ImageSharp/tests/ImageSharp.Formats.Tiff.Tests/TestUtilities/Tiff/TiffIfdParser.cs

// <copyright file="TiffIfdParser.cs" company="James Jackson-South">
// Copyright (c) James Jackson-South and contributors.
// Licensed under the Apache License, Version 2.0.
// </copyright>

namespace ImageSharp.Tests
{
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Text;
    using ImageSharp.Formats.Tiff;
    using Xunit;

    /// <summary>
    /// A utility data structure to decode Tiff IFD entries in unit tests.
    /// </summary>
    internal static class TiffIfdParser
    {
        public static int? GetInteger(this List<TiffIfdEntry> entries, ushort tag)
        {
            TiffIfdEntry entry = entries.FirstOrDefault(e => e.Tag == tag);

            if (entry.Tag == 0)
                return null;

            Assert.Equal(1u, entry.Count);

            switch (entry.Type)
            {
                case TiffType.Byte:
                    return entry.Value[0];
                case TiffType.SByte:
                    return (sbyte)entry.Value[0];
                case TiffType.Short:
                    return BitConverter.ToUInt16(entry.Value, 0);
                case TiffType.SShort:
                    return BitConverter.ToInt16(entry.Value, 0);
                case TiffType.Long:
                    return (int)BitConverter.ToUInt32(entry.Value, 0);
                case TiffType.SLong:
                    return BitConverter.ToInt32(entry.Value, 0);
                default:
                    Assert.True(1 == 1, "TIFF IFD entry is not convertable to an integer.");
                    return null;
            }
        }

        public static Rational? GetUnsignedRational(this List<TiffIfdEntry> entries, ushort tag)
        {
            TiffIfdEntry entry = entries.FirstOrDefault(e => e.Tag == tag);

            if (entry.Tag == 0)
                return null;

            Assert.Equal(TiffType.Rational, entry.Type);
            Assert.Equal(1u, entry.Count);

            uint numerator = BitConverter.ToUInt32(entry.Value, 0);
            uint denominator = BitConverter.ToUInt32(entry.Value, 4);

            return new Rational(numerator, denominator);
        }

        public static string GetAscii(this List<TiffIfdEntry> entries, ushort tag)
        {
            TiffIfdEntry entry = entries.FirstOrDefault(e => e.Tag == tag);

            if (entry.Tag == 0)
                return null;

            Assert.Equal(TiffType.Ascii, entry.Type);

            return Encoding.UTF8.GetString(entry.Value, 0, (int)entry.Count);
        }
    }
}