public async Task Index()

in src/CustomerSite/Controllers/HomeController.cs [211:311]
95 lines of code
9 McCabe index (conditional complexity)

    public async Task<IActionResult> Index(string token = null)
    {
        try
        {
            this.logger.Info(HttpUtility.HtmlEncode($"Landing page with token {token}"));
            SubscriptionResult subscriptionDetail = new SubscriptionResult();
            SubscriptionResultExtension subscriptionExtension = new SubscriptionResultExtension();

            this.applicationConfigService.SaveFileToDisk("LogoFile", "contoso-sales.png");
            this.applicationConfigService.SaveFileToDisk("FaviconFile", "favicon.ico");

            if (this.User.Identity.IsAuthenticated)
            {
                var userId = this.userService.AddUser(this.GetCurrentUserDetail());
                var currentUserId = this.userService.GetUserIdFromEmailAddress(this.CurrentUserEmailAddress);
                this.subscriptionService = new SubscriptionService(this.subscriptionRepository, this.planRepository, userId);
                this.logger.Info("User authenticated successfully");
                if (!string.IsNullOrEmpty(token))
                {
                    this.TempData["ShowWelcomeScreen"] = null;
                    token = token.Replace(' ', '+');
                    var newSubscription = await this.apiService.ResolveAsync(token).ConfigureAwait(false);
                    if (newSubscription != null && newSubscription.SubscriptionId != default)
                    {
                        Offers offers = new Offers()
                        {
                            OfferId = newSubscription.OfferId,
                            OfferName = newSubscription.OfferId,
                            UserId = currentUserId,
                            CreateDate = DateTime.Now,
                            OfferGuid = Guid.NewGuid(),
                        };
                        Guid newOfferId = this.offersRepository.Add(offers);

                        var subscriptionPlanDetail = await this.apiService.GetAllPlansForSubscriptionAsync(newSubscription.SubscriptionId).ConfigureAwait(false);
                        subscriptionPlanDetail.ForEach(x =>
                        {
                            x.OfferId = newOfferId;
                            x.PlanGUID = Guid.NewGuid();
                        });
                        this.subscriptionService.AddUpdateAllPlanDetailsForSubscription(subscriptionPlanDetail);

                        var currentPlan = this.planRepository.GetById(newSubscription.PlanId);
                        var subscriptionData = await this.apiService.GetSubscriptionByIdAsync(newSubscription.SubscriptionId).ConfigureAwait(false);
                        var subscribeId = this.subscriptionService.AddOrUpdatePartnerSubscriptions(subscriptionData);
                        if (subscribeId > 0 && subscriptionData.SaasSubscriptionStatus == SubscriptionStatusEnum.PendingFulfillmentStart)
                        {
                            SubscriptionAuditLogs auditLog = new SubscriptionAuditLogs()
                            {
                                Attribute = Convert.ToString(SubscriptionLogAttributes.Status),
                                SubscriptionId = subscribeId,
                                NewValue = SubscriptionStatusEnum.PendingFulfillmentStart.ToString(),
                                OldValue = "None",
                                CreateBy = currentUserId,
                                CreateDate = DateTime.Now,
                            };
                            this.subscriptionLogRepository.Save(auditLog);
                        }

                        subscriptionExtension = this.subscriptionService.GetSubscriptionsBySubscriptionId(newSubscription.SubscriptionId, true);
                        subscriptionExtension.ShowWelcomeScreen = false;
                        subscriptionExtension.CustomerEmailAddress = this.CurrentUserEmailAddress;
                        subscriptionExtension.CustomerName = this.CurrentUserName;
                        subscriptionExtension.SubscriptionParameters = this.subscriptionService.GetSubscriptionsParametersById(newSubscription.SubscriptionId, currentPlan.PlanGuid);
                        subscriptionExtension.IsAutomaticProvisioningSupported = Convert.ToBoolean(this.applicationConfigRepository.GetValueByName("IsAutomaticProvisioningSupported"));
                        subscriptionExtension.AcceptSubscriptionUpdates = Convert.ToBoolean(this.applicationConfigRepository.GetValueByName("AcceptSubscriptionUpdates"));
                    }
                }
                else
                {
                    this.TempData["ShowWelcomeScreen"] = "True";
                    subscriptionExtension.ShowWelcomeScreen = true;
                    return this.View(subscriptionExtension);
                }
            }
            else
            {
                if (!string.IsNullOrEmpty(token))
                {
                    return this.Challenge(
                        new AuthenticationProperties
                        {
                            RedirectUri = "/?token=" + token,
                        }, OpenIdConnectDefaults.AuthenticationScheme);
                }
                else
                {
                    this.TempData["ShowWelcomeScreen"] = "True";
                    subscriptionExtension.ShowWelcomeScreen = true;
                    return this.View(subscriptionExtension);
                }
            }

            return this.View(subscriptionExtension);
        }
        catch (Exception ex)
        {
            this.logger.LogError($"Message:{ex.Message} :: {ex.InnerException}   ");
            return this.View("Error", ex);
        }
    }