Application Insights Publisher (#281)

* Adds Application Insights publisher

* Change readonly to const

* Update src/Microsoft.FeatureManagement.Telemetry.ApplicationInsights/ApplicationInsightsTelemetryPublisher.cs

Co-authored-by: Jimmy Campbell <jimmyca@microsoft.com>

* Update src/Microsoft.FeatureManagement.Telemetry.ApplicationInsights/ApplicationInsightsTelemetryPublisher.cs

Co-authored-by: Jimmy Campbell <jimmyca@microsoft.com>

---------

Co-authored-by: Jimmy Campbell <jimmyca@microsoft.com>

src/Microsoft.FeatureManagement.Telemetry.ApplicationInsights/ApplicationInsightsTelemetryPublisher.cs

@@ -0,0 +1,70 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+//
+using Microsoft.ApplicationInsights;
+
+namespace Microsoft.FeatureManagement.Telemetry.ApplicationInsights
+{
+    /// <summary>
+    /// Used to publish data from evaluation events to Application Insights
+    /// </summary>
+    public class ApplicationInsightsTelemetryPublisher : ITelemetryPublisher
+    {
+        private const string _eventName = "FeatureEvaluation";
+        private readonly TelemetryClient _telemetryClient;
+
+        public ApplicationInsightsTelemetryPublisher(TelemetryClient telemetryClient)
+        {
+            _telemetryClient = telemetryClient ?? throw new ArgumentNullException(nameof(telemetryClient));
+        }
+
+        /// <summary>
+        /// Publishes a custom event to Application Insights using data from the given evaluation event.
+        /// </summary>
+        /// <param name="evaluationEvent"> The event to publish.</param>
+        /// <param name="cancellationToken"> A cancellation token.</param>
+        /// <returns>Returns a ValueTask that represents the asynchronous operation</returns>
+        public ValueTask PublishEvent(EvaluationEvent evaluationEvent, CancellationToken cancellationToken)
+        {
+            ValidateEvent(evaluationEvent);
+
+            FeatureDefinition featureDefinition = evaluationEvent.FeatureDefinition;
+
+            Dictionary<string, string> properties = new Dictionary<string, string>()
+            {
+                { "FeatureName", featureDefinition.Name },
+                { "IsEnabled", evaluationEvent.IsEnabled.ToString() }
+            };
+
+            if (evaluationEvent.Variant != null)
+            {
+                properties["Variant"] = evaluationEvent.Variant.Name;
+            }
+
+            if (featureDefinition.TelemetryMetadata != null)
+            {
+                foreach (KeyValuePair<string, string> kvp in featureDefinition.TelemetryMetadata)
+                {
+                    properties[kvp.Key] = kvp.Value;
+                }
+            }
+
+            _telemetryClient.TrackEvent(_eventName, properties);
+
+            return new ValueTask();
+        }
+
+        private void ValidateEvent(EvaluationEvent evaluationEvent)
+        {
+            if (evaluationEvent == null)
+            {
+                throw new ArgumentNullException(nameof(evaluationEvent));
+            }
+
+            if (evaluationEvent.FeatureDefinition == null)
+            {
+                throw new ArgumentNullException(nameof(evaluationEvent.FeatureDefinition));
+            }
+        }
+    }
+}

src/Microsoft.FeatureManagement.Telemetry.ApplicationInsights/Microsoft.FeatureManagement.Telemetry.ApplicationInsights.csproj

@@ -0,0 +1,17 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net6.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.ApplicationInsights" Version="2.21.0" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Microsoft.FeatureManagement\Microsoft.FeatureManagement.csproj" />
+  </ItemGroup>
+
+</Project>