/**
 * The mesh's tools, for whoever is on a machine (novox/hq design 25 §7, design 34).
 *
 * Two surfaces over one thing. A command line, for somebody at a terminal; an MCP server, for an
 * agent. Both are adapters over the same three calls — what tools are there, what does this one take,
 * call it — because a second way of reaching a tool is a second thing to keep correct.
 *
 * **It uses the same client a module's runtime uses.** Not a second protocol and not a bridge: the
 * caller connects as its own bus user — a person's, or the console's — publishes on the tool subjects
 * that account permits, and the server refuses anything else. So "what may this ask" is answered by the
 * same permission list that answers it for a module, and there is nothing here for an audit to read
 * separately.
 *
 * What the caller may NOT do is the more interesting half, and none of it is enforced here — it is the
 * account (design 25 §4): it cannot publish an event, so it cannot claim a module said something; it
 * has no consumer, so there is no delivery to acknowledge; and it cannot answer a request, so it cannot
 * impersonate a module on a bus where anyone may serve a tool.
 */
import { readFile } from "node:fs/promises";

import type { Broker } from "@novox/mesh-sdk/messaging";

import { connectNats, type Answered, type Credential } from "./broker-nats.js";
import { TOOLS_VERB, type ToolsAnswer } from "./runtime.js";

/** Where the catalogue answers which modules the mesh holds. */
const CATALOGUE_MODULES = "mesh-catalog.catalog_modules";

/** Where the mesh answers every role's tools, from its records: the mesh-controller seat's own
 *  `tools` verb (novox/hq ADR 0154, design 33 §5). */
const SEAT_TOOLS = "seat:mesh-controller.tools";

/** A tool as its module describes it. */
export interface Tool {
  /** The module that serves it — or, for a role's tool, the seat. */
  module: string;
  name: string;
  description?: string;
  /** The JSON schema of what it takes, as the module declared it. */
  input?: unknown;
  /** True for a role's tool: addressed to the seat, answered by whoever holds it (ADR 0132). */
  seat?: boolean;
  /** A role's scope: `node` for a seat held once per machine, whose verb is asked of one machine
   *  (design 33 §4) and takes `node` for it; `mesh` or absent otherwise. */
  scope?: string;
  /** Where the tool is answered, as the mesh issued it (ADR 0160): the plain subject first when the
   *  module answers for itself anywhere, then one per machine. Absent for a runtime older than this. */
  subjects?: string[];
}

/**
 * What the mesh could say about its tools when asked (design 34 §3).
 *
 * **Silence is named, never dropped.** A module the catalogue holds and nothing answered for is in
 * `notAnswering`, because a tool that is not offered looks exactly like a tool that does not exist,
 * and those need different people to fix them.
 */
export interface Listing {
  tools: Tool[];
  /** Modules the catalogue holds whose runtime did not answer `tools`: not assigned, not up, or built
   *  before the runtime answered it. Each may still be called by name. The mesh's own records are
   *  listed here as `mesh-controller (seat)` when the control plane did not answer. */
  notAnswering: string[];
}

/** The seats and the verbs each declares, from the last listing, so a call can tell a role's tool
 *  from a module's when the two share a prefix (a module and a seat may share a name). */
export type Seats = Map<string, Set<string>>;

/** The roles' tools, keyed the way `toolKey` names them. */
export function seatsIn(have: Listing): Seats {
  const seats: Seats = new Map();
  for (const t of have.tools) {
    if (!t.seat) continue;
    if (!seats.has(t.module)) seats.set(t.module, new Set());
    seats.get(t.module)!.add(t.name);
  }
  return seats;
}

/** The key a call uses for `<prefix>.<name>`: a role's when the prefix is a seat declaring that
 *  verb, a module's otherwise. Both names for one capability are deliberate and bounded (ADR 0132);
 *  the seat wins only for a verb it actually declares, so a module's own tool is never shadowed. */
export function toolKey(name: string, seats?: Seats): string {
  if (name.startsWith("seat:")) return name;
  const dot = name.indexOf(".");
  if (dot < 0) return name;
  const prefix = name.slice(0, dot);
  const verb = name.slice(dot + 1);
  if (seats?.get(prefix)?.has(verb)) return `seat:${prefix}.${verb}`;
  return name;
}

