Uwaa/HTTP/MIMEType.cs

using System.Text.Json;
using System.Text.Json.Serialization;

namespace Uwaa.HTTP;

//TODO: Add support for parameters

/// <summary>
/// Represents a Multipurpose Internet Mail Extensions type, which indicates the nature and format of a document/file/chunk of data.
/// </summary>
[JsonConverter(typeof(MIMETypeConverter))]
public readonly record struct MIMEType
{
    public static explicit operator string(MIMEType type) => type.ToString();

    public static implicit operator MIMEType(string type) => new MIMEType(type);

    /// <summary>
    /// The first part of the MIME type, representing the general category into which the data type falls.
    /// </summary>
    public readonly string? Type { get; init; }

    /// <summary>
    /// The second part of the MIME type, identifying the exact kind of data the MIME type represents.
    /// </summary>
    public readonly string? Subtype { get; init; }

    /// <summary>
    /// Parses a MIME type string.
    /// </summary>
    /// <param name="text">The string to parse.</param>
    /// <exception cref="FormatException">Thrown if MIME type is missing a subtype.</exception>
    public MIMEType(ReadOnlySpan<char> text)
    {
        if (text == "*/*")
        {
            Type = null;
            Subtype = null;
            return;
        }

        int spl = text.IndexOf('/');
        if (spl == -1)
        {
            //MIME types need a subtype to be valid.
            throw new FormatException("The provided MIME type is missing a subtype.");
        }

        int end = text.IndexOf(';');
        if (end == -1)
            end = text.Length;

        if (spl == 1 && text[0] == '*')
            Type = null;
        else
            Type = new string(text[..spl]);

        if (spl == text.Length - 2 && text[^1] == '*')
            Subtype = null;
        else
            Subtype = new string(text[(spl + 1)..end]);
    }

    /// <summary>
    /// Constructs a MIME type from its two components.
    /// </summary>
    public MIMEType(string? type, string? subType)
    {
        Type = type;
        Subtype = subType;
    }

    /// <summary>
    /// Determines if the given MIME type matches the pattern specified by this MIME type.
    /// </summary>
    public readonly bool Match(MIMEType type)
    {
        return (Type == null || Type.Equals(type.Type, StringComparison.OrdinalIgnoreCase)) && (Subtype == null || Subtype.Equals(type.Subtype, StringComparison.OrdinalIgnoreCase));
    }

    /// <summary>
    /// Generates a string for the MIME type.
    /// </summary>
    public override readonly string ToString() => $"{Type ?? "*"}/{Subtype ?? "*"}";
}

class MIMETypeConverter : JsonConverter<MIMEType>
{
    public sealed override bool CanConvert(Type typeToConvert) => typeToConvert == typeof(MIMEType);

    public override MIMEType Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        string? str = reader.GetString() ?? throw new JsonException("Cannot read MIME type");
        return new MIMEType(str);
    }

    public override void Write(Utf8JsonWriter writer, MIMEType status, JsonSerializerOptions options)
    {
        writer.WriteStringValue(status.ToString());
    }
}