// The connections to groups' nodes that search opens — and the music queue,
// which plays across groups — one per group, with one ceiling on how many are
// negotiated at once. A module of its own so the shell can hold a pool without
// loading the search page.

import { hubFetch, ensureFreshToken } from './hub-client.js';

// How many connections search negotiates at once — a ceiling on concurrency,
// never a batch (see `inFlight` in search-page.js), and one ceiling for everything: the
// sweep, the warm-up and a tile asking for its group all go through
// `ConnectionPool.connect`, which holds it. Three separate ceilings used to add
// up behind each other's backs, past what the hub admits per account.
//
// Six, sized for twenty groups on a phone: a connection there takes about two
// seconds, so three at a time is fourteen seconds to reach them all and six is
// seven, and a node that is down holds one place in six rather than one in
// three. The hub admits 32 pending offers per account (signaling.py), which
// leaves room for the search page on three devices at once plus their reconnections.
const MAX_IN_FLIGHT = 6;
// One WebRTC peer connection per group the search view touches. The cap bounds
// how many a busy account (many groups on the hub) keeps open at once; groups
// past it connect lazily when a tile of theirs scrolls into view (media-tiles.js's
// LazyTile → onNeedConn). Was 3, which meant any account with more than three
// groups thrashed the pool: an evicted transport left a stale `_tRef` on every
// tile of that group, and MediaThumb / useMediaMeta gave up on it with no
// retry — so posters rendered for a moment, then fell back to a spinner for
// good. grenet (one shared group) never hit it; cbesson (many) always did.
const MAX_POOL_SIZE = 12;

// How long a connection attempt may make **no progress**, not how long it may
// take. Search used a flat 10 s for the whole of `connect()`, which is the hub
// round trip, ICE gathering (capped at 4 s in transport.js), DTLS, the
// DataChannel opening and the handshake's own round trips. Opening the same
// group from the sidebar has no such deadline and gets the transport's own 30 s,
// so a link slow enough to need twelve seconds — a phone on 4G — failed here and
// worked from there, for the same work against the same node.
//
// A node that is not answering produces no progress event and still fails in
// `SEARCH_STALL_MS`, which is what keeps the fan-out bounded: a dead group holds
// one of the `MAX_IN_FLIGHT` places for this long, so the number that matters
// for a page full of unreachable groups is this one. A hub that refuses an offer
// for load *is* answering, and transport.js reports each retry as progress.
// `SEARCH_MAX_MS` bounds the other case — a node that answers ICE and then stops
// — because a deadline that only ever resets has none.
const SEARCH_STALL_MS = 10000;
const SEARCH_MAX_MS = 30000;

// -- Connecting to a group ----------------------------------------------------

/**
 * A live connection to one of the nodes serving `groupId`, and its ack — or
 * null when the hub lists no node at all.
 *
 * Every node the hub lists, in turn, exactly as group-page.js does since
 * 2026-09-11: the list is in hub registration order, and its head is not
 * necessarily a node that answers. Search took `nodes[0]` and stopped, so a
 * group with a second, working node counted as unreachable here while it
 * opened fine from the sidebar. A refusal naming a state of this browser (a
 * code, a passphrase, a device) is the same from every node and stops the
 * walk; `not_hosted`, a timeout or a failed connection moves on.
 */
async function connectToGroup(hubBase, groupId, token, bundleKey, username, userId) {
  const nodesData = await hubFetch(`/v1/groups/${groupId}/nodes`, { token });
  if (!nodesData.nodes || !nodesData.nodes.length) return null;

  const live = (await ensureFreshToken()) || token;
  let lastErr = null;
  for (const n of nodesData.nodes) {
    const transport = new window.MeshBayTransport(hubBase, live);
    transport.onNeedToken = async () => (await ensureFreshToken()) || token;
    let stallTimer, capTimer;
    const stopTimers = () => {
      clearTimeout(stallTimer);
      clearTimeout(capTimer);
      transport.onConnectProgress = null;
    };
    try {
      const ack = await Promise.race([
        transport.connect(
          n.node_id, live, groupId, null, null, bundleKey,
          username, userId, null),
        new Promise((_, reject) => {
          const giveUp = () => reject(new Error('Connection timeout'));
          stallTimer = setTimeout(giveUp, SEARCH_STALL_MS);
          capTimer = setTimeout(giveUp, SEARCH_MAX_MS);
          // Each step the transport reports — the peer answering ICE, the
          // channel opening — buys another window, never more than the cap.
          transport.onConnectProgress = () => {
            clearTimeout(stallTimer);
            stallTimer = setTimeout(giveUp, SEARCH_STALL_MS);
          };
        }),
      ]);
      stopTimers();
      return { transport, ack };
    } catch (e) {
      stopTimers();
      lastErr = e;
      try { transport.close(); } catch {}
      if (e.reason && e.reason !== 'not_hosted') throw e;
    }
  }
  throw (lastErr || new Error('no node served this group'));
}

