trustgraph/ts/packages/flow/src/gateway/dispatch/manager.ts

/**
 * Dispatcher manager — routes requests to backend services via pub/sub.
 *
 * Maintains a service registry mapping service names to NATS topic pairs.
 * Applies wire format translation on requests (client → internal) and
 * reverse translation on responses (internal → client).
 *
 * Python reference: trustgraph-flow/trustgraph/gateway/dispatch/manager.py
 */

import { Effect, Exit, Scope, SynchronizedRef } from "effect";
import {
  loadMessagingRuntimeConfig,
  makeNatsBackend,
  makePubSubService,
  makeRequestResponseFactoryService,
  messagingDeliveryError,
  messagingLifecycleError,
  type EffectRequestResponse,
  type PubSubBackend,
  type RequestResponseFactoryService,
} from "@trustgraph/base";
import type { GatewayConfig } from "../server.js";
import { translateRequest, translateResponse } from "./serialize.js";

export type Responder = (response: unknown, complete: boolean) => Promise<void>;

// ---------- Service registry ----------

/**
 * Flow-scoped request/response services.
 * These are resolved within a specific flow's interface definitions.
 * Topic pattern: tg.flow.<name>-request / tg.flow.<name>-response
 */
const FLOW_SERVICES: ReadonlyMap<string, { request: string; response: string }> = new Map([
  ["agent",               { request: "agent-request",               response: "agent-response" }],
  ["text-completion",     { request: "text-completion-request",     response: "text-completion-response" }],
  ["prompt",              { request: "prompt-request",              response: "prompt-response" }],
  ["graph-rag",           { request: "graph-rag-request",           response: "graph-rag-response" }],
  ["document-rag",        { request: "document-rag-request",        response: "document-rag-response" }],
  ["embeddings",          { request: "embeddings-request",          response: "embeddings-response" }],
  ["graph-embeddings",    { request: "graph-embeddings-request",    response: "graph-embeddings-response" }],
  ["document-embeddings", { request: "doc-embeddings-request",      response: "doc-embeddings-response" }],
  ["triples",             { request: "triples-request",             response: "triples-response" }],
  ["mcp-tool",            { request: "mcp-tool-request",            response: "mcp-tool-response" }],
]);

/**
 * Global services (not flow-scoped).
 * These always use fixed topics regardless of which flow is active.
 */
const GLOBAL_SERVICES: ReadonlyMap<string, { request: string; response: string }> = new Map([
  ["config",                  { request: "config-request",                  response: "config-response" }],
  ["flow",                    { request: "flow-request",                    response: "flow-response" }],
  ["librarian",               { request: "librarian-request",               response: "librarian-response" }],
  ["knowledge",               { request: "knowledge-request",               response: "knowledge-response" }],
  ["collection-management",   { request: "collection-management-request",   response: "collection-management-response" }],
]);

/**
 * Services that support streaming responses (multiple messages per request).
 * The completion flag is determined by checking for end-of-stream markers.
 */
const STREAMING_SERVICES = new Set([
  "agent",
  "text-completion",
  "graph-rag",
  "document-rag",
  "triples",
  "knowledge",
  "librarian",
]);

function topicName(name: string): string {
  return `tg.flow.${name}`;
}

// ---------- Manager ----------

export interface DispatcherManager {
  readonly start: () => Promise<void>;
  readonly stop: () => Promise<void>;
  readonly dispatchGlobalService: (
    kind: string,
    request: Record<string, unknown>,
  ) => Promise<unknown>;
  readonly dispatchGlobalServiceStreaming: (
    kind: string,
    request: Record<string, unknown>,
    responder: Responder,
  ) => Promise<void>;
  readonly dispatchFlowService: (
    flow: string,
    kind: string,
    request: Record<string, unknown>,
  ) => Promise<unknown>;
  readonly dispatchFlowServiceStreaming: (
    flow: string,
    kind: string,
    request: Record<string, unknown>,
    responder: Responder,
  ) => Promise<void>;
  readonly publishToTopic: (
    topic: string,
    message: unknown,
    id?: string,
  ) => Promise<void>;
}