/**
 * A person's credential, as `operator issue` prints it.
 *
 * The same shape a module is handed, minus the parts a module needs and a person does not: no node,
 * because a person is not on a machine, and no module, because they are not one.
 */
export interface PersonCredential extends Credential {
  person?: string;
  invokes?: string[];
}

/** Read the credential from the file `operator issue` produced. */
export async function credentialFrom(path: string): Promise<PersonCredential> {
  const raw = await readFile(path, "utf8");
  let held: PersonCredential;
  try {
    held = JSON.parse(raw) as PersonCredential;
  } catch (e) {
    throw new Error(
      `${path} is not a credential this mesh issued: ${(e as Error).message}. ` +
        "It is the JSON `operator issue` printed, saved verbatim.",
    );
  }
  if (!held.url || !held.user || !held.password) {
    throw new Error(
      `${path} names no bus, user or password. It is the JSON \`operator issue\` printed, saved ` +
        "verbatim — not an edited copy of it.",
    );
  }
  return held;
}

/** Connect as this person. The module name the runtime wants is their own user, because every subject
 *  it derives is for a tool somebody else serves. */
export async function connectAs(held: PersonCredential): Promise<Broker> {
  return connectNats({ ...held, module: held.user });
}

/**
 * Connect as the console: the module credential the mesh delivered (novox/hq ADR 0152), read from
 * the same variable every runtime reads. It names the node and the module, so the account's inbox
 * and subjects derive from what the mesh authorised and from nothing in this process's environment.
 */
export async function connectAsTheConsole(path: string): Promise<{ bus: Broker; who: string }> {
  const raw = await readFile(path, "utf8");
  let held: Credential;
  try {
    held = JSON.parse(raw) as Credential;
  } catch (e) {
    throw new Error(`${path} is not a broker credential: ${(e as Error).message}`);
  }
  if (!held.url || !held.module || !held.user) {
    throw new Error(
      `${path} names no bus, module or user: the console runs on the credential the mesh sealed to ` +
        "this machine for it, and nothing else",
    );
  }
  return { bus: await connectNats(held), who: `${held.node ?? "?"}.${held.module}` };
}

/**
 * What tools the mesh has, asked of the modules (design 34 §3).
 *
 * The catalogue says which modules the mesh holds; each module says what it serves, through the one
 * verb its runtime answers for it. **Asked, not configured**: a client carrying its own list would be a
 * list that goes stale the first time a module is assigned. Every module is asked at once, and the bus
 * refuses at once a request nothing serves, so the cost is bounded by the modules that are up.
 */
export async function toolsOn(bus: Broker): Promise<Listing> {
  const [answered, roles] = await Promise.all([
    bus.request<Record<string, never>, { modules?: { module: string }[] }>(CATALOGUE_MODULES, {}),
    // The roles' tools, from the mesh's records (design 33 §5). Asked beside the modules rather
    // than first: a control plane that is restarting must not hide every module's tools with it.
    bus
      .request<Record<string, never>, { seats?: { seat: string; scope?: string; tools?: ToolsAnswer["tools"] }[] }>(
        SEAT_TOOLS,
        {},
      )
      .catch(() => undefined),
  ]);
  const names = (answered.modules ?? []).map((m) => m.module).filter((m) => typeof m === "string");

