using Microsoft.AspNetCore.Authentication;
using Microsoft.AspNetCore.Authentication.JwtBearer;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using Microsoft.IdentityModel.Tokens;
using Microsoft.Net.Http.Headers;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Security.Claims;
using System.Text.Encodings.Web;
using System.Threading.Tasks;

namespace PoweredSoft.DynamicJwtBearer
{
    public class DynamicJwtBearerHandler : JwtBearerHandler
    {
        private readonly IDynamicJwtBearerHanderConfigurationResolver dynamicJwtBearerHanderConfigurationResolver;

        public DynamicJwtBearerHandler(IOptionsMonitor<JwtBearerOptions> options, ILoggerFactory logger, UrlEncoder encoder, ISystemClock clock, IDynamicJwtBearerHanderConfigurationResolver dynamicJwtBearerHanderConfigurationResolver) : base(options, logger, encoder, clock)
        {
            this.dynamicJwtBearerHanderConfigurationResolver = dynamicJwtBearerHanderConfigurationResolver;
        }

        /// <summary>
        /// Searches the 'Authorization' header for a 'Bearer' token. If the 'Bearer' token is found, it is validated using <see cref="TokenValidationParameters"/> set in the options.
        /// </summary>
        /// <returns></returns>
        protected override async Task<AuthenticateResult> HandleAuthenticateAsync()
        {
            string token = null;
            try
            {
                // Give application opportunity to find from a different location, adjust, or reject token
                var messageReceivedContext = new MessageReceivedContext(Context, Scheme, Options);

                // event can set the token
                await Events.MessageReceived(messageReceivedContext);
                if (messageReceivedContext.Result != null)
                {
                    return messageReceivedContext.Result;
                }

                // If application retrieved token from somewhere else, use that.
                token = messageReceivedContext.Token;

                if (string.IsNullOrEmpty(token))
                {
                    string authorization = Request.Headers[HeaderNames.Authorization];

                    // If no authorization header found, nothing to process further
                    if (string.IsNullOrEmpty(authorization))
                    {
                        return AuthenticateResult.NoResult();
                    }

                    if (authorization.StartsWith("Bearer ", StringComparison.OrdinalIgnoreCase))
                    {
                        token = authorization.Substring("Bearer ".Length).Trim();
                    }

                    // If no token found, no further work possible
                    if (string.IsNullOrEmpty(token))
                    {
                        return AuthenticateResult.NoResult();
                    }
                }

                var currentConfiguration = await this.dynamicJwtBearerHanderConfigurationResolver.ResolveCurrentOpenIdConfiguration(Context);
                var validationParameters = Options.TokenValidationParameters.Clone();
                if (currentConfiguration != null)
                {
                    var issuers = new[] { currentConfiguration.Issuer };
                    validationParameters.ValidIssuers = validationParameters.ValidIssuers?.Concat(issuers) ?? issuers;

                    validationParameters.IssuerSigningKeys = validationParameters.IssuerSigningKeys?.Concat(currentConfiguration.SigningKeys)
                        ?? currentConfiguration.SigningKeys;
                }

                List<Exception> validationFailures = null;
                SecurityToken validatedToken;
                foreach (var validator in Options.SecurityTokenValidators)
                {
                    if (validator.CanReadToken(token))
                    {
                        ClaimsPrincipal principal;
                        try
                        {
                            principal = validator.ValidateToken(token, validationParameters, out validatedToken);
                        }
                        catch (Exception ex)
                        {
                            Logger.TokenValidationFailed(ex);

                            // Refresh the configuration for exceptions that may be caused by key rollovers. The user can also request a refresh in the event.
                            if (Options.RefreshOnIssuerKeyNotFound && Options.ConfigurationManager != null
                                && ex is SecurityTokenSignatureKeyNotFoundException)
                            {
                                Options.ConfigurationManager.RequestRefresh();
                            }

                            if (validationFailures == null)
                            {
                                validationFailures = new List<Exception>(1);
                            }
                            validationFailures.Add(ex);
                            continue;
                        }

                        Logger.TokenValidationSucceeded();

                        var tokenValidatedContext = new TokenValidatedContext(Context, Scheme, Options)
                        {
                            Principal = principal,
                            SecurityToken = validatedToken
                        };

                        await Events.TokenValidated(tokenValidatedContext);
                        if (tokenValidatedContext.Result != null)
                        {
                            return tokenValidatedContext.Result;
                        }

                        if (Options.SaveToken)
                        {
                            tokenValidatedContext.Properties.StoreTokens(new[]
                            {
                                new AuthenticationToken { Name = "access_token", Value = token }
                            });
                        }

                        tokenValidatedContext.Success();
                        return tokenValidatedContext.Result;
                    }
                }

                if (validationFailures != null)
                {
                    var authenticationFailedContext = new AuthenticationFailedContext(Context, Scheme, Options)
                    {
                        Exception = (validationFailures.Count == 1) ? validationFailures[0] : new AggregateException(validationFailures)
                    };

                    await Events.AuthenticationFailed(authenticationFailedContext);
                    if (authenticationFailedContext.Result != null)
                    {
                        return authenticationFailedContext.Result;
                    }

                    return AuthenticateResult.Fail(authenticationFailedContext.Exception);
                }

                return AuthenticateResult.Fail("No SecurityTokenValidator available for token: " + token ?? "[null]");
            }
            catch (Exception ex)
            {
                Logger.ErrorProcessingMessage(ex);

                var authenticationFailedContext = new AuthenticationFailedContext(Context, Scheme, Options)
                {
                    Exception = ex
                };

                await Events.AuthenticationFailed(authenticationFailedContext);
                if (authenticationFailedContext.Result != null)
                {
                    return authenticationFailedContext.Result;
                }

                throw;
            }
        }
    }
}