// Encrypted cross-device state sync via Nostr (opt-out, configurable relays).
//
// The wallet's Nostr identity is derived from the same seed (NIP-06,
// m/44'/1237'/0'/0/0). Wallet state is encrypted to ourselves (NIP-44) and
// published as a single parameterized-replaceable event (kind 30078, NIP-78)
// to the configured relays — so any device with the seed can pull the latest
// state without re-scanning, and a relay only ever keeps the newest copy.
//
// Sync is on by default (relay.coinos.io) but can be turned off or pointed at
// other relays in Settings; the preference lives in localStorage.

import * as nip06 from 'nostr-tools/nip06';
import * as nip44 from 'nostr-tools/nip44';
import { getPublicKey, finalizeEvent } from 'nostr-tools/pure';
import { Relay } from 'nostr-tools/relay';

const DTAG = 'bitcoin-wallet';
const SYNC_KEY = 'btc-wallet-sync';
export const DEFAULT_SYNC_RELAYS = ['wss://relay.coinos.io'];

// --- sync preference (enabled + relays), global, persisted in localStorage ---
export function getSyncConfig() {
  try {
    const raw = localStorage.getItem(SYNC_KEY);
    if (raw) {
      const c = JSON.parse(raw);
      const relays = Array.isArray(c.relays) ? c.relays : [];
      return {
        enabled: c.enabled !== false,
        relays: relays.length ? relays : DEFAULT_SYNC_RELAYS,
      };
    }
  } catch {}
  return { enabled: true, relays: DEFAULT_SYNC_RELAYS }; // default: on, coinos relay
}

export function setSyncConfig({ enabled, relays }) {
  try {
    localStorage.setItem(SYNC_KEY, JSON.stringify({ enabled: !!enabled, relays: relays || DEFAULT_SYNC_RELAYS }));
  } catch {}
}

export class NostrSync {
  constructor() {
    this.sk = null;
    this.pk = null;
    this.ck = null; // self conversation key for NIP-44
    this.relays = DEFAULT_SYNC_RELAYS;
    this._conns = new Map(); // url -> Relay
  }

  load(mnemonic, passphrase = '') {
    this.sk = nip06.privateKeyFromSeedWords(mnemonic, passphrase || undefined);
    this.pk = getPublicKey(this.sk);
    this.ck = nip44.getConversationKey(this.sk, this.pk);
  }

  unload() {
    this.sk = this.pk = this.ck = null;
    this._closeAll();
  }

  _closeAll() {
    for (const r of this._conns.values()) {
      try {
        r.close();
      } catch {}
    }
    this._conns.clear();
  }

  // Point at a new relay list, closing connections that are no longer used.
  setRelays(relays) {
    const next = Array.isArray(relays) && relays.length ? relays : DEFAULT_SYNC_RELAYS;
    for (const url of [...this._conns.keys()]) {
      if (!next.includes(url)) {
        try {
          this._conns.get(url).close();
        } catch {}
        this._conns.delete(url);
      }
    }
    this.relays = next;
  }

  async _connect(url) {
    const existing = this._conns.get(url);
    if (existing && existing.connected) return existing;
    const r = await Relay.connect(url);
    this._conns.set(url, r);
    return r;
  }

  // Encrypt + publish the latest state to every relay (best-effort).
  async publish(stateObj) {
    if (!this.sk) return;
    let evt;
    try {
      const content = nip44.encrypt(JSON.stringify(stateObj), this.ck);
      evt = finalizeEvent(
        { kind: 30078, created_at: Math.floor(Date.now() / 1000), tags: [['d', DTAG]], content },
        this.sk
      );
    } catch {
      return;
    }
    await Promise.allSettled(
      this.relays.map(async (url) => {
        const relay = await this._connect(url);
        await relay.publish(evt);
      })
    );
  }

  // Fetch from every relay; return the newest decrypted state, or null.
  async fetch() {
    if (!this.sk) return null;
    const results = await Promise.allSettled(this.relays.map((url) => this._fetchOne(url)));
    let best = null;
    for (const res of results) {
      const v = res.status === 'fulfilled' ? res.value : null;
      if (v && (!best || (v.savedAt || 0) > (best.savedAt || 0))) best = v;
    }
    return best;
  }

  async _fetchOne(url) {
    const relay = await this._connect(url);
    return new Promise((resolve) => {
      let result = null;
      const sub = relay.subscribe([{ kinds: [30078], authors: [this.pk], '#d': [DTAG], limit: 1 }], {
        onevent: (e) => {
          try {
            result = JSON.parse(nip44.decrypt(e.content, this.ck));
          } catch {}
        },
        oneose: () => {
          try {
            sub.close();
          } catch {}
          resolve(result);
        },
      });
      setTimeout(() => {
        try {
          sub.close();
        } catch {}
        resolve(result);
      }, 6000);
    });
  }
}