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using System;

using System.IO;

using System.Threading;

using System.Threading.Tasks;

namespace HashifyNet.Core

{

/// <summary>

/// Common interface to non-cryptographic hash functions that can be computed over a stream of data without buffering.

/// </summary>

public abstract class StreamableHashFunctionBase<CName>

: HashFunctionBase<CName>,

IStreamableHashFunction<CName> where CName : IHashConfig<CName>

{

/// <summary>

/// Creates a new transformer that will process data and hold the internal state using this hash function's algorithm.

/// </summary>

/// <returns>A new instance of <see cref="IBlockTransformer"/> that can process input iteratively and produce a final <see cref="IHashValue"/> for that input.</returns>

public abstract IBlockTransformer CreateBlockTransformer();

/// <summary>

/// Computes hash value for given stream.

/// </summary>

/// <param name="data">Stream of data to hash.</param>

/// <returns>

/// Hash value of the data.

/// </returns>

/// <exception cref="ArgumentNullException"><paramref name="data"/></exception>

/// <exception cref="ArgumentException">Stream must be readable.;<paramref name="data"/></exception>

/// <exception cref="ArgumentException">Stream must be seekable for this type of hash function.;<paramref name="data"/></exception>

/// <inheritdoc />

public IHashValue ComputeHash(Stream data) => ComputeHash(data, CancellationToken.None);

/// <summary>

/// Computes hash value for given stream.

/// </summary>

/// <param name="data">Stream of data to hash.</param>

/// <param name="cancellationToken">A cancellation token to observe while calculating the hash value.</param>

/// <returns>

/// Hash value of the data.

/// </returns>

/// <exception cref="ArgumentNullException"><paramref name="data"/></exception>

/// <exception cref="ArgumentException">Stream must be readable.;<paramref name="data"/></exception>

/// <exception cref="ArgumentException">Stream must be seekable for this type of hash function.;<paramref name="data"/></exception>

/// <exception cref="TaskCanceledException">The <paramref name="cancellationToken"/> was canceled.</exception>

public IHashValue ComputeHash(Stream data, CancellationToken cancellationToken)

{

if (data == null)

{

throw new ArgumentNullException(nameof(data));

}

if (!data.CanRead)

{

throw new ArgumentException("Stream must be readable.", nameof(data));

}

return ComputeHashInternal(data, cancellationToken);

}

/// <summary>

/// Computes hash value for given stream asynchronously.

/// </summary>

/// <param name="data">Stream of data to hash.</param>

/// <returns>

/// Hash value of the data.

/// </returns>

/// <remarks>

/// All stream IO is done via ReadAsync.

/// </remarks>

/// <exception cref="ArgumentNullException"><paramref name="data"/></exception>

/// <exception cref="ArgumentException">Stream must be readable.;<paramref name="data"/></exception>

/// <exception cref="ArgumentException">Stream must be seekable for this type of hash function.;<paramref name="data"/></exception>

public Task<IHashValue> ComputeHashAsync(Stream data) => ComputeHashAsync(data, CancellationToken.None);

/// <summary>

/// Computes hash value for given stream asynchronously.

/// </summary>

/// <param name="data">Stream of data to hash.</param>

/// <param name="cancellationToken">A cancellation token to observe while calculating the hash value.</param>

/// <returns>

/// Hash value of the data.

/// </returns>

/// <remarks>

/// All stream IO is done via ReadAsync.

/// </remarks>

/// <exception cref="ArgumentNullException"><paramref name="data"/></exception>

/// <exception cref="ArgumentException">Stream must be readable.;<paramref name="data"/></exception>

/// <exception cref="ArgumentException">Stream must be seekable for this type of hash function.;<paramref name="data"/></exception>

/// <exception cref="TaskCanceledException">The <paramref name="cancellationToken"/> was canceled.</exception>

public Task<IHashValue> ComputeHashAsync(Stream data, CancellationToken cancellationToken)

{

if (data == null)

{

throw new ArgumentNullException(nameof(data));

}

if (!data.CanRead)

{

throw new ArgumentException("Stream must be readable.", nameof(data));

}

return ComputeHashAsyncInternal(data, cancellationToken);

}

/// <summary>

/// Computes hash value for given array segment.

/// </summary>

/// <param name="data">Array segment of data to hash.</param>

/// <param name="cancellationToken">A cancellation token to observe while calculating the hash value.</param>

/// <returns>

/// Hash value of the data.

/// </returns>

/// <exception cref="TaskCanceledException">The <paramref name="cancellationToken"/> was canceled.</exception>

protected override IHashValue ComputeHashInternal(ReadOnlySpan<byte> data, CancellationToken cancellationToken)

{

var blockTransformer = CreateBlockTransformer();

if (!data.IsEmpty)

{

blockTransformer.TransformBytes(data, cancellationToken);

}

return blockTransformer.FinalizeHashValue(cancellationToken);

}

/// <summary>

/// Computes hash value for given stream.

/// </summary>

/// <param name="data">Stream of data to hash.</param>

/// <param name="cancellationToken">A cancellation token to observe while calculating the hash value.</param>

/// <returns>

/// Hash value of the data.

/// </returns>

/// <exception cref="ArgumentNullException"><paramref name="data"/></exception>

/// <exception cref="ArgumentException">Stream must be readable.;<paramref name="data"/></exception>

/// <exception cref="ArgumentException">Stream must be seekable for this type of hash function.;<paramref name="data"/></exception>

/// <exception cref="TaskCanceledException">The <paramref name="cancellationToken"/> was canceled.</exception>

protected IHashValue ComputeHashInternal(Stream data, CancellationToken cancellationToken)

{

var blockTransformer = CreateBlockTransformer();

var buffer = new byte[4096];

while (true)

{

var bytesRead = data.Read(buffer, 0, 4096);

if (bytesRead == 0)

{

break;

}

blockTransformer.TransformBytes(buffer, 0, bytesRead, cancellationToken);

}

return blockTransformer.FinalizeHashValue(cancellationToken);

}

/// <summary>

/// Computes hash value for given stream asynchronously.

/// </summary>

/// <param name="data">Stream of data to hash.</param>

/// <param name="cancellationToken">A cancellation token to observe while calculating the hash value.</param>

/// <returns>

/// Hash value of the data.

/// </returns>

/// <remarks>

/// All stream IO is done via ReadAsync.

/// </remarks>

/// <exception cref="ArgumentNullException"><paramref name="data"/></exception>

/// <exception cref="ArgumentException">Stream must be readable.;<paramref name="data"/></exception>

/// <exception cref="ArgumentException">Stream must be seekable for this type of hash function.;<paramref name="data"/></exception>

/// <exception cref="TaskCanceledException">The <paramref name="cancellationToken"/> was canceled.</exception>

protected async Task<IHashValue> ComputeHashAsyncInternal(Stream data, CancellationToken cancellationToken)

{

var blockTransformer = CreateBlockTransformer();

var buffer = new byte[4096];

while (true)

{

var bytesRead = await data.ReadAsync(buffer, 0, 4096, cancellationToken)

.ConfigureAwait(false);

if (bytesRead == 0)

{

break;

}

blockTransformer.TransformBytes(buffer, 0, bytesRead, cancellationToken);

}

return blockTransformer.FinalizeHashValue(cancellationToken);

}

}

}