import { createRunner } from '../../systems-lab/src/runner.js';

export const CHANNEL = 'docs:backend:request';
export const CONTRACT = 'docs:backend:service';

/** Fixed virtual routes. Status and headers form a response contract, not an HTTP listener. */
export function createBackend({ onTrace, onWorkers, onState }) {
  const active = new Set();
  let disposed = false;
  const respond = (status, body, execution = null) => ({ status, headers: { 'content-type': 'application/json' }, body, execution });
  const trace = (stage, detail) => { if (!disposed) onTrace({ stage, detail }); };
  return {
    async handle(request, context) {
      if (disposed) throw new Error('El proveedor está desmontado.');
      trace('RPC', `${context.caller.appName} → ${context.channel} @${context.version}`);
      if (!request || typeof request.path !== 'string' || typeof request.body !== 'string') return respond(400, { error: 'Solicitud inválida' });
      if (request.method !== 'POST') return respond(405, { error: 'Usa POST' });
      if (new TextEncoder().encode(request.body).length > 4096) return respond(413, { error: 'Límite de 4096 bytes UTF-8' });
      const routes = { '/validate': 'manifest', '/uppercase': 'uppercase', '/failure': 'fail', '/slow': 'spin' };
      if (!Object.hasOwn(routes, request.path)) return respond(404, { error: 'Ruta virtual no encontrada' });
      trace('Ruta', `${request.method} ${request.path} → WASI ${routes[request.path]}`);
      return new Promise((resolve, reject) => {
        let settled = false;
        let runner;
        const finish = (error, result) => {
          if (settled) return;
          settled = true;
          context.signal.removeEventListener('abort', abort);
          runner.dispose();
          active.delete(cancel);
          if (error) reject(error); else resolve(result);
        };
        const abort = () => { trace('Cancelación', 'AbortSignal de WU → Worker.terminate()'); runner.cancel(); };
        const cancel = () => finish(new Error('Proveedor liberado durante la solicitud.'));
        runner = createRunner({
          workerUrl: '/microfrontends/systems-lab/worker.js', timeoutMs: 2500,
          onWorkers,
          onState(change) { if (!disposed) onState(change); },
          onResult(receipt) {
            if (receipt.outcome === 'cancelled') { finish(context.signal.reason || new Error('Solicitud cancelada')); return; }
            if (receipt.outcome !== 'completed') { finish(null, respond(receipt.outcome === 'timeout' ? 504 : 500, { error: receipt.stderr }, receipt)); return; }
            let body;
            if (request.path === '/validate') {
              try { body = JSON.parse(receipt.stdout); }
              catch { finish(null, respond(500, { error: 'El invitado no devolvió JSON válido' }, receipt)); return; }
            } else body = { output: receipt.stdout, error: receipt.stderr || undefined };
            const status = receipt.exitCode === 0 ? 200 : receipt.exitCode === 2 ? 422 : 500;
            trace('WASI', `exit=${receipt.exitCode}; ${receipt.syscalls.length} llamadas al host; Worker liberado`);
            finish(null, respond(status, body, receipt));
          },
        });
        active.add(cancel);
        context.signal.addEventListener('abort', abort, { once: true });
        if (context.signal.aborted) { finish(context.signal.reason || new Error('Solicitud cancelada')); return; }
        try { runner.run({ mode: 'wasi', operation: routes[request.path], text: request.body }); }
        catch (error) { finish(error); }
      });
    },
    dispose() { disposed = true; for (const cancel of [...active]) cancel(); },
  };
}