feat(PostIt): add dedicated blog reader and video playback

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/PostIt/Directory.Packages.props

@@ -21,6 +21,7 @@
     <PackageVersion Include="Mapsui" Version="5.1.0" />
     <PackageVersion Include="Mapsui.Avalonia12" Version="5.1.0" />
     <PackageVersion Include="MarkdownViewer.Core" Version="1.0.6-47" />
+    <PackageVersion Include="Markdown.Avalonia.Tight" Version="12.0.0-a3" />
     <PackageVersion Include="Material.Avalonia" Version="3.21.0" />
     <PackageVersion Include="AvaloniaUI.DiagnosticsSupport" Version="2.2.3" />
     <PackageVersion Include="CommunityToolkit.Mvvm" Version="8.4.2" />

src/PostIt/PostIt.Tests/BlogReaderTests.cs

@@ -0,0 +1,201 @@
+using System.Net;
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Controls.Templates;
+using Avalonia.Headless.XUnit;
+using Avalonia.Threading;
+using Avalonia.VisualTree;
+using Markdown.Avalonia;
+using ColorTextBlock.Avalonia;
+using PostIt.Models;
+using PostIt.Services;
+using PostIt.ViewModels;
+using PostIt.Views;
+using PostIt.Views.Blogs;
+using Yavsc.Api.Client;
+using Yavsc.Blogspot;
+
+namespace PostIt.Tests;
+
+public class BlogReaderTests
+{
+    private static BlogPostDto Post(string article = "Texte du billet.") => new()
+    {
+        Id = 42,
+        Title = "Un billet à lire",
+        Article = article,
+        AuthorId = "user-id-not-login",
+        Author = new BlogPostAuthorDto { UserName = "paul" },
+        DateModified = DateTime.UtcNow
+    };
+
+    private static BlogsViewModel CreateViewModel(BlogResourceService? resources = null)
+        => new(new BlogApiClient(new RecordingYavscApiClient(new CallRecorder()), "https://blogs.example.test/api/v1/"),
+            new Settings { Authentication = new AuthenticationSettings { Authority = "https://org.example.test" } },
+            resources: resources);
+
+    [Fact]
+    public void Selecting_a_post_defaults_to_reading_and_uses_the_author_login()
+    {
+        var vm = CreateViewModel();
+        vm.SelectedPost = Post();
+        Assert.False(vm.IsEditing);
+        Assert.Equal("paul", vm.ReaderAuthor);
+        Assert.Equal("https://org.example.test/files/paul/", vm.ReaderBaseUrl);
+        Assert.Equal("Texte du billet.", vm.ReaderArticle);
+    }
+
+    [Fact]
+    public void Reading_does_not_publish_or_discard_unsaved_editor_changes()
+    {
+        var vm = CreateViewModel();
+        vm.SelectedPost = Post();
+        vm.EditPostCommand.Execute(null);
+        vm.DraftArticle = "Modifications non enregistrées";
+        vm.ReadPostCommand.Execute(null);
+        Assert.False(vm.IsEditing);
+        Assert.Equal("Texte du billet.", vm.ReaderArticle);
+        Assert.Equal("Modifications non enregistrées", vm.DraftArticle);
+        Assert.True(vm.IsDraftModified);
+        vm.EditPostCommand.Execute(null);
+        Assert.True(vm.IsEditing);
+        Assert.Equal("Modifications non enregistrées", vm.DraftArticle);
+    }
+
+    [Fact]
+    public void New_post_is_an_explicit_action_and_protects_unsaved_changes()
+    {
+        var vm = CreateViewModel();
+        vm.SelectedPost = Post();
+        vm.NewPostCommand.Execute(null);
+        Assert.True(vm.IsEditing);
+        Assert.Null(vm.SelectedPost);
+        Assert.Empty(vm.DraftTitle);
+        Assert.Empty(vm.DraftArticle!);
+        vm.DraftTitle = "Nouveau brouillon";
+        vm.NewPostCommand.Execute(null);
+        Assert.Equal("Nouveau brouillon", vm.DraftTitle);
+        Assert.Equal(StatusSeverity.Warning, vm.ActionStatus.Severity);
+    }
+
+    [AvaloniaFact]
+    public async Task Reader_hides_editor_and_wires_hyperlinks_to_the_application()
+    {
+        var vm = CreateViewModel();
+        await vm.InitializeAsync();
+        vm.SelectedPost = Post("[Vidéo](clip.mp4)");
+        var page = new BlogsPage { DataContext = vm };
+        var nav = new NavigationPage();
+        await nav.PushAsync(page);
+        var window = new Window { Width = 800, Height = 700, Content = nav };
+        try
+        {
+            window.Show();
+            Dispatcher.UIThread.RunJobs();
+            window.UpdateLayout();
+            Assert.True(page.FindControl<Grid>("PostReader")!.IsVisible);
+            Assert.False(page.FindControl<Grid>("PostEditor")!.IsVisible);
+            Assert.False(page.SaveButton.IsVisible);
+            var reader = page.FindControl<MarkdownScrollViewer>("ArticleReader")!;
+            Assert.Equal(vm.ReaderArticle, reader.Markdown);