  const asked = await Promise.allSettled(
    names.map((module) => bus.request<Record<string, never>, ToolsAnswer>(`${module}.${TOOLS_VERB}`, {})),
  );
  const tools: Tool[] = [];
  const notAnswering: string[] = [];
  if (roles) {
    for (const s of roles.seats ?? []) {
      // A node-scoped seat's tool is asked of one machine (design 33 §4): listed with its scope, so
      // a caller names the machine and the call carries it — `seat:<seat>.<verb>@<node>`. Left out
      // of the listing, the verb never resolved as a seat's and nothing served it (ADR 0169).
      for (const t of s.tools ?? []) {
        tools.push({ module: s.seat, name: t.name, description: t.description, input: t.input, seat: true, scope: s.scope });
      }
    }
  } else {
    notAnswering.push("mesh-controller (seat)");
  }
  asked.forEach((outcome, i) => {
    const module = names[i]!;
    if (outcome.status === "fulfilled" && typeof outcome.value?.failed === "string") {
      // The runtime answered for it and serves nothing: the bundle failed to load (ADR 0175). Said
      // with the reason, because "not answering" would send somebody to check an assignment that
      // is fine.
      notAnswering.push(`${module} (its tools bundle failed to load: ${outcome.value.failed})`);
    } else if (outcome.status === "fulfilled" && Array.isArray(outcome.value?.tools)) {
      for (const t of outcome.value.tools) {
        tools.push({ module, name: t.name, description: t.description, input: t.input, subjects: t.subjects });
      }
    } else {
      notAnswering.push(module);
    }
  });
  tools.sort((a, b) => `${a.module}.${a.name}`.localeCompare(`${b.module}.${b.name}`));
  notAnswering.sort();
  return { tools, notAnswering };
}

/** Call one tool. The key is `<module>.<tool>`, which is what a person types and what the account
 *  permits — one vocabulary, so a refusal names the thing they asked for. */
/** Call a tool and learn which machine answered (novox/hq ADR 0159). `<module>.<tool>@<node>` asks
 *  the instance on one machine; without it, whichever instance answers first does, and the answer
 *  says which. */
export async function callTool(
  bus: Broker,
  key: string,
  args: unknown,
  seats?: Seats,
  listing?: Listing,
): Promise<Answered<unknown>> {
  const at = key.indexOf("@");
  const name = at < 0 ? key : key.slice(0, at);
  const node = at < 0 ? "" : key.slice(at + 1);
  if (!name.includes(".")) {
    throw new Error(
      `"${key}" does not name a tool: write <module>.<tool>, as \`mesh tools\` lists them, ` +
        "or <module>.<tool>@<node> for the instance on one machine",
    );
  }
  const resolved = toolKey(name, seats) + (node ? `@${node}` : "");
  // Where the tool is answered is the module's to say and the mesh's to issue (ADR 0160): when the
  // listing carried subjects for it, the call goes to one of those and composes nothing.
  const on = subjectListed(name, node, listing);
  const asking = bus as Broker & { ask?: <Req, Res>(k: string, b: Req, on?: string) => Promise<Answered<Res>> };
  if (typeof asking.ask === "function") return asking.ask<unknown, unknown>(resolved, args ?? {}, on);
  return { result: await bus.request<unknown, unknown>(resolved, args ?? {}) };
}

/** The subject the listing says answers `<module>.<tool>` — the machine's when one is named, else
 *  the plain one — or undefined when the listing said none, and the key is composed as before. */
export function subjectListed(name: string, node: string, listing?: Listing): string | undefined {
  if (!listing) return undefined;
  const dot = name.indexOf(".");
  const module = name.slice(0, dot);
  const tool = name.slice(dot + 1);
  const found = listing.tools.find((t) => t.module === module && t.name === tool && !t.seat);
  const subjects = found?.subjects ?? [];
  if (subjects.length === 0) return undefined;
  if (node) return subjects.find((s) => s.endsWith(`.${node}`));
  return subjects[0];
}

/**
 * Why a call failed, said so that the remedy is in the words.
 *
 * Three answers a person actually gets, and they need different things done: nobody serves that tool,
 * the mesh refused this account, or the tool itself failed. Without this they are one timeout and a
 * stack trace.
 */
export function whyItFailed(key: string, err: unknown): string {
  const message = err instanceof Error ? err.message : String(err);
  if (/no responders|503/i.test(message)) {
    return `nothing serves ${key}. The module may not be assigned to any machine, or it is down` +
      (key.startsWith("seat:") ? ", or nothing holds that seat" : "") +
      " — `mesh tools` lists what answered.";
  }
  if (/permissions violation|authorization/i.test(message)) {
    return `this account may not call ${key}. What it may call was fixed when it was issued — a ` +
      "person's by `operator issue`, the console's by its manifest.";
  }
  if (/timeout/i.test(message)) {
    return `${key} did not answer in time. Something is serving it, so this is the tool being slow ` +
      "rather than absent.";
  }
  return `${key} failed: ${message}`;
}