public async Task <IActionResult> OnPostAsync(string id)
        {
            // Get the current user.
            var user = await _userManager.GetUserAsync(User);

            // Check if there isn't any ID provided.
            if (string.IsNullOrEmpty(id))
            {
                // Display a message.
                TempData["StatusMessage"] = "Error: No ID has been provided.";
                // Redirect to the index page.
                return(RedirectToPage("/Content/DatabaseTypes/PPI/Created/Analyses/Index"));
            }
            // Get the items with the provided ID.
            var items = _context.Analyses
                        .Where(item => item.AnalysisDatabases.Any(item1 => item1.Database.DatabaseType.Name == "PPI"))
                        .Where(item => item.IsPublic || item.AnalysisUsers.Any(item1 => item1.User == user))
                        .Where(item => item.Id == id);

            // Check if there were no items found.
            if (items == null || !items.Any())
            {
                // Display a message.
                TempData["StatusMessage"] = "Error: No item has been found with the provided ID, or you don't have access to it.";
                // Redirect to the index page.
                return(RedirectToPage("/Content/DatabaseTypes/PPI/Created/Analyses/Index"));
            }
            // Define the view.
            View = new ViewModel
            {
                Analysis = items
                           .Include(item => item.AnalysisUsers)
                           .ThenInclude(item => item.User)
                           .Include(item => item.AnalysisUserInvitations)
                           .First()
            };
            // Check if the user does not exist.
            if (user == null)
            {
                // Display a message.
                TempData["StatusMessage"] = "Error: You need to be logged in to add a user to the analysis.";
                // Redirect to the index page.
                return(RedirectToPage("/Content/DatabaseTypes/PPI/Created/Analyses/Details/Accounts/Users/Index", new { id = View.Analysis.Id }));
            }
            // Check if the reCaptcha is valid.
            if (!await _reCaptchaChecker.IsValid(Input.ReCaptchaToken))
            {
                // Add an error to the model.
                ModelState.AddModelError(string.Empty, "The reCaptcha verification failed.");
                // Return the page.
                return(Page());
            }
            // Check if the provided model is not valid.
            if (!ModelState.IsValid)
            {
                // Add an error to the model.
                ModelState.AddModelError(string.Empty, "An error was encountered. Please check again the input fields.");
                // Return the page.
                return(Page());
            }
            // Check if the provided e-mail address already has access to the network.
            if (View.Analysis.AnalysisUsers.Any(item => item.User.Email == Input.Email) || View.Analysis.AnalysisUserInvitations.Any(item => item.Email == Input.Email))
            {
                // Add an error to the model.
                ModelState.AddModelError(string.Empty, "The user with the provided e-mail already has access to the network.");
                // Return the page.
                return(Page());
            }
            // Try to get the user with the provided e-mail address.
            var userToAdd = _context.Users
                            .FirstOrDefault(item => item.Email == Input.Email);

            // Check if any user has been found.
            if (userToAdd != null)
            {
                // Define a new task.
                var task = new AnalysisUsersTask
                {
                    Items = new List <AnalysisUserInputModel>
                    {
                        new AnalysisUserInputModel
                        {
                            Analysis = new AnalysisInputModel
                            {
                                Id = View.Analysis.Id
                            },
                            User = new UserInputModel
                            {
                                Id = userToAdd.Id
                            }
                        }
                    }
                };
                // Try to run the task.
                try
                {
                    // Run the task.
                    await task.CreateAsync(_serviceProvider, CancellationToken.None);
                }
                catch (Exception exception)
                {
                    // Add an error to the model.
                    ModelState.AddModelError(string.Empty, exception.Message);
                    // Redisplay the page.
                    return(Page());
                }
            }
            else
            {
                // Define a new task.
                var task = new AnalysisUserInvitationsTask
                {
                    Items = new List <AnalysisUserInvitationInputModel>
                    {
                        new AnalysisUserInvitationInputModel
                        {
                            Analysis = new AnalysisInputModel
                            {
                                Id = View.Analysis.Id
                            },
                            Email = Input.Email
                        }
                    }
                };
                // Try to run the task.
                try
                {
                    // Run the task.
                    await task.CreateAsync(_serviceProvider, CancellationToken.None);
                }
                catch (Exception exception)
                {
                    // Add an error to the model.
                    ModelState.AddModelError(string.Empty, exception.Message);
                    // Redisplay the page.
                    return(Page());
                }
            }
            // Define the view model for the e-mail.
            var emailAddedToAnalysisViewModel = new EmailAddedToAnalysisViewModel
            {
                Email          = user.Email,
                Name           = View.Analysis.Name,
                Url            = _linkGenerator.GetUriByPage(HttpContext, "/Content/DatabaseTypes/PPI/Created/Analyses/Details/Index", handler: null, values: new { id = View.Analysis.Id }),
                AddedEmail     = Input.Email,
                ApplicationUrl = _linkGenerator.GetUriByPage(HttpContext, "/Index", handler: null, values: null)
            };
            // Send the defined e-mails.
            await _emailSender.SendAddedToAnalysisEmailAsync(emailAddedToAnalysisViewModel);