+            Assert.Equal(vm.ReaderBaseUrl, reader.AssetPathRoot);
+            Assert.Same(vm.OpenResourceCommand, Assert.IsAssignableFrom<IMarkdownEngine2>(reader.Engine).HyperlinkCommand);
+            vm.EditPostCommand.Execute(null);
+            Assert.False(page.FindControl<Grid>("PostReader")!.IsVisible);
+            Assert.True(page.FindControl<Grid>("PostEditor")!.IsVisible);
+            Assert.True(page.SaveButton.IsVisible);
+        }
+        finally
+        {
+            window.Close();
+        }
+    }
+
+    [AvaloniaFact]
+    public async Task Long_reading_content_scrolls_and_clears_when_selection_is_removed()
+    {
+        var vm = CreateViewModel();
+        await vm.InitializeAsync();
+        vm.SelectedPost = Post(string.Join("\n\n", Enumerable.Range(0, 100).Select(i => $"Paragraphe {i}.")));
+        var page = new BlogsPage { DataContext = vm };
+        var nav = new NavigationPage();
+        await nav.PushAsync(page);
+        var window = new Window { Width = 800, Height = 700, Content = nav };
+        try
+        {
+            window.Show();
+            Dispatcher.UIThread.RunJobs();
+            window.UpdateLayout();
+            var reader = page.FindControl<MarkdownScrollViewer>("ArticleReader")!;
+            var scroll = reader.GetVisualDescendants().OfType<ScrollViewer>().Single();
+            Assert.InRange(scroll.Viewport.Height, 1, window.ClientSize.Height);
+            Assert.True(scroll.Extent.Height > scroll.Viewport.Height);
+            scroll.ScrollToEnd();
+            Assert.True(scroll.Offset.Y > 0);
+            vm.SelectedPost = null;
+            Dispatcher.UIThread.RunJobs();
+            Assert.Empty(reader.Markdown!);
+        }
+        finally
+        {
+            window.Close();
+        }
+    }
+
+    [AvaloniaFact]
+    public async Task Clicking_a_user_video_pushes_a_dedicated_video_viewmodel()
+    {
+        using var client = new HttpClient(new BlogResourceServiceTests.StubHandler(request =>
+        {
+            Assert.Equal("https://org.example.test/files/paul/clip.mp4", request.RequestUri!.AbsoluteUri);
+            var response = new HttpResponseMessage(HttpStatusCode.OK);
+            response.Content.Headers.ContentType = new("video/mp4");
+            return response;
+        }));
+        var vm = CreateViewModel(new BlogResourceService(client));
+        vm.SelectedPost = Post();
+        var app = (App)Application.Current!;
+        var root = new MainView();
+        app.AttachMainWindow(root);
+        var template = new FuncDataTemplate<VideoPageViewModel>((_, _) => new ContentPage());
+        app.DataTemplates.Insert(0, template);
+        try
+        {
+            var page = new BlogsPage { DataContext = vm };
+            var reader = page.FindControl<MarkdownScrollViewer>("ArticleReader")!;
+            Dispatcher.UIThread.RunJobs();
+            var engine = Assert.IsAssignableFrom<IMarkdownEngine2>(reader.Engine);
+            var link = Assert.IsType<CHyperlink>(Assert.Single(engine.ParseGamutInline("[Vidéo](clip.mp4)")));
+            Assert.NotNull(link.Command);
+            link.Command(link.CommandParameter!);
+            Assert.NotNull(vm.OpenResourceCommand.ExecutionTask);
+            await vm.OpenResourceCommand.ExecutionTask;
+            var target = Assert.IsType<VideoPageViewModel>(root.NavRoot.NavigationStack.Last().DataContext);
+            Assert.Equal("https://org.example.test/files/paul/clip.mp4", target.Source.AbsoluteUri);
+            Assert.Equal("video/mp4", target.MimeType);
+        }
+        finally
+        {
+            app.DataTemplates.Remove(template);
+        }
+    }
+
+    [AvaloniaFact]
+    public void Video_viewmodel_resolves_to_a_page_with_a_vlc_control()
+    {
+        var vm = new VideoPageViewModel(new Uri("https://org.example.test/files/paul/clip.mp4"), "video/mp4");
+        var page = Assert.IsType<VideoPage>(new ViewLocator().Build(vm));
+        Assert.NotNull(page.FindControl<LibVLCSharp.Avalonia.VideoView>("Video"));
+    }
+
+    [Fact]
+    public async Task Broken_resource_reports_an_error_and_releases_busy_state()
+    {
+        using var client = new HttpClient(new BlogResourceServiceTests.StubHandler(_ => new(HttpStatusCode.NotFound)));
+        var vm = CreateViewModel(new BlogResourceService(client));
+        vm.SelectedPost = Post();
+        await vm.OpenResourceCommand.ExecuteAsync("absent.mp4");
+        Assert.False(vm.IsBusy);
+        Assert.Equal(StatusSeverity.Error, vm.ActionStatus.Severity);
+    }
+}

