the-nexus/nostr-identity.js

// ═══════════════════════════════════════════
// NOSTR IDENTITY — Silent Signing, No Extension Popup
// ═══════════════════════════════════════════
// Generates a secp256k1 keypair on first visit and persists it in localStorage.
// Signs NIP-01 events locally — no window.nostr extension required.
// If window.nostr (NIP-07) is present it is preferred; our key acts as fallback.

const NOBLE_SECP_CDN = 'https://cdn.jsdelivr.net/npm/@noble/secp256k1@2.1.0/+esm';
const LS_KEY         = 'nexus-nostr-privkey';

// ─── module state ────────────────────────────────────────────────────────────
let _privKeyBytes = null; // Uint8Array (32 bytes)
let _pubKeyHex    = null; // hex string (32 bytes / x-only)
let _usingNip07   = false;
let _secp         = null; // lazy-loaded @noble/secp256k1

// ─── helpers ─────────────────────────────────────────────────────────────────

function hexToBytes(hex) {
  const b = new Uint8Array(hex.length / 2);
  for (let i = 0; i < hex.length; i += 2) b[i / 2] = parseInt(hex.slice(i, i + 2), 16);
  return b;
}

function bytesToHex(bytes) {
  return Array.from(bytes, b => b.toString(16).padStart(2, '0')).join('');
}

async function sha256Hex(data) {
  const buf = await crypto.subtle.digest('SHA-256', data);
  return bytesToHex(new Uint8Array(buf));
}

async function loadSecp() {
  if (!_secp) _secp = await import(NOBLE_SECP_CDN);
  return _secp;
}

/** Serialize a Nostr event to canonical JSON bytes for ID hashing (NIP-01). */
function serializeEvent(ev) {
  const arr = [0, ev.pubkey, ev.created_at, ev.kind, ev.tags, ev.content];
  return new TextEncoder().encode(JSON.stringify(arr));
}

// ─── public API ──────────────────────────────────────────────────────────────

/**
 * Initialise the identity.
 * Loads or generates a keypair; checks for NIP-07 extension.
 * @returns {{ pubKey: string, npub: string, source: 'nip07'|'local' }}
 */
export async function init() {
  const secp = await loadSecp();

  // Load or generate local keypair
  const stored = localStorage.getItem(LS_KEY);
  if (stored && /^[0-9a-f]{64}$/i.test(stored)) {
    _privKeyBytes = hexToBytes(stored);
  } else {
    _privKeyBytes = secp.utils.randomPrivateKey();
    localStorage.setItem(LS_KEY, bytesToHex(_privKeyBytes));
  }

  // x-only Schnorr public key (32 bytes)
  _pubKeyHex = bytesToHex(secp.schnorr.getPublicKey(_privKeyBytes));

  let source = 'local';

  // Prefer NIP-07 extension when available (no popup needed for getPublicKey)
  if (window.nostr) {
    try {
      const ext = await window.nostr.getPublicKey();
      if (ext && /^[0-9a-f]{64}$/i.test(ext)) {
        _pubKeyHex = ext;
        _usingNip07 = true;
        source = 'nip07';
      }
    } catch {
      // Extension rejected or errored — fall back to local key
    }
  }

  return { pubKey: _pubKeyHex, npub: getNpub(), source };
}

/** Hex public key (x-only / 32 bytes). Null until init() resolves. */
export function getPublicKey() { return _pubKeyHex; }

/**
 * Human-readable abbreviated npub for HUD display.
 * We show a truncated hex with an npub… prefix to avoid a full bech32 dep.
 */
export function getNpub() {
  if (!_pubKeyHex) return null;
  return 'npub…' + _pubKeyHex.slice(-8);
}

/**
 * Sign a Nostr event (NIP-01).
 * Fills in id and sig. Uses NIP-07 extension if it was detected at init time,
 * otherwise signs locally with our generated key — zero popups either way.
 *
 * @param {{ kind?: number, tags?: string[][], content: string, created_at?: number }} partial
 * @returns {Promise<object>} Complete signed event
 */
export async function signEvent(partial) {
  const event = {
    pubkey:     _pubKeyHex,
    created_at: partial.created_at ?? Math.floor(Date.now() / 1000),
    kind:       partial.kind ?? 1,
    tags:       partial.tags ?? [],
    content:    partial.content ?? '',
  };

  event.id = await sha256Hex(serializeEvent(event));

  // Try NIP-07 first when present (it signed getPublicKey silently, so it may
  // also sign events silently depending on the extension configuration)
  if (_usingNip07 && window.nostr) {
    try {
      return await window.nostr.signEvent(event);
    } catch {
      // Extension declined — sign locally as fallback
    }
  }

  // Local Schnorr signing with @noble/secp256k1
  const secp = await loadSecp();
  const sig  = secp.schnorr.sign(hexToBytes(event.id), _privKeyBytes);
  event.sig  = bytesToHex(sig);
  return event;
}

/**
 * Replace the stored private key (e.g. imported from another client).
 * The module must be re-initialised (call init() again) after importing.
 * @param {string} hexPrivKey 64-char hex string
 */
export function importKey(hexPrivKey) {
  if (!/^[0-9a-f]{64}$/i.test(hexPrivKey)) throw new Error('Invalid private key: expected 64 hex chars');
  localStorage.setItem(LS_KEY, hexPrivKey.toLowerCase());
  // Caller should await init() to refresh public key
}