// The tool-serving harness. A module declares its tools through registerModuleTools; a runtime
// (the mesh's per-node tool host) collects the registrations and serves them through the command
// surface. HOW a tool is declared and served is settled and lives here; the tools themselves, and
// the API client they call, live in the module (novox/hq ADR 0044).

import type { ToolDefinition } from "../contracts/index.js";
import type { Broker } from "../messaging/index.js";

export type { ToolDefinition };

/** One tool invocation crossing the broker: which tool, and its arguments. */
export interface Invocation {
  readonly tool: string;
  readonly args: Readonly<Record<string, unknown>>;
}

/** A module contributes its tools as a function of its resolved environment. Returning [] (e.g.
 *  when a token is absent) is normal — the module simply exposes nothing until it can. */
export type ToolContributor = (env: NodeJS.ProcessEnv) => ToolDefinition[];

interface Registration {
  readonly module: string;
  readonly contribute: ToolContributor;
}

const registrations: Registration[] = [];

/**
 * Declare the tools a module exposes. Called once, at module-tool load time, from the module's
 * tools/ entrypoint. The client and the tool implementations are imported from the module itself.
 */
export function registerModuleTools(module: string, contribute: ToolContributor): void {
  registrations.push({ module, contribute });
}

/**
 * Collect every registered module's tools against an environment. The tool runtime calls this
 * after loading the assigned modules' tool entrypoints. A module whose contributor throws is
 * skipped with its error surfaced, never taking the others down.
 */
export function collectTools(env: NodeJS.ProcessEnv = process.env): { module: string; tools: ToolDefinition[] }[] {
  return registrations.map(({ module, contribute }) => {
    try {
      return { module, tools: contribute(env) };
    } catch (err) {
      console.error(`[tools] ${module}: contributor failed, exposing none: ${err}`);
      return { module, tools: [] };
    }
  });
}

/** List the tools every registered module exposes — for discovery, without invoking anything. */
export function listTools(env: NodeJS.ProcessEnv = process.env): { module: string; name: string; description: string }[] {
  return collectTools(env).flatMap(({ module, tools }) =>
    tools.map((t) => ({ module, name: t.name, description: t.description })),
  );
}

/**
 * Serve the registered modules' tools over the mesh broker — the tool runtime's core. It collects
 * every module's tools, indexes them by name, and answers `tools.invoke` requests by running the
 * named tool and returning its result. This is the stable half of serving; a specific tool's work
 * (and its client) lives in its module. Returns a stop function.
 *
 * A duplicate tool name across modules is refused loudly rather than one silently shadowing the
 * other — two tools answering one name is a fault, not a race to resolve.
 */
export async function serveTools(broker: Broker, env: NodeJS.ProcessEnv = process.env): Promise<() => void> {
  // Each tool is served on its own key, namespaced by its module (novox/hq ADR 0052): a caller
  // invokes `<module>.<tool>`, only the module that serves it answers, and the module's account is
  // scoped to serve.<module>.* — so one module cannot answer another's calls. The module is the
  // namespace, so a tool name need only be unique within its module, not across the whole mesh.
  const stops: Array<() => void> = [];
  for (const { module, tools } of collectTools(env)) {
    const seen = new Set<string>();
    for (const t of tools) {
      if (seen.has(t.name)) {
        throw new Error(`${module} exposes two tools named ${t.name} — refused`);
      }
      seen.add(t.name);
      const stop = await broker.handle<Readonly<Record<string, unknown>>, unknown>(
        toolKey(module, t.name),
        (args) => t.run(args ?? {}),
      );
      stops.push(stop);
    }
  }
  return () => {
    for (const stop of stops) stop();
  };
}

/** The broker key a tool is served on and invoked by — the module namespaces the tool (ADR 0052). */
export function toolKey(module: string, tool: string): string {
  return `${module}.${tool}`;
}

/** Invoke a module's tool over the broker — the caller's side of serving. */
export async function invokeTool(
  broker: Broker,
  module: string,
  tool: string,
  args: Readonly<Record<string, unknown>> = {},
): Promise<unknown> {
  return broker.request(toolKey(module, tool), args);
}

/** Testing/inspection: drop all registrations. */
export function resetTools(): void {
  registrations.length = 0;
}