namespace HeuristicLab.Problems.ProgramSynthesis.Push.Generators {
  using System;
  using System.Linq;

  using HeuristicLab.Core;
  using HeuristicLab.Random;

  public class StringGenerator {
    public const int DefaultRandomNameLength = 10;

    private static readonly char[] chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890".ToCharArray();
    private static readonly char[] lowercaseChars = "abcdefghijklmnopqrstuvwxyz".ToCharArray();
    private static readonly char[] uppercaseChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ".ToCharArray();
    private static readonly char[] digitChars = "1234567890".ToCharArray();
    private const char space = ' ';

    private int index;

    public string GetNext() {
      var length = index < chars.Length ? 1 : (int)Math.Log(index, chars.Length) + 1;
      var result = new char[length];
      var tmp = index;
      index++;

      for (var i = length; i > 0; i--) {
        var a = (int)Math.Pow(chars.Length, i - 1);
        var b = tmp / a;

        result[length - i] = chars[b];

        tmp -= a * b;
      }

      return new string(result);
    }

    public static string RandomName(IRandom random) {
      return RandomName(DefaultRandomNameLength, random);
    }

    public static string RandomName(int length = DefaultRandomNameLength, IRandom random = null) {
      random = random ?? new FastRandom();
      var name = new char[length];

      for (var i = 0; i < length; i++)
        name[i] = chars[random.Next(chars.Length)];

      return new string(name);
    }

    public static string RandomString(bool allowLowercase, bool allowUppercase, bool allowSpace, double spaceProbability, int length, IRandom random = null) {
      if (!allowLowercase && !allowUppercase) return string.Empty;

      random = random ?? new FastRandom();
      var name = new char[length];

      var sourceChars = Enumerable.Empty<char>();
      if (allowLowercase) sourceChars = sourceChars.Concat(lowercaseChars);
      if (allowUppercase) sourceChars = sourceChars.Concat(uppercaseChars);

      var chars = sourceChars.ToList();

      for (var i = 0; i < name.Length; i++) {
        name[i] = allowSpace && spaceProbability >= random.NextDouble()
          ? space
          : chars[random.Next(0, chars.Count)];
      }

      return new string(name);
    }

    public static char RandomChar(int from, int to, IRandom random = null) {
      if (from > to) throw new InvalidOperationException();

      random = random ?? new FastRandom();

      return Convert.ToChar(from == to ? from : random.Next(from, to));
    }
  }
}