using System;
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace Swan {
  /// <summary>
  /// Provides various extension methods for byte arrays and streams.
  /// </summary>
  public static class ByteArrayExtensions {
    /// <summary>
    /// Converts an array of bytes to its lower-case, hexadecimal representation.
    /// </summary>
    /// <param name="bytes">The bytes.</param>
    /// <param name="addPrefix">if set to <c>true</c> add the 0x prefix tot he output.</param>
    /// <returns>
    /// The specified string instance; no actual conversion is performed.
    /// </returns>
    /// <exception cref="ArgumentNullException">bytes.</exception>
    public static String ToLowerHex(this Byte[] bytes, Boolean addPrefix = false) => ToHex(bytes, addPrefix, "x2");

    /// <summary>
    /// Converts an array of bytes to its upper-case, hexadecimal representation.
    /// </summary>
    /// <param name="bytes">The bytes.</param>
    /// <param name="addPrefix">if set to <c>true</c> [add prefix].</param>
    /// <returns>
    /// The specified string instance; no actual conversion is performed.
    /// </returns>
    /// <exception cref="ArgumentNullException">bytes.</exception>
    public static String ToUpperHex(this Byte[] bytes, Boolean addPrefix = false) => ToHex(bytes, addPrefix, "X2");

    /// <summary>
    /// Converts an array of bytes to a sequence of dash-separated, hexadecimal,
    /// uppercase characters.
    /// </summary>
    /// <param name="bytes">The bytes.</param>
    /// <returns>
    /// A string of hexadecimal pairs separated by hyphens, where each pair represents
    /// the corresponding element in value; for example, "7F-2C-4A-00".
    /// </returns>
    public static String ToDashedHex(this Byte[] bytes) => BitConverter.ToString(bytes);

    /// <summary>
    /// Converts an array of bytes to a base-64 encoded string.
    /// </summary>
    /// <param name="bytes">The bytes.</param>
    /// <returns>A <see cref="String" /> converted from an array of bytes.</returns>
    public static String ToBase64(this Byte[] bytes) => Convert.ToBase64String(bytes);

    /// <summary>
    /// Converts a set of hexadecimal characters (uppercase or lowercase)
    /// to a byte array. String length must be a multiple of 2 and
    /// any prefix (such as 0x) has to be avoided for this to work properly.
    /// </summary>
    /// <param name="this">The hexadecimal.</param>
    /// <returns>
    /// A byte array containing the results of encoding the specified set of characters.
    /// </returns>
    /// <exception cref="ArgumentNullException">hex.</exception>
    public static Byte[] ConvertHexadecimalToBytes(this String @this) {
      if(String.IsNullOrWhiteSpace(@this)) {
        throw new ArgumentNullException(nameof(@this));
      }

      return Enumerable.Range(0, @this.Length / 2).Select(x => Convert.ToByte(@this.Substring(x * 2, 2), 16)).ToArray();
    }

    /// <summary>
    /// Gets the bit value at the given offset.
    /// </summary>
    /// <param name="this">The b.</param>
    /// <param name="offset">The offset.</param>
    /// <param name="length">The length.</param>
    /// <returns>
    /// Bit value at the given offset.
    /// </returns>
    public static Byte GetBitValueAt(this Byte @this, Byte offset, Byte length = 1) => (Byte)((@this >> offset) & ~(0xff << length));

    /// <summary>
    /// Sets the bit value at the given offset.
    /// </summary>
    /// <param name="this">The b.</param>
    /// <param name="offset">The offset.</param>
    /// <param name="length">The length.</param>
    /// <param name="value">The value.</param>
    /// <returns>Bit value at the given offset.</returns>
    public static Byte SetBitValueAt(this Byte @this, Byte offset, Byte length, Byte value) {
      Int32 mask = ~(0xff << length);
      Byte valueAt = (Byte)(value & mask);

      return (Byte)((valueAt << offset) | (@this & ~(mask << offset)));
    }

    /// <summary>
    /// Sets the bit value at the given offset.
    /// </summary>
    /// <param name="this">The b.</param>
    /// <param name="offset">The offset.</param>
    /// <param name="value">The value.</param>
    /// <returns>Bit value at the given offset.</returns>
    public static Byte SetBitValueAt(this Byte @this, Byte offset, Byte value) => @this.SetBitValueAt(offset, 1, value);