src/PostIt/PostIt.Tests/BlogResourceServiceTests.cs

@@ -0,0 +1,137 @@
+using System.Net;
+using System.Net.Http.Headers;
+using PostIt.Services;
+
+namespace PostIt.Tests;
+
+public class BlogResourceServiceTests
+{
+    private const string Authority = "https://yavsc.pschneider.fr";
+
+    [Theory]
+    [InlineData("IMG-20260923-WA0001.jpg", Authority + "/files/paul/IMG-20260923-WA0001.jpg")]
+    [InlineData("blogs/42/vidéo.mp4", Authority + "/files/paul/blogs/42/vid%C3%A9o.mp4")]
+    [InlineData("/files/alice/video.webm", Authority + "/files/alice/video.webm")]
+    [InlineData(Authority + "/files/paul/photo.jpg", Authority + "/files/paul/photo.jpg")]
+    [InlineData("https://elsewhere.test/page", "https://elsewhere.test/page")]
+    [InlineData("//elsewhere.test/page", "https://elsewhere.test/page")]
+    public void Resolves_links_against_org_user_login_not_blogs_host(string link, string expected)
+        => Assert.Equal(expected, BlogResourceService.Resolve(link, Authority + "/connect/", "paul").AbsoluteUri);
+
+    [Fact]
+    public void Encodes_login_and_keeps_trailing_slash()
+        => Assert.Equal(Authority + "/files/paul%20test/",
+            BlogResourceService.GetUserBaseUri(Authority, "paul test").AbsoluteUri);
+
+    [Theory]
+    [InlineData(Authority + "/files/paul/movie.mp4", true)]
+    [InlineData(Authority + "/files/alice/blogs/42/movie.mp4?download=1", true)]
+    [InlineData(Authority + "/files/paul/", false)]
+    [InlineData(Authority + "/files/paul", false)]
+    [InlineData(Authority + "/files/", false)]
+    [InlineData(Authority + "/files-other/paul/movie.mp4", false)]
+    [InlineData(Authority + "/page.mp4", false)]
+    [InlineData("https://blogs.pschneider.fr/files/paul/movie.mp4", false)]
+    [InlineData("https://yavsc.pschneider.fr.evil.test/files/paul/movie.mp4", false)]
+    [InlineData("https://yavsc.pschneider.fr:8443/files/paul/movie.mp4", false)]
+    [InlineData("http://yavsc.pschneider.fr/files/paul/movie.mp4", false)]
+    [InlineData("https://user@yavsc.pschneider.fr/files/paul/movie.mp4", false)]
+    public void Recognizes_only_files_on_the_configured_org_origin(string link, bool expected)
+        => Assert.Equal(expected, BlogResourceService.IsUserResource(new Uri(link), Authority));
+
+    [Theory]
+    [InlineData("javascript:alert(1)")]
+    [InlineData("file:///tmp/video.mp4")]
+    [InlineData("data:video/mp4;base64,AAAA")]
+    public void Rejects_non_web_links(string link)
+        => Assert.Throws<InvalidOperationException>(() => BlogResourceService.Resolve(link, Authority, "paul"));
+
+    [Theory]
+    [InlineData("video/webm", "movie.jpg", "video/webm")]
+    [InlineData("image/jpeg", "movie.mp4", "image/jpeg")]
+    [InlineData("application/octet-stream", "movie.MP4", "video/mp4")]
+    [InlineData(null, "movie.webm", "video/webm")]
+    [InlineData(null, "IMG-20260923-WA0001.jpg", "image/jpeg")]
+    [InlineData(null, "file.unknown", "application/octet-stream")]
+    public async Task Prefers_server_mime_with_extension_fallback(string? mime, string file, string expected)
+    {
+        using var client = new HttpClient(new StubHandler(request =>
+        {
+            Assert.Equal(HttpMethod.Head, request.Method);
+            return Response(HttpStatusCode.OK, mime);
+        }));
+        var service = new BlogResourceService(client);
+        Assert.Equal(expected, await service.GetMimeTypeAsync(new Uri($"{Authority}/files/paul/{file}?v=1"),
+            TestContext.Current.CancellationToken));
+    }
+
+    [Theory]
+    [InlineData(HttpStatusCode.MethodNotAllowed)]
+    [InlineData(HttpStatusCode.NotImplemented)]
+    public async Task Falls_back_to_a_ranged_get_when_head_is_not_supported(HttpStatusCode status)
+    {
+        var calls = 0;
+        using var client = new HttpClient(new StubHandler(request =>
+        {
+            calls++;
+            if (request.Method == HttpMethod.Head)
+                return Response(status, null);
+            Assert.Equal(HttpMethod.Get, request.Method);
+            Assert.Equal("bytes=0-0", request.Headers.Range?.ToString());
+            return Response(HttpStatusCode.PartialContent, "video/mp4");
+        }));
+        Assert.Equal("video/mp4", await new BlogResourceService(client)
+            .GetMimeTypeAsync(new Uri($"{Authority}/files/paul/movie"), TestContext.Current.CancellationToken));
+        Assert.Equal(2, calls);
+    }
+
+    [Theory]
+    [InlineData(HttpStatusCode.NotFound)]
+    [InlineData(HttpStatusCode.Unauthorized)]
+    [InlineData(HttpStatusCode.InternalServerError)]
+    public async Task Does_not_disguise_http_errors_as_a_mime_guess(HttpStatusCode status)
+    {
+        using var client = new HttpClient(new StubHandler(_ => Response(status, null)));
+        await Assert.ThrowsAsync<HttpRequestException>(() => new BlogResourceService(client)
+            .GetMimeTypeAsync(new Uri($"{Authority}/files/paul/movie.mp4"), TestContext.Current.CancellationToken));
+    }
+
+    [Theory]
+    [InlineData("photo.jpg", Authority + "/files/paul/photo.jpg")]
+    [InlineData("/files/alice/photo.jpg", Authority + "/files/alice/photo.jpg")]
+    [InlineData(Authority + "/files/alice/photo.jpg", Authority + "/files/alice/photo.jpg")]
+    public async Task Inline_images_use_the_same_user_base_and_support_root_relative_paths(string link, string expected)
+    {
+        using var client = new HttpClient(new StubHandler(request =>
+        {
+            Assert.Equal(expected, request.RequestUri!.AbsoluteUri);
+            return Response(HttpStatusCode.OK, "image/jpeg");
+        }));
+        var resolver = new BlogImageResolver(client) { AssetPathRoot = Authority + "/files/paul/" };
+        await using var stream = await resolver.ResolveImageResource(link);
+        Assert.NotNull(stream);
+    }
+
+    [Theory]
+    [InlineData("file:///etc/passwd")]
+    [InlineData("data:image/png;base64,AAAA")]
+    public async Task Inline_images_cannot_read_local_files_or_non_web_schemes(string link)
+    {
+        var resolver = new BlogImageResolver { AssetPathRoot = Authority + "/files/paul/" };
+        await Assert.ThrowsAsync<InvalidOperationException>(() => resolver.ResolveImageResource(link));
+    }
+
+    private static HttpResponseMessage Response(HttpStatusCode status, string? mime)
+    {
+        var response = new HttpResponseMessage(status) { Content = new ByteArrayContent([]) };
+        if (mime is not null)
+            response.Content.Headers.ContentType = new MediaTypeHeaderValue(mime);
+        return response;
+    }
+
+    internal sealed class StubHandler(Func<HttpRequestMessage, HttpResponseMessage> respond) : HttpMessageHandler
+    {
+        protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
+            => Task.FromResult(respond(request));
+    }
+}

src/PostIt/PostIt.Tests/MainPageSaveTests.cs

@@ -42,6 +42,7 @@ public class MainPageSaveTests
         var api = new RecordingYavscApiClient(recorder);
         var blog = new BlogApiClient(api, "http://localhost/");
         var viewModel = new BlogsViewModel(blog);
+        viewModel.NewPostCommand.Execute(null);
 
