using AutoMapper;
using AutoMapper.QueryableExtensions;
using Marco.Pms.DataAccess.Data;
using Marco.Pms.Model.Activities;
using Marco.Pms.Model.Dtos.Project;
using Marco.Pms.Model.Employees;
using Marco.Pms.Model.Entitlements;
using Marco.Pms.Model.MongoDBModels;
using Marco.Pms.Model.Projects;
using Marco.Pms.