using System;
using System.Configuration;
using System.IdentityModel.Tokens;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Security.Claims;
using System.ServiceModel.Security.Tokens;
using System.Threading;
using System.Threading.Tasks;
using iiie.Authentication.DBO;

namespace iiie.Authentication.Business.JWT
{
    /// <summary>
    /// Handler for token authentication
    /// </summary>
    public abstract class TokenValidationHandler
         : DelegatingHandler
    {
        /// <summary>
        /// Gets the token from the HTTP AUthorization header
        /// </summary>
        /// <param name="request">The HTTP request</param>
        /// <param name="token">The variable to store the token</param>
        /// <returns>True if the token has been found, false otherwise</returns>
        private static bool TryRetrieveToken(HttpRequestMessage request, out string token)
        {
            token = null;
            var auth = request.Headers.Authorization;
            if (auth == null || auth.Scheme != "Bearer")
                return false;
            token = auth.Parameter;
            return true;
        }

        /// <summary>
        /// Contructs a user dbo from the specified username and salt
        /// </summary>
        /// <param name="username">The username of the verified token</param>
        /// <param name="salt">The salt in the token</param>
        /// <returns>The user dbo, or null if user is not valid</returns>
        protected abstract BasicUserDbo GetUserDbo(string username, string salt);

        /// <summary>
        /// Attempts to verify user token
        /// </summary>
        /// <param name="request">The HTTP request</param>
        /// <param name="cancellationToken">Token used for cancelation</param>
        /// <returns>The HTTP response</returns>
        protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
        {
            HttpStatusCode statusCode;
            string token;

            if (!TryRetrieveToken(request, out token))
            {
                return base.SendAsync(request, cancellationToken);
            }

            try
            {
                JwtSecurityTokenHandler tokenHandler = new JwtSecurityTokenHandler
                {
                    Configuration = new SecurityTokenHandlerConfiguration()
                    {
                        MaxClockSkew = new TimeSpan(0, 1, 0)
                    }
                };

                var stringValidator = ConfigurationManager.AppSettings["StringValidator"];
                TokenValidationParameters validationParameters = new TokenValidationParameters()
                {
                    RequireSignedTokens = true,
                    RequireExpirationTime = true,
                    ValidAudience = stringValidator,
                    ValidateIssuerSigningKey = true,
                    ValidIssuer = "urn:" + stringValidator,
                    IssuerSigningToken = new BinarySecretSecurityToken(Convert.FromBase64String(ConfigurationManager.AppSettings["CredentialKey"]))
                };

                SecurityToken validateToken;
                ClaimsPrincipal claim = tokenHandler.ValidateToken(token, validationParameters, out validateToken);
                Thread.CurrentPrincipal = claim;

                var name = ((ClaimsIdentity)claim.Identity).Claims.FirstOrDefault(x => x.Type == ClaimTypes.Name);
                var salt = ((ClaimsIdentity)claim.Identity).Claims.FirstOrDefault(x => x.Type == ClaimTypes.Authentication);

                if (name == null || salt == null)
                    statusCode = HttpStatusCode.Unauthorized;
                else
                {
                    var user = GetUserDbo(name.Value, salt.Value);
                    if (user == null)
                        statusCode = HttpStatusCode.Unauthorized;
                    else
                    {
                        UserStorage.BasicUserDbo = user;
                        return base.SendAsync(request, cancellationToken);
                    }
                }
            }
            catch (Exception e)
            {
                statusCode = HttpStatusCode.Unauthorized;
            }
            return Task<HttpResponseMessage>.Factory.StartNew(() =>
               new HttpResponseMessage(statusCode), cancellationToken);
        }
    }
}