using System.Text;
using System.Diagnostics.CodeAnalysis;


namespace MaksIT.Core.Security;

public static class Base32Encoder {
  private static readonly char[] Base32Alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567".ToCharArray();
  private const string PaddingChar = "=";

  public static bool TryEncode(
    byte[] data,
    [NotNullWhen(true)] out string? encoded,
    [NotNullWhen(false)] out string? errorMessage
  ) {
    try {
      ArgumentNullException.ThrowIfNull(data);
      if (data.Length == 0) throw new ArgumentException("Data cannot be empty.", nameof(data));

      var result = new StringBuilder();
      int buffer = data[0];
      int next = 1;
      int bitsLeft = 8;
      while (bitsLeft > 0 || next < data.Length) {
        if (bitsLeft < 5) {
          if (next < data.Length) {
            buffer <<= 8;
            buffer |= (data[next++] & 0xFF);
            bitsLeft += 8;
          }
          else {
            int pad = 5 - bitsLeft;
            buffer <<= pad;
            bitsLeft += pad;
          }
        }

        int index = (buffer >> (bitsLeft - 5)) & 0x1F;
        bitsLeft -= 5;
        result.Append(Base32Alphabet[index]);
      }

      // Padding for a complete block
      int padding = result.Length % 8;
      if (padding > 0) {
        for (int i = padding; i < 8; i++) {
          result.Append(PaddingChar);
        }
      }

      encoded = result.ToString();
      errorMessage = null;
      return true;
    }
    catch (Exception ex) {
      encoded = null;
      errorMessage = ex.Message;
      return false;
    }
  }

  public static bool TryDecode(
    string base32,
    [NotNullWhen(true)] out byte[]? decoded,
    [NotNullWhen(false)] out string? errorMessage
  ) {
    try {
      ArgumentNullException.ThrowIfNull(base32);
      if (string.IsNullOrWhiteSpace(base32)) throw new ArgumentException("Base32 string cannot be empty.", nameof(base32));

      base32 = base32.TrimEnd(PaddingChar.ToCharArray());
      int byteCount = base32.Length * 5 / 8;
      byte[] result = new byte[byteCount];

      int buffer = 0;
      int bitsLeft = 0;
      int index = 0;

      foreach (char c in base32) {
        int charValue = CharToValue(c);
        if (charValue < 0) {
          throw new FormatException("Invalid base32 character.");
        }

        buffer <<= 5;
        buffer |= charValue & 0x1F;
        bitsLeft += 5;

        if (bitsLeft >= 8) {
          result[index++] = (byte)(buffer >> (bitsLeft - 8));
          bitsLeft -= 8;
        }
      }

      decoded = result;
      errorMessage = null;
      return true;
    }
    catch (Exception ex) {
      decoded = null;
      errorMessage = ex.Message;
      return false;
    }
  }

  private static int CharToValue(char c) {
    if (c >= 'A' && c <= 'Z') {
      return c - 'A';
    }

    if (c >= '2' && c <= '7') {
      return c - '2' + 26;
    }

    return -1; // Invalid character
  }
}