/**
 * discovery — a GENERIC discovery-index surface, reusing the ONE deposit +
 * materialization mechanism (`inbox.ts`). GENERIC by construction: this module
 * knows no application domain (no event, no meeting-point). The consumer submits
 * an opaque reference and interprets the entries it reads back.
 *
 * ── The mechanism (see docs/decisions/discovery-model.md) ─────────────────
 * Access and discovery are separate concerns. A public entity is world-readable
 * with its NURI; the discovery index is how a client learns that NURI exists
 * without holding a grant to read its creator's other documents. There is one
 * global index — an owned document (public read), fed via its own inbox. A
 * creator deposits a reference into the index's inbox; reading the index folds
 * those deposits into entries, deduplicating identical references along the way.
 *
 * ── The special account (polyfill owner) ──────────────────────────────────
 * Ownership of a truly global index is undecided in the real platform, where an
 * identity's apps and services see only what that identity shares. The polyfill
 * therefore parks ownership on a reserved special account in the shim
 * ({@link INDEX_ACCOUNT}). Its `public` scope document is the index document;
 * deposits land in that document's inbox (a stable NURI: every client opening the
 * same shared wallet resolves the same account, so the same document). This is
 * the app-facing discovery path, in place of a cross-account fan-out
 * (`store-registry.ts` `listEntityDocs`), which survives only as an internal
 * fallback (see {@link readIndex}).
 *
 * ── Real target vs this emulation ─────────────────────────────────────────
 * The intended real shape is: `submitToIndex` seals a reference into the index
 * document's own inbox (a future `inbox_post_link`), and reading the index is a
 * query on the materialized index document. Here, everything runs in-lib on the
 * shared wallet (deposit via `inbox.post`, fold via `inbox.read`). Against real
 * NextGraph the special account gives way to the decided global-index owner and
 * `readIndex` points at that document; the consumer surface (`submitToIndex` /
 * `readIndex`) is designed to survive that change unchanged.
 *
 * All NextGraph I/O routes through `inbox.ts` (which routes through the `docs`
 * primitives, the real injected `ng`), so this module imports no `@ng-org`
 * package.
 */

import * as inbox from "./inbox";
import { subscribeDoc } from "./subscribe";
import { ensureAccount, reservedAccount } from "./store-registry";
import { getCaps } from "./polyfill";
import type { Nuri, PrincipalId } from "./types";

/**
 * The reserved special account that owns the global discovery index in the
 * polyfill. It hosts the index document but is never a real identity. It lives in
 * the registry's reserved namespace ({@link reservedAccount}), whose key
 * `normalizeId` can never produce, so an id of "index"/"@index" cannot hijack it
 * (it normalizes to "index", a disjoint key). Removed against real NextGraph
 * (see file header).
 */
export const INDEX_ACCOUNT = reservedAccount("index");

/** One entry as materialized from the discovery index. */
export interface IndexEntry {
  /** The reference submitted by a creator (opaque — the consumer interprets it). */
  ref: unknown;
  /** The submitter, if identified; `null` when the submission was anonymous. */
  from: PrincipalId | null;
  /** Submission timestamp (ms epoch). */
  ts: number;
}

/** Options for {@link submitToIndex}. */
export interface SubmitOptions {
  /**
   * Who is submitting. Omit for the current identity, or pass `null` for an
   * anonymous submission. `from` is bound to the current identity by the inbox
   * (naming another identity is rejected as a spoof — see {@link inbox.post}).
   */
  from?: PrincipalId | null;
  /**
   * The NURI of the document being made discoverable. When given, the index
   * admits only a public document: one under a non-public (protected/private)
   * read policy is refused, so the world-readable index never exposes a governed
   * document's NURI. Omit it only for a ref with no addressable document (rare);
   * a governed document passes it so the guard can fire.
   */
  doc?: Nuri;
  /** Optional deposit timestamp (ms epoch). Omitted → `Date.now()`. Passing it
   *  keeps tests deterministic. */
  ts?: number;
}

/**
 * Resolve the NURI of the index document — the stable inbox where discovery
 * submissions land. The special account owns this document (its `public` scope
 * document, a real repo NURI from `docCreate`); deposits go into that document's
 * inbox exactly as host-registration deposits go into a host inbox. Because the
 * special account lives in the shim (persisted in the shared wallet's private
 * store), EVERY client opening the same wallet resolves the same account → the
 * same document NURI → ONE shared index for all clients. Distinct from
 * host-registration inboxes because it is a distinct document NURI.
 */
async function indexInboxNuri(): Promise<Nuri> {
  // Ensure the special account exists (idempotent) so its scope documents are
  // created and stably resolvable across clients.
  const record = await ensureAccount(INDEX_ACCOUNT);
  return record.docPublic;
}

