GravatarImageSourceSilly.cs

public class GravatarImageSource : ImageSource
{
	/// <summary>The backing store for the <see cref="Email" /> bindable property.</summary>
	public static readonly BindableProperty? EmailProperty = BindableProperty.Create(nameof(Email), typeof(string), typeof(GravatarImageSource), defaultValue: GravatarImageSourceDefaults.DefaultEmail, propertyChanged: OnEmailPropertyChanged);

	/// <summary>The backing store for the <see cref="Image" /> bindable property.</summary>
	public static readonly BindableProperty ImageProperty = BindableProperty.Create(nameof(Image), typeof(DefaultImage), typeof(GravatarImageSource), defaultValue: GravatarImageSourceDefaults.Defaultimage, propertyChanged: OnDefaultImagePropertyChanged);

	/// <summary>Gets or sets the email address.</summary>
	public string? Email
	{
		get => (string)GetValue(EmailProperty);
		set => SetValue(EmailProperty, value);
	}

	/// <summary>Gets or sets the default image.</summary>
	public DefaultImage Image
	{
		get => (DefaultImage)GetValue(ImageProperty);
		set => SetValue(ImageProperty, value);
	}

	static void OnDefaultImagePropertyChanged(BindableObject bindable, object oldValue, object newValue)
	{
		var gravatarImageSource = (GravatarImageSource)bindable;
		gravatarImageSource.HandleDefaultImageChanged((DefaultImage)newValue);
	}

	static void OnEmailPropertyChanged(BindableObject bindable, object oldValue, object newValue)
	{
		var gravatarImageSource = (GravatarImageSource)bindable;
		gravatarImageSource.HandleEmailChanged((string?)newValue);
	}

	const int gravatarSize = 100;

	void HandleDefaultImageChanged(DefaultImage newValue)
	{
		var uri = new Uri($"https://www.gravatar.com/avatar/{GetMd5Hash(Email)}?s={gravatarSize}&d={DefaultGravatarName(newValue)}");
    // Can we assume that Parent always will be an `Image`?
		(this.Parent as Image)!.Source = uri;
	}

	void HandleEmailChanged(string? newValue)
	{
		var uri = new Uri($"https://www.gravatar.com/avatar/{GetMd5Hash(newValue)}?s={gravatarSize}&d={DefaultGravatarName(Image)}");
    // Can we assume that Parent always will be an `Image`?
		(this.Parent as Image)!.Source = uri;
	}

	static string GetMd5Hash(ReadOnlySpan<char> str)
	{
		if (str.Length is 0)
		{
			str = "MCT";
		}

		using var md5 = MD5.Create();
		Span<byte> hash = md5.ComputeHash(Encoding.UTF8.GetBytes(str.ToArray()));
		return BitConverter.ToString(hash.ToArray(), 0, hash.Length).Replace("-", string.Empty, StringComparison.OrdinalIgnoreCase).ToLowerInvariant();
	}

	static string DefaultGravatarName(DefaultImage defaultGravatar)
			=> defaultGravatar switch
			{
				DefaultImage.FileNotFound => "404",
				DefaultImage.MysteryPerson => "mp",
				_ => $"{defaultGravatar}".ToLower(),
			};

}