// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System;
using Microsoft.AspNetCore.HeaderPropagation;
using Microsoft.Extensions.Options;

namespace Microsoft.Extensions.DependencyInjection
{
    /// <summary>
    /// <see cref="IHttpClientBuilder"/> extension methods for <see cref="HeaderPropagationMiddleware"/> which propagates request headers to an <see cref="System.Net.Http.HttpClient"/>.
    /// </summary>
    public static class HeaderPropagationHttpClientBuilderExtensions
    {
        /// <summary>
        /// Adds a message handler for propagating headers collected by the <see cref="HeaderPropagationMiddleware"/> to a outgoing request.
        /// </summary>
        /// <remarks>
        /// When using this method, all the configured headers will be applied to the outgoing HTTP requests.
        /// </remarks>
        /// <param name="builder">The <see cref="IHttpClientBuilder"/> to add the message handler to.</param>
        /// <returns>The <see cref="IHttpClientBuilder"/> so that additional calls can be chained.</returns>
        public static IHttpClientBuilder AddHeaderPropagation(this IHttpClientBuilder builder)
        {
            if (builder == null)
            {
                throw new ArgumentNullException(nameof(builder));
            }

            builder.Services.AddHeaderPropagation();

            builder.AddHttpMessageHandler(services =>
            {
                var options = new HeaderPropagationMessageHandlerOptions();
                var middlewareOptions = services.GetRequiredService<IOptions<HeaderPropagationOptions>>();
                for (var i = 0; i < middlewareOptions.Value.Headers.Count; i++)
                {
                    var header = middlewareOptions.Value.Headers[i];
                    options.Headers.Add(header.CapturedHeaderName, header.CapturedHeaderName);
                }
                return new HeaderPropagationMessageHandler(options, services.GetRequiredService<HeaderPropagationValues>());
            });

            return builder;
        }

        /// <summary>
        /// Adds a message handler for propagating headers collected by the <see cref="HeaderPropagationMiddleware"/> to a outgoing request,
        /// explicitly specifying which headers to propagate.
        /// </summary>
        /// <remarks>This also allows to redefine the name to use for a header in the outgoing request.</remarks>
        /// <param name="builder">The <see cref="IHttpClientBuilder"/> to add the message handler to.</param>
        /// <param name="configure">A delegate used to configure the <see cref="HeaderPropagationMessageHandlerOptions"/>.</param>
        /// <returns>The <see cref="IHttpClientBuilder"/> so that additional calls can be chained.</returns>
        public static IHttpClientBuilder AddHeaderPropagation(this IHttpClientBuilder builder, Action<HeaderPropagationMessageHandlerOptions> configure)
        {
            if (builder == null)
            {
                throw new ArgumentNullException(nameof(builder));
            }

            if (configure == null)
            {
                throw new ArgumentNullException(nameof(configure));
            }

            builder.Services.AddHeaderPropagation();

            builder.AddHttpMessageHandler(services =>
            {
                var options = new HeaderPropagationMessageHandlerOptions();
                configure(options);
                return new HeaderPropagationMessageHandler(options, services.GetRequiredService<HeaderPropagationValues>());
            });

            return builder;
        }
    }
}