export const dispatcherManagerFlowServiceNames = (): readonly string[] => [
  ...FLOW_SERVICES.keys(),
];

export const dispatcherManagerGlobalServiceNames = (): readonly string[] => [
  ...GLOBAL_SERVICES.keys(),
];

export const dispatcherManagerIsStreamingService = (kind: string): boolean =>
  STREAMING_SERVICES.has(kind);

export const dispatcherManagerIsCompleteResponse = (response: unknown): boolean => {
  if (typeof response !== "object" || response === null) return true;
  const res = response as Record<string, unknown>;
  return (
    res.complete === true ||
    res.endOfStream === true ||
    res.endOfSession === true ||
    res.end_of_stream === true ||
    res.end_of_session === true ||
    res.end_of_dialog === true ||
    res.eos === true ||
    // error responses are always final
    (res.error !== undefined && res.error !== null)
  );
};

type RequestorMap = Map<string, EffectRequestResponse<unknown, unknown>>;

interface DispatcherRuntime {
  readonly scope: Scope.Closeable;
  readonly requestors: SynchronizedRef.SynchronizedRef<RequestorMap>;
  readonly factory: RequestResponseFactoryService;
}

export function makeDispatcherManager(config: GatewayConfig): DispatcherManager {
  const pubsub: PubSubBackend = config.pubsub ?? makeNatsBackend(config.natsUrl ?? "nats://localhost:4222");
  let runtime: DispatcherRuntime | null = null;

  const start = async (): Promise<void> => {
    if (runtime !== null) return;

    runtime = await Effect.runPromise(
      Effect.gen(function* () {
        const scope = yield* Scope.make();
        return yield* Effect.gen(function* () {
          const messagingConfig = yield* loadMessagingRuntimeConfig();
          const requestors = yield* SynchronizedRef.make<RequestorMap>(new Map());
          return {
            scope,
            requestors,
            factory: makeRequestResponseFactoryService(makePubSubService(pubsub), messagingConfig),
          } satisfies DispatcherRuntime;
        }).pipe(
          Effect.onError((cause) => Scope.close(scope, Exit.failCause(cause))),
        );
      }),
    );
  };

  const stop = async (): Promise<void> => {
    const current = runtime;
    runtime = null;

    if (current !== null) {
      await Effect.runPromise(Scope.close(current.scope, Exit.void));
    }

    await pubsub.close();
  };

  // ---------- Internal helpers ----------

  const ensureRuntime = async (): Promise<DispatcherRuntime> => {
    if (runtime === null) {
      await start();
    }
    if (runtime === null) {
      throw messagingLifecycleError("gateway-dispatcher", "start", "Dispatcher manager failed to start");
    }
    return runtime;
  };

  const getRequestor = async (
    requestTopic: string,
    responseTopic: string,
    key: string,
  ): Promise<EffectRequestResponse<unknown, unknown>> => {
    const current = await ensureRuntime();

    return await Effect.runPromise(
      SynchronizedRef.modifyEffect(current.requestors, (requestors) => {
        const cached = requestors.get(key);
        if (cached !== undefined) {
          return Effect.succeed([cached, requestors] as const);
        }

        return current.factory.make<unknown, unknown>({
          requestTopic,
          responseTopic,
          subscription: `gateway-${key}`,
        }).pipe(
          Scope.provide(current.scope),
          Effect.map((requestor) => {
            const next = new Map(requestors);
            next.set(key, requestor);
            return [requestor, next] as const;
          }),
        );
      }),
    );
  };

  const resolveGlobalTopics = (
    kind: string,
  ): { requestTopic: string; responseTopic: string } => {
    const entry = GLOBAL_SERVICES.get(kind);
    if (entry !== undefined) {
      return {
        requestTopic: topicName(entry.request),
        responseTopic: topicName(entry.response),
      };
    }
    // Fallback: derive from kind name directly
    return {
      requestTopic: topicName(`${kind}-request`),
      responseTopic: topicName(`${kind}-response`),
    };
  };

  const resolveFlowTopics = (
    kind: string,
  ): { requestTopic: string; responseTopic: string } => {
    const entry = FLOW_SERVICES.get(kind);
    if (entry !== undefined) {
      return {
        requestTopic: topicName(entry.request),
        responseTopic: topicName(entry.response),
      };
    }
    // Fallback: derive from kind name directly
    return {
      requestTopic: topicName(`${kind}-request`),
      responseTopic: topicName(`${kind}-response`),
    };
  };

