// Node-RED's MQTT broker config node, pointed at the broker the mesh bound — `mqtt-topic`.
//
// **Why a step.** Node-RED keeps a broker as a config node in its flows (`flows.json`) and the login
// and password in its encrypted credentials file, both of them Node-RED's to write. So this reads the
// binding and the pair credential and makes the broker node say the same thing through Node-RED's
// admin API — `GET /flows`, then `POST /flows` with the changed node and its `credentials`, deployed
// as "nodes" so only what changed restarts — with the module's own `api-token`.
//
// **Which broker nodes are the mesh's.** Never guessed: a flow may talk to a broker that has nothing
// to do with this mesh. The step owns the node it creates itself (id `mesh-mqtt-topic`, "mesh:
// mqtt-topic") and the ones an assignment names in settings (`mqtt.brokers`: node ids — how ace's
// existing broker node, which every one of its MQTT flows uses, is handed over). With none named and
// none made yet, it makes one, so a fresh Node-RED has a broker the flows can pick.
//
// **Only the connection, and only when it differs.** Host, port, TLS off (the broker serves plain
// MQTT), login, password. Every other field of the node — client id, keepalive, birth/close/will
// messages — is left as it is. Node-RED never hands a stored password back, so the step keeps a
// digest of what it last wrote: equal host/port/login and an equal digest is "already as the mesh
// says".
//
// **Nothing loses its connection without someone seeing it.** The broker is asked first whether it
// takes the delivered login; if not, nothing is written and the step fails saying why.
//
// Pure logic over two seams (Node-RED, the broker), tested against fakes (test/mqtt.test.ts).

import { createHash } from "node:crypto";

import type { Probe } from "./probe.js";

export const PROVISION = "mqtt-topic";
/** The id and name of the broker node the step makes when none is named. */
export const MESH_BROKER_ID = "mesh-mqtt-topic";
export const MESH_BROKER_NAME = "mesh: mqtt-topic";

/** What the mesh wrote at `binds.mqtt-topic`. */
export interface Binding {
  provision?: string;
  from?: string;
  at?: string;
  as?: string;
  serves?: Record<string, unknown>;
}

export type Outcome =
  | { what: string; result: "unchanged"; note?: string }
  | { what: string; result: "written"; fields: string[]; note?: string }
  | { what: string; result: "refused"; problem: string };

/** A flow node; a broker config node carries `broker`, `port`, `usetls`. */
export interface FlowNode {
  id: string;
  type: string;
  [key: string]: unknown;
}

/** Node-RED's admin API, as the step uses it. */
export interface NodeRed {
  /** The whole flow configuration and its revision (API v2). */
  flows(): Promise<{ rev: string; flows: FlowNode[] }>;
  /** A node's stored credentials as Node-RED shows them: the user, and only whether a password is set. */
  credentials(type: string, id: string): Promise<{ user?: string; has_password?: boolean }>;
  /** Deploy the configuration against the revision it was read at; "nodes" restarts only what changed. */
  deploy(rev: string, flows: FlowNode[]): Promise<void>;
}

export interface Marks {
  get(name: string): Promise<string | undefined>;
  set(name: string, digest: string): Promise<void>;
}

export interface Deps {
  nodered: NodeRed;
  probe: Probe;
  marks: Marks;
}

export interface Wanted {
  host: string;
  port: number;
  user: string;
  password: string;
}

export function digest(...parts: (string | number)[]): string {
  return createHash("sha256").update(parts.map(String).join("\u0000")).digest("hex");
}

function isLoopback(host: string): boolean {
  const h = host.toLowerCase();
  return h === "localhost" || h === "::1" || h === "[::1]" || /^127\./.test(h);
}

/**
 * The broker and login the mesh says Node-RED uses. A loopback `at` — what the mesh hands a machine
 * that is not on the private network — is refused: from Node-RED's own container it is Node-RED.
 */
export function wanted(binding: Binding | undefined, credential: string | undefined): { ok: true; want: Wanted } | { ok: false; problem: string } {
  if (!binding) return { ok: false, problem: `no binding for ${PROVISION} was delivered — the mesh writes it before this step runs` };
  const host = typeof binding.at === "string" ? binding.at.trim() : "";
  if (!host) return { ok: false, problem: `the ${PROVISION} binding names no host (at)` };
  if (isLoopback(host)) {
    return {
      ok: false,
      problem:
        `the ${PROVISION} binding says the broker is at ${host}, which from Node-RED's own container is Node-RED ` +
        `itself; put the machine on the private network so the broker has an address Node-RED can dial`,
    };
  }
  const port = Number(binding.serves?.port);
  if (!Number.isInteger(port) || port <= 0 || port > 65535) {
    return { ok: false, problem: `the ${PROVISION} binding serves no usable port (${String(binding.serves?.port)})` };
  }
  const scheme = binding.serves?.scheme;
  if (scheme !== undefined && scheme !== "mqtt") return { ok: false, problem: `the ${PROVISION} binding serves scheme ${String(scheme)}; this step writes plain MQTT` };
  const user = typeof binding.as === "string" ? binding.as.trim() : "";
  if (!user) return { ok: false, problem: `the ${PROVISION} binding names no login (as)` };
  const password = (credential ?? "").replace(/\n$/, "");
  if (!password) return { ok: false, problem: `the ${PROVISION} credential is empty or was not delivered` };
  return { ok: true, want: { host, port, user, password } };
}

