using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;

namespace Swan.Cryptography {
  /// <summary>
  /// Use this class to compute a hash in MD4, SHA1, SHA256 or SHA512.
  /// </summary>
  public static class Hasher {
    private static readonly Lazy<MD5> Md5Hasher = new Lazy<MD5>(MD5.Create, true);
    private static readonly Lazy<SHA1> SHA1Hasher = new Lazy<SHA1>(SHA1.Create, true);
    private static readonly Lazy<SHA256> SHA256Hasher = new Lazy<SHA256>(SHA256.Create, true);
    private static readonly Lazy<SHA512> SHA512Hasher = new Lazy<SHA512>(SHA512.Create, true);

    /// <summary>
    /// Computes the MD5 hash of the given stream.
    /// Do not use for large streams as this reads ALL bytes at once.
    /// </summary>
    /// <param name="this">The stream.</param>
    /// <param name="createHasher">if set to <c>true</c> [create hasher].</param>
    /// <returns>
    /// The computed hash code.
    /// </returns>
    /// <exception cref="ArgumentNullException">stream.</exception>
    [Obsolete("Use a better hasher.")]
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Codequalität", "IDE0067:Objekte verwerfen, bevor Bereich verloren geht", Justification = "<Ausstehend>")]
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Stil", "IDE0045:In bedingten Ausdruck konvertieren", Justification = "<Ausstehend>")]
    public static Byte[] ComputeMD5(Stream @this, Boolean createHasher = false) {
      if(@this == null) {
        throw new ArgumentNullException(nameof(@this));
      }

      MD5 md5 = MD5.Create();
      const Int32 bufferSize = 4096;

      Byte[] readAheadBuffer = new Byte[bufferSize];
      Int32 readAheadBytesRead = @this.Read(readAheadBuffer, 0, readAheadBuffer.Length);

      do {
        Int32 bytesRead = readAheadBytesRead;
        Byte[] buffer = readAheadBuffer;

        readAheadBuffer = new Byte[bufferSize];
        readAheadBytesRead = @this.Read(readAheadBuffer, 0, readAheadBuffer.Length);

        if(readAheadBytesRead == 0) {
          _ = md5.TransformFinalBlock(buffer, 0, bytesRead);
        } else {
          _ = md5.TransformBlock(buffer, 0, bytesRead, buffer, 0);
        }
      }
      while(readAheadBytesRead != 0);

      return md5.Hash;
    }

    /// <summary>
    /// Computes the MD5 hash of the given string using UTF8 byte encoding.
    /// </summary>
    /// <param name="value">The input string.</param>
    /// <param name="createHasher">if set to <c>true</c> [create hasher].</param>
    /// <returns>The computed hash code.</returns>
    [Obsolete("Use a better hasher.")]
    public static Byte[] ComputeMD5(String value, Boolean createHasher = false) =>        ComputeMD5(Encoding.UTF8.GetBytes(value), createHasher);

    /// <summary>
    /// Computes the MD5 hash of the given byte array.
    /// </summary>
    /// <param name="data">The data.</param>
    /// <param name="createHasher">if set to <c>true</c> [create hasher].</param>
    /// <returns>The computed hash code.</returns>
    [Obsolete("Use a better hasher.")]
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Codequalität", "IDE0067:Objekte verwerfen, bevor Bereich verloren geht", Justification = "<Ausstehend>")]
    public static Byte[] ComputeMD5(Byte[] data, Boolean createHasher = false) =>        (createHasher ? MD5.Create() : Md5Hasher.Value).ComputeHash(data);

    /// <summary>
    /// Computes the SHA-1 hash of the given string using UTF8 byte encoding.
    /// </summary>
    /// <param name="this">The input string.</param>
    /// <param name="createHasher">if set to <c>true</c> [create hasher].</param>
    /// <returns>
    /// The computes a Hash-based Message Authentication Code (HMAC) 
    /// using the SHA1 hash function.
    /// </returns>
    [Obsolete("Use a better hasher.")]
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Codequalität", "IDE0067:Objekte verwerfen, bevor Bereich verloren geht", Justification = "<Ausstehend>")]
    public static Byte[] ComputeSha1(String @this, Boolean createHasher = false) {
      Byte[] inputBytes = Encoding.UTF8.GetBytes(@this);
      return (createHasher ? SHA1.Create() : SHA1Hasher.Value).ComputeHash(inputBytes);
    }


    /// <summary>
    /// Computes the SHA-256 hash of the given string using UTF8 byte encoding.
    /// </summary>
    /// <param name="value">The input string.</param>
    /// <param name="createHasher">if set to <c>true</c> [create hasher].</param>
    /// <returns>
    /// The computes a Hash-based Message Authentication Code (HMAC) 
    /// by using the SHA256 hash function.
    /// </returns>
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Codequalität", "IDE0067:Objekte verwerfen, bevor Bereich verloren geht", Justification = "<Ausstehend>")]
    public static Byte[] ComputeSha256(String value, Boolean createHasher = false) {
      Byte[] inputBytes = Encoding.UTF8.GetBytes(value);
      return (createHasher ? SHA256.Create() : SHA256Hasher.Value).ComputeHash(inputBytes);
    }


    /// <summary>
    /// Computes the SHA-512 hash of the given string using UTF8 byte encoding.
    /// </summary>
    /// <param name="value">The input string.</param>
    /// <param name="createHasher">if set to <c>true</c> [create hasher].</param>
    /// <returns>
    /// The computes a Hash-based Message Authentication Code (HMAC) 
    /// using the SHA512 hash function.
    /// </returns>
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Codequalität", "IDE0067:Objekte verwerfen, bevor Bereich verloren geht", Justification = "<Ausstehend>")]
    public static Byte[] ComputeSha512(String value, Boolean createHasher = false) {
      Byte[] inputBytes = Encoding.UTF8.GetBytes(value);
      return (createHasher ? SHA512.Create() : SHA512Hasher.Value).ComputeHash(inputBytes);
    }
  }
}