ImageSharp/src/ImageSharp/Formats/Png/PngChunk.cs

// Copyright (c) Six Labors.
// Licensed under the Six Labors Split License.
#nullable disable

using System.Buffers;

namespace SixLabors.ImageSharp.Formats.Png;

/// <summary>
/// Stores header information about a chunk.
/// </summary>
internal readonly struct PngChunk
{
    public PngChunk(int length, PngChunkType type, IMemoryOwner<byte> data = null)
    {
        this.Length = length;
        this.Type = type;
        this.Data = data;
    }

    /// <summary>
    /// Gets the length.
    /// An unsigned integer giving the number of bytes in the chunk's
    /// data field. The length counts only the data field, not itself,
    /// the chunk type code, or the CRC. Zero is a valid length
    /// </summary>
    public int Length { get; }

    /// <summary>
    /// Gets the chunk type.
    /// The value is the equal to the UInt32BigEndian encoding of its 4 ASCII characters.
    /// </summary>
    public PngChunkType Type { get; }

    /// <summary>
    /// Gets the data bytes appropriate to the chunk type, if any.
    /// This field can be of zero length or null.
    /// </summary>
    public IMemoryOwner<byte> Data { get; }

    /// <summary>
    /// Gets a value indicating whether the given chunk is critical to decoding
    /// </summary>
    /// <param name="handling">The segment handling behavior.</param>
    public bool IsCritical(SegmentIntegrityHandling handling)
        => handling switch
        {
            SegmentIntegrityHandling.IgnoreNone => true,
            SegmentIntegrityHandling.IgnoreNonCritical => this.Type is PngChunkType.Header or PngChunkType.Palette or PngChunkType.Data or PngChunkType.FrameData,
            SegmentIntegrityHandling.IgnoreData => this.Type is PngChunkType.Header or PngChunkType.Palette,
            _ => false,
        };
}