Add MicCheck.Client library with FeatureClient.IsEnabledAsync

Client-side SDK for checking feature flag state against the flags API,
with unit tests mocking HttpMessageHandler.

src/MicCheck.Client/Common/Guard.cs

@@ -0,0 +1,40 @@
+namespace MicCheck.Common;
+
+internal static class Guard
+{
+    public static void Null<T>(T t, string parameterName) where T : class
+    {
+        if (t is null)
+            throw new ArgumentNullException(parameterName, $"{nameof(parameterName)} can not be null");
+    }
+
+    public static void Empty(string value, string parameterName)
+    {
+        if (string.IsNullOrWhiteSpace(value))
+            throw new ArgumentException($"{parameterName} can not be empty", parameterName);
+    }
+
+    public static void Empty<T>(IEnumerable<T> collection, string parameterName)
+    {
+        if (collection == null || !collection.Any())
+            throw new ArgumentException($"{parameterName} can not be empty", parameterName);
+    }
+
+    public static void Negative(int value, string parameterName)
+    {
+        if (value < 0)
+            throw new ArgumentOutOfRangeException(parameterName, $"{parameterName} must be a positive number or zero");
+    }
+
+    public static void NegativeOrZero(int value, string parameterName)
+    {
+        if (value <= 0)
+            throw new ArgumentOutOfRangeException(parameterName, $"{nameof(parameterName)} must be a positive number greater then zero");
+    }
+
+    public static void Default<T>(T value, string parameterName)
+    {
+        if (EqualityComparer<T>.Default.Equals(value, default))
+            throw new ArgumentException($"{parameterName} can not be a default value", parameterName);
+    }
+}

src/MicCheck.Client/FeatureClient.cs

@@ -0,0 +1,22 @@
+using System.Net.Http.Json;
+using MicCheck.Common;
+
+namespace MicCheck;
+
+public class FeatureClient(HttpClient httpClient) : IFeatureClient
+{
+    public async Task<bool> IsEnabledAsync(string featureName, bool defaultValue = false, CancellationToken cancellationToken = default)
+    {
+        Guard.Empty(featureName, nameof(featureName));
+
+        var flags = await httpClient.GetFromJsonAsync<List<FlagResult>>("api/v1/flags", cancellationToken);
+        var match = flags?.FirstOrDefault(flag => string.Equals(flag.Feature.Name, featureName, StringComparison.OrdinalIgnoreCase));
+
+        return match?.Enabled ?? defaultValue;
+    }
+}
+
+public interface IFeatureClient
+{
+    Task<bool> IsEnabledAsync(string featureName, bool defaultValue = false, CancellationToken cancellationToken = default);
+}

src/MicCheck.Client/FlagResult.cs

@@ -0,0 +1,5 @@
+namespace MicCheck;
+
+public record FlagResult(int Id, FeatureSummary Feature, bool Enabled, string? FeatureStateValue);
+
+public record FeatureSummary(int Id, string Name, string Type);

src/MicCheck.Client/MicCheck.Client.csproj

@@ -0,0 +1,12 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <LangVersion>latest</LangVersion>
+    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
+    <RootNamespace>MicCheck</RootNamespace>
+  </PropertyGroup>
+
+</Project>