// Wallet sign-in (SIWE / EIP-4361) for InstantAdPay.
// Pattern lifted from the RM Circle messages.js implementation (proven with
// MetaMask's friendly sign-in UI). One free signature, cannot move funds.
//
// Difference from RM Circle: a wallet WITHOUT an on-chain member id still gets
// a session — free members exist site-side only until their payout activation
// or first purchase writes them on-chain (spec §4).
const fs = require('fs');
const path = require('path');
const crypto = require('crypto');
const { keccak256 } = require('./vendor/sha3');
const secp = require('./vendor/secp256k1');

let DATA_DIR = null;
let chain = null;
let IS_PROD = false;
let SITE = 'instantadpay.com';

const CHALLENGE_TTL = 10 * 60 * 1000;
const SESSION_TTL = 30 * 24 * 60 * 60 * 1000; // 30 days
const challenges = new Map(); // addressLower -> {message, exp}
let sessions = new Map();     // token -> {address, memberId, expires}

const SESS_FILE = () => path.join(DATA_DIR, 'sessions.json');
function loadSessions() {
  try {
    const o = JSON.parse(fs.readFileSync(SESS_FILE(), 'utf8'));
    sessions = new Map(Object.entries(o).filter(([, s]) => s.expires > Date.now()));
  } catch (e) { sessions = new Map(); }
}
function saveSessions() {
  try {
    const tmp = SESS_FILE() + '.tmp';
    fs.writeFileSync(tmp, JSON.stringify(Object.fromEntries(sessions)), { mode: 0o600 });
    fs.renameSync(tmp, SESS_FILE());
  } catch (e) { console.error('session save failed', e.message); }
}

function init(opts) {
  DATA_DIR = opts.dataDir; chain = opts.chain; IS_PROD = !!opts.isProd;
  if (opts.site) SITE = opts.site;
  loadSessions();
}

// ---- crypto ----
function personalDigest(msg) {
  const m = Buffer.from(msg, 'utf8');
  const pre = Buffer.from('\x19Ethereum Signed Message:\n' + m.length, 'utf8');
  return Buffer.from(keccak256(Buffer.concat([pre, m])), 'hex');
}
function recoverAddress(msg, signature) {
  const raw = Buffer.from(String(signature).replace(/^0x/, ''), 'hex');
  if (raw.length !== 65) throw new Error('Bad signature length');
  let v = raw[64]; if (v >= 27) v -= 27;
  if (v !== 0 && v !== 1) throw new Error('Bad signature recovery byte');
  const pub = secp.recoverPublicKey(personalDigest(msg), raw.slice(0, 64), v, false);
  return '0x' + keccak256(Buffer.from(pub.slice(1))).slice(-40);
}
const ADDR_RE = /^0x[0-9a-fA-F]{40}$/;
function checksumAddress(address) {
  const a = address.toLowerCase().replace(/^0x/, '');
  const h = keccak256(a);
  let out = '0x';
  for (let i = 0; i < a.length; i++) out += parseInt(h[i], 16) >= 8 ? a[i].toUpperCase() : a[i];
  return out;
}

// ---- auth flow ----
function makeChallenge(address) {
  if (!ADDR_RE.test(address || '')) return { error: 'Bad address' };
  const a = address.toLowerCase();
  const nonce = crypto.randomBytes(16).toString('hex');
  const chainId = chain.getConfig().chainId;
  const message = `${SITE} wants you to sign in with your Ethereum account:\n${checksumAddress(a)}\n\nInstantAdPay member sign-in. This signature is free and cannot move funds or approve anything.\n\nURI: https://${SITE}\nVersion: 1\nChain ID: ${chainId}\nNonce: ${nonce}\nIssued At: ${new Date().toISOString()}`;
  challenges.set(a, { message, exp: Date.now() + CHALLENGE_TTL });
  return { message };
}
async function verifyChallenge(address, signature) {
  const a = (address || '').toLowerCase();
  const ch = challenges.get(a);
  if (!ch || ch.exp < Date.now()) return { error: 'Challenge expired - tap sign-in again.' };
  let rec;
  try { rec = recoverAddress(ch.message, signature); } catch (e) { return { error: 'Invalid signature: ' + e.message }; }
  if (rec !== a) return { error: 'Your wallet signed with a different account than the page is using ('
    + rec.slice(0, 6) + '…' + rec.slice(-4) + '). Switch accounts and tap sign-in again.' };
  challenges.delete(a);
  return { ok: true, address: a };
}
// Sessions carry {email, address, memberId} — email accounts are the normal
// join path; the wallet fields fill in when one is linked at purchase time.
function mintSession(fields) {
  const token = crypto.randomBytes(32).toString('hex');
  sessions.set(token, Object.assign({ email: null, address: null, memberId: 0 }, fields,
    { expires: Date.now() + SESSION_TTL }));
  saveSessions();
  return token;
}
function updateSession(token, fields) {
  const s = sessions.get(token);
  if (!s) return;
  sessions.set(token, Object.assign({}, s, fields));
  saveSessions();
}
function sessionCookie(token) {
  return `iap.sid=${encodeURIComponent(token)}; Path=/; HttpOnly; SameSite=Lax; Max-Age=${SESSION_TTL / 1000}${IS_PROD ? '; Secure' : ''}`;
}
function clearCookie() { return 'iap.sid=; Path=/; HttpOnly; SameSite=Lax; Max-Age=0'; }
function fromRequest(req) {
  const m = /(?:^|;\s*)iap\.sid=([^;]+)/.exec(req.headers.cookie || '');
  if (!m) return null;
  const token = decodeURIComponent(m[1]);
  const s = sessions.get(token);
  if (!s || s.expires < Date.now()) return null;
  return Object.assign({ token }, s);
}
async function refreshMemberId(sess) {
  // called after an on-chain action so the session learns its new member id
  if (!sess.address) return sess.memberId || 0;
  try {
    const id = await chain.memberIdByAccount(sess.address);
    if (id && id !== sess.memberId) updateSession(sess.token, { memberId: id });
    return id || sess.memberId || 0;
  } catch (e) { return sess.memberId || 0; }
}
function logout(req) {
  const s = fromRequest(req);
  if (s) { sessions.delete(s.token); saveSessions(); }
}

module.exports = { init, makeChallenge, verifyChallenge, mintSession, updateSession, sessionCookie, clearCookie, fromRequest, refreshMemberId, logout };