         var page = new BlogsPage { DataContext = viewModel };
         // MainPage is a ContentPage (a Page, not a Control), so it

src/PostIt/PostIt.Tests/MarkdownEditorScrollTests.cs

@@ -55,7 +55,7 @@ public class MarkdownEditorScrollTests
     [InlineData(true)]
     public void Blog_page_bounds_the_article_viewport(bool preview)
     {
-        var page = new BlogsPage();
+        var page = new BlogsPage { DataContext = new PostIt.ViewModels.BlogsViewModel { IsEditing = true } };
         var editor = page.GetLogicalDescendants().OfType<MarkdownEditorControl>().Single();
         editor.MarkdownText = LongArticle;
         editor.IsPreviewVisible = preview;

src/PostIt/PostIt/Helpers/ServiceCollectionHelpers.cs

@@ -44,6 +44,7 @@ public static class ServiceCollectionHelpers
         services.AddTransient<MainWindow>();
         services.AddTransient<MainView>();
         services.AddTransient<BlogsPage>();
+        services.AddTransient<VideoPage>();
 
 
         // Models

src/PostIt/PostIt/PostIt.csproj

@@ -39,6 +39,7 @@
     <PackageReference Include="CommunityToolkit.Mvvm" />
     <PackageReference Include="IdentityModel.OidcClient" />
     <PackageReference Include="MarkdownViewer.Core" />
+    <PackageReference Include="Markdown.Avalonia.Tight" />
     <PackageReference Include="Microsoft.AspNetCore.SignalR.Client" />
     <PackageReference Include="Microsoft.Extensions.DependencyInjection" />
     <PackageReference Include="Mono.Options" />

src/PostIt/PostIt/Services/BlogImageResolver.cs

@@ -0,0 +1,33 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Net.Http;
+using System.Threading.Tasks;
+using Markdown.Avalonia.Utils;
+
+namespace PostIt.Services;
+
+public sealed class BlogImageResolver : IPathResolver
+{
+    private static readonly HttpClient Client = new() { Timeout = TimeSpan.FromSeconds(15) };
+    private readonly HttpClient _client;
+
+    public BlogImageResolver() : this(Client) { }
+
+    public BlogImageResolver(HttpClient client) => _client = client;
+
+    public string? AssetPathRoot { get; set; }
+    public IEnumerable<string>? CallerAssemblyNames { get; set; }
+
+    public async Task<Stream?> ResolveImageResource(string relativeOrAbsolutePath)
+    {
+        var uri = !relativeOrAbsolutePath.StartsWith("/", StringComparison.Ordinal)
+            && Uri.TryCreate(relativeOrAbsolutePath, UriKind.Absolute, out var absolute)
+            ? absolute
+            : new Uri(new Uri(AssetPathRoot ?? throw new InvalidOperationException(
+                "La base des fichiers de l'auteur est indisponible.")), relativeOrAbsolutePath);
+        if (uri.Scheme != Uri.UriSchemeHttps && uri.Scheme != Uri.UriSchemeHttp)
+            throw new InvalidOperationException("Les images du billet doivent utiliser HTTP ou HTTPS.");
+        return await _client.GetStreamAsync(uri);
+    }
+}

src/PostIt/PostIt/Services/BlogResourceService.cs

@@ -0,0 +1,98 @@
+using System;
+using System.Net;
+using System.Net.Http;
+using System.Threading;
+using System.Threading.Tasks;
+using Yavsc.Abstract.Files;
+
+namespace PostIt.Services;
+
+public sealed class BlogResourceService
+{
+    private static readonly HttpClient SharedClient = new() { Timeout = TimeSpan.FromSeconds(15) };
+    private readonly HttpClient _client;
+
+    public BlogResourceService() : this(SharedClient) { }
+
+    public BlogResourceService(HttpClient client) => _client = client;
+
+    public static Uri GetUserBaseUri(string authority, string login)
+    {
+        if (string.IsNullOrWhiteSpace(login))
+            throw new InvalidOperationException("Le login de l'auteur est nécessaire pour résoudre ses fichiers.");
+        return FileServerUrlHelpers.GetUserFilesUri(GetAuthority(authority), Uri.EscapeDataString(login) + "/");
+    }
+
+    public static Uri Resolve(string link, string authority, string login)
+    {
+        if (string.IsNullOrWhiteSpace(link))
+            throw new ArgumentException("Le lien est vide.", nameof(link));
+        var origin = GetAuthority(authority);
+        var uri = link.StartsWith("/", StringComparison.Ordinal)
+            ? new Uri(origin, link)
+            : Uri.TryCreate(link, UriKind.Absolute, out var absolute)
+                ? absolute
+                : new Uri(GetUserBaseUri(authority, login), link);
+        if (uri.Scheme != Uri.UriSchemeHttps && uri.Scheme != Uri.UriSchemeHttp)
+            throw new InvalidOperationException("Seuls les liens HTTP et HTTPS sont pris en charge.");
+        return uri;
+    }
+
+    public static bool IsUserResource(Uri uri, string authority)
+    {
+        var root = FileServerUrlHelpers.GetUserFilesBaseUri(GetAuthority(authority));
+        if (!root.IsBaseOf(uri) || !string.IsNullOrEmpty(uri.UserInfo))
+            return false;
+        var path = uri.AbsolutePath[root.AbsolutePath.Length..];
+        var separator = path.IndexOf('/');
+        return separator > 0 && separator < path.Length - 1;
+    }
+
+    public async Task<string> GetMimeTypeAsync(Uri uri, CancellationToken cancellationToken = default)
+    {
+        using var head = new HttpRequestMessage(HttpMethod.Head, uri);
+        using var response = await _client.SendAsync(head, HttpCompletionOption.ResponseHeadersRead, cancellationToken);
+        if (response.StatusCode is HttpStatusCode.MethodNotAllowed or HttpStatusCode.NotImplemented)
+        {
+            using var get = new HttpRequestMessage(HttpMethod.Get, uri);
+            get.Headers.Range = new System.Net.Http.Headers.RangeHeaderValue(0, 0);
+            using var fallback = await _client.SendAsync(get, HttpCompletionOption.ResponseHeadersRead, cancellationToken);
+            fallback.EnsureSuccessStatusCode();
+            return GetMimeType(fallback, uri);
+        }
+        response.EnsureSuccessStatusCode();
+        return GetMimeType(response, uri);
+    }
+
+    private static string GetMimeType(HttpResponseMessage response, Uri uri)
+    {
+        var mime = response.Content.Headers.ContentType?.MediaType;
+        if (!string.IsNullOrEmpty(mime) && !mime.Equals("application/octet-stream", StringComparison.OrdinalIgnoreCase))
+            return mime;
+        return System.IO.Path.GetExtension(uri.AbsolutePath).ToLowerInvariant() switch
+        {
+            ".mp4" or ".m4v" => "video/mp4",
+            ".webm" => "video/webm",
+            ".ogv" => "video/ogg",
+            ".ogg" => "audio/ogg",
+            ".mov" => "video/quicktime",
+            ".mkv" => "video/x-matroska",
+            ".avi" => "video/x-msvideo",
+            ".jpg" or ".jpeg" => "image/jpeg",
+            ".png" => "image/png",
+            ".gif" => "image/gif",
+            ".webp" => "image/webp",
+            ".pdf" => "application/pdf",
+            _ => mime ?? "application/octet-stream"
+        };
+    }
+
+    private static Uri GetAuthority(string authority)
+    {
+        if (!Uri.TryCreate(authority, UriKind.Absolute, out var uri)
+            || (uri.Scheme != Uri.UriSchemeHttps && uri.Scheme != Uri.UriSchemeHttp)
+            || !string.IsNullOrEmpty(uri.UserInfo))
+            throw new InvalidOperationException("L'URL de Yavsc.Org est invalide dans les paramètres d'authentification.");
+        return new Uri(uri.GetLeftPart(UriPartial.Authority) + "/");
+    }
+}