    /// <summary>
    /// Splits a byte array delimited by the specified sequence of bytes.
    /// Each individual element in the result will contain the split sequence terminator if it is found to be delimited by it.
    /// For example if you split [1,2,3,4] by a sequence of [2,3] this method will return a list with 2 byte arrays, one containing [1,2,3] and the
    /// second one containing 4. Use the Trim extension methods to remove terminator sequences.
    /// </summary>
    /// <param name="this">The buffer.</param>
    /// <param name="offset">The offset at which to start splitting bytes. Any bytes before this will be discarded.</param>
    /// <param name="sequence">The sequence.</param>
    /// <returns>
    /// A byte array containing the results the specified sequence of bytes.
    /// </returns>
    /// <exception cref="System.ArgumentNullException">
    /// buffer
    /// or
    /// sequence.
    /// </exception>
    public static List<Byte[]> Split(this Byte[] @this, Int32 offset, params Byte[] sequence) {
      if(@this == null) {
        throw new ArgumentNullException(nameof(@this));
      }

      if(sequence == null) {
        throw new ArgumentNullException(nameof(sequence));
      }

      Int32 seqOffset = offset.Clamp(0, @this.Length - 1);

      List<Byte[]> result = new List<Byte[]>();

      while(seqOffset < @this.Length) {
        Int32 separatorStartIndex = @this.GetIndexOf(sequence, seqOffset);

        if(separatorStartIndex >= 0) {
          Byte[] item = new Byte[separatorStartIndex - seqOffset + sequence.Length];
          Array.Copy(@this, seqOffset, item, 0, item.Length);
          result.Add(item);
          seqOffset += item.Length;
        } else {
          Byte[] item = new Byte[@this.Length - seqOffset];
          Array.Copy(@this, seqOffset, item, 0, item.Length);
          result.Add(item);
          break;
        }
      }

      return result;
    }

    /// <summary>
    /// Clones the specified buffer, byte by byte.
    /// </summary>
    /// <param name="this">The buffer.</param>
    /// <returns>
    /// A byte array containing the results of encoding the specified set of characters.
    /// </returns>
    /// <exception cref="System.ArgumentNullException">this</exception>
    public static Byte[] DeepClone(this Byte[] @this) {
      if(@this == null) {
        throw new ArgumentNullException(nameof(@this));
      }

      Byte[] result = new Byte[@this.Length];
      Array.Copy(@this, result, @this.Length);
      return result;
    }

    /// <summary>
    /// Removes the specified sequence from the start of the buffer if the buffer begins with such sequence.
    /// </summary>
    /// <param name="buffer">The buffer.</param>
    /// <param name="sequence">The sequence.</param>
    /// <returns>
    /// A new trimmed byte array.
    /// </returns>
    /// <exception cref="ArgumentNullException">buffer.</exception>
    public static Byte[] TrimStart(this Byte[] buffer, params Byte[] sequence) {
      if(buffer == null) {
        throw new ArgumentNullException(nameof(buffer));
      }

      if(buffer.StartsWith(sequence) == false) {
        return buffer.DeepClone();
      }

      Byte[] result = new Byte[buffer.Length - sequence.Length];
      Array.Copy(buffer, sequence.Length, result, 0, result.Length);
      return result;
    }

    /// <summary>
    /// Removes the specified sequence from the end of the buffer if the buffer ends with such sequence.
    /// </summary>
    /// <param name="buffer">The buffer.</param>
    /// <param name="sequence">The sequence.</param>
    /// <returns>
    /// A byte array containing the results of encoding the specified set of characters.
    /// </returns>
    /// <exception cref="ArgumentNullException">buffer.</exception>
    public static Byte[] TrimEnd(this Byte[] buffer, params Byte[] sequence) {
      if(buffer == null) {
        throw new ArgumentNullException(nameof(buffer));
      }

      if(buffer.EndsWith(sequence) == false) {
        return buffer.DeepClone();
      }

      Byte[] result = new Byte[buffer.Length - sequence.Length];
      Array.Copy(buffer, 0, result, 0, result.Length);
      return result;
    }

    /// <summary>
    /// Removes the specified sequence from the end and the start of the buffer 
    /// if the buffer ends and/or starts with such sequence.
    /// </summary>
    /// <param name="buffer">The buffer.</param>
    /// <param name="sequence">The sequence.</param>
    /// <returns>A byte array containing the results of encoding the specified set of characters.</returns>
    public static Byte[] Trim(this Byte[] buffer, params Byte[] sequence) {
      Byte[] trimStart = buffer.TrimStart(sequence);
      return trimStart.TrimEnd(sequence);
    }