// -- Connection pool ----------------------------------------------------------

/**
 * Every connection the search page makes, and the only way it makes one.
 *
 * The sweep, the warm-up and a tile asking for its group all come here, so the
 * page has one ceiling on how many it negotiates at once (`MAX_IN_FLIGHT`) and
 * one connection per group. The sweep used to open its own, fetch the index,
 * close it, and leave the warm-up to open the same group again straight after:
 * two offers per group per visit, and on 4G the two overlapped, which is how a
 * phone ran into the hub's per-account ceilings with five groups.
 */
class ConnectionPool {
  constructor(hubBase, onEvict) {
    this._hubBase = hubBase;
    this._connections = new Map();
    this._connecting = new Map();
    // Called with a groupId whenever this pool closes that group's connection
    // (eviction, close or closeAll). SearchPage uses it to drop its own record
    // so it never hands a tile a `_tRef` pointing at a transport closed here.
    this._onEvict = onEvict || (() => {});
    // Negotiations under way, and those waiting for one of the places.
    this._active = 0;
    this._waiting = [];
    this._closed = false;
  }

  get size() { return this._connections.size; }

  get closed() { return this._closed; }

  /** Whether `groupId` has a connection here that using costs no offer. */
  has(groupId) {
    const conn = this._connections.get(groupId);
    return !!(conn && conn.transport.connected);
  }

  /**
   * The group's connection, negotiating one if there is none.
   *
   * `hold` keeps it from being evicted until `release` — the sweep holds each
   * group while its index is on the way, because with more groups than the pool
   * keeps, the connection it is reading from would otherwise be the oldest one
   * and closed under it.
   */
  async connect(groupId, token, bundleKey, username, userId, { hold = false } = {}) {
    if (this._closed) throw new Error('Search was closed');
    let conn = this._connections.get(groupId);
    if (!(conn && conn.transport.connected)) {
      let p = this._connecting.get(groupId);
      if (!p) {
        p = this._negotiate(groupId, token, bundleKey, username, userId);
        this._connecting.set(groupId, p);
        p.finally(() => this._connecting.delete(groupId)).catch(() => {});
      }
      conn = await p;
    }
    conn.lastUsed = Date.now();
    if (hold) conn.holds += 1;
    this._evict();
    return conn;
  }

  release(conn) {
    conn.holds = Math.max(0, conn.holds - 1);
    this._evict();
  }

  /** Drop one group's connection, e.g. one that stopped answering. */
  close(groupId) {
    const conn = this._connections.get(groupId);
    if (!conn) return;
    try { conn.transport.close(); } catch {}
    this._connections.delete(groupId);
    this._onEvict(groupId);
  }

  async _negotiate(groupId, token, bundleKey, username, userId) {
    await this._takePlace();
    let conn;
    try {
      // Waiting for a place is not part of any deadline: `connectToGroup`'s
      // timers start inside `_doConnect`, once this negotiation is really on.
      if (this._closed) throw new Error('Search was closed');
      conn = await this._doConnect(groupId, token, bundleKey, username, userId);
    } finally {
      this._givePlace();
    }
    if (this._closed) {
      try { conn.transport.close(); } catch {}
      throw new Error('Search was closed');
    }
    // A connection that dropped is replaced, and closed so its own reconnect
    // loop does not keep negotiating a second one for the same group.
    const stale = this._connections.get(groupId);
    if (stale && stale.transport !== conn.transport) {
      try { stale.transport.close(); } catch {}
    }
    this._connections.set(groupId, conn);
    return conn;
  }

  _takePlace() {
    if (this._active < MAX_IN_FLIGHT) {
      this._active += 1;
      return Promise.resolve();
    }
    return new Promise((resolve) => this._waiting.push(resolve));
  }

  _givePlace() {
    const next = this._waiting.shift();
    if (next) next();          // handed straight over: `_active` is unchanged
    else this._active -= 1;
  }

  async _doConnect(groupId, token, bundleKey, username, userId) {
    const found = await connectToGroup(
      this._hubBase, groupId, token, bundleKey, username, userId);
    if (!found) throw new Error('offline');
    const { transport, ack } = found;

    let gek = null;
    if (transport.gekRaw && window.MeshBayCrypto) {
      gek = await window.MeshBayCrypto.importGEK(
        window.MeshBayCrypto.b64encode(transport.gekRaw));
    }
    return { transport, gek, ack, lastUsed: Date.now(), holds: 0 };
  }

  _evict() {
    while (this._connections.size > MAX_POOL_SIZE) {
      let oldestId = null, oldestTime = Infinity;
      for (const [id, conn] of this._connections) {
        if (conn.holds > 0) continue;
        if (conn.lastUsed < oldestTime) { oldestTime = conn.lastUsed; oldestId = id; }
      }
      // Everything over the size is held: it goes when it is released.
      if (!oldestId) break;
      this.close(oldestId);
    }
  }

  closeAll() {
    // In-flight negotiations see this when they finish and close what they got.
    this._closed = true;
    for (const [id, conn] of this._connections) {
      try { conn.transport.close(); } catch {}
      this._onEvict(id);
    }
    this._connections.clear();
  }
}

export { ConnectionPool, MAX_IN_FLIGHT, MAX_POOL_SIZE };