// Helpers of the tests of the key of words: the words of a case of
// test/vectors/wordkey_vectors.json, and the String of bytes that hold a
// surrogate, as utf8Bytes writes one.

import 'dart:typed_data';

import 'package:datekeys/src/bytes.dart';

/// The bytes of each hexadecimal word of [c].
List<Uint8List> wordBytes(Map<String, Object?> c) => [
  for (final w in (c['words']! as List).cast<String>()) fromHex(w),
];

/// The String whose [utf8Bytes] are [b], also when they hold a surrogate,
/// which utf8Bytes writes as the three bytes of its code point; null for
/// other bytes that are not valid UTF-8.
String? fromWtf8(Uint8List b) {
  final units = <int>[];
  for (var i = 0; i < b.length;) {
    if (b[i] == 0xed &&
        i + 2 < b.length &&
        b[i + 1] >= 0xa0 &&
        b[i + 1] <= 0xbf &&
        b[i + 2] & 0xc0 == 0x80) {
      units.add(0xd000 | (b[i + 1] & 0x3f) << 6 | b[i + 2] & 0x3f);
      i += 3;
      continue;
    }
    final (r, size) = decodeRune(b, i);
    if (size == 1 && b[i] >= 0x80) return null;
    units.addAll(String.fromCharCode(r).codeUnits);
    i += size;
  }
  return String.fromCharCodes(units);
}