// What a dollar is worth in POL right now.
//
// Mission blocks are priced in dollars ($30 entry, $10 listing) because that is how Marty thinks
// about them and how a buyer judges them. The faucet pays in POL. So something has to convert,
// and it has to be a rate nobody can argue with.
//
// It is read from the InstantAdPay contract's own quote: the contract stores each package's price
// in cents and quotes the POL to pay right now, so priceCents / quoteWei IS the rate members are
// already paying at today. No third-party price feed, no oracle to trust, no disagreement between
// what a mission costs here and what a package costs there.
//
// Cached for a few minutes and fail-soft: a purchase is refused rather than priced off a stale or
// missing rate, because getting this wrong silently means selling delivery below cost.
'use strict';
const https = require('https');

const IAP = '0xbe1eca72aff47d13d8e907e523f55eb9e2d365e0';
const RPCS = ['https://polygon-bor-rpc.publicnode.com', 'https://1rpc.io/matic'];
const SEL_COUNT = '0xe0f6ef87';   // productCount()
const SEL_PRODUCT = '0xbf712fd6'; // products(uint32) -> priceCents is word 0, active word 3
const SEL_QUOTE = '0x7de85694';   // quoteWei(uint32)
const TTL = 5 * 60000;

let cache = { usdPerPol: 0, at: 0 };

function rpc(method, params) {
  const body = JSON.stringify({ jsonrpc: '2.0', id: 1, method, params });
  return new Promise((resolve, reject) => {
    let i = 0;
    const attempt = () => {
      const u = new URL(RPCS[i]);
      const rq = https.request({ hostname: u.hostname, path: u.pathname, method: 'POST', timeout: 12000,
        headers: { 'Content-Type': 'application/json', 'Content-Length': Buffer.byteLength(body) } }, res => {
        let d = ''; res.on('data', c => d += c);
        res.on('end', () => {
          try { const j = JSON.parse(d); if (j.error) throw new Error(j.error.message); resolve(j.result); }
          catch (e) { if (++i < RPCS.length) attempt(); else reject(e); }
        });
      });
      rq.on('error', () => { if (++i < RPCS.length) attempt(); else reject(new Error('rpc unreachable')); });
      rq.on('timeout', () => { rq.destroy(); });
      rq.end(body);
    };
    attempt();
  });
}
const call = data => rpc('eth_call', [{ to: IAP, data }, 'latest']);
const enc = n => BigInt(n).toString(16).padStart(64, '0');
const word = (r, i) => r.slice(2 + i * 64, 2 + (i + 1) * 64);

// Walk the catalogue until a product quotes a non-zero POL cost, then take cents / POL from it.
async function fetchRate() {
  const n = parseInt(word(await call(SEL_COUNT), 0), 16);
  for (let id = 1; id <= Math.min(n, 12); id++) {
    let wei = 0n, cents = 0;
    try { wei = BigInt('0x' + word(await call(SEL_QUOTE + enc(id)), 0)); } catch (e) { continue; }
    if (wei <= 0n) continue;
    try {
      const p = await call(SEL_PRODUCT + enc(id));
      cents = parseInt(word(p, 0), 16);                      // priceCents
      const active = parseInt(word(p, 3), 16) === 1;
      const exists = parseInt(word(p, 4), 16) === 1;
      if (!active || !exists) cents = 0;
    } catch (e) { /* fall through */ }
    if (!cents) continue;
    const pol = Number(wei / 10n ** 12n) / 1e6;
    if (pol > 0) return (cents / 100) / pol;   // dollars per POL
  }
  throw new Error('no product quoted a usable price');
}

// dollars per POL, e.g. 0.1019
async function usdPerPol(force) {
  if (!force && cache.usdPerPol > 0 && Date.now() - cache.at < TTL) return cache.usdPerPol;
  const r = await fetchRate();
  if (!(r > 0) || !isFinite(r)) throw new Error('rate came back unusable');
  cache = { usdPerPol: r, at: Date.now() };
  return r;
}

// POL needed for a price in cents. Throws rather than guessing: a purchase priced off a rate we
// could not read is a purchase that might sell delivery below cost.
async function polForCents(cents) {
  const rate = await usdPerPol();
  const pol = (Number(cents) / 100) / rate;
  return Math.round(pol * 10000) / 10000;
}

module.exports = { usdPerPol, polForCents, _cache: () => cache };