import 'dart:math';

Random _rnd = Random.secure();

typedef StringGeneratorFunction = String Function();

class StringGenerators {
  static const String letters = 'abcdefghijklmnopqrstuvwxyz';
  static const String numbers = '1234567890';
  static const String symbols = '_';

  static String getRandomString(
    final int length, {
    final hasLowercaseLetters = false,
    final hasUppercaseLetters = false,
    final hasNumbers = false,
    final hasSymbols = false,
    final isStrict = false,
  }) {
    String chars = '';

    if (hasLowercaseLetters) {
      chars += letters;
    }

    if (hasUppercaseLetters) {
      chars += letters.toUpperCase();
    }

    if (hasNumbers) {
      chars += numbers;
    }

    if (hasSymbols) {
      chars += symbols;
    }

    assert(chars.isNotEmpty, 'chart empty');

    if (!isStrict) {
      return genString(length, chars);
    }

    String res = '';
    int loose = length;
    if (hasLowercaseLetters) {
      loose -= 1;
      res += genString(1, letters);
    }
    if (hasUppercaseLetters) {
      loose -= 1;
      res += genString(1, letters.toUpperCase());
    }
    if (hasNumbers) {
      loose -= 1;
      res += genString(1, numbers.toUpperCase());
    }
    if (hasSymbols) {
      loose -= 1;
      res += genString(1, symbols);
    }
    res += genString(loose, chars);

    final List<String> shuffledlist = res.split('')..shuffle();
    return shuffledlist.join();
  }

  static String genString(final int length, final String chars) =>
      String.fromCharCodes(
        Iterable.generate(
          length,
          (final _) => chars.codeUnitAt(
            _rnd.nextInt(chars.length),
          ),
        ),
      );

  static StringGeneratorFunction userPassword = () => getRandomString(
        8,
        hasLowercaseLetters: true,
        hasUppercaseLetters: true,
        hasNumbers: true,
        isStrict: true,
      );

  static StringGeneratorFunction passwordSalt = () => getRandomString(
        8,
        hasLowercaseLetters: true,
      );

  static StringGeneratorFunction simpleId = () => getRandomString(
        5,
        hasLowercaseLetters: true,
      );

  static StringGeneratorFunction dbPassword = () => getRandomString(
        40,
        hasLowercaseLetters: true,
        hasUppercaseLetters: true,
        hasNumbers: true,
        hasSymbols: true,
      );

  static StringGeneratorFunction storageName = () => getRandomString(
        6,
        hasLowercaseLetters: true,
        hasUppercaseLetters: false,
        hasNumbers: true,
      );

  static StringGeneratorFunction apiToken = () => getRandomString(
        64,
        hasLowercaseLetters: true,
        hasUppercaseLetters: true,
        hasNumbers: true,
      );
}