using System;
using System.Net.Http.Headers;
using System.Text;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Filters;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;

namespace AMWD.Common.AspNetCore.BasicAuthentication
{
	/// <summary>
	/// A basic authentication as attribute to use for specific actions.
	/// </summary>
	public class BasicAuthenticationAttribute : ActionFilterAttribute
	{
		private readonly ILogger<BasicAuthenticationAttribute> logger;
		private readonly IServiceScopeFactory serviceScopeFactory;

		/// <summary>
		/// Initializes a new instance of the <see cref="BasicAuthenticationAttribute"/> class.
		/// </summary>
		/// <param name="logger">A logger.</param>
		/// <param name="serviceScopeFactory">A service scope factory.</param>
		public BasicAuthenticationAttribute(ILogger<BasicAuthenticationAttribute> logger, IServiceScopeFactory serviceScopeFactory)
		{
			this.logger = logger;
			this.serviceScopeFactory = serviceScopeFactory;
		}

		/// <summary>
		/// Gets or sets a username to validate.
		/// </summary>
		public string Username { get; set; }

		/// <summary>
		/// Gets or sets a password to validate.
		/// </summary>
		public string Password { get; set; }

		/// <summary>
		/// Gets or sets a realm used on authentication header.
		/// </summary>
		public string Realm { get; set; }

		/// <inheritdoc/>
		public override async Task OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next)
		{
			await DoValidation(context);
			await base.OnActionExecutionAsync(context, next);
		}

		private async Task DoValidation(ActionExecutingContext context)
		{
			if (context.Result != null)
				return;

			if (context.HttpContext.Request.Headers.ContainsKey("Authorization"))
			{
				SetAuthenticateRequest(context);
				return;
			}

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

				if (!string.IsNullOrWhiteSpace(Username) && !string.IsNullOrWhiteSpace(Password))
				{
					if (Username == credentials[0] && Password == credentials[1])
						return;
				}

				using var scope = serviceScopeFactory.CreateScope();
				var validator = scope.ServiceProvider.GetService<IBasicAuthenticationValidator>();

				var principal = await validator?.ValidateAsync(credentials[0], credentials[1], context.HttpContext.GetRemoteIpAddress());
				if (principal == null)
					SetAuthenticateRequest(context);
			}
			catch (Exception ex)
			{
				logger.LogError(ex, $"Failed to execute the basic authentication attribute: {ex.Message}");
				context.Result = new StatusCodeResult(StatusCodes.Status500InternalServerError);
			}
		}

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

			context.Result = new UnauthorizedResult();
		}
	}
}