//
//  Author:
//    Natalia Portillo claunia@claunia.com
//
//  Copyright (c) 2017, © Claunia.com
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using System.IO;
using System.Security.Cryptography;
using System.Text;

namespace osrepodbmgr
{
    /// <summary>
    /// Provides a UNIX similar API to .NET SHA256.
    /// </summary>
    public class SHA256Context
    {
        SHA256 _sha256Provider;

        /// <summary>
        /// Initializes the SHA256 hash provider
        /// </summary>
        public void Init()
        {
            _sha256Provider = SHA256.Create();
        }

        /// <summary>
        /// Updates the hash with data.
        /// </summary>
        /// <param name="data">Data buffer.</param>
        /// <param name="len">Length of buffer to hash.</param>
        public void Update(byte[] data, uint len)
        {
            _sha256Provider.TransformBlock(data, 0, (int)len, data, 0);
        }

        /// <summary>
        /// Updates the hash with data.
        /// </summary>
        /// <param name="data">Data buffer.</param>
        public void Update(byte[] data)
        {
            Update(data, (uint)data.Length);
        }

        /// <summary>
        /// Returns a byte array of the hash value.
        /// </summary>
        public byte[] Final()
        {
            _sha256Provider.TransformFinalBlock(new byte[0], 0, 0);
            return _sha256Provider.Hash;
        }

        /// <summary>
        /// Returns a hexadecimal representation of the hash value.
        /// </summary>
        public string End()
        {
            _sha256Provider.TransformFinalBlock(new byte[0], 0, 0);
            StringBuilder sha256Output = new StringBuilder();

            for(int i = 0; i < _sha256Provider.Hash.Length; i++)
            {
                sha256Output.Append(_sha256Provider.Hash[i].ToString("x2"));
            }

            return sha256Output.ToString();
        }

        /// <summary>
        /// Gets the hash of a file
        /// </summary>
        /// <param name="filename">File path.</param>
        public byte[] File(string filename)
        {
            FileStream fileStream = new FileStream(filename, FileMode.Open);
            return _sha256Provider.ComputeHash(fileStream);
        }

        /// <summary>
        /// Gets the hash of a file in hexadecimal and as a byte array.
        /// </summary>
        /// <param name="filename">File path.</param>
        /// <param name="hash">Byte array of the hash value.</param>
        public string File(string filename, out byte[] hash)
        {
            FileStream fileStream = new FileStream(filename, FileMode.Open);
            hash = _sha256Provider.ComputeHash(fileStream);
            StringBuilder sha256Output = new StringBuilder();

            for(int i = 0; i < hash.Length; i++)
            {
                sha256Output.Append(hash[i].ToString("x2"));
            }

            return sha256Output.ToString();
        }

        /// <summary>
        /// Gets the hash of the specified data buffer.
        /// </summary>
        /// <param name="data">Data buffer.</param>
        /// <param name="len">Length of the data buffer to hash.</param>
        /// <param name="hash">Byte array of the hash value.</param>
        public string Data(byte[] data, uint len, out byte[] hash)
        {
            hash = _sha256Provider.ComputeHash(data, 0, (int)len);
            StringBuilder sha256Output = new StringBuilder();

            for(int i = 0; i < hash.Length; i++)
            {
                sha256Output.Append(hash[i].ToString("x2"));
            }

            return sha256Output.ToString();
        }

        /// <summary>
        /// Gets the hash of the specified data buffer.
        /// </summary>
        /// <param name="data">Data buffer.</param>
        /// <param name="hash">Byte array of the hash value.</param>
        public string Data(byte[] data, out byte[] hash)
        {
            return Data(data, (uint)data.Length, out hash);
        }
    }
}