    /// <summary>
    /// Determines if the specified buffer ends with the given sequence of bytes.
    /// </summary>
    /// <param name="buffer">The buffer.</param>
    /// <param name="sequence">The sequence.</param>
    /// <returns>
    /// True if the specified buffer is ends; otherwise, false.
    /// </returns>
    /// <exception cref="ArgumentNullException">buffer.</exception>
    public static Boolean EndsWith(this Byte[] buffer, params Byte[] sequence) {
      if(buffer == null) {
        throw new ArgumentNullException(nameof(buffer));
      }

      Int32 startIndex = buffer.Length - sequence.Length;
      return buffer.GetIndexOf(sequence, startIndex) == startIndex;
    }

    /// <summary>
    /// Determines if the specified buffer starts with the given sequence of bytes.
    /// </summary>
    /// <param name="buffer">The buffer.</param>
    /// <param name="sequence">The sequence.</param>
    /// <returns><c>true</c> if the specified buffer starts; otherwise, <c>false</c>.</returns>
    public static Boolean StartsWith(this Byte[] buffer, params Byte[] sequence) => buffer.GetIndexOf(sequence) == 0;

    /// <summary>
    /// Determines whether the buffer contains the specified sequence.
    /// </summary>
    /// <param name="buffer">The buffer.</param>
    /// <param name="sequence">The sequence.</param>
    /// <returns>
    ///   <c>true</c> if [contains] [the specified sequence]; otherwise, <c>false</c>.
    /// </returns>
    public static Boolean Contains(this Byte[] buffer, params Byte[] sequence) => buffer.GetIndexOf(sequence) >= 0;

    /// <summary>
    /// Determines whether the buffer exactly matches, byte by byte the specified sequence.
    /// </summary>
    /// <param name="buffer">The buffer.</param>
    /// <param name="sequence">The sequence.</param>
    /// <returns>
    ///   <c>true</c> if [is equal to] [the specified sequence]; otherwise, <c>false</c>.
    /// </returns>
    /// <exception cref="ArgumentNullException">buffer.</exception>
    public static Boolean IsEqualTo(this Byte[] buffer, params Byte[] sequence) {
      if(ReferenceEquals(buffer, sequence)) {
        return true;
      }

      if(buffer == null) {
        throw new ArgumentNullException(nameof(buffer));
      }

      return buffer.Length == sequence.Length && buffer.GetIndexOf(sequence) == 0;
    }

    /// <summary>
    /// Returns the first instance of the matched sequence based on the given offset.
    /// If no matches are found then this method returns -1.
    /// </summary>
    /// <param name="buffer">The buffer.</param>
    /// <param name="sequence">The sequence.</param>
    /// <param name="offset">The offset.</param>
    /// <returns>The index of the sequence.</returns>
    /// <exception cref="ArgumentNullException">
    /// buffer
    /// or
    /// sequence.
    /// </exception>
    public static Int32 GetIndexOf(this Byte[] buffer, Byte[] sequence, Int32 offset = 0) {
      if(buffer == null) {
        throw new ArgumentNullException(nameof(buffer));
      }

      if(sequence == null) {
        throw new ArgumentNullException(nameof(sequence));
      }

      if(sequence.Length == 0) {
        return -1;
      }

      if(sequence.Length > buffer.Length) {
        return -1;
      }

      Int32 seqOffset = offset < 0 ? 0 : offset;

      Int32 matchedCount = 0;
      for(Int32 i = seqOffset; i < buffer.Length; i++) {
        if(buffer[i] == sequence[matchedCount]) {
          matchedCount++;
        } else {
          matchedCount = 0;
        }

        if(matchedCount == sequence.Length) {
          return i - (matchedCount - 1);
        }
      }

      return -1;
    }

    /// <summary>
    /// Appends the Memory Stream with the specified buffer.
    /// </summary>
    /// <param name="stream">The stream.</param>
    /// <param name="buffer">The buffer.</param>
    /// <returns>
    /// The same MemoryStream instance.
    /// </returns>
    /// <exception cref="ArgumentNullException">
    /// stream
    /// or
    /// buffer.
    /// </exception>
    public static MemoryStream Append(this MemoryStream stream, Byte[] buffer) {
      if(stream == null) {
        throw new ArgumentNullException(nameof(stream));
      }

      if(buffer == null) {
        throw new ArgumentNullException(nameof(buffer));
      }

      stream.Write(buffer, 0, buffer.Length);
      return stream;
    }

    /// <summary>
    /// Appends the Memory Stream with the specified buffer.
    /// </summary>
    /// <param name="stream">The stream.</param>
    /// <param name="buffer">The buffer.</param>
    /// <returns>
    /// Block of bytes to the current stream using data read from a buffer.
    /// </returns>
    /// <exception cref="ArgumentNullException">buffer.</exception>
    public static MemoryStream Append(this MemoryStream stream, IEnumerable<Byte> buffer) => Append(stream, buffer?.ToArray());

