// Live SSE consumer for the swarm-relayed agent turn-state header
// (`GET /api/agents/{name}/state/stream`, swarm-controller's
// `agent_state_stream.rs`). Same transport shape as `useSwarmTermStream`
// — one core-NATS subject relayed as bare SSE `data`, no envelope, no
// replay — but the payload here is a full header that *replaces* the
// last one rather than an appendable row, so there is nothing to
// coalesce: each event is just the latest value.
//
// **No seed on attach.** `agent_state_stream.rs`'s own module doc names
// this limitation: the subject is published on transition only, so an
// agent that has sat idle since before this hook mounted announces
// nothing until its next change. `header` stays `null` until the first
// event lands — callers should render no badges in that gap rather than
// a stale or guessed one (there is no swarm-level endpoint today that
// can seed turn_state/model/ctx/cost synchronously — `GET
// /api/agents/status`'s snapshot carries only `status_text`/`running`).
import { useEffect, useState } from "preact/hooks";

export type ConnectionState = "connecting" | "open" | "reconnecting" | "closed";

export interface TokenUsage {
  input_tokens?: number;
  output_tokens?: number;
  cache_read_input_tokens?: number;
  cache_creation_input_tokens?: number;
}

// Mirrors `hive_agent::swarm_agent_state::AgentStateMsg` field-for-field
// — see that struct's own doc comment for why `turn_state_since` (an
// ISO 8601 string here, unlike the per-agent page's unix-seconds
// `/api/state`) and `agent_state` (the swarm `AgentState` enum, not a
// bare `paused: bool`) diverge from the per-agent page's own shape.
export interface AgentStateHeader {
  turn_state: "idle" | "thinking" | "compacting";
  turn_state_since: string;
  agent_state: "up" | "offline" | "paused" | "destroyed";
  model: string;
  resolved_model: string | null;
  context_window_tokens: number;
  ctx_usage: TokenUsage | null;
  cost_usage: TokenUsage | null;
}

export interface UseSwarmAgentStateStreamResult {
  header: AgentStateHeader | null;
  connection: ConnectionState;
}

export function useSwarmAgentStateStream(
  streamUrl: string,
): UseSwarmAgentStateStreamResult {
  const [header, setHeader] = useState<AgentStateHeader | null>(null);
  const [connection, setConnection] = useState<ConnectionState>("connecting");

  useEffect(() => {
    setHeader(null);
    setConnection("connecting");
    const es = new EventSource(streamUrl);
    es.onopen = () => setConnection("open");
    es.onmessage = (e) => {
      try {
        setHeader(JSON.parse(e.data) as AgentStateHeader);
      } catch {
        // Malformed payload: drop it silently. Unlike the terminal
        // preview there is no row list to append a "[parse err]" line
        // to here, and one bad header isn't worth degrading the whole
        // badge cluster over — the next valid header replaces it.
      }
    };
    es.onerror = () => {
      setConnection(
        es.readyState === 0 /* CONNECTING */ ? "reconnecting" : "closed",
      );
    };
    return () => es.close();
  }, [streamUrl]);

  return { header, connection };
}