            // Define the view model for the e-mail.
            var emailWasAddedToAnalysisViewModel = new EmailWasAddedToAnalysisViewModel
            {
                Email          = Input.Email,
                Name           = View.Analysis.Name,
                Url            = _linkGenerator.GetUriByPage(HttpContext, "/Content/DatabaseTypes/PPI/Created/Analyses/Details/Index", handler: null, values: new { id = View.Analysis.Id }),
                AddedByEmail   = user.Email,
                ApplicationUrl = _linkGenerator.GetUriByPage(HttpContext, "/Index", handler: null, values: null)
            };
            // Send the defined e-mails.
            await _emailSender.SendWasAddedToAnalysisEmailAsync(emailWasAddedToAnalysisViewModel);

            // Display a message to the user.
            TempData["StatusMessage"] = "Success: 1 user added successfully to the analysis.";
            // Redirect to the users page.
            return(RedirectToPage("/Content/DatabaseTypes/PPI/Created/Analyses/Details/Accounts/Users/Index", new { id = View.Analysis.Id }));
        }
        public async Task <IActionResult> OnPostAsync()
        {
            // Get the current user.
            var user = await _userManager.GetUserAsync(User);

            // Check if there isn't any ID provided.
            if (string.IsNullOrEmpty(Input.Id))
            {
                // Display a message.
                TempData["StatusMessage"] = "Error: No ID has been provided.";
                // Redirect to the index page.
                return(RedirectToPage("/Content/DatabaseTypes/PPI/Created/Analyses/Index"));
            }
            // Get the items with the provided ID.
            var items = _context.Analyses
                        .Where(item => item.AnalysisDatabases.Any(item1 => item1.Database.DatabaseType.Name == "PPI"))
                        .Where(item => item.IsPublic || item.AnalysisUsers.Any(item1 => item1.User == user))
                        .Where(item => item.Id == Input.Id);

            // Check if there were no items found.
            if (items == null || !items.Any())
            {
                // Display a message.
                TempData["StatusMessage"] = "Error: No item has been found with the provided ID, or you don't have access to it.";
                // Redirect to the index page.
                return(RedirectToPage("/Content/DatabaseTypes/PPI/Created/Analyses/Index"));
            }
            // Define the view.
            View = new ViewModel
            {
                Analysis = items
                           .First()
            };
            // Check if the user does not exist.
            if (user == null)
            {
                // Display a message.
                TempData["StatusMessage"] = "Error: You need to be logged in to remove a user from the analysis.";
                // Redirect to the index page.
                return(RedirectToPage("/Content/DatabaseTypes/PPI/Created/Analyses/Details/Accounts/Users/Index", new { id = View.Analysis.Id }));
            }
            // Get all of the network users and network user invitations.
            var analysisUsers = _context.AnalysisUsers
                                .Include(item => item.User)
                                .Where(item => item.Analysis == View.Analysis)
                                .Where(item => Input.Emails.Contains(item.User.Email))
                                .AsEnumerable();
            var analysisUserInvitations = _context.AnalysisUserInvitations
                                          .Where(item => item.Analysis == View.Analysis)
                                          .Where(item => Input.Emails.Contains(item.Email))
                                          .AsEnumerable();

