import type { FastifyInstance } from 'fastify';
import type { Sql } from '../db.js';

// v2.6 Phase 1-UX (design §9b): chat-scoped "resumed vs new session" indicator.
// `agent_sessions` is keyed (chat_id, agent) — the tab/chat is the agent-context
// unit (P1.5-b). The route param is a SESSION id, so we resolve every chat in the
// session and return the union of their agent_sessions rows. A session with two
// opencode tabs yields two rows (one per chat); the frontend keys the chip per
// chat, but the wire shape is a flat per-(chat,agent) list.
//
// has_session = agent_session_id IS NOT NULL — i.e. a native backend session id
// (opencode/ACP) was created and stored, so switching back resumes rather than
// starts fresh.
export interface AgentSessionRow {
  agent: string;
  status: string;
  has_session: boolean;
  last_active_at: string | null;
  // v2.6.8 per-(chat,agent) running token/cost totals (sampling-streamjson-tokens
  // #8). BIGINT columns arrive as strings over the wire; the frontend coerces.
  input_tokens: number;
  output_tokens: number;
  cost: number;
}

export function registerAgentSessionRoutes(app: FastifyInstance, sql: Sql): void {
  // GET /api/sessions/:sessionId/agent-sessions — list the agent-session rows for
  // every chat in the session (drives the AgentComposerBar resumed/new chip).
  app.get<{ Params: { sessionId: string } }>(
    '/api/sessions/:sessionId/agent-sessions',
    async (req, reply) => {
      const sessionId = req.params.sessionId;

      const session = await sql<{ id: string }[]>`SELECT id FROM sessions WHERE id = ${sessionId}`;
      if (session.length === 0) {
        reply.code(404);
        return { error: 'session not found' };
      }

      // Join through chats so the session-scoped param resolves to its (chat,agent)
      // rows. last_active_at first → the frontend reads the freshest activity.
      const rows = await sql<AgentSessionRow[]>`
        SELECT
          a.agent AS agent,
          a.status AS status,
          (a.agent_session_id IS NOT NULL) AS has_session,
          a.last_active_at AS last_active_at,
          a.input_tokens AS input_tokens,
          a.output_tokens AS output_tokens,
          a.cost AS cost
        FROM agent_sessions a
        JOIN chats c ON c.id = a.chat_id
        WHERE c.session_id = ${sessionId}
        ORDER BY a.last_active_at DESC NULLS LAST, a.agent ASC
      `;
      return rows;
    },
  );
}