Added backups of all data, restorable on another computer (#1008)

Co-authored-by: Thorsten Sommer <SommerEngineering@users.noreply.github.com>

app/Tests/Chat/ChatThreadFilePathTests.cs

@@ -0,0 +1,106 @@
+using AIStudio.Chat;
+
+namespace AIStudio.Tests.Chat;
+
+/// <summary>
+/// Checks that rewriting the file paths of a chat reaches every one of them, and nothing else.
+/// </summary>
+/// <remarks>
+/// Moving a chat, copying it, and writing it into a backup or reading it back all change the paths
+/// a chat stores. A path left out points at a place where the file is no longer, and the file drops
+/// out of the chat without a word: a transcript of the message which is still being written, or an
+/// image the model no longer gets to see.
+/// </remarks>
+[TestFixture]
+public sealed class ChatThreadFilePathTests
+{
+    private static readonly DateTimeOffset START = new(2026, 10, 14, 9, 0, 0, TimeSpan.Zero);
+
+    private static readonly string OLD_DIRECTORY = Path.Combine(Path.GetTempPath(), "old-chat");
+
+    private static readonly string NEW_DIRECTORY = Path.Combine(Path.GetTempPath(), "new-chat");
+
+    [Test]
+    public void EveryPathOfTheChatIsRewritten()
+    {
+        var document = new FileAttachment(FileAttachmentType.DOCUMENT, "report.pdf", Old("report.pdf"), 1024);
+        var transcript = new ManagedTranscriptAttachment("meeting.md", Old("meeting.md"), 512, "meeting.mp3", false);
+        var picture = new FileAttachmentImage("chart.png", Old("chart.png"), 2048);
+        var photo = new ContentImage { SourceType = ContentImageSource.LOCAL_PATH, Source = Old("photo.jpg") };
+        var chat = new ChatThread
+        {
+            ChatId = Guid.NewGuid(),
+            Name = "Quarterly report",
+            Blocks = [Block(new ContentText { Text = "Summarize the report", FileAttachments = [document, transcript, picture] }), Block(photo)],
+        };
+        chat.Draft.AddAttachments([new ManagedTranscriptAttachment("call.md", Old("call.md"), 256, "call.m4a", false)]);
+
+        chat.RewriteFilePaths(Move);
+
+        var message = (ContentText)chat.Blocks[0].Content!;
+        Assert.Multiple(() =>
+        {
+            Assert.That(message.FileAttachments.Select(attachment => attachment.FilePath), Is.EqualTo(new[] { New("report.pdf"), New("meeting.md"), New("chart.png") }));
+            Assert.That(photo.Source, Is.EqualTo(New("photo.jpg")), "The model gets such an image from its path.");
+            Assert.That(chat.Draft.FileAttachments.Select(attachment => attachment.FilePath), Is.EqualTo(new[] { New("call.md") }), "The draft is the one place every path rewrite once forgot.");
+        });
+    }
+
+    [Test]
+    public void WhatTheRewriteLeavesAloneStaysAsItIs()
+    {
+        var elsewhere = new FileAttachment(FileAttachmentType.DOCUMENT, "notes.txt", Path.Combine(Path.GetTempPath(), "elsewhere", "notes.txt"), 64);
+        var linked = new ContentImage { SourceType = ContentImageSource.URL, Source = "https://example.org/chart.png" };
+        var chat = new ChatThread
+        {
+            ChatId = Guid.NewGuid(),
+            Name = "Notes",
+            Blocks = [Block(new ContentText { Text = "Read my notes", FileAttachments = [elsewhere] }), Block(linked)],
+        };
+
+        chat.RewriteFilePaths(Move);
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(((ContentText)chat.Blocks[0].Content!).FileAttachments.Single(), Is.SameAs(elsewhere));
+            Assert.That(linked.Source, Is.EqualTo("https://example.org/chart.png"), "Only an image held by a local path has a path to rewrite.");
+        });
+    }
+
+    [Test]
+    public void AnAttachmentKeepsItsKindAtItsNewPlace()
+    {
+        var transcript = new ManagedTranscriptAttachment("meeting.md", Old("meeting.md"), 512, "meeting.mp3", true);
+        var picture = new FileAttachmentImage("chart.png", Old("chart.png"), 2048);
+        var document = new FileAttachment(FileAttachmentType.DOCUMENT, "report.pdf", Old("report.pdf"), 1024);
+
+        var movedTranscript = transcript.WithFilePath(New("meeting.md"));
+        var movedPicture = picture.WithFilePath(New("chart.png"));
+        var movedDocument = document.WithFilePath(New("report.pdf"));
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(movedTranscript, Is.EqualTo(new ManagedTranscriptAttachment("meeting.md", New("meeting.md"), 512, "meeting.mp3", true)), "A transcript has to stay a transcript, or deleting the chat leaves its file behind.");
+            Assert.That(movedPicture, Is.TypeOf<FileAttachmentImage>());
+            Assert.That(((FileAttachmentImage)movedPicture).Source, Is.EqualTo(New("chart.png")), "The model gets the image from its source, not from its path.");
+            Assert.That(movedPicture.FilePathAsUrl, Is.EqualTo(new FileAttachmentImage("chart.png", New("chart.png"), 2048).FilePathAsUrl), "The preview of the image loads it from there.");
+            Assert.That(movedDocument, Is.EqualTo(new FileAttachment(FileAttachmentType.DOCUMENT, "report.pdf", New("report.pdf"), 1024)));
+        });
+    }
+
+    private static string Old(string fileName) => Path.Combine(OLD_DIRECTORY, fileName);
+
+    private static string New(string fileName) => Path.Combine(NEW_DIRECTORY, fileName);
+
+    private static string Move(string path) => path.StartsWith(OLD_DIRECTORY, StringComparison.Ordinal)
+        ? Path.Combine(NEW_DIRECTORY, Path.GetRelativePath(OLD_DIRECTORY, path))
+        : path;
+
+    private static ContentBlock Block(IContent content) => new()
+    {
+        Time = START,
+        ContentType = content is ContentImage ? ContentType.IMAGE : ContentType.TEXT,
+        Content = content,
+        Role = ChatRole.USER,
+    };
+}