using PdfSharpCore.Pdf.IO;

using System;

namespace PdfSharpCore.Pdf.Filters

{

internal static class StreamDecoder

{

// PdfReference, chapter 7.4.4.3

/// <summary>

/// Further decodes a stream of bytes that were processed by the Flate- or LZW-decoder.

/// </summary>

/// <param name="data">The data to decode</param>

/// <param name="decodeParms">Parameters for the decoder. If this is null, <paramref name="data"/> is returned unchanged</param>

/// <returns>The decoded data as a byte-array</returns>

/// <exception cref="PdfReaderException"></exception>

/// <exception cref="NotImplementedException"></exception>

public static byte[] Decode(byte[] data, PdfDictionary decodeParms)

{

if (decodeParms == null)

return data;

var predictor = decodeParms.Elements.GetInteger("/Predictor");

var colors = decodeParms.Elements.GetInteger("/Colors");

var bpc = decodeParms.Elements.GetInteger("/BitsPerComponent");

var columns = decodeParms.Elements.GetInteger("/Columns");

// set up defaults according to the spec

if (predictor < 1)

predictor = 1;

if (colors < 1)

colors = 1;

if (bpc < 1)

bpc = 8;

if (columns < 1)

columns = 1;

if (predictor == 1) // no prediction, return data as is

return data;

// TIFF predictor. TODO: implement

if (predictor == 2)

throw new NotImplementedException("TIFF predictor is not implemented");

// PNG predictors

if (predictor >= 10 && predictor <= 15)

{

if (bpc != 1 && bpc != 2 && bpc != 4 && bpc != 8 && bpc != 16)

throw new PdfReaderException("Invalid number of bits per component");

var stride = (bpc * colors * columns + 7) / 8;

var rows = data.Length / (stride + 1);

var unfilteredData = new byte[rows * stride];

PngFilter.Unfilter(stride, (bpc * colors + 7) / 8, data, unfilteredData);

return unfilteredData;

}

throw new PdfReaderException("Invalid predictor " + predictor);

}

}

}