//! `swarmctl agent create` — queue the swarm-controller's agent-creation
//! job graph.
//!
//! `POST /api/agents` inserts a DAG and returns as soon as it is
//! *inserted*. This verb prints the queued node id and stops: the graph's
//! last node only *publishes* a deploy, after which the hive converges on
//! its own clock, so even a settled graph would not mean the agent is up
//! and there is nothing here that could be waited on honestly.
//!
//! Transport is a bare `hyper` HTTP/1.1 client handshaked onto a
//! [`tokio::net::UnixStream`] via [`hyper_util::rt::TokioIo`] — the
//! controller has no TCP port, so this crate speaks plain HTTP directly
//! over the socket rather than pulling in a full client stack for one
//! POST.
//!
//! The two shapes below **mirror** the controller's own private
//! `CreateAgentRequest` / `CreateAgentResponse` rather than sharing them:
//! this crate does not link `swarm-controller` and there is no wire
//! crate between them. The seam is narrow and both ends validate, so
//! drift surfaces as a 400 naming the field.
//!
//! Long-form rationale for all three: `swarmctl/README.md`.

use std::path::Path;

use anyhow::{Context as _, Result, bail};
use http_body_util::{BodyExt as _, Full};
use hyper_util::rt::TokioIo;
use serde::{Deserialize, Serialize};
use tokio::net::UnixStream;

/// Body of `POST /api/agents`. Mirrors the controller's own
/// `CreateAgentRequest` — see this module's doc comment.
#[derive(Serialize)]
struct CreateAgentRequest<'a> {
    name: &'a str,
    /// Where the agent's deploy message is addressed. Required by the
    /// endpoint and not defaulted anywhere, because it is only knowable
    /// from the operator making the choice.
    hive: &'a str,
}

/// Success body of `POST /api/agents`.
#[derive(Deserialize)]
struct CreateAgentResponse {
    node_id: u64,
    /// Name collisions the controller **allowed through** — it is the
    /// "warn now, refuse later" step, so an empty list is the normal case
    /// and the field is omitted from the JSON entirely when it is empty.
    #[serde(default)]
    warnings: Vec<String>,
}

/// Run `swarmctl agent create`.
///
/// Synchronous on purpose: every other verb in this crate is, and this is
/// the only one that needs a reactor at all. A current-thread runtime
/// built here keeps that cost inside the one arm that incurs it, the same
/// way `PathArgs::resolve` is called only in the arms that need the
/// deployment's env vars.
pub(crate) fn create(socket: &Path, name: &str, hive: &str) -> Result<()> {
    // Client-side before the round trip, so a typo is an immediate local
    // error rather than a 400 the operator has to wait for. The controller
    // validates both again — that is the gate that matters, this is the
    // one that is fast.
    let name = parse_ident(name, "agent name")?;
    let hive = parse_ident(hive, "hive")?;

    let rt = tokio::runtime::Builder::new_current_thread()
        .enable_io()
        .build()
        .context("starting a tokio runtime for the controller request")?;
    let resp = rt.block_on(post_create(socket, &name, &hive))?;

    println!("queued: job node {}", resp.node_id);
    println!(
        "agent {name:?} will be deployed to hive {hive:?} once the job graph runs; \
         `swarmctl` does not wait for it"
    );
    // stderr, and after the id: the id is the result, these are asides the
    // operator should still not have to go find in the daemon's journal.
    for warning in &resp.warnings {
        eprintln!("warning: {warning}");
    }
    Ok(())
}

/// Parse a CLI-supplied name into a validated identifier, naming which
/// argument was wrong — `invalid hive` and `invalid agent name` send the
/// operator to different flags.
fn parse_ident(value: &str, what: &str) -> Result<String> {
    hive_types::Ident::parse(value)
        .map(hive_types::Ident::into_string)
        .map_err(|reason| anyhow::anyhow!("invalid {what} {value:?}: {reason}"))
}

/// One `POST /api/agents` round trip over the controller's unix socket.
async fn post_create(socket: &Path, name: &str, hive: &str) -> Result<CreateAgentResponse> {
    let body = serde_json::to_vec(&CreateAgentRequest { name, hive })
        .context("serialising the create-agent request")?;

    let stream = UnixStream::connect(socket)
        .await
        .with_context(|| connect_hint(socket))?;
    let (mut sender, conn) = hyper::client::conn::http1::handshake(TokioIo::new(stream))
        .await
        .with_context(|| format!("HTTP handshake with {}", socket.display()))?;
    // Drives the connection's I/O; a one-shot POST has nothing to do with
    // the join handle, and a connection that dies surfaces as an error on
    // `send_request` or on reading the body.
    tokio::spawn(conn);

    let req = hyper::Request::builder()
        .method(hyper::Method::POST)
        .uri("/api/agents")
        // A unix socket has no authority of its own, but HTTP/1.1 requires
        // the header; the controller routes on the path alone.
        .header(hyper::header::HOST, "localhost")
        .header(hyper::header::CONTENT_TYPE, "application/json")
        .body(Full::new(bytes::Bytes::from(body)))
        .context("building the create-agent request")?;

    let resp = sender
        .send_request(req)
        .await
        .context("sending the create-agent request to swarm-controller")?;
    let status = resp.status();
    let body = resp
        .into_body()
        .collect()
        .await
        .context("reading swarm-controller's response")?
        .to_bytes();

    if !status.is_success() {
        bail!("{}", describe_error(status, &body));
    }
    serde_json::from_slice(&body).with_context(|| {
        format!(
            "swarm-controller answered {status} but its body is not a create-agent response: {}",
            String::from_utf8_lossy(&body).trim()
        )
    })
}