src/PostIt/PostIt/ViewLocator.cs

@@ -42,6 +42,7 @@ public class ViewLocator : IDataTemplate
         return data switch
         {
             BlogsViewModel => services.GetRequiredService<BlogsPage>(),
+            VideoPageViewModel => services.GetRequiredService<VideoPage>(),
             Settings => services.GetRequiredService<SettingsPage>(),
             AboutPageViewModel => services.GetRequiredService<AboutPage>(),
             HomePageViewModel => services.GetRequiredService<HomePage>(),

src/PostIt/PostIt/ViewModels/Blogs/BlogsViewModel.cs

@@ -13,6 +13,8 @@ using Yavsc.Api.Client;
 using Yavsc.Abstract.Files;
 using Yavsc.Server.Helpers;
 using AvaloniaEdit.Document;
+using Avalonia.Controls;
+using PostIt.Services;
 
 namespace PostIt.ViewModels;
 
@@ -141,8 +143,85 @@ public partial class BlogsViewModel : ViewModelBase, IActionStatusViewModel
     public partial ObservableCollection<BlogUploadFile> DraftAttachments { get; set; }
 
     [ObservableProperty]
+    [NotifyPropertyChangedFor(nameof(ReaderArticle))]
+    [NotifyPropertyChangedFor(nameof(ReaderAuthor))]
     public partial BlogPostDto? SelectedPost { get; set; }
 
+    [ObservableProperty]
+    public partial bool IsEditing { get; set; }
+
+    [ObservableProperty]
+    public partial string? ReaderBaseUrl { get; private set; }
+
+    public string ReaderArticle => ReaderBaseUrl is not null ? SelectedPost?.Article ?? string.Empty : string.Empty;
+    public string ReaderAuthor => SelectedPost?.Author?.UserName ?? SelectedPost?.AuthorId ?? string.Empty;
+
+    private readonly BlogResourceService _resources = new();
+
+    [RelayCommand]
+    private void NewPost()
+    {
+        if (IsDraftModified)
+        {
+            this.SetWarningStatus("Enregistrez vos modifications avant de créer un autre billet.");
+            return;
+        }
+        SelectedPost = null;
+        DraftTitle = string.Empty;
+        DraftArticle = string.Empty;
+        DraftAttachments.Clear();
+        _pendingAttachmentLinks.Clear();
+        DraftIsPublished = false;
+        MarkDraftSaved();
+        IsEditing = true;
+    }
+
+    [RelayCommand]
+    private void EditPost() => IsEditing = true;
+
+    [RelayCommand]
+    private void ReadPost()
+    {
+        IsEditing = false;
+        UpdateReader();
+    }
+
+    [RelayCommand]
+    private async Task OpenResourceAsync(string? link)
+    {
+        try
+        {
+            IsBusy = true;
+            var uri = BlogResourceService.Resolve(link ?? string.Empty,
+                Settings.Authentication.Authority, ReaderAuthor);
+            if (BlogResourceService.IsUserResource(uri, Settings.Authentication.Authority))
+            {
+                this.SetInfoStatus("Détection du type de fichier...");
+                var mime = await _resources.GetMimeTypeAsync(uri);
+                if (mime.StartsWith("video/", StringComparison.OrdinalIgnoreCase)
+                    && !OperatingSystem.IsBrowser() && !OperatingSystem.IsAndroid() && !OperatingSystem.IsIOS())
+                {
+                    await ((App)Application.Current!).PushPageAsync(new VideoPageViewModel(uri, mime));
+                    this.SetInfoStatus($"Vidéo : {mime}");
+                    return;
+                }
+                this.SetInfoStatus($"Ouverture dans le navigateur ({mime}).");
+            }
+            var topLevel = TopLevel.GetTopLevel(((App)Application.Current!).View!)
+                ?? throw new InvalidOperationException("La fenêtre de l'application est indisponible.");
+            if (!await topLevel.Launcher.LaunchUriAsync(uri))
+                throw new InvalidOperationException("Le système n'a pas pu ouvrir ce lien.");
+        }
+        catch (Exception ex)
+        {
+            this.SetErrorStatus($"Impossible d'ouvrir le lien : {ex.Message}");
+        }
+        finally
+        {
+            IsBusy = false;
+        }
+    }
+
     [ObservableProperty]
     public partial bool IsBusy { get; set; }
 
