Adds telemetry pipeline (#259)

* Adds telemetry pipeline. Adds evaluationevent, publisher interface, and a publisher instance for app insights.

* Use await insead of .result

* Reverting unused dependency removal

* Update src/Microsoft.FeatureManagement/FeatureDefinition.cs

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

* Update src/Microsoft.FeatureManagement/FeatureDefinition.cs

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

* Update src/Microsoft.FeatureManagement.AppInsightsTelemetryPublisher/TelemetryPublisherAppInsights.cs

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

* Removed factory pattern for publisher DI

* Update src/Microsoft.FeatureManagement/FeatureManager.cs

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

* Resolve misc. comments

* Adjusts descriptions for FeatureDefinition properties

* Rename AppInsights to ApplicationInsights

* Resolves project reference in sln

* Adjusts ServiceCollectionExtensions to use TryAddSingleton

* Removes langversion from .csproj

* Temp

* Adds explicit null checkts before publishing fields to app insights

* Addressing misc. comments

* Removing project reference for example project

* Syncing telemetry and variants

* Adds null check for feature definitions

* Adjusted TelemetryPublishers to no longer be inserted into DI

* Resolving comments

* Removing Application Insights project

* Converts some variables to inline

* Resolving misc. comments

* Moves AddTelemetryPublisher to be an extension method

* Removing IVariantFeatureManager GetFeatureNamesAsync definition, as it should it it's own PR

* Remove unused dependency

* Resolving comments

* Remove invisible character changes

* Remove Dependency Injection package

* Update src/Microsoft.FeatureManagement/FeatureManagerSnapshot.cs

* Update src/Microsoft.FeatureManagement/IVariantFeatureManager.cs

* Persists cancellation token to PublishEvent and adds null check for null publisher collection

* Adds TargetingContext to the EvaluationResult

* Resolving comments

* Removes TargetingContext from EvaluationEvent for now

* Moves tags, etag, and label under 'TelemetryMetadata'

* Adjusts telemetry metadata to already be a flattened dictionary

* Removes bind in favor of ToDictionary. Removes unused using

---------

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

Microsoft.FeatureManagement.sln

@@ -19,7 +19,7 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "ConsoleApp", "examples\Cons
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "TargetingConsoleApp", "examples\TargetingConsoleApp\TargetingConsoleApp.csproj", "{6558C21E-CF20-4278-AA08-EB9D1DF29D66}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "RazorPages", "examples\RazorPages\RazorPages.csproj", "{BA29A1BB-81D5-4EB1-AF37-6ECF64AF27E2}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "RazorPages", "examples\RazorPages\RazorPages.csproj", "{BA29A1BB-81D5-4EB1-AF37-6ECF64AF27E2}"
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Tests.FeatureManagement.AspNetCore", "tests\Tests.FeatureManagement.AspNetCore\Tests.FeatureManagement.AspNetCore.csproj", "{FC0DC3E2-5646-4AEC-A7DB-2D6167BC3BB4}"
 EndProject

src/Microsoft.FeatureManagement/ConfigurationFeatureDefinitionProvider.cs

@@ -148,6 +148,10 @@ We support
 
             var enabledFor = new List<FeatureFilterConfiguration>();
 
+            bool telemetryEnabled = false;
+
+            Dictionary<string, string> telemetryMetadata = null;
+
             string val = configurationSection.Value; // configuration[$"{featureName}"];
 
             if (string.IsNullOrEmpty(val))
@@ -283,6 +287,17 @@ We support
                         variants.Add(variant);
                     }
                 }
+
+                telemetryEnabled = configurationSection.GetValue<bool>("TelemetryEnabled");
+
+                IConfigurationSection telemetryMetadataSection = configurationSection.GetSection("TelemetryMetadata");
+
+                if (telemetryMetadataSection.Exists())
+                {
+                    telemetryMetadata = new Dictionary<string, string>();
+
+                    telemetryMetadata = telemetryMetadataSection.GetChildren().ToDictionary(x => x.Key, x => x.Value);
+                }
             }
 
