FeatureManagementBuilderExtensions.cs

// Copyright (c) Microsoft Corporation.
// Licensed under the MIT license.
//
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.DependencyInjection.Extensions;
using Microsoft.FeatureManagement.FeatureFilters;
using System;
using System.Collections.Generic;
using System.Linq;

namespace Microsoft.FeatureManagement
{
    /// <summary>
    /// Extensions used to add feature management functionality.
    /// </summary>
    public static class FeatureManagementBuilderExtensions
    {
        /// <summary>
        /// Adds an <see cref="ITargetingContextAccessor"/> to be used for targeting and registers the targeting filter 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 WithTargeting<T>(this IFeatureManagementBuilder builder) where T : ITargetingContextAccessor
        {
            //
            // Register the targeting context accessor with the same lifetime as the feature manager
            if (builder.Services.Any(descriptor => descriptor.ServiceType == typeof(IFeatureManager) && descriptor.Lifetime == ServiceLifetime.Scoped))
            {
                builder.Services.TryAddScoped(typeof(ITargetingContextAccessor), typeof(T));
            }
            else
            {
                builder.Services.TryAddSingleton(typeof(ITargetingContextAccessor), typeof(T));
            }

            builder.AddFeatureFilter<TargetingFilter>();

            return builder;
        }

        /// <summary>
        /// Adds a <see cref="VariantServiceProvider{TService}"/> to the feature management system.
        /// </summary>
        /// <param name="builder">The <see cref="IFeatureManagementBuilder"/> used to customize feature management functionality.</param>
        /// <param name="featureName">The feature flag that should be used to determine which variant of the service should be used. The <see cref="VariantServiceProvider{TService}"/> will return different implementations of TService according to the assigned variant.</param>
        /// <returns>A <see cref="IFeatureManagementBuilder"/> that can be used to customize feature management functionality.</returns>
        /// <exception cref="ArgumentNullException">Thrown if feature name parameter is null.</exception>
        /// <exception cref="InvalidOperationException">Thrown if a variant service of the type has already been added.</exception>
        public static IFeatureManagementBuilder WithVariantService<TService>(this IFeatureManagementBuilder builder, string featureName) where TService : class
        {
            if (string.IsNullOrEmpty(featureName))
            {
                throw new ArgumentNullException(nameof(featureName));
            }

            if (builder.Services.Any(descriptor => descriptor.ServiceType == typeof(IVariantServiceProvider<TService>)))
            {
                throw new InvalidOperationException($"A variant service of {typeof(TService).FullName} has already been added.");
            }

            if (builder.Services.Any(descriptor => descriptor.ServiceType == typeof(IFeatureManager) && descriptor.Lifetime == ServiceLifetime.Scoped))
            {
                builder.Services.AddScoped<IVariantServiceProvider<TService>>(sp => new VariantServiceProvider<TService>(
                    featureName,
                    sp.GetRequiredService<IVariantFeatureManager>(),
                    sp));
            }
            else
            {
                builder.Services.AddSingleton<IVariantServiceProvider<TService>>(sp => new VariantServiceProvider<TService>(
                    featureName,
                    sp.GetRequiredService<IVariantFeatureManager>(),
                    sp));
            }

            return builder;
        }

        /// <summary>
        /// Adds a <see cref="FeatureServiceProvider{TService,TEnabled,TDisabled}"/> to the feature management system.
        /// </summary>
        /// <param name="builder">The <see cref="IFeatureManagementBuilder"/> used to customize feature management functionality.</param>
        /// <param name="featureName">The feature flag that should be used to determine which implementation of the service should be used. The <see cref="IFeatureServiceProvider{TService}"/> will return different implementations of TService according to the feature status.</param>
        /// <param name="options">Options used to configure the feature service provider.</param>
        /// <returns>A <see cref="IFeatureManagementBuilder"/> that can be used to customize feature management functionality.</returns>
        /// <exception cref="ArgumentNullException">Thrown if feature name parameter is null.</exception>
        /// <exception cref="InvalidOperationException">Thrown if a feature service of the type has already been added.</exception>
        public static IFeatureManagementBuilder WithFeatureService<TService, TEnabled, TDisabled>(this IFeatureManagementBuilder builder, string featureName, FeatureServiceProviderOptions options = null)
            where TService : class
            where TEnabled : class, TService
            where TDisabled : class, TService
        {
            if (string.IsNullOrEmpty(featureName))
            {
                throw new ArgumentNullException(nameof(featureName));
            }

            options ??= new FeatureServiceProviderOptions();

            if (builder.Services.Any(descriptor => descriptor.ServiceType == typeof(IFeatureServiceProvider<TService>)))
            {
                throw new InvalidOperationException($"A feature service of {typeof(TService).FullName} has already been added.");
            }

            if (builder.Services.Any(descriptor => descriptor.ServiceType == typeof(IFeatureManager) && descriptor.Lifetime == ServiceLifetime.Scoped))
            {
                builder.Services.AddScoped<IFeatureServiceProvider<TService>>(sp => new FeatureServiceProvider<TService, TEnabled, TDisabled>(
                    sp,
                    sp.GetRequiredService<IFeatureManager>(),
                    featureName,
                    options));
            }
            else
            {
                builder.Services.AddSingleton<IFeatureServiceProvider<TService>>(sp => new FeatureServiceProvider<TService, TEnabled, TDisabled>(
                    sp,
                    sp.GetRequiredService<IFeatureManager>(),
                    featureName,
                    options));
            }

            return builder;
        }
    }
}