/**
 * Invoices for the paid wave.
 *
 * Design in short:
 *   One operator receive address (PROMETHEUS_PAYMENT_ADDRESS) collects every
 *   payment. We distinguish invoices by amount — the base is the USD-pegged
 *   fee (PROMETHEUS_LISTING_FEE_USD, default 1 USD), plus a random 1..256 sat
 *   jitter so two in-flight invoices never expect the same amount at the same
 *   time. The mempool watcher matches incoming (address, amount) pairs to a
 *   pending invoice and marks it paid.
 *
 * This file owns invoice creation and status transitions. The mempool watcher
 * (service/payment-watcher.js) is a separate concern — it calls `tryMatchPayment()`
 * here with (address, amount, txid) as the only state it needs to tell us.
 *
 * The HD-wallet alternative (one address per invoice) is specifically NOT what
 * we do, because deriving + spending from many addresses requires a seeded
 * wallet on the server and a signing operation to consolidate. One address +
 * amount-matching is the shape BitPay used for years; it is simple, auditable
 * and only costs the admin a bit of accounting on the UTXO side.
 */

import { randomBytes } from 'node:crypto';
import {
  insertInvoice, getInvoice, markInvoicePaid, markInvoiceExpired,
  matchPendingInvoice, markListingPaid, getListing, invoicesForListing,
} from './db.js';
import { usdToSats } from './price.js';

const INVOICE_TTL_MS = 20 * 60 * 1000; // 20 min, matches the quote lock
const JITTER_MAX = 256;                 // random 1..256 sats added to the base
const FREE_TIER_BYTES = 100 * 1024 * 1024;        // 100 MiB free
const PER_TIER_BYTES  = 100 * 1024 * 1024;        // $1 USD per 100 MiB above the free tier

export const RECEIVE_ADDRESS = process.env.PROMETHEUS_PAYMENT_ADDRESS || '';
export const PAYMENT_REQUIRED = process.env.PAYMENT_REQUIRED === '1';

/**
 * Size-tiered listing fee in USD. 100 MiB free, then $1 per started 100-MiB
 * tier above that.
 *
 *   0        -   100 MiB  → $0  (free)
 *   100.01   -   200 MiB  → $1
 *   200.01   -   300 MiB  → $2
 *   ...
 *   1900.01  -  2000 MiB  → $19
 *   2000.01  -  2048 MiB  → $20  (ceiling at 2 GiB)
 *
 * Returns an integer; the oracle converts to sats at invoice time. The size
 * threshold is EXACTLY at tier boundaries — a 100.000 MiB file is free, a
 * 100.001 MiB file is the first paid tier at $1.
 */
export function priceUsdForSize(sizeBytes) {
  const n = Number(sizeBytes) || 0;
  if (n <= FREE_TIER_BYTES) return 0;
  return Math.ceil((n - FREE_TIER_BYTES) / PER_TIER_BYTES);
}

// Back-compat export; still read in admin-pages.js as a display hint.
// Represents the first paid tier.
export const LISTING_FEE_USD = 1;

export function paymentsConfigured() {
  return RECEIVE_ADDRESS.length > 0;
}

export function paymentsRequired() {
  return PAYMENT_REQUIRED && paymentsConfigured();
}

/**
 * True if this listing needs an invoice before publishing.
 * Combines the operator policy (PAYMENT_REQUIRED) with the size tier:
 * when PAYMENT_REQUIRED is on, ONLY listings with a non-zero size-tier
 * price are gated — the free tier (≤100 MiB) always publishes immediately.
 */
export function listingNeedsPayment(sizeBytes) {
  if (!paymentsRequired()) return false;
  return priceUsdForSize(sizeBytes) > 0;
}

