using System;
using System.Linq;
using System.Net.Http.Headers;
using System.Security.Claims;
using System.Text;
using System.Threading.Tasks;
using AMWD.Common.AspNetCore.BasicAuthentication;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Filters;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;

namespace Microsoft.AspNetCore.Authorization
{
	/// <summary>
	/// A basic authentication as attribute to use for specific actions.
	/// </summary>
	[AttributeUsage(AttributeTargets.Class | AttributeTargets.Method, AllowMultiple = true, Inherited = true)]
	public class BasicAuthenticationAttribute : Attribute, IAsyncAuthorizationFilter
	{
		/// <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 async Task OnAuthorizationAsync(AuthorizationFilterContext context)
		{
			var logger = context.HttpContext.RequestServices.GetService<ILogger<BasicAuthenticationAttribute>>();
			try
			{
				var validatorResult = await TrySetHttpUser(context);
				bool isAllowAnonymous = context.ActionDescriptor.EndpointMetadata.OfType<AllowAnonymousAttribute>().Any();
				if (isAllowAnonymous)
					return;

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

				var authHeader = AuthenticationHeaderValue.Parse(context.HttpContext.Request.Headers["Authorization"]);
				byte[] decoded = Convert.FromBase64String(authHeader.Parameter);
				string plain = Encoding.UTF8.GetString(decoded);

				// See: https://www.rfc-editor.org/rfc/rfc2617, page 6
				string username = plain.Split(':').First();
				string password = plain[(username.Length + 1)..];

				if (!string.IsNullOrWhiteSpace(Username) && !string.IsNullOrWhiteSpace(Password))
				{
					if (Username == username && Password == password)
						return;
				}

				if (validatorResult == null)
					SetAuthenticateRequest(context);
			}
			catch (Exception ex)
			{
				logger?.LogError(ex, $"Failed to execute the basic authentication attribute: {ex.InnerException?.Message ?? ex.Message}");
				context.Result = new StatusCodeResult(StatusCodes.Status500InternalServerError);
			}
		}

		private void SetAuthenticateRequest(AuthorizationFilterContext context)
		{
			var validator = context.HttpContext.RequestServices.GetService<IBasicAuthenticationValidator>();
			string realm = string.IsNullOrWhiteSpace(Realm)
				? string.IsNullOrWhiteSpace(validator?.Realm)
					? null
					: validator.Realm
				: Realm;

			context.HttpContext.Response.Headers["WWW-Authenticate"] = "Basic";
			if (!string.IsNullOrWhiteSpace(realm))
				context.HttpContext.Response.Headers["WWW-Authenticate"] = $"Basic realm=\"{realm.Trim().Replace("\"", "")}\"";

			context.HttpContext.Response.StatusCode = StatusCodes.Status401Unauthorized;
			context.Result = new StatusCodeResult(StatusCodes.Status401Unauthorized);
		}

		private async Task<ClaimsPrincipal> TrySetHttpUser(AuthorizationFilterContext context)
		{
			var logger = context.HttpContext.RequestServices.GetService<ILogger<BasicAuthenticationAttribute>>();
			try
			{
				if (context.HttpContext.Request.Headers.ContainsKey("Authorization"))
				{
					var authHeader = AuthenticationHeaderValue.Parse(context.HttpContext.Request.Headers["Authorization"]);
					byte[] decoded = Convert.FromBase64String(authHeader.Parameter);
					string plain = Encoding.UTF8.GetString(decoded);

					// See: https://www.rfc-editor.org/rfc/rfc2617, page 6
					string username = plain.Split(':').First();
					string password = plain[(username.Length + 1)..];

					var validator = context.HttpContext.RequestServices.GetService<IBasicAuthenticationValidator>();
					if (validator == null)
						return null;

					var result = await validator.ValidateAsync(username, password, context.HttpContext.GetRemoteIpAddress());
					if (result == null)
						return null;

					context.HttpContext.User = result;
					return result;
				}
				return null;
			}
			catch (Exception ex)
			{
				logger?.LogError(ex, $"Using validator to get HTTP user failed: {ex.InnerException?.Message ?? ex.Message}");
				return null;
			}
		}
	}
}