@@ -258,6 +337,7 @@ public partial class BlogsViewModel : ViewModelBase, IActionStatusViewModel
             }
 
             await RefreshPostsAsync();
+            UpdateReader();
         });
     }
 
@@ -503,12 +583,14 @@ public partial class BlogsViewModel : ViewModelBase, IActionStatusViewModel
     /// <see cref="BlogApiClient"/>. Production code uses the
     /// (Settings, BlogApiClient) overload below.
     /// </summary>
-    public BlogsViewModel(BlogApiClient blogClient, Settings? settings = null, IServiceProvider? services = null)
+    public BlogsViewModel(BlogApiClient blogClient, Settings? settings = null, IServiceProvider? services = null,
+        BlogResourceService? resources = null)
     {
         WindowTitle = "Blog";
         SettingsModel = new Settings();
         BlogClient = blogClient ?? throw new ArgumentNullException(nameof(blogClient)); ;
         Services = services;
+        _resources = resources ?? new BlogResourceService();
         Init(settings);
     }
 
@@ -523,6 +605,9 @@ public partial class BlogsViewModel : ViewModelBase, IActionStatusViewModel
 
     partial void OnSelectedPostChanged(BlogPostDto? value)
     {
+        UpdateReader();
+        if (!_preserveDraft)
+            IsEditing = false;
         if (_preserveDraft) return;
         // Mirror the selection into the editor buffer so the
         // XAML-bound TextBox/TextEditor show the right content
@@ -542,6 +627,25 @@ public partial class BlogsViewModel : ViewModelBase, IActionStatusViewModel
         UpdateCommandStates();
     }
 
+    private void UpdateReader()
+    {
+        string? baseUrl = null;
+        try
+        {
+            if (SelectedPost is not null)
+                baseUrl = BlogResourceService.GetUserBaseUri(
+                    Settings.Authentication.Authority, ReaderAuthor).AbsoluteUri;
+        }
+        catch (Exception ex) when (ex is ArgumentException or InvalidOperationException or UriFormatException)
+        {
+            this.SetErrorStatus($"Impossible de résoudre les ressources du billet : {ex.Message}");
+        }
+        ReaderBaseUrl = baseUrl;
+        OnPropertyChanged(nameof(SelectedPost));
+        OnPropertyChanged(nameof(ReaderArticle));
+        OnPropertyChanged(nameof(ReaderAuthor));
+    }
+
     partial void OnIsBusyChanged(bool value) => UpdateCommandStates();
 
     // Save's CanExecute depends on the buffer: the button must

src/PostIt/PostIt/ViewModels/Blogs/VideoPageViewModel.cs

@@ -0,0 +1,12 @@
+using System;
+
+namespace PostIt.ViewModels;
+
+public sealed class VideoPageViewModel(Uri source, string mimeType) : ViewModelBase
+{
+    public Uri Source { get; } = source;
+    public string MimeType { get; } = mimeType;
+    public string Title => Uri.UnescapeDataString(System.IO.Path.GetFileName(Source.AbsolutePath));
+    public override bool CanNavigateNext { get => false; protected set { } }
+    public override bool CanNavigatePrevious { get => true; protected set { } }
+}