    /// <summary>
    /// Appends the Memory Stream with the specified set of buffers.
    /// </summary>
    /// <param name="stream">The stream.</param>
    /// <param name="buffers">The buffers.</param>
    /// <returns>
    /// Block of bytes to the current stream using data read from a buffer.
    /// </returns>
    /// <exception cref="ArgumentNullException">buffers.</exception>
    public static MemoryStream Append(this MemoryStream stream, IEnumerable<Byte[]> buffers) {
      if(buffers == null) {
        throw new ArgumentNullException(nameof(buffers));
      }

      foreach(Byte[] buffer in buffers) {
        _ = Append(stream, buffer);
      }

      return stream;
    }

    /// <summary>
    /// Converts an array of bytes into text with the specified encoding.
    /// </summary>
    /// <param name="buffer">The buffer.</param>
    /// <param name="encoding">The encoding.</param>
    /// <returns>A <see cref="System.String" /> that contains the results of decoding the specified sequence of bytes.</returns>
    public static String ToText(this IEnumerable<Byte> buffer, Encoding encoding) => encoding.GetString(buffer.ToArray());

    /// <summary>
    /// Converts an array of bytes into text with UTF8 encoding.
    /// </summary>
    /// <param name="buffer">The buffer.</param>
    /// <returns>A <see cref="System.String" /> that contains the results of decoding the specified sequence of bytes.</returns>
    public static String ToText(this IEnumerable<Byte> buffer) => buffer.ToText(Encoding.UTF8);

    /// <summary>
    /// Reads the bytes asynchronous.
    /// </summary>
    /// <param name="stream">The stream.</param>
    /// <param name="length">The length.</param>
    /// <param name="bufferLength">Length of the buffer.</param>
    /// <param name="cancellationToken">The cancellation token.</param>
    /// <returns>
    /// A byte array containing the results of encoding the specified set of characters.
    /// </returns>
    /// <exception cref="ArgumentNullException">stream.</exception>
    public static async Task<Byte[]> ReadBytesAsync(this Stream stream, Int64 length, Int32 bufferLength, CancellationToken cancellationToken = default) {
      if(stream == null) {
        throw new ArgumentNullException(nameof(stream));
      }

      using MemoryStream dest = new MemoryStream();
      try {
        Byte[] buff = new Byte[bufferLength];
        while(length > 0) {
          if(length < bufferLength) {
            bufferLength = (Int32)length;
          }

          Int32 nread = await stream.ReadAsync(buff, 0, bufferLength, cancellationToken).ConfigureAwait(false);
          if(nread == 0) {
            break;
          }

          dest.Write(buff, 0, nread);
          length -= nread;
        }
      } catch {
        // ignored
      }

      return dest.ToArray();
    }

    /// <summary>
    /// Reads the bytes asynchronous.
    /// </summary>
    /// <param name="stream">The stream.</param>
    /// <param name="length">The length.</param>
    /// <param name="cancellationToken">The cancellation token.</param>
    /// <returns>
    /// A byte array containing the results of encoding the specified set of characters.
    /// </returns>
    /// <exception cref="ArgumentNullException">stream.</exception>
    public static async Task<Byte[]> ReadBytesAsync(this Stream stream, Int32 length, CancellationToken cancellationToken = default) {
      if(stream == null) {
        throw new ArgumentNullException(nameof(stream));
      }

      Byte[] buff = new Byte[length];
      Int32 offset = 0;
      try {
        while(length > 0) {
          Int32 nread = await stream.ReadAsync(buff, offset, length, cancellationToken).ConfigureAwait(false);
          if(nread == 0) {
            break;
          }

          offset += nread;
          length -= nread;
        }
      } catch {
        // ignored
      }

      return new ArraySegment<Byte>(buff, 0, offset).ToArray();
    }

    private static String ToHex(Byte[] bytes, Boolean addPrefix, String format) {
      if(bytes == null) {
        throw new ArgumentNullException(nameof(bytes));
      }

      StringBuilder sb = new StringBuilder(bytes.Length * 2);

      foreach(Byte item in bytes) {
        _ = sb.Append(item.ToString(format, CultureInfo.InvariantCulture));
      }

      return $"{(addPrefix ? "0x" : String.Empty)}{sb}";
    }
  }
}