            // Define the view items.
            View.Items = analysisUsers
                         .Select(item => new ItemModel
            {
                Email           = item.User.Email,
                DateTimeCreated = item.DateTimeCreated
            })
                         .Concat(analysisUserInvitations
                                 .Select(item => new ItemModel
            {
                Email           = item.Email,
                DateTimeCreated = item.DateTimeCreated
            }));
            // Check if there weren't any items found.
            if (View.Items == null || !View.Items.Any())
            {
                // Display a message.
                TempData["StatusMessage"] = "Error: No users have been found with the provided e-mails.";
                // Redirect to the index page.
                return(RedirectToPage("/Content/DatabaseTypes/PPI/Created/Analyses/Details/Accounts/Users/Index", new { id = View.Analysis.Id }));
            }
            // Define the status of the selected items.
            View.IsCurrentUserSelected = View.Items
                                         .Any(item => item.Email == user.Email);
            View.AreAllUsersSelected = !_context.AnalysisUsers
                                       .Where(item => item.Analysis == View.Analysis)
                                       .Select(item => item.User.Email)
                                       .AsEnumerable()
                                       .Except(View.Items.Select(item => item.Email))
                                       .Any();
            // Check if there aren't any emails provided.
            if (Input.Emails == null || !Input.Emails.Any())
            {
                // Display a message.
                TempData["StatusMessage"] = "Error: No or invalid emails have been provided.";
                // Redirect to the index page.
                return(RedirectToPage("/Content/DatabaseTypes/PPI/Created/Analyses/Details/Accounts/Users/Index", new { id = View.Analysis.Id }));
            }
            // Check if the reCaptcha is valid.
            if (!await _reCaptchaChecker.IsValid(Input.ReCaptchaToken))
            {
                // Add an error to the model.
                ModelState.AddModelError(string.Empty, "The reCaptcha verification failed.");
                // Return the page.
                return(Page());
            }
            // Check if the provided model isn't valid.
            if (!ModelState.IsValid)
            {
                // Add an error to the model.
                ModelState.AddModelError(string.Empty, "An error has been encountered. Please check again the input fields.");
                // Redisplay the page.
                return(Page());
            }
            // Save the number of items found.
            var itemCount = analysisUsers.Count() + analysisUserInvitations.Count();
            // Define the new tasks.
            var analysisUsersTask = new AnalysisUsersTask
            {
                Items = analysisUsers.Select(item => new AnalysisUserInputModel
                {
                    Analysis = new AnalysisInputModel
                    {
                        Id = View.Analysis.Id
                    },
                    User = new UserInputModel
                    {
                        Id = item.User.Id
                    }
                })
            };
            var analysisUserInvitationsTask = new AnalysisUserInvitationsTask
            {
                Items = analysisUserInvitations.Select(item => new AnalysisUserInvitationInputModel
                {
                    Analysis = new AnalysisInputModel
                    {
                        Id = View.Analysis.Id
                    },
                    Email = item.Email
                })
            };

            // Try to run the tasks.
            try
            {
                // Run the tasks.
                await analysisUsersTask.DeleteAsync(_serviceProvider, CancellationToken.None);

                await analysisUserInvitationsTask.DeleteAsync(_serviceProvider, CancellationToken.None);
            }
            catch (Exception exception)
            {
                // Add an error to the model.
                ModelState.AddModelError(string.Empty, exception.Message);
                // Redisplay the page.
                return(Page());
            }
            // Check if all of the users have been selected.
            if (View.AreAllUsersSelected && !View.Analysis.IsPublic)
            {
                // Define a new task.
                var task = new BackgroundTask
                {
                    DateTimeCreated = DateTime.UtcNow,
                    Name            = $"{nameof(IContentTaskManager)}.{nameof(IContentTaskManager.DeleteAnalysesAsync)}",
                    IsRecurring     = false,
                    Data            = JsonSerializer.Serialize(new AnalysesTask
                    {
                        Items = new List <AnalysisInputModel>
                        {
                            new AnalysisInputModel
                            {
                                Id = View.Analysis.Id
                            }
                        }
                    })
                };
                // Mark the task for addition.
                _context.BackgroundTasks.Add(task);
                // Save the changes to the database.
                await _context.SaveChangesAsync();

                // Create a new Hangfire background job.
                var jobId = BackgroundJob.Enqueue <IContentTaskManager>(item => item.DeleteAnalysesAsync(task.Id, CancellationToken.None));
                // Display a message.
                TempData["StatusMessage"] = $"Success: A new background job was created to delete 1 analysis.";
                // Redirect to the index page.
                return(RedirectToPage("/Content/DatabaseTypes/PPI/Created/Analyses/Index"));
            }
            // Display a message.
            TempData["StatusMessage"] = $"Success: {itemCount} user{(itemCount != 1 ? "s" : string.Empty)} removed successfully.";
            // Check if the current user was selected.
            if (View.IsCurrentUserSelected && !View.Analysis.IsPublic)
            {
                // Redirect to the index page.
                return(RedirectToPage("/Content/DatabaseTypes/PPI/Created/Analyses/Index"));
            }
            // Redirect to the index page.
            return(RedirectToPage("/Content/DatabaseTypes/PPI/Created/Analyses/Details/Accounts/Users/Index", new { id = View.Analysis.Id }));
        }