src/PostIt/PostIt/Views/Blogs/BlogsPage.axaml

@@ -2,13 +2,12 @@
   x:Class="PostIt.Views.Blogs.BlogsPage"
   xmlns="https://github.com/avaloniaui"
   xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-  xmlns:AvaloniaEdit="clr-namespace:AvaloniaEdit;assembly=AvaloniaEdit"
   xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
   xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
-  xmlns:md="using:MarkdownViewer.Core.Controls"
+  xmlns:reader="clr-namespace:Markdown.Avalonia;assembly=Markdown.Avalonia"
+  xmlns:services="using:PostIt.Services"
   xmlns:models="using:Yavsc.Blogspot"
   xmlns:postitControls="using:PostIt.Controls"
-  xmlns:views="using:PostIt.Views.Blogs"
   xmlns:vm="using:PostIt.ViewModels"
   HorizontalAlignment="Stretch"
   VerticalAlignment="Stretch"
@@ -25,7 +24,7 @@
     </Style>
   </ContentPage.Styles>
   <Grid
-    RowDefinitions="Auto,Auto,*"
+    RowDefinitions="Auto,Auto,*,Auto"
     Margin="5,5,10,5"
     HorizontalAlignment="Stretch"
     VerticalAlignment="Stretch">
@@ -36,23 +35,30 @@
         <TextBlock
           FontSize="20"
           FontWeight="SemiBold"
-          Text="Blog Posts" />
+          Text="Billets de blog" />
         <TextBox
           HorizontalAlignment="Right"
-          PlaceholderText="Filter by title or author..."
+          PlaceholderText="Rechercher un titre ou un auteur..."
           Text="{Binding SearchText, Mode=TwoWay}" />
       </WrapPanel>
       <CommandBar x:Name="BlogsCommandBar"
        Grid.Row="1"
        HorizontalAlignment="Right" IsDynamicOverflowEnabled="True">
         <CommandBar.PrimaryCommands>
-          <CommandBarButton Command="{Binding RefreshAsync}" Label="Refresh">
+          <CommandBarButton Command="{Binding RefreshCommand}" Label="Actualiser">
             <CommandBarButton.Icon>
               <PathIcon Data="{StaticResource RefreshIcon}" />
             </CommandBarButton.Icon>
           </CommandBarButton>
+          <CommandBarButton x:Name="NewPostButton" Command="{Binding NewPostCommand}" Label="Nouveau billet" />
+          <CommandBarButton x:Name="ReadPostButton" Command="{Binding ReadPostCommand}"
+                            IsVisible="{Binding IsEditing}" Label="Lire" />
+          <CommandBarButton x:Name="EditPostButton" Command="{Binding EditPostCommand}"
+                            IsEnabled="{Binding SelectedPost, Converter={x:Static ObjectConverters.IsNotNull}}"
+                            IsVisible="{Binding !IsEditing}" Label="Modifier" />
           <CommandBarButton
             x:Name="SaveButton"
+            IsVisible="{Binding IsEditing}"
             Command="{Binding SaveCommand}"
             Classes.modified="{Binding IsDraftModified}"
             IsEnabled="{Binding !IsBusy}"
@@ -61,13 +67,14 @@
               <PathIcon Data="{StaticResource SaveIcon}" />
             </CommandBarButton.Icon>
           </CommandBarButton>
-          <CommandBarButton Command="{Binding DeleteAsync}" Label="Delete">
+          <CommandBarButton Command="{Binding DeleteCommand}" IsVisible="{Binding IsEditing}" Label="Supprimer">
             <CommandBarButton.Icon>
               <PathIcon Data="{StaticResource DeleteIcon}" />
             </CommandBarButton.Icon>
           </CommandBarButton>
           <CommandBarButton
             x:Name="AddAttachmentButton"
+            IsVisible="{Binding IsEditing}"
             Click="AddAttachment_Click"
             IsEnabled="{Binding !IsBusy}"
             Label="Ajouter fichiers">
@@ -77,6 +84,7 @@
           </CommandBarButton>
           <CommandBarButton
             x:Name="ManageAclButton"
+            IsVisible="{Binding IsEditing}"
             Command="{Binding ManageAclAsync}"
             Label="ACL">
             <CommandBarButton.Icon>
@@ -92,6 +100,7 @@
             </CommandBarButton.Icon>
           </CommandBarButton>
           <CommandBarToggleButton
+            IsVisible="{Binding IsEditing}"
             Command="{Binding TogglePublishCommand}"
             IsChecked="{Binding DraftIsPublished, Mode=TwoWay}"
             Label="Publié">
@@ -99,13 +108,14 @@
               <PathIcon Data="{StaticResource PublishedIcon}" />
             </CommandBarToggleButton.Icon>
           </CommandBarToggleButton>
-          <CommandBarToggleButton IsChecked="{Binding IsMarkdownViewerVisible, Mode=TwoWay}" Label="Aperçu">
+          <CommandBarToggleButton IsVisible="{Binding IsEditing}" IsChecked="{Binding IsMarkdownViewerVisible, Mode=TwoWay}" Label="Aperçu">
             <CommandBarToggleButton.Icon>
               <PathIcon Data="{StaticResource MarkdownIcon}" />
             </CommandBarToggleButton.Icon>
           </CommandBarToggleButton>
           <CommandBarButton
             x:Name="OpenSignatureDevButton"
+            IsVisible="{Binding IsEditing}"
             Command="{Binding OpenSignatureDevAsync}"
             Label="[DEV] Signature">
             <CommandBarButton.Icon>
@@ -173,7 +183,8 @@
           HorizontalAlignment="Stretch"
           ResizeDirection="Rows" />
 
-        <Grid
+        <Grid x:Name="PostEditor"
+          IsVisible="{Binding IsEditing}"
           Grid.Row="2"
           HorizontalAlignment="Stretch"
           VerticalAlignment="Stretch"
@@ -183,7 +194,6 @@
             <RowDefinition Height="Auto" />
             <RowDefinition Height="*" />
             <RowDefinition Height="Auto" />
-            <RowDefinition Height="Auto" />
           </Grid.RowDefinitions>
           <Grid.ColumnDefinitions>
             <ColumnDefinition Width="*" />
@@ -226,9 +236,37 @@
             </StackPanel>
           </Border>
 
-          <postitControls:StatusBar Grid.Row="4" DataContext="{Binding ActionStatus}" x:Name="StatusBar" />
-
+        </Grid>
+        <Grid x:Name="PostReader" Grid.Row="2" IsVisible="{Binding !IsEditing}"
+              RowDefinitions="Auto,Auto,*" MaxWidth="900" HorizontalAlignment="Stretch" RowSpacing="12">
+          <TextBlock Text="{Binding SelectedPost.Title}" FontSize="28" FontWeight="SemiBold"
+                     TextWrapping="Wrap" />
+          <WrapPanel Grid.Row="1" Orientation="Horizontal"
+                     IsVisible="{Binding SelectedPost, Converter={x:Static ObjectConverters.IsNotNull}}">
+            <TextBlock Text="{Binding ReaderAuthor}" Margin="0,0,16,0" />
+            <TextBlock Text="{Binding SelectedPost.DateModified, StringFormat='Mis à jour le {0:dd/MM/yyyy HH:mm}'}"
+                       Opacity="0.65" />
+          </WrapPanel>
+          <reader:MarkdownScrollViewer x:Name="ArticleReader" Grid.Row="2"
+                                       AssetPathRoot="{Binding ReaderBaseUrl}"
+                                       Markdown="{Binding ReaderArticle}"
+                                       SaveScrollValueWhenContentUpdated="False">
+            <reader:MarkdownScrollViewer.Plugins>
+              <reader:MdAvPlugins>
+                <reader:MdAvPlugins.PathResolver>
+                  <services:BlogImageResolver />
+                </reader:MdAvPlugins.PathResolver>
+              </reader:MdAvPlugins>
+            </reader:MarkdownScrollViewer.Plugins>
+            <reader:MarkdownScrollViewer.Engine>
+              <reader:Markdown HyperlinkCommand="{Binding ((vm:BlogsViewModel)DataContext).OpenResourceCommand, ElementName=ArticleReader}" />
+            </reader:MarkdownScrollViewer.Engine>
+          </reader:MarkdownScrollViewer>
+          <TextBlock Grid.RowSpan="3" IsVisible="{Binding SelectedPost, Converter={x:Static ObjectConverters.IsNull}}"
+                     Text="Choisissez un billet dans la liste pour le lire."
+                     HorizontalAlignment="Center" VerticalAlignment="Center" TextWrapping="Wrap" />
         </Grid>
       </Grid>
+      <postitControls:StatusBar Grid.Row="3" DataContext="{Binding ActionStatus}" x:Name="StatusBar" />
   </Grid>
 </ContentPage>

src/PostIt/PostIt/Views/Blogs/BlogsPage.axaml.cs

@@ -14,15 +14,12 @@ public partial class BlogsPage : ContentPage
         InitializeComponent();
     }
 
