// Electrum (Fulcrum) JSON-RPC over WebSocket for the wallet. One live
// connection at a time, chosen by walking the server list in order; the
// caller gets a stable `call()` that reconnects transparently on the next
// request after a drop. Notifications (headers / scripthash subscriptions)
// fan out to `onNotify`.
module.exports = function makeElectrum({ WebSocket, log = () => {} }) {
  const CALL_TIMEOUT_MS = 20000;
  const CONNECT_TIMEOUT_MS = 10000;
  const PING_EVERY_MS = 60000;
  const RECONNECT_MIN_MS = 2000;
  const RECONNECT_MAX_MS = 60000;

  class Connection {
    constructor(url) {
      this.url = url;
      this.id = 0;
      this.pending = new Map();
      this.buf = "";
      this.closed = false;
      this.onNotify = null;
      this.onClose = null;
    }
    connect() {
      return new Promise((resolve, reject) => {
        const ws = new WebSocket(this.url);
        this.ws = ws;
        const fail = (e) => { if (!this.closed) { this.closed = true; reject(e instanceof Error ? e : new Error("electrum ws error: " + this.url)); } };
        // A server that accepts the TCP connection and then says nothing
        // used to hold the whole server walk hostage; give up and move on.
        const connectTimer = setTimeout(() => { fail(new Error("electrum connect timeout: " + this.url)); try { ws.close(); } catch {} }, CONNECT_TIMEOUT_MS);
        ws.on("open", () => clearTimeout(connectTimer));
        ws.on("close", () => clearTimeout(connectTimer));
        ws.on("open", async () => {
          // A RANGE, not a flat "1.4". Fulcrum only attaches `token_data` to
          // listunspent results once protocol >= 1.5 is negotiated, and with
          // a flat 1.4 it silently omits it — which is why imported BCH
          // wallets showed no CashTokens at all. A [min, max] pair lets a
          // modern server pick 1.5.3 while an older one still settles on 1.4,
          // so nothing that worked before stops working.
          try {
            const v = await this.call("server.version", ["theseus-bchwallet", ["1.4", "1.5.3"]]);
            this.serverVersion = Array.isArray(v) ? v[0] : null;
            this.protocolVersion = Array.isArray(v) ? v[1] : null;
            resolve(this);
          }
          catch (e) { fail(e); this.close(); }
        });
        ws.on("error", fail);
        ws.on("message", (d) => this._onData(String(d)));
        ws.on("close", () => {
          this.closed = true;
          for (const p of this.pending.values()) p.reject(new Error("electrum connection closed"));
          this.pending.clear();
          if (this.onClose) this.onClose();
        });
      });
    }
    _onData(chunk) {
      this.buf += chunk;
      let nl;
      while ((nl = this.buf.indexOf("\n")) >= 0) {
        const line = this.buf.slice(0, nl).trim();
        this.buf = this.buf.slice(nl + 1);
        if (line) this._handleLine(line);
      }
      const rest = this.buf.trim();
      if (rest) { try { JSON.parse(rest); this._handleLine(rest); this.buf = ""; } catch {} }
    }
    _handleLine(line) {
      let msg;
      try { msg = JSON.parse(line); } catch { return; }
      if (msg.id != null && this.pending.has(msg.id)) {
        const p = this.pending.get(msg.id);
        this.pending.delete(msg.id);
        clearTimeout(p.timer);
        if (msg.error) p.reject(new Error(typeof msg.error === "object" ? (msg.error.message || JSON.stringify(msg.error)) : String(msg.error)));
        else p.resolve(msg.result);
      } else if (msg.method && this.onNotify) {
        this.onNotify(msg.method, msg.params || []);
      }
    }
    call(method, params = []) {
      if (this.closed) return Promise.reject(new Error("electrum connection closed"));
      const id = ++this.id;
      return new Promise((resolve, reject) => {
        const timer = setTimeout(() => {
          if (this.pending.has(id)) { this.pending.delete(id); reject(new Error(`electrum timeout: ${method}`)); }
        }, CALL_TIMEOUT_MS);
        this.pending.set(id, { resolve, reject, timer });
        try { this.ws.send(JSON.stringify({ id, method, params }) + "\n"); }
        catch (e) { clearTimeout(timer); this.pending.delete(id); reject(e); }
      });
    }
    close() { this.closed = true; try { this.ws.close(); } catch {} }
  }