/**
 * Create a new invoice for a listing. Returns the invoice row.
 * Throws if the listing's size falls in the free tier (caller shouldn't ask).
 */
export async function createInvoice(listingId) {
  if (!paymentsConfigured()) {
    throw new Error('payments not configured — set PROMETHEUS_PAYMENT_ADDRESS');
  }
  const listing = getListing(listingId);
  if (!listing) throw new Error(`no such listing: ${listingId}`);

  const usd = priceUsdForSize(listing.download_size);
  if (usd === 0) {
    throw new Error(`listing is in the free tier (${listing.download_size} bytes); no invoice needed`);
  }

  const { sats: baseSats, rate_sat_per_usd } = await usdToSats(usd);
  const jitter = (randomBytes(1)[0] % JITTER_MAX) + 1;
  const amount_sat = baseSats + jitter;

  const now = Date.now();
  const row = {
    id: freshInvoiceId(),
    listing_id: listingId,
    address: RECEIVE_ADDRESS,
    amount_sat,
    amount_usd: String(usd),
    rate_sat_per_usd,
    issued_at: new Date(now).toISOString(),
    expires_at: new Date(now + INVOICE_TTL_MS).toISOString(),
  };
  insertInvoice(row);
  return { ...row, status: 'pending' };
}

/**
 * Called by the mempool watcher when it sees a (presumably-settlement) tx.
 * Matches to the single pending invoice with that (address, amount) and marks
 * it paid, plus flips the listing's payment_status. Returns the invoice row
 * on success, null on no-match.
 */
export function tryMatchPayment({ address, amount_sat, txid, by = 'watcher' }) {
  const invoice = matchPendingInvoice(address, amount_sat);
  if (!invoice) return null;

  const paid_at = new Date().toISOString();
  const ok = markInvoicePaid({ id: invoice.id, paid_at, paid_txid: txid, paid_by: by });
  if (!ok) return null;

  markListingPaid(invoice.listing_id);
  return { ...invoice, status: 'paid', paid_at, paid_txid: txid, paid_by: by };
}

/**
 * Manual admin confirmation path — same effect as the watcher reconciling a
 * payment, but attributed differently in the audit trail.
 */
export function manuallyMarkPaid(invoiceId, { txid, actor }) {
  const invoice = getInvoice(invoiceId);
  if (!invoice) throw new Error(`no such invoice: ${invoiceId}`);
  if (invoice.status === 'paid') return invoice;

  const paid_at = new Date().toISOString();
  markInvoicePaid({
    id: invoiceId, paid_at,
    paid_txid: txid || '(no txid supplied)',
    paid_by: `manual:${actor}`,
  });
  markListingPaid(invoice.listing_id);
  return { ...invoice, status: 'paid', paid_at, paid_txid: txid, paid_by: `manual:${actor}` };
}

/**
 * Expire a specific invoice if its deadline has passed. Harmless on an
 * already-paid or already-expired one. Returns true if a transition happened.
 */
export function reapInvoice(id) {
  return markInvoiceExpired(id);
}

/**
 * Public shape of an invoice for the UI / API.
 */
export function toPublic(invoice) {
  return {
    id: invoice.id,
    listing_id: invoice.listing_id,
    address: invoice.address,
    amount_sat: invoice.amount_sat,
    amount_bch: (invoice.amount_sat / 1e8).toFixed(8),
    amount_usd: invoice.amount_usd,
    issued_at: invoice.issued_at,
    expires_at: invoice.expires_at,
    status: invoice.status,
    paid_at: invoice.paid_at || undefined,
    paid_txid: invoice.paid_txid || undefined,
    paid_by: invoice.paid_by || undefined,
    bitcoincash_uri: `bitcoincash:${invoice.address}?amount=${(invoice.amount_sat / 1e8).toFixed(8)}&label=${encodeURIComponent('Prometheus listing: ' + invoice.listing_id)}`,
  };
}

/** Fresh base32-ish id. 12 bytes = 96 bits = plenty for an invoice. */
function freshInvoiceId() {
  return randomBytes(12).toString('base64url');
}