hash-wallet/cw_core/lib/lnurl.dart

import 'dart:convert';

import 'package:bech32/bech32.dart';
import 'package:cw_core/amount/money.dart';
import 'package:cw_core/crypto_currency.dart';
import 'package:cw_core/utils/proxy_wrapper.dart';

const _BOLT_PREFIXES = ["lnbcrt", "lntbs", "lnbc", "lntb"];
const _LUD17_PREFIXES = ['lnurlw', 'lnurlc', 'lnurlp', 'keyauth'];

bool isBolt11ZeroInvoice(String invoice) {
  try {
    final request = Bech32Codec().decode(invoice.replaceFirst("lightning:", ""), invoice.length);


    final prefix = _BOLT_PREFIXES
        .firstWhere((prefix) => request.hrp.startsWith(prefix), orElse: () => "");

    return request.hrp.length == prefix.length;
  } catch(e) {
    return false;
  }
}

/// Get the amount of a Bolt 11 Invoice in
int? _getAmountBolt11Msat(String invoice) {
  final request = Bech32Codec().decode(invoice.replaceFirst("lightning:", ""), invoice.length);

  final prefix = _BOLT_PREFIXES.firstWhere(
        (prefix) => request.hrp.startsWith(prefix),
    orElse: () => throw FormatException('Invalid BOLT11 invoice: unknown HRP prefix.'),
  );

  final amountPart = request.hrp.substring(prefix.length);
  if (amountPart.isEmpty) return null; // zero-amount invoice

  final hasMultiplier = RegExp(r'[munp]$').hasMatch(amountPart);
  final multiplier = hasMultiplier ? amountPart[amountPart.length - 1] : '';
  final numberStr = hasMultiplier ? amountPart.substring(0, amountPart.length - 1) : amountPart;

  if (numberStr.isEmpty || !RegExp(r'^\d+$').hasMatch(numberStr)) {
    throw FormatException('Invalid BOLT11 invoice: invalid amount number in HRP.');
  }

  final amount = int.parse(numberStr);

  switch (multiplier) {
    case '': // bitcoin
      return amount * 100000000000;
    case 'm': // milli-bitcoin
      return amount * 100000000;
    case 'u': // micro-bitcoin
      return amount * 100000;
    case 'n': // nano-bitcoin
      return amount * 100;
    case 'p':
      if (amount % 10 != 0) {
        throw FormatException('Invalid BOLT11 invoice: amount not representable in whole msat.');
      }
      return amount ~/ 10;
    default:
      throw FormatException('Invalid BOLT11 invoice: unknown amount multiplier.');
  }
}

Money? getBolt11Amount(String invoice) {
  final msat = _getAmountBolt11Msat(invoice);
  if (msat == null || msat % 1000 != 0) return null;
  return Money.fromInt(msat ~/ 1000, CryptoCurrency.btcln);
}

class LNURL {
  static Future<Money?> getPayRequestAmount(String lnurl) async {
    final url = decode(lnurl);
    final response = await ProxyWrapper().get(clearnetUri: url);

    if (response.statusCode != 200) return null;

    try {
      final body = jsonDecode(response.body) as Map;
      final tag = body["tag"] as String?;

      if (tag != "payRequest") return null;

      final msat = body["minSendable"] as int?;
      final maxSendable = body["maxSendable"] as int?;

      // if minSendable and maxSendable are the same we assume a specific payment request
      if (msat != maxSendable)
        return null;

      if (msat == null || msat % 1000 != 0) return null;
      return Money.fromInt(msat ~/ 1000, CryptoCurrency.btcln);
    } catch (_) {
      return null;
    }
  }

  static String encode(String url) {
    final raw = _convert(utf8.encode(url), 8, 5, true);
    return const Bech32Codec().encode(Bech32('lnurl', raw), 999);
  }

  static Uri decode(String encodedUrl) {
    Uri decodedUri;

    /// The URL doesn't have to be encoded at all as per LUD-17: Protocol schemes and raw (non bech32-encoded) URLs.
    /// https://github.com/lnurl/luds/blob/luds/17.md
    /// Handle non bech32-encoded LNURL
    decodedUri = Uri.parse(encodedUrl);
    for (final prefix in _LUD17_PREFIXES) {
      if (decodedUri.scheme.contains(prefix)) {
        decodedUri = decodedUri.replace(scheme: prefix);
      }
    }
    if (_LUD17_PREFIXES.contains(decodedUri.scheme)) {
      /// If the non-bech32 LNURL is a Tor address, the port has to be http instead of https for the clearnet LNURL so check if the host ends with '.onion' or '.onion.'
      decodedUri = decodedUri.replace(
          scheme: decodedUri.host.endsWith('onion') || decodedUri.host.endsWith('onion.')
              ? 'http'
              : 'https');
    } else {
      /// Try to parse the input as a lnUrl. Will throw an error if it fails.
      final lnUrl = _findLnUrl(encodedUrl);

      /// Decode the lnurl using bech32
      final bech32 = const Bech32Codec().decode(lnUrl, lnUrl.length);
      decodedUri = Uri.parse(utf8.decode(_convert(bech32.data, 5, 8, false)));
    }
    return decodedUri;
  }
}

/// Parse and return a given lnurl string if it's valid. Will remove
/// `lightning:` from the beginning of it if present.
String _findLnUrl(String input) {
  final res = RegExp(r',*?((lnurl)([0-9]+[a-z0-9]+))').allMatches(input.toLowerCase());

  if (res.length != 1)
    throw ArgumentError('Not a valid lnurl string');
  return res.first.group(0)!;
}

/// Taken from bech32 (bitcoinjs): https://github.com/bitcoinjs/bech32
List<int> _convert(List<int> data, int inBits, int outBits, bool pad) {
  var value = 0;
  var bits = 0;
  final maxV = (1 << outBits) - 1;

  final result = <int>[];
  for (final dataValue in data) {
    value = (value << inBits) | dataValue;
    bits += inBits;

    while (bits >= outBits) {
      bits -= outBits;
      result.add((value >> bits) & maxV);
    }
  }

  if (pad) {
    if (bits > 0) result.add((value << (outBits - bits)) & maxV);
  } else {
    if (bits >= inBits) throw Exception('[BECH32] Excess padding');
    if ((value << (outBits - bits)) & maxV > 0) throw Exception('[BECH32] Non-zero padding');
  }

  return result;
}