/**
 * The NURI of the global discovery-index document (the inbox where submissions
 * land). Exposed so a reactive reader ({@link watchShape}) that folds discovery
 * into the public read-set can SUBSCRIBE to this document and re-resolve when a
 * new public entity is announced. This is exactly {@link watchIndex}'s subscribe
 * anchor. Removed against real NextGraph along with the special account.
 */
export async function indexDocNuri(): Promise<Nuri> {
  return indexInboxNuri();
}

/**
 * Submit a reference to the global discovery index — the SDK act "make this
 * discoverable". Deposits `ref` into the index document's inbox via
 * {@link inbox.post}; reading the index ({@link readIndex}) folds it into an
 * entry. `ref` is opaque here (the consumer serializes whatever a client needs to
 * later locate the entity — e.g. an entity document NURI plus discovery metadata).
 * `from` follows the inbox convention (anonymous when `null`).
 *
 * When `opts.doc` names the document being surfaced, a document under a
 * non-public read policy (protected/private) is refused: the global index is
 * world-readable, so admitting a governed document's NURI would expose it past
 * its scope.
 */
export async function submitToIndex(ref: unknown, opts?: SubmitOptions): Promise<void> {
  const doc = opts?.doc;
  if (doc !== undefined) {
    const caps = getCaps();
    // A governed doc is submittable ONLY if it is public (anonymous may read it).
    if (caps.governsRead(doc) && !caps.canRead(doc, null)) {
      throw new Error(
        "[ng-eventually] submitToIndex: only PUBLIC documents may be submitted to " +
          "the discovery index — a protected/private document must not be surfaced.",
      );
    }
  }
  const target = await indexInboxNuri();
  await inbox.post(target, {
    payload: ref,
    ...(opts && "from" in opts ? { from: opts.from } : {}),
    ...(opts?.ts !== undefined ? { ts: opts.ts } : {}),
  });
}

/**
 * Read the global discovery index. Reads every submission from the index inbox,
 * deduplicates by serialized `ref` (a duplicate submission surfaces once — the
 * discovery model's moderation point), and returns the entries sorted by `ts`
 * ascending. Against real NextGraph this becomes a query on the materialized
 * index document.
 */
export async function readIndex(): Promise<IndexEntry[]> {
  const target = await indexInboxNuri();
  const deposits = await inbox.read(target);
  const seen = new Set<string>();
  const entries: IndexEntry[] = [];
  for (const d of deposits) {
    // Dedup on the serialized reference — the materialization moderation point.
    const key = JSON.stringify(d.payload ?? null);
    if (seen.has(key)) continue;
    seen.add(key);
    entries.push({ ref: d.payload, from: d.from, ts: d.ts });
  }
  return entries;
}

/**
 * Watch the discovery index — **event-driven, not polled**. Subscribes to the
 * index document via {@link subscribeDoc} (the platform's `doc_subscribe` push):
 * `onEntries` fires once on the initial state push and again on every subsequent
 * change to the index document — a local submission OR a broker-synced remote one.
 * Returns an unsubscribe. (Deduplication is applied on each read.)
 *
 * The `intervalMs` option is accepted for signature compatibility but IGNORED:
 * there is no polling. The index is a single document, so this is immune to the
 * ORM fan-out hang (see {@link subscribeDoc}).
 */
export function watchIndex(
  onEntries: (entries: IndexEntry[]) => void,
  _opts?: { intervalMs?: number },
): () => void {
  let stopped = false;
  let lastCount = -1;
  let unsubscribe: (() => void) | null = null;

  const refresh = async (): Promise<void> => {
    if (stopped) return;
    try {
      const entries = await readIndex();
      if (!stopped && entries.length !== lastCount) {
        lastCount = entries.length;
        onEntries(entries);
      }
    } catch (error) {
      console.error("[discovery] watchIndex read failed:", error);
    }
  };

  // The index document NURI is resolved async (ensureAccount); subscribe once it
  // is known. The initial State push fires the first read (onEntries fires once),
  // each later Patch a re-read.
  void (async () => {
    try {
      const anchor = await indexInboxNuri();
      if (stopped) return;
      unsubscribe = subscribeDoc(anchor, () => void refresh());
    } catch (error) {
      console.error("[discovery] watchIndex subscribe failed:", error);
    }
  })();

  return () => {
    stopped = true;
    if (unsubscribe) {
      unsubscribe();
      unsubscribe = null;
    }
  };
}