow::{Context as _, Result, bail};

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

/// `applied/main`, and whether `target` descends from it. Fast-forwarding
/// `main` to a `target` that does not is a rewind: it drops every commit on
/// `main` that `target` lacks.
async fn applied_main_under(applied_dir: &std::path::Path, target: &str) -> Result<(String, bool)> {
    let current_main = lifecycle::git_rev_parse(applied_dir, "refs/heads/main")
        .await
        .map_err(|e| anyhow::anyhow!("read applied/main: {e:#}"))?;
    let descends = lifecycle::git_is_ancestor(applied_dir, &current_main, target)
        .await
        .map_err(|e| anyhow::anyhow!("ancestry check {current_main}..{target}: {e:#}"))?;
    Ok((current_main, descends))
}

/// What [`advance_applied_to_rev`] did to `applied/main`.
#[derive(Debug, PartialEq, Eq)]
pub(crate) enum RevAdvance {
    /// `applied/main` already was the rev, so there is nothing to deploy.
    AlreadyApplied,
    /// `applied/main` was fast-forwarded to the rev.
    Advanced,
    /// The rev is an ancestor of `applied/main`, so a later commit already
    /// carries it and there is nothing to deploy. Deploy requests are not
    /// ordered: two merges' requests can arrive in either order, and a
    /// meta-update cascade fast-forwards `main` to the forge's on its own.
    Superseded,
}

/// Fast-forward `agent`'s `applied/main` to `rev`, a commit the swarm asks
/// this hive to deploy, so the next relocking rebuild builds it.
///
/// No eval-verify on this path: a config that does not evaluate fails the
/// rebuild instead, with `applied/main` already at `rev`.
///
/// # Errors
///
/// Returns an error if the forge fetch fails, if `rev` has diverged from
/// `applied/main` (neither descendant nor ancestor), or if `main` moved during the fast-forward. `main` does not
/// move in any of these.
pub(crate) async fn advance_applied_to_rev(agent: &str, rev: &str) -> Result<RevAdvance> {
    advance_applied_main(
        &crate::paths::applied_dir(agent),
        rev,
        crate::forge::fetch_forge_main(agent),
    )
    .await
}

/// [`advance_applied_to_rev`] with the forge fetch passed in, so it is
/// testable against a local repo.
///
/// `applied/main` is compared to `rev` twice: before the fetch, so an applied
/// rev costs no forge round-trip, and after it, because a meta-update cascade
/// fast-forwards `main` to the forge's and may do so meanwhile.
async fn advance_applied_main<T>(
    applied_dir: &std::path::Path,
    rev: &str,
    fetch: impl std::future::Future<Output = Result<T>>,
) -> Result<RevAdvance> {
    let main = lifecycle::git_rev_parse(applied_dir, "refs/heads/main")
        .await
        .map_err(|e| anyhow::anyhow!("read applied/main: {e:#}"))?;
    if main == rev {
        return Ok(RevAdvance::AlreadyApplied);
    }
    fetch.await.context("fetch the forge config main")?;
    let (main, descends) = applied_main_under(applied_dir, rev).await?;
    if main == rev {
        return Ok(RevAdvance::AlreadyApplied);
    }
    if !descends {
        let contained = lifecycle::git_is_ancestor(applied_dir, rev, &main)
            .await
            .map_err(|e| anyhow::anyhow!("ancestry check {rev}..{main}: {e:#}"))?;
        if contained {
            return Ok(RevAdvance::Superseded);
        }
        bail!(
            "{rev} does not descend from applied/main ({main}); fast-forwarding to it would \
             discard commits"
        );
    }
    ff_applied_main(applied_dir, rev, &main).await?;
    Ok(RevAdvance::Advanced)
}

/// Fast-forward `applied/main` to `target` and sync the working tree.
///
/// Compare-and-swap, not a bare set: `main` must still be `expected_main`, the
/// sha the caller's ancestry gate ([`applied_main_under`]) ran against. A plain
/// `update-ref` moves the branch to `target` whatever it currently points at,
/// which turns "fast-forward" into "discard anything that landed in the
/// meantime" — the gate only proves `target` safe against the `main` observed
/// *then*, so this is what makes that proof still true *now*.
async fn ff_applied_main(
    applied_dir: &std::path::Path,
    target: &str,
    expected_main: &str,
) -> Result<()> {
    lifecycle::git_update_ref_cas(applied_dir, "refs/heads/main", target, expected_main)
        .await
        .map_err(|e| {
            anyhow::anyhow!("ff main {expected_main} -> {target} (concurrent move?): {e:#}")
        })?;
    lifecycle::git_read_tree_reset(applied_dir, "refs/heads/main")
        .await
        .map_err(|e| anyhow::anyhow!("read-tree to main: {e:#}"))
}

