using System;
using System.Linq;
using System.Net.Http.Headers;
using System.Text;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Http;

namespace AMWD.Common.AspNetCore.BasicAuthentication
{
	/// <summary>
	/// Implements a basic authentication.
	/// </summary>
	public class BasicAuthenticationMiddleware
	{
		private readonly RequestDelegate next;
		private readonly IBasicAuthenticationValidator validator;

		/// <summary>
		/// Initializes a new instance of the <see cref="BasicAuthenticationMiddleware"/> class.
		/// </summary>
		/// <param name="next">The following delegate in the process chain.</param>
		/// <param name="validator">A basic authentication validator.</param>
		public BasicAuthenticationMiddleware(RequestDelegate next, IBasicAuthenticationValidator validator)
		{
			this.next = next;
			this.validator = validator;
		}

		/// <summary>
		/// The delegate invokation.
		/// Performs the authentication check.
		/// </summary>
		/// <param name="httpContext">The corresponding HTTP context.</param>
		/// <returns>An awaitable task.</returns>
		public async Task InvokeAsync(HttpContext httpContext)
		{
			if (!httpContext.Request.Headers.ContainsKey("Authorization"))
			{
				SetAuthenticateRequest(httpContext, validator.Realm);
				return;
			}

			try
			{
				var authHeader = AuthenticationHeaderValue.Parse(httpContext.Request.Headers["Authorization"]);
				byte[] decoded = Convert.FromBase64String(authHeader.Parameter);
				string plain = Encoding.UTF8.GetString(decoded);
				string[] credentials = plain.Split(':', 2, StringSplitOptions.RemoveEmptyEntries);

				var principal = await validator.ValidateAsync(credentials.First(), credentials.Last(), httpContext.GetRemoteIpAddress());
				if (principal == null)
				{
					SetAuthenticateRequest(httpContext, validator.Realm);
					return;
				}

				await next.Invoke(httpContext);
			}
			catch
			{
				SetAuthenticateRequest(httpContext, validator.Realm);
			}
		}

		private static void SetAuthenticateRequest(HttpContext httpContext, string realm)
		{
			httpContext.Response.Headers["WWW-Authenticate"] = "Basic";
			if (!string.IsNullOrWhiteSpace(realm))
				httpContext.Response.Headers["WWW-Authenticate"] += $" realm=\"{realm.Replace("\"", "")}\"";

			httpContext.Response.StatusCode = StatusCodes.Status401Unauthorized;
		}
	}
}