/** The broker node ids an assignment named in settings (`mqtt.brokers`), or none. */
export function namedBrokers(settings: unknown): string[] {
  const brokers = (settings as { mqtt?: { brokers?: unknown } } | undefined)?.mqtt?.brokers;
  return Array.isArray(brokers) ? brokers.filter((b): b is string => typeof b === "string" && b.length > 0) : [];
}

/** A new broker node, Node-RED 5's defaults, pointed at the broker. */
export function newBrokerNode(want: Wanted): FlowNode {
  return {
    id: MESH_BROKER_ID, type: "mqtt-broker", name: MESH_BROKER_NAME,
    broker: want.host, port: String(want.port), clientid: "", autoConnect: true, usetls: false,
    protocolVersion: "4", keepalive: "60", cleansession: true, autoUnsubscribe: true,
    birthTopic: "", birthQos: "0", birthRetain: "false", birthPayload: "", birthMsg: {},
    closeTopic: "", closeQos: "0", closeRetain: "false", closePayload: "", closeMsg: {},
    willTopic: "", willQos: "0", willRetain: "false", willPayload: "", willMsg: {},
    userProps: "", sessionExpiry: "",
  };
}

const markFor = (id: string, w: Wanted): string => digest("nodered-mqtt", id, w.host, w.port, w.user, w.password);

function scrub(err: unknown, secret: string): string {
  let text = err instanceof Error ? err.message : String(err);
  for (const form of new Set([secret, encodeURIComponent(secret)])) text = text.split(form).join("***");
  return text;
}

/**
 * Bring the mesh's broker nodes in line with the binding: one outcome per node. Never throws. A node
 * the settings name that is not in the flows is refused (the others are still put right).
 */
export async function reconcileBrokers(deps: Deps, binding: Binding | undefined, credential: string | undefined, named: readonly string[]): Promise<Outcome[]> {
  const w = wanted(binding, credential);
  if ("problem" in w) return [{ what: "mqtt", result: "refused", problem: w.problem }];
  const want = w.want;

  let note: string | undefined;
  try {
    const probe = await deps.probe(want.host, want.port, want.user, want.password, "#");
    if (probe.connack === 4 || probe.connack === 5) {
      return [{
        what: "mqtt",
        result: "refused",
        problem:
          `the broker at ${want.host}:${want.port} does not (yet) take the login ${want.user} with the delivered password ` +
          `(CONNACK ${probe.connack}); mosquitto's provisioner creates it from the grant — nothing was written`,
      }];
    }
    if (probe.connack !== 0) return [{ what: "mqtt", result: "refused", problem: `the broker at ${want.host}:${want.port} answered CONNACK ${probe.connack}; nothing was written` }];
    if (probe.suback === 0x80) note = `warning: ${want.user} may not subscribe to every topic; flows subscribing outside its grant will get nothing`;
  } catch (err) {
    return [{ what: "mqtt", result: "refused", problem: `the broker at ${want.host}:${want.port} could not be asked: ${scrub(err, want.password)}; nothing was written` }];
  }

  const outcomes: Outcome[] = [];
  for (let attempt = 0; attempt < 2; attempt++) {
    outcomes.length = 0;
    try {
      const { rev, flows } = await deps.nodered.flows();
      const targets = named.length > 0 ? [...named] : [MESH_BROKER_ID];
      const changed: { id: string; fields: string[] }[] = [];
      for (const id of targets) {
        let node = flows.find((n) => n.id === id);
        if (node && node.type !== "mqtt-broker") {
          outcomes.push({ what: `broker ${id}`, result: "refused", problem: `node ${id} is a ${node.type}, not an mqtt-broker` });
          continue;
        }
        if (!node) {
          if (id !== MESH_BROKER_ID) {
            outcomes.push({ what: `broker ${id}`, result: "refused", problem: `the settings name broker node ${id}, and Node-RED's flows have no such node` });
            continue;
          }
          node = newBrokerNode(want);
          flows.push(node);
          node.credentials = { user: want.user, password: want.password };
          changed.push({ id, fields: ["node"] });
          continue;
        }
        const fields: string[] = [];
        if (String(node.broker ?? "") !== want.host) fields.push("broker");
        if (Number(node.port ?? 0) !== want.port) fields.push("port");
        if (node.usetls === true) fields.push("usetls");
        const creds = await deps.nodered.credentials("mqtt-broker", id);
        if ((creds.user ?? "") !== want.user) fields.push("user");
        if (!creds.has_password || (await deps.marks.get(`broker-${id}`)) !== markFor(id, want)) fields.push("password");
        if (fields.length === 0) {
          outcomes.push(note ? { what: `broker ${id}`, result: "unchanged", note } : { what: `broker ${id}`, result: "unchanged" });
          continue;
        }
        node.broker = want.host;
        node.port = String(want.port);
        node.usetls = false;
        node.credentials = { user: want.user, password: want.password };
        changed.push({ id, fields });
      }
      if (changed.length > 0) {
        await deps.nodered.deploy(rev, flows);
        for (const c of changed) {
          await deps.marks.set(`broker-${c.id}`, markFor(c.id, want));
          outcomes.push({ what: `broker ${c.id}`, result: "written", fields: c.fields, ...(note ? { note } : {}) });
        }
      }
      return outcomes;
    } catch (err) {
      // A deploy against a revision someone else changed meanwhile (409) is read again once.
      if (attempt === 0 && /\b409\b/.test(String(err))) continue;
      return [...outcomes, { what: "mqtt", result: "refused", problem: scrub(err, want.password) }];
    }
  }
  return outcomes;
}