-    protected override void OnApplyTemplate(TemplateAppliedEventArgs e)
+    protected override async void OnApplyTemplate(TemplateAppliedEventArgs e)
     {
         base.OnApplyTemplate(e);
         if (DataContext is ViewModels.BlogsViewModel vm)
         {
-            if (!vm.IsLoaded)
-            {
-                vm.RefreshAsync().Wait();
-            }
+            await vm.InitializeAsync();
         }
     }
 

src/PostIt/PostIt/Views/Blogs/VideoPage.axaml

@@ -0,0 +1,19 @@
+<ContentPage
+    x:Class="PostIt.Views.Blogs.VideoPage"
+    xmlns="https://github.com/avaloniaui"
+    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+    xmlns:vlc="clr-namespace:LibVLCSharp.Avalonia;assembly=LibVLCSharp.Avalonia"
+    xmlns:vm="using:PostIt.ViewModels"
+    x:DataType="vm:VideoPageViewModel">
+    <Grid RowDefinitions="Auto,*,Auto,Auto" Margin="16" RowSpacing="12">
+        <TextBlock Text="{Binding Title}" FontSize="22" TextWrapping="Wrap" />
+        <Border Grid.Row="1" Background="Black">
+            <vlc:VideoView x:Name="Video" />
+        </Border>
+        <StackPanel Grid.Row="2" Orientation="Horizontal" Spacing="12">
+            <Button x:Name="PlayButton" Content="Lire / Pause" Click="PlayPause_Click" />
+            <Button Content="Ouvrir dans le navigateur" Click="OpenExternal_Click" />
+        </StackPanel>
+        <TextBlock x:Name="PlaybackStatus" Grid.Row="3" TextWrapping="Wrap" />
+    </Grid>
+</ContentPage>

src/PostIt/PostIt/Views/Blogs/VideoPage.axaml.cs

@@ -0,0 +1,108 @@
+using System;
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Interactivity;
+using Avalonia.Threading;
+using LibVLCSharp.Shared;
+using PostIt.ViewModels;
+
+namespace PostIt.Views.Blogs;
+
+public partial class VideoPage : ContentPage
+{
+    private LibVLC? _libVlc;
+    private MediaPlayer? _player;
+    private Media? _media;
+
+    public VideoPage() => InitializeComponent();
+
+    protected override void OnNavigatedTo(NavigatedToEventArgs e)
+    {
+        base.OnNavigatedTo(e);
+        ReleasePlayer();
+        if (DataContext is not VideoPageViewModel vm)
+            return;
+        try
+        {
+            Core.Initialize();
+            _libVlc = new LibVLC();
+            _player = new MediaPlayer(_libVlc);
+            _player.EncounteredError += Player_EncounteredError;
+            _media = new Media(_libVlc, vm.Source);
+            Video.MediaPlayer = _player;
+            PlayButton.IsEnabled = true;
+            PlaybackStatus.Text = vm.MimeType;
+            if (!_player.Play(_media))
+                PlaybackStatus.Text = "Impossible de démarrer la vidéo. Vous pouvez l'ouvrir dans le navigateur.";
+        }
+        catch (Exception ex) when (ex is VLCException or DllNotFoundException or EntryPointNotFoundException
+            or BadImageFormatException or PlatformNotSupportedException)
+        {
+            ReleasePlayer();
+            PlaybackStatus.Text = $"Lecture vidéo indisponible : {ex.Message}. Vérifiez l'installation de LibVLC.";
+        }
+    }
+
+    protected override void OnNavigatedFrom(NavigatedFromEventArgs e)
+    {
+        ReleasePlayer();
+        base.OnNavigatedFrom(e);
+    }
+
+    protected override void OnDetachedFromVisualTree(VisualTreeAttachmentEventArgs e)
+    {
+        ReleasePlayer();
+        base.OnDetachedFromVisualTree(e);
+    }
+
+    private void ReleasePlayer()
+    {
+        PlayButton.IsEnabled = false;
+        Video.MediaPlayer = null;
+        if (_player is not null)
+        {
+            _player.EncounteredError -= Player_EncounteredError;
+            _player.Stop();
+            _player.Dispose();
+            _player = null;
+        }
+        _media?.Dispose();
+        _media = null;
+        _libVlc?.Dispose();
+        _libVlc = null;
+    }
+
+    private void Player_EncounteredError(object? sender, EventArgs e)
+        => Dispatcher.UIThread.Post(() =>
+        {
+            if (ReferenceEquals(sender, _player))
+                PlaybackStatus.Text = "Impossible de lire cette vidéo. Vous pouvez l'ouvrir dans le navigateur.";
+        });
+
+    private void PlayPause_Click(object? sender, RoutedEventArgs e)
+    {
+        if (_player is null || _media is null)
+            return;
+        if (_player.IsPlaying)
+            _player.Pause();
+        else if (!_player.Play())
+            PlaybackStatus.Text = "Impossible de reprendre la vidéo.";
+    }
+
+    private async void OpenExternal_Click(object? sender, RoutedEventArgs e)
+    {
+        if (DataContext is not VideoPageViewModel vm)
+            return;
+        try
+        {
+            var topLevel = TopLevel.GetTopLevel(this)
+                ?? throw new InvalidOperationException("La fenêtre de lecture est indisponible.");
+            if (!await topLevel.Launcher.LaunchUriAsync(vm.Source))
+                PlaybackStatus.Text = "Impossible d'ouvrir le navigateur.";
+        }
+        catch (Exception ex)
+        {
+            PlaybackStatus.Text = $"Impossible d'ouvrir le navigateur : {ex.Message}";
+        }
+    }
+}