/// Tear down a sub-agent container. By default this is non-destructive to
/// persistent state: the proposed/applied config repos and the Claude
/// credentials dir under `/var/lib/hyperhive/{agents,applied}/<name>/` are
/// kept, so recreating an agent of the same name reuses prior config + creds
/// (no re-login). The ephemeral runtime dir under `/run/hyperhive/agents/`
/// is cleared because its contents (the mcp socket) don't survive restarts
/// anyway. With `purge=true` the persistent trees are also wiped — config
/// history, claude creds, notes — there is no undo.
/// The bootstrap/root container is destroyable like any other: it's
/// imperative infra that `auto_update::ensure_root_agent` recreates on the
/// next hive-c0re startup if absent, so destroying it is transient rather
/// than something to refuse at the API.
///
/// Submits the teardown DAG and returns — it does not wait for the container to
/// go away. Same contract as every other lifecycle op (`rebuild`, `kill`,
/// `restart`, `start`): the queue owns the work, the caller gets an
/// acknowledgement. Progress is visible as real nodes on the dashboard.
pub fn destroy(coord: &Arc<Coordinator>, name: &str, purge: bool) {
    tracing::info!(%name, purge, "destroy");
    if let Err(e) = coord.job_queue.insert_job(|b| {
        crate::job_queue::templates::destroy(b, name, purge);
        Vec::new()
    }) {
        tracing::error!(agent = %name, error = ?e, "destroy: insert failed");
    }
    coord.emit_rebuild_queue_snapshot();
}

#[cfg(test)]
mod tests {
    use super::{RevAdvance, advance_applied_main};
    use crate::lifecycle;

    /// A repo with `main` at `b`, child of `a`, and `c`, a sibling of `b` off
    /// `a`. Returns the dir and the shas `[a, b, c]`.
    async fn repo() -> (tempfile::TempDir, [String; 3]) {
        let dir = tempfile::tempdir().expect("tempdir");
        let path = dir.path();
        let commit = |msg: &'static str| async move {
            lifecycle::git(
                path,
                &[
                    "-c",
                    "user.name=t",
                    "-c",
                    "user.email=t@t",
                    "commit",
                    "-q",
                    "--allow-empty",
                    "-m",
                    msg,
                ],
            )
            .await
            .expect("commit");
            lifecycle::git_rev_parse(path, "HEAD").await.expect("HEAD")
        };
        lifecycle::git(path, &["init", "-q", "--initial-branch=main"])
            .await
            .expect("init");
        let a = commit("a").await;
        let b = commit("b").await;
        lifecycle::git(path, &["checkout", "-q", "-b", "side", &a])
            .await
            .expect("branch");
        let c = commit("c").await;
        lifecycle::git(path, &["checkout", "-q", "main"])
            .await
            .expect("checkout main");
        (dir, [a, b, c])
    }

    async fn main_of(dir: &tempfile::TempDir) -> String {
        lifecycle::git_rev_parse(dir.path(), "refs/heads/main")
            .await
            .expect("main")
    }

    #[tokio::test]
    async fn the_applied_rev_is_a_no_op_without_a_fetch() {
        let (dir, [_, b, _]) = repo().await;
        let fetched = std::cell::Cell::new(false);
        let fetch = async {
            fetched.set(true);
            anyhow::Ok(())
        };
        let outcome = advance_applied_main(dir.path(), &b, fetch).await;
        assert_eq!(outcome.expect("no-op"), RevAdvance::AlreadyApplied);
        assert!(!fetched.get(), "an applied rev must not reach the forge");
        assert_eq!(main_of(&dir).await, b);
    }

    #[tokio::test]
    async fn a_rev_not_descending_from_main_is_refused_and_main_stays() {
        let (dir, [_, b, c]) = repo().await;
        let outcome = advance_applied_main(dir.path(), &c, async { anyhow::Ok(()) }).await;
        let err = outcome.expect_err("a sibling of main is not a fast-forward");
        assert!(
            format!("{err:#}").contains("does not descend from applied/main"),
            "{err:#}"
        );
        assert_eq!(main_of(&dir).await, b);
    }

    #[tokio::test]
    async fn an_ancestor_of_main_is_superseded_not_refused() {
        let (dir, [a, b, _]) = repo().await;
        let outcome = advance_applied_main(dir.path(), &a, async { anyhow::Ok(()) }).await;
        assert_eq!(outcome.expect("no-op"), RevAdvance::Superseded);
        assert_eq!(main_of(&dir).await, b);
    }

    #[tokio::test]
    async fn a_descendant_rev_fast_forwards_main() {
        let (dir, [a, b, _]) = repo().await;
        lifecycle::git_update_ref(dir.path(), "refs/heads/main", &a)
            .await
            .expect("rewind main");
        let outcome = advance_applied_main(dir.path(), &b, async { anyhow::Ok(()) }).await;
        assert_eq!(outcome.expect("fast-forward"), RevAdvance::Advanced);
        assert_eq!(main_of(&dir).await, b);
    }

    #[tokio::test]
    async fn a_failed_fetch_leaves_main_alone() {
        let (dir, [a, b, _]) = repo().await;
        lifecycle::git_update_ref(dir.path(), "refs/heads/main", &a)
            .await
            .expect("rewind main");
        let outcome = advance_applied_main(dir.path(), &b, async {
            Err::<(), _>(anyhow::anyhow!("forge down"))
        })
        .await;
        assert!(outcome.is_err());
        assert_eq!(main_of(&dir).await, a);
    }
}