// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System.Globalization;
using System.Net.Http;
using Microsoft.AspNetCore.HeaderPropagation;
using Microsoft.Extensions.DependencyInjection;
 
namespace Microsoft.AspNetCore.Builder;
 
/// <summary>
/// <see cref="IApplicationBuilder"/> extension methods for <see cref="HeaderPropagationMiddleware"/> which propagates request headers to an <see cref="HttpClient"/>.
/// </summary>
public static class HeaderPropagationApplicationBuilderExtensions
{
    private static readonly string _unableToFindServices = string.Format(
        CultureInfo.CurrentCulture,
        "Unable to find the required services. Please add all the required services by calling '{0}.{1}' inside the call to 'ConfigureServices(...)' in the application startup code.",
        nameof(IServiceCollection),
        nameof(HeaderPropagationServiceCollectionExtensions.AddHeaderPropagation));
 
    /// <summary>
    /// Adds a middleware that collect headers to be propagated to a <see cref="HttpClient"/>.
    /// </summary>
    /// <param name="app">The <see cref="IApplicationBuilder"/> to add the middleware to.</param>
    /// <returns>A reference to the <paramref name="app"/> after the operation has completed.</returns>
    public static IApplicationBuilder UseHeaderPropagation(this IApplicationBuilder app)
    {
        ArgumentNullException.ThrowIfNull(app);
 
        if (app.ApplicationServices.GetService<HeaderPropagationValues>() == null)
        {
            throw new InvalidOperationException(_unableToFindServices);
        }
 
        return app.UseMiddleware<HeaderPropagationMiddleware>();
    }
}