sourcegit/src/Views/Avatar.cs

using Avalonia;
using Avalonia.Controls;
using Avalonia.Media;
using Avalonia.Media.Imaging;
using System;
using System.Globalization;
using System.Security.Cryptography;
using System.Text;

namespace SourceGit.Views {
    public class Avatar : Control, Models.IAvatarHost {
        private static readonly GradientStops[] FALLBACK_GRADIENTS = [
            new GradientStops() { new GradientStop(Colors.Orange, 0), new GradientStop(Color.FromRgb(255, 213, 134), 1) },
            new GradientStops() { new GradientStop(Colors.DodgerBlue, 0), new GradientStop(Colors.LightSkyBlue, 1) },
            new GradientStops() { new GradientStop(Colors.LimeGreen, 0), new GradientStop(Color.FromRgb(124, 241, 124), 1) },
            new GradientStops() { new GradientStop(Colors.Orchid, 0), new GradientStop(Color.FromRgb(248, 161, 245), 1) },
            new GradientStops() { new GradientStop(Colors.Tomato, 0), new GradientStop(Color.FromRgb(252, 165, 150), 1) },
        ];

        public static readonly StyledProperty<FontFamily> FallbackFontFamilyProperty =
            AvaloniaProperty.Register<Avatar, FontFamily>(nameof(FallbackFontFamily));

        public FontFamily FallbackFontFamily {
            get => GetValue(FallbackFontFamilyProperty);
            set => SetValue(FallbackFontFamilyProperty, value);
        }

        public static readonly StyledProperty<Models.User> UserProperty =
            AvaloniaProperty.Register<Avatar, Models.User>(nameof(User));

        public Models.User User {
            get => GetValue(UserProperty);
            set => SetValue(UserProperty, value);
        }

        static Avatar() {
            AffectsRender<Avatar>(FallbackFontFamilyProperty);
            UserProperty.Changed.AddClassHandler<Avatar>(OnUserPropertyChanged);
        }

        public Avatar() {
            var refetch = new MenuItem() { Header = App.Text("RefetchAvatar") };
            refetch.Click += (o, e) => {
                if (User != null) {
                    _image = Models.AvatarManager.Request(_emailMD5, true);
                    InvalidateVisual();
                }
            };

            ContextMenu = new ContextMenu();
            ContextMenu.Items.Add(refetch);

            Models.AvatarManager.Subscribe(this);
        }

        public override void Render(DrawingContext context) {
            if (User == null) return;

            float corner = (float)Math.Max(2, Bounds.Width / 16);
            if (_image != null) {
                var rect = new Rect(0, 0, Bounds.Width, Bounds.Height);
                context.PushClip(new RoundedRect(rect, corner));
                context.DrawImage(_image, rect);
            } else {
                Point textOrigin = new Point((Bounds.Width - _fallbackLabel.Width) * 0.5, (Bounds.Height - _fallbackLabel.Height) * 0.5);
                context.DrawRectangle(_fallbackBrush, null, new Rect(0, 0, Bounds.Width, Bounds.Height), corner, corner);
                context.DrawText(_fallbackLabel, textOrigin);
            }            
        }

        public void OnAvatarResourceReady(string md5, Bitmap bitmap) {
            if (_emailMD5 == md5) {
                _image = bitmap;
                InvalidateVisual();
            }
        }

        private static void OnUserPropertyChanged(Avatar avatar, AvaloniaPropertyChangedEventArgs e) {
            if (avatar.User == null) {
                avatar._emailMD5 = null;
                return;
            }

            var placeholder = string.IsNullOrWhiteSpace(avatar.User.Name) ? "?" : avatar.User.Name.Substring(0, 1);
            var chars = placeholder.ToCharArray();
            var sum = 0;
            foreach (var c in chars) sum += Math.Abs(c);

            var hash = MD5.Create().ComputeHash(Encoding.Default.GetBytes(avatar.User.Email.ToLower().Trim()));
            var builder = new StringBuilder();
            foreach (var c in hash) builder.Append(c.ToString("x2"));
            var md5 = builder.ToString();
            if (avatar._emailMD5 != md5) {
                avatar._emailMD5 = md5;
                avatar._image = Models.AvatarManager.Request(md5, false);
            }

            avatar._fallbackBrush = new LinearGradientBrush {
                GradientStops = FALLBACK_GRADIENTS[sum % FALLBACK_GRADIENTS.Length],
                StartPoint = new RelativePoint(0, 0, RelativeUnit.Relative),
                EndPoint = new RelativePoint(0, 1, RelativeUnit.Relative),
            };

            var typeface = avatar.FallbackFontFamily == null ? Typeface.Default : new Typeface(avatar.FallbackFontFamily);

            avatar._fallbackLabel = new FormattedText(
                placeholder, 
                CultureInfo.CurrentCulture, 
                FlowDirection.LeftToRight,
                typeface,
                avatar.Width * 0.65,
                Brushes.White);

            avatar.InvalidateVisual();
        }

        private FormattedText _fallbackLabel = null;
        private LinearGradientBrush _fallbackBrush = null;
        private string _emailMD5 = null;
        private Bitmap _image = null;
    }
}