Add default PostHog SDK client facade

.changeset/tidy-ducks-juggle.md

@@ -0,0 +1,5 @@
+---
+"PostHog": minor
+---
+
+Add the static `PostHogSdk` facade in the `PostHog.Sdk` namespace.

src/PostHog/NoOpPostHogClient.cs

@@ -0,0 +1,139 @@
+using System.Text.Json;
+using PostHog;
+using PostHog.Api;
+using PostHog.Features;
+using PostHog.Json;
+
+namespace PostHog.Sdk;
+
+internal sealed class NoOpPostHogClient : IPostHogClient, IFeatureFlagEvaluationsHost
+{
+    static readonly IReadOnlyDictionary<string, FeatureFlag> EmptyFeatureFlags = new Dictionary<string, FeatureFlag>();
+
+    NoOpPostHogClient()
+    {
+    }
+
+    internal static NoOpPostHogClient Instance { get; } = new();
+
+    public Task<ApiResult> AliasAsync(string previousId, string newId, CancellationToken cancellationToken)
+        => Task.FromResult(new ApiResult(0));
+
+    public Task<ApiResult> IdentifyAsync(
+        string distinctId,
+        Dictionary<string, object>? personPropertiesToSet,
+        Dictionary<string, object>? personPropertiesToSetOnce,
+        CancellationToken cancellationToken)
+        => Task.FromResult(new ApiResult(0));
+
+    public Task<ApiResult> GroupIdentifyAsync(
+        string type,
+        StringOrValue<int> key,
+        Dictionary<string, object>? properties,
+        CancellationToken cancellationToken)
+        => Task.FromResult(new ApiResult(0));
+
+    public Task<ApiResult> GroupIdentifyAsync(
+        string distinctId,
+        string type,
+        StringOrValue<int> key,
+        Dictionary<string, object>? properties,
+        CancellationToken cancellationToken)
+        => Task.FromResult(new ApiResult(0));
+
+    public bool Capture(
+        string distinctId,
+        string eventName,
+        Dictionary<string, object>? properties,
+        GroupCollection? groups,
+        bool sendFeatureFlags,
+        DateTimeOffset? timestamp = null)
+        => false;
+
+    public bool Capture(
+        string distinctId,
+        string eventName,
+        Dictionary<string, object>? properties,
+        GroupCollection? groups,
+        FeatureFlagEvaluations? flags,
+        DateTimeOffset? timestamp = null)
+        => false;
+
+    public bool CaptureException(
+        Exception exception,
+        string distinctId,
+        Dictionary<string, object>? properties,
+        GroupCollection? groups,
+        bool sendFeatureFlags,
+        DateTimeOffset? timestamp = null)
+        => false;
+
+    public bool CaptureException(
+        Exception exception,
+        string distinctId,
+        Dictionary<string, object>? properties,
+        GroupCollection? groups,
+        FeatureFlagEvaluations? flags,
+        DateTimeOffset? timestamp = null)
+        => false;
+
+    public Task<bool> IsFeatureEnabledAsync(
+        string featureKey,
+        string distinctId,
+        FeatureFlagOptions? options,
+        CancellationToken cancellationToken)
+        => Task.FromResult(false);
+
+    public Task<FeatureFlag?> GetFeatureFlagAsync(
+        string featureKey,
+        string distinctId,
+        FeatureFlagOptions? options,
+        CancellationToken cancellationToken)
+        => Task.FromResult<FeatureFlag?>(null);
+
+    public Task<JsonDocument?> GetRemoteConfigPayloadAsync(string key, CancellationToken cancellationToken)
+        => Task.FromResult<JsonDocument?>(null);
+
+    public Task<IReadOnlyDictionary<string, FeatureFlag>> GetAllFeatureFlagsAsync(
+        string distinctId,
+        AllFeatureFlagsOptions? options,
+        CancellationToken cancellationToken)
+        => Task.FromResult(EmptyFeatureFlags);
+
+    public Task<FeatureFlagEvaluations> EvaluateFlagsAsync(
+        string distinctId,
+        AllFeatureFlagsOptions? options,
+        CancellationToken cancellationToken)
+        => Task.FromResult(FeatureFlagEvaluations.Empty(this, distinctId));
+
+    public Task LoadFeatureFlagsAsync(CancellationToken cancellationToken)
+        => Task.CompletedTask;
+
+    public Task FlushAsync()
+        => Task.CompletedTask;
+
+    public string Version => Versioning.VersionConstants.Version;
+
+    public void Dispose()
+    {
+    }
+
+    public ValueTask DisposeAsync()
+        => default;
+
+    void IFeatureFlagEvaluationsHost.CaptureFeatureFlagCalled(
+        string distinctId,
+        string featureKey,
+        EvaluatedFlagRecord? record,
+        GroupCollection? groups,
+        string? requestId,
+        long? evaluatedAt,
+        long? flagDefinitionsLoadedAt,
+        IReadOnlyCollection<string> errors)
+    {
+    }
+
+    void IFeatureFlagEvaluationsHost.LogFilterWarning(string message)
+    {
+    }
+}