  // ---------- Global service dispatch ----------

  const dispatchGlobalService = async (
    kind: string,
    request: Record<string, unknown>,
  ): Promise<unknown> => {
    const { requestTopic, responseTopic } = resolveGlobalTopics(kind);
    const rr = await getRequestor(requestTopic, responseTopic, `global:${kind}`);

    const translated = translateRequest(kind, request);
    const response = await Effect.runPromise(rr.request(translated));
    return translateResponse(kind, response);
  };

  const dispatchGlobalServiceStreaming = async (
    kind: string,
    request: Record<string, unknown>,
    responder: Responder,
  ): Promise<void> => {
    const { requestTopic, responseTopic } = resolveGlobalTopics(kind);
    const rr = await getRequestor(requestTopic, responseTopic, `global:${kind}`);
    const translated = translateRequest(kind, request);

    await Effect.runPromise(
      rr.request(translated, {
        recipient: (response) => {
          const translatedRes = translateResponse(kind, response);
          const complete = dispatcherManagerIsCompleteResponse(translatedRes);
          return Effect.tryPromise({
            try: async () => {
              await responder(translatedRes, complete);
              return complete;
            },
            catch: (error) => messagingDeliveryError(responseTopic, "stream-responder", error),
          });
        },
      }),
    );
  };

  // ---------- Flow-scoped service dispatch ----------

  const dispatchFlowService = async (
    flow: string,
    kind: string,
    request: Record<string, unknown>,
  ): Promise<unknown> => {
    const { requestTopic, responseTopic } = resolveFlowTopics(kind);
    const rr = await getRequestor(
      requestTopic,
      responseTopic,
      `flow:${flow}:${kind}`,
    );

    const translated = translateRequest(kind, request);
    const response = await Effect.runPromise(rr.request(translated));
    return translateResponse(kind, response);
  };

  const dispatchFlowServiceStreaming = async (
    flow: string,
    kind: string,
    request: Record<string, unknown>,
    responder: Responder,
  ): Promise<void> => {
    const { requestTopic, responseTopic } = resolveFlowTopics(kind);
    const rr = await getRequestor(
      requestTopic,
      responseTopic,
      `flow:${flow}:${kind}`,
    );
    const translated = translateRequest(kind, request);

    await Effect.runPromise(
      rr.request(translated, {
        recipient: (response) => {
          const translatedRes = translateResponse(kind, response);
          const complete = dispatcherManagerIsCompleteResponse(translatedRes);
          return Effect.tryPromise({
            try: async () => {
              await responder(translatedRes, complete);
              return complete;
            },
            catch: (error) => messagingDeliveryError(responseTopic, "stream-responder", error),
          });
        },
      }),
    );
  };

  // ---------- Fire-and-forget publish ----------

  /**
   * Publish a single message to an arbitrary topic (no request/response).
   * Used for injecting documents into the processing pipeline.
   */
  const publishToTopic = async (topic: string, message: unknown, id?: string): Promise<void> => {
    const producer = await pubsub.createProducer<unknown>({ topic });
    const messageId = id ?? `pub-${Date.now()}-${Math.random().toString(36).slice(2, 8)}`;
    await producer.send(message, { id: messageId });
    await producer.close();
  };

  return {
    start,
    stop,
    dispatchGlobalService,
    dispatchGlobalServiceStreaming,
    dispatchFlowService,
    dispatchFlowServiceStreaming,
    publishToTopic,
  };
}