Initial implementation of virtual event stream handler for accent colors

src/Nomad/ModifiableAccentColor.cs

@@ -0,0 +1,101 @@
+using Ipfs;
+using OwlCore.ComponentModel;
+using OwlCore.Kubo;
+using OwlCore.Nomad;
+using OwlCore.Nomad.Kubo;
+using WindowsAppCommunity.Sdk.Models;
+
+namespace WindowsAppCommunity.Sdk.Nomad;
+
+/// <inheritdoc cref="IModifiableAccentColor" />
+public class ModifiableAccentColor : NomadKuboEventStreamHandler<ValueUpdateEvent>, IModifiableAccentColor, IDelegable<ReadOnlyAccentColor>
+{
+    /// <inheritdoc />
+    public required ReadOnlyAccentColor Inner { get; init; }
+
+    /// <summary>
+    /// A unique identifier for this instance, persistent across machines and reruns.
+    /// </summary>
+    public required string Id { get; init; }
+
+    /// <inheritdoc />
+    public string? AccentColor => Inner.AccentColor;
+
+    /// <inheritdoc />
+    public event EventHandler<string?>? AccentColorUpdated;
+
+    /// <inheritdoc />
+    public override async Task ApplyEntryUpdateAsync(ValueUpdateEvent updateEvent, CancellationToken cancellationToken)
+    {
+        cancellationToken.ThrowIfCancellationRequested();
+
+        if (updateEvent.TargetId != Id)
+            return;
+
+        string? accentColor = null;
+
+        if (updateEvent is { Unset: false, Value: not null })
+        {
+            (accentColor, _) = await Client.ResolveDagCidAsync<string>(updateEvent.Value!,  nocache: !KuboOptions.UseCache, cancellationToken);
+        }
+
+        await ApplyEntryUpdateAsync(updateEvent, accentColor, cancellationToken);
+    }
+
+    /// <summary>
+    /// Applies an event stream update event and raises the relevant events.
+    /// </summary>
+    /// <param name="updateEvent">The update event to apply.</param>
+    /// <param name="accentColor">The resolved accent color data for this event.</param>
+    /// <param name="cancellationToken">A token that can be used to cancel the ongoing operation.</param>
+    public Task ApplyEntryUpdateAsync(ValueUpdateEvent updateEvent, string? accentColor, CancellationToken cancellationToken)
+    {
+        cancellationToken.ThrowIfCancellationRequested();
+
+        if (updateEvent.EventId is not nameof(UpdateAccentColorAsync))
+            return Task.CompletedTask;
+
+        Inner.Inner.AccentColor = accentColor;
+        AccentColorUpdated?.Invoke(this, accentColor);
+
+        return Task.CompletedTask;
+    }
+
+    /// <inheritdoc cref="INomadKuboEventStreamHandler{TEventEntryContent}.AppendNewEntryAsync" />
+    public override async Task<EventStreamEntry<Cid>> AppendNewEntryAsync(ValueUpdateEvent updateEvent, CancellationToken cancellationToken = default)
+    {
+        // Use extension method for code deduplication (can't use inheritance).
+        var localUpdateEventCid = await Client.Dag.PutAsync(updateEvent, pin: KuboOptions.ShouldPin, cancel: cancellationToken);
+        var newEntry = await this.AppendEventStreamEntryAsync(localUpdateEventCid, updateEvent.EventId, updateEvent.TargetId, cancellationToken);
+        return newEntry;
+    }
+
+    /// <inheritdoc />
+    public override Task ResetEventStreamPositionAsync(CancellationToken cancellationToken)
+    {
+        EventStreamPosition = null;
+        Inner.Inner.AccentColor = null;
+
+        return Task.CompletedTask;
+    }
+
+    /// <inheritdoc />
+    public async Task UpdateAccentColorAsync(string? accentColor, CancellationToken cancellationToken)
+    {
+        bool unset = accentColor is null;
+
+        DagCid? valueCid = null;
+        if (!unset)
+        {
+            Cid cid = await Client.Dag.PutAsync(accentColor!, pin: KuboOptions.ShouldPin, cancel: cancellationToken);
+            valueCid = (DagCid)cid;
+        }
+
+        var updateEvent = new ValueUpdateEvent(Id, nameof(UpdateAccentColorAsync), null, valueCid, unset);
+
+        await ApplyEntryUpdateAsync(updateEvent, accentColor, cancellationToken);
+        var appendedEntry = await AppendNewEntryAsync(updateEvent, cancellationToken);
+
+        EventStreamPosition = appendedEntry;
+    }
+}

src/Nomad/ReadOnlyAccentColor.cs

@@ -0,0 +1,23 @@
+using Ipfs.CoreApi;
+using OwlCore.ComponentModel;
+using WindowsAppCommunity.Sdk.Models;
+
+namespace WindowsAppCommunity.Sdk.Nomad;
+
+/// <inheritdoc cref="IReadOnlyAccentColor" />
+public class ReadOnlyAccentColor : IReadOnlyAccentColor, IDelegable<IAccentColor>
+{
+    /// <summary>
+    /// The client to use for communicating with ipfs.
+    /// </summary>
+    public required ICoreApi Client { get; init; }
+
+    /// <inheritdoc />
+    public required IAccentColor Inner { get; init; }
+
+    /// <inheritdoc />
+    public string? AccentColor => Inner.AccentColor;
+
+    /// <inheritdoc />
+    public event EventHandler<string?>? AccentColorUpdated;
+}