  class Client {
    constructor(servers) {
      this.servers = servers.slice();
      this.conn = null;
      this.connecting = null;
      this.subscriptions = new Map();   // method+key -> params (replayed on reconnect)
      this.onNotify = null;
      this.onServer = null;             // (url|null) connection state for the UI
      this.disposed = false;
      this._reconnectTimer = null;
      this._reconnectDelay = RECONNECT_MIN_MS;
      this._pingTimer = null;
    }
    setServers(servers) {
      this.servers = servers.slice();
      this.disconnect();
      this._scheduleReconnect(250);      // keep the live feed going on the new list
    }
    // A wallet with live subscriptions used to go quiet for good when its
    // server dropped: the connection was only re-opened by the next call(),
    // and nothing calls while the user is just looking at a balance. Come
    // back on our own, with backoff, for as long as anything is subscribed.
    _scheduleReconnect(delay) {
      if (this.disposed || !this.subscriptions.size || this._reconnectTimer) return;
      const wait = delay != null ? delay : this._reconnectDelay;
      this._reconnectTimer = setTimeout(() => {
        this._reconnectTimer = null;
        if (this.disposed || (this.conn && !this.conn.closed)) return;
        this._ensure().then(
          () => { this._reconnectDelay = RECONNECT_MIN_MS; },
          () => { this._reconnectDelay = Math.min(RECONNECT_MAX_MS, this._reconnectDelay * 2); this._scheduleReconnect(); },
        );
      }, wait);
      if (this._reconnectTimer.unref) this._reconnectTimer.unref();
    }
    // A half-dead socket (laptop slept, NAT dropped the flow) never fires
    // "close". Ping it; a ping that fails or times out closes it, which
    // lands in the reconnect path above.
    _armPing(c) {
      clearInterval(this._pingTimer);
      this._pingTimer = setInterval(() => {
        if (this.disposed || this.conn !== c || c.closed) { clearInterval(this._pingTimer); return; }
        c.call("server.ping", []).catch(() => { try { c.close(); } catch {} });
      }, PING_EVERY_MS);
      if (this._pingTimer.unref) this._pingTimer.unref();
    }
    // Stop for good: no reconnects, no pings, and any later call() fails
    // instead of quietly resurrecting the connection of a removed wallet.
    dispose() {
      this.disposed = true;
      clearTimeout(this._reconnectTimer); this._reconnectTimer = null;
      clearInterval(this._pingTimer); this._pingTimer = null;
      this.subscriptions.clear();
      this.disconnect();
    }
    get url() { return this.conn && !this.conn.closed ? this.conn.url : null; }
    // The protocol the live connection settled on. Callers use it to decide
    // whether listunspent will carry `token_data` (>= 1.5) or whether they
    // have to classify tokens the expensive way, by fetching each UTXO's
    // parent transaction.
    get protocolVersion() { return this.conn && !this.conn.closed ? (this.conn.protocolVersion || null) : null; }
    // True when the server will report CashTokens on listunspent itself.
    get hasTokenData() {
      const v = String(this.protocolVersion || "");
      const m = /^(\d+)\.(\d+)/.exec(v);
      if (!m) return false;
      const major = Number(m[1]), minor = Number(m[2]);
      return major > 1 || (major === 1 && minor >= 5);
    }
    async _ensure() {
      if (this.disposed) throw new Error("electrum client disposed");
      if (this.conn && !this.conn.closed) return this.conn;
      if (this.connecting) return this.connecting;
      this.connecting = (async () => {
        let lastErr;
        for (const url of this.servers) {
          try {
            const c = await new Connection(url).connect();
            if (this.disposed) { c.close(); throw new Error("electrum client disposed"); }
            c.onNotify = (m, p) => { if (this.onNotify) this.onNotify(m, p); };
            c.onClose = () => {
              if (this.conn !== c) return;
              this.conn = null;
              if (this.onServer) this.onServer(null);
              this._scheduleReconnect();
            };
            this.conn = c;
            log("connected", url);
            if (this.onServer) this.onServer(url);
            this._armPing(c);
            // Re-arm subscriptions so a reconnect keeps the live feed, and
            // hand each answer on as if it were a notification: whatever
            // changed while we were away (a new tip, a payment) is in that
            // answer, and the wallet only refreshes when it is told.
            for (const [method, params] of this.subscriptions.values()) {
              c.call(method, params).then((result) => {
                if (!this.onNotify || this.conn !== c) return;
                this.onNotify(method, method === "blockchain.headers.subscribe" ? [result] : [...params, result]);
              }, () => {});
            }
            return c;
          } catch (e) { lastErr = e; log("failed", url, e?.message); if (this.disposed) break; }
        }
        throw lastErr || new Error("no electrum server reachable");
      })();
      try { return await this.connecting; }
      finally { this.connecting = null; }
    }
    async call(method, params = []) {
      const c = await this._ensure();
      return c.call(method, params);
    }
    // Remember a subscription so it survives reconnects.
    async subscribe(method, params = []) {
      this.subscriptions.set(method + ":" + JSON.stringify(params), [method, params]);
      return this.call(method, params);
    }
    clearSubscriptions() { this.subscriptions.clear(); }
    disconnect() {
      clearInterval(this._pingTimer); this._pingTimer = null;
      if (this.conn) { const c = this.conn; this.conn = null; c.close(); }
      if (this.onServer) this.onServer(null);
    }
  }

  return { Client };
};