             return new FeatureDefinition()
@@ -292,7 +307,9 @@ We support
                 RequirementType = requirementType,
                 Status = featureStatus,
                 Allocation = allocation,
-                Variants = variants
+                Variants = variants,
+                TelemetryEnabled = telemetryEnabled,
+                TelemetryMetadata = telemetryMetadata
             };
         }
 

src/Microsoft.FeatureManagement/FeatureDefinition.cs

@@ -42,5 +42,15 @@ public class FeatureDefinition
         /// A list of variant definitions that specify a configuration to return when assigned.
         /// </summary>
         public IEnumerable<VariantDefinition> Variants { get; set; } = Enumerable.Empty<VariantDefinition>();
+
+        /// <summary>
+        /// A flag to enable or disable sending telemetry events to the registered <see cref="ITelemetryPublisher">.
+        /// </summary>
+        public bool TelemetryEnabled { get; set; }
+
+        /// <summary>
+        /// A container for metadata relevant to telemetry.
+        /// </summary>
+        public IReadOnlyDictionary<string, string> TelemetryMetadata { get; set; }
     }
 }

src/Microsoft.FeatureManagement/FeatureManagementBuilderExtensions.cs

@@ -0,0 +1,40 @@
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.FeatureManagement.Telemetry;
+using System;
+using System.Collections.Generic;
+
+namespace Microsoft.FeatureManagement
+{
+    /// <summary>
+    /// Extensions used to add feature management functionality.
+    /// </summary>
+    public static class FeatureManagementBuilderExtensions
+    {
+        /// <summary>
+        /// Adds a telemetry publisher to the feature management system.
+        /// </summary>
+        /// <param name="builder">The <see cref="IFeatureManagementBuilder"/> used to customize feature management functionality.</param>
+        /// <returns>A <see cref="IFeatureManagementBuilder"/> that can be used to customize feature management functionality.</returns>
+        public static IFeatureManagementBuilder AddTelemetryPublisher<T>(this IFeatureManagementBuilder builder) where T : ITelemetryPublisher
+        {
+            builder.AddTelemetryPublisher(sp => ActivatorUtilities.CreateInstance(sp, typeof(T)) as ITelemetryPublisher);
+
+            return builder;
+        }
+
+        private static IFeatureManagementBuilder AddTelemetryPublisher(this IFeatureManagementBuilder builder, Func<IServiceProvider, ITelemetryPublisher> factory)
+        {
+            builder.Services.Configure<FeatureManagementOptions>(options =>
+            {
+                if (options.TelemetryPublisherFactories == null)
+                {
+                    options.TelemetryPublisherFactories = new List<Func<IServiceProvider, ITelemetryPublisher>>();
+                }
+
+                options.TelemetryPublisherFactories.Add(factory);
+            });
+
+            return builder;
+        }
+    }
+}

src/Microsoft.FeatureManagement/FeatureManagementOptions.cs

@@ -1,6 +1,10 @@
 // Copyright (c) Microsoft Corporation.
 // Licensed under the MIT license.
 //
+using Microsoft.FeatureManagement.Telemetry;
+using System;
+using System.Collections.Generic;
+
 namespace Microsoft.FeatureManagement
 {
     /// <summary>
@@ -22,5 +26,11 @@ public class FeatureManagementOptions
         /// The default value is true.
         /// </summary>
         public bool IgnoreMissingFeatures { get; set; } = true;
+
+        /// <summary>
+        /// Holds a collection of factories that can be used to create <see cref="ITelemetryPublisher"/> instances.
+        /// This avoids the need to add the publishers to the service collection.
+        /// </summary>
+        internal ICollection<Func<IServiceProvider, ITelemetryPublisher>> TelemetryPublisherFactories { get; set; }
     }
 }