using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace PspCrypto.Security.Cryptography
{
    //
    // This abstract class represents a reusable hash object and can wrap a CNG or WinRT hash object.
    //
    internal abstract class HashProvider : IDisposable
    {
        // Adds new data to be hashed. This can be called repeatedly in order to hash data from noncontiguous sources.
        public void AppendHashData(byte[] data, int offset, int count)
        {
            ArgumentNullException.ThrowIfNull(data);

            // AppendHashData can be called via exposed APIs (e.g. a type that derives from
            // HMACSHA1 and calls HashCore) and could be passed bad data from there.  It could
            // also receive a bad count from HashAlgorithm reading from a Stream that returns
            // an invalid number of bytes read.  Since our implementations of AppendHashDataCore
            // end up using unsafe code, we want to be sure the arguments are valid.
            if (offset < 0)
                throw new ArgumentOutOfRangeException(nameof(offset), "Non-negative number required.");
            if (count < 0)
                throw new ArgumentOutOfRangeException(nameof(count), "Non-negative number required.");
            if (data.Length - offset < count)
                throw new ArgumentException("Offset and length were out of bounds for the array or count is greater than the number of elements from index to the end of the source collection.");

            AppendHashData(new ReadOnlySpan<byte>(data, offset, count));
        }

        public abstract void AppendHashData(ReadOnlySpan<byte> data);

        // Compute the hash based on the appended data and resets the HashProvider for more hashing.
        public abstract int FinalizeHashAndReset(Span<byte> destination);

        public abstract int GetCurrentHash(Span<byte> destination);

        public byte[] FinalizeHashAndReset()
        {
            byte[] ret = new byte[HashSizeInBytes];

            int written = FinalizeHashAndReset(ret);
            Debug.Assert(written == HashSizeInBytes);

            return ret;
        }

        public bool TryFinalizeHashAndReset(Span<byte> destination, out int bytesWritten)
        {
            if (destination.Length < HashSizeInBytes)
            {
                bytesWritten = 0;
                return false;
            }

            bytesWritten = FinalizeHashAndReset(destination);
            return true;
        }

        // Returns the length of the byte array returned by FinalizeHashAndReset.
        public abstract int HashSizeInBytes { get; }

        // Releases any native resources and keys used by the HashProvider.
        public void Dispose()
        {
            Dispose(true);
            GC.SuppressFinalize(this);
        }

        // Releases any native resources and keys used by the HashProvider.
        public abstract void Dispose(bool disposing);

        public abstract void Reset();
    }
}
