PNG/ImageHeader.cs

namespace Uwaa.PNG;

/// <summary>
/// The high level information about the image.
/// </summary>
public readonly struct ImageHeader
{
    internal static readonly byte[] HeaderBytes = { 73, 72, 68, 82 };

    internal static readonly byte[] ValidationHeader = { 137, 80, 78, 71, 13, 10, 26, 10 };

    static readonly Dictionary<ColorType, HashSet<byte>> PermittedBitDepths = new Dictionary<ColorType, HashSet<byte>>
    {
        {ColorType.None, new HashSet<byte> {1, 2, 4, 8, 16}},
        {ColorType.ColorUsed, new HashSet<byte> {8, 16}},
        {ColorType.PaletteUsed | ColorType.ColorUsed, new HashSet<byte> {1, 2, 4, 8}},
        {ColorType.AlphaChannelUsed, new HashSet<byte> {8, 16}},
        {ColorType.AlphaChannelUsed | ColorType.ColorUsed, new HashSet<byte> {8, 16}},
    };

    /// <summary>
    /// The width of the image in pixels.
    /// </summary>
    public int Width { get; }

    /// <summary>
    /// The height of the image in pixels.
    /// </summary>
    public int Height { get; }

    /// <summary>
    /// The bit depth of the image.
    /// </summary>
    public byte BitDepth { get; }

    /// <summary>
    /// The color type of the image.
    /// </summary>
    public ColorType ColorType { get; }

    /// <summary>
    /// The interlace method used by the image..
    /// </summary>
    public InterlaceMethod InterlaceMethod { get; }

    /// <summary>
    /// Create a new <see cref="ImageHeader"/>.
    /// </summary>
    public ImageHeader(int width, int height, byte bitDepth, ColorType colorType, InterlaceMethod interlaceMethod)
    {
        if (width == 0)
            throw new ArgumentOutOfRangeException(nameof(width), "Invalid width (0) for image.");

        if (height == 0)
            throw new ArgumentOutOfRangeException(nameof(height), "Invalid height (0) for image.");

        if (!PermittedBitDepths.TryGetValue(colorType, out var permitted) || !permitted.Contains(bitDepth))
            throw new ArgumentException($"The bit depth {bitDepth} is not permitted for color type {colorType}.");

        Width = width;
        Height = height;
        BitDepth = bitDepth;
        ColorType = colorType;
        InterlaceMethod = interlaceMethod;
    }

    public override string ToString()
    {
        return $"w: {Width}, h: {Height}, bitDepth: {BitDepth}, colorType: {ColorType}, interlace: {InterlaceMethod}.";
    }
}