/// Turn a failed response into one line the operator can act on.
///
/// The controller answers errors as RFC 9457 `application/problem+json`,
/// where the actionable sentence is `detail` — a 400 for an unknown hive
/// names the hives that *would* have worked. Printing the raw body instead
/// would bury that in JSON punctuation, and printing only the status would
/// throw it away. Falls back through `title` to the raw body so a response
/// from something that is *not* the controller is still shown rather than
/// reduced to a bare number.
fn describe_error(status: hyper::StatusCode, body: &[u8]) -> String {
    let text = String::from_utf8_lossy(body);
    let text = text.trim();
    let field = |v: &serde_json::Value, k: &str| {
        v.get(k)
            .and_then(serde_json::Value::as_str)
            .map(str::trim)
            .filter(|s| !s.is_empty())
            .map(str::to_owned)
    };
    let detail = serde_json::from_str::<serde_json::Value>(text)
        .ok()
        .and_then(|v| field(&v, "detail").or_else(|| field(&v, "title")));
    match detail {
        Some(detail) => format!("swarm-controller refused the request ({status}): {detail}"),
        None if text.is_empty() => format!("swarm-controller refused the request ({status})"),
        None => format!("swarm-controller refused the request ({status}): {text}"),
    }
}

/// Message for a socket that could not be dialled.
///
/// Worth spelling out because the three ways this fails need three
/// different fixes and `No such file or directory (os error 2)` names
/// none of them: the daemon is off, it binds elsewhere, or this host is
/// not the one running it at all. No group-membership case to mention
/// here — `swarmctl` already runs as root.
fn connect_hint(socket: &Path) -> String {
    format!(
        "could not connect to swarm-controller at {} — is it running on this host? \
         (`systemctl status swarm-controller`). The path comes from \
         `--controller-socket` or `SWARM_CONTROLLER_SOCKET`, which the \
         swarm-controller nix module sets from `socketPath`",
        socket.display()
    )
}

#[cfg(test)]
mod tests {
    use super::{CreateAgentResponse, describe_error, parse_ident};

    /// The endpoint omits `warnings` entirely when there are none, so the
    /// normal response must still decode — a missing field here would make
    /// every successful creation fail to parse.
    #[test]
    fn a_response_without_warnings_decodes() {
        let resp: CreateAgentResponse =
            serde_json::from_str(r#"{"node_id":7}"#).expect("the normal shape decodes");
        assert_eq!(resp.node_id, 7);
        assert!(resp.warnings.is_empty());
    }

    #[test]
    fn warnings_are_carried_through() {
        let resp: CreateAgentResponse =
            serde_json::from_str(r#"{"node_id":9,"warnings":["reserved name"]}"#).expect("decodes");
        assert_eq!(resp.warnings, vec!["reserved name".to_owned()]);
    }

    /// The whole point of parsing problem+json: the 400 for an unknown
    /// hive carries the roster of hives that would have worked, and that
    /// sentence has to reach the operator's terminal intact.
    #[test]
    fn a_problem_json_detail_reaches_the_operator() {
        let body = r#"{"status":400,"title":"Bad Request","detail":"hive \"tyop\" is not in this swarm — known hives: alpha, beta"}"#;
        let msg = describe_error(hyper::StatusCode::BAD_REQUEST, body.as_bytes());
        assert!(msg.contains("known hives: alpha, beta"), "{msg}");
        assert!(msg.contains("400"), "{msg}");
        // No JSON punctuation: the operator gets prose, not a body dump.
        assert!(!msg.contains('{'), "{msg}");
    }

    /// A response from something that is not the controller (an nginx
    /// error page, a proxy) must still be shown rather than swallowed.
    #[test]
    fn a_non_json_body_is_shown_verbatim() {
        let msg = describe_error(hyper::StatusCode::BAD_GATEWAY, b"  502 Bad Gateway  ");
        assert!(msg.contains("502 Bad Gateway"), "{msg}");
    }

    #[test]
    fn an_empty_body_still_names_the_status() {
        let msg = describe_error(hyper::StatusCode::INTERNAL_SERVER_ERROR, b"");
        assert!(msg.contains("500"), "{msg}");
    }

    /// Which argument was wrong has to be in the message: `agent create`
    /// takes two identifiers and they are fixed in different places.
    #[test]
    fn an_invalid_ident_names_the_argument_it_came_from() {
        let err = parse_ident("Not An Ident", "hive").expect_err("rejected");
        let msg = err.to_string();
        assert!(msg.contains("invalid hive"), "{msg}");
        assert!(msg.contains("Not An Ident"), "{msg}");

        assert!(
            parse_ident("scribe-01", "agent name").is_ok(),
            "a normal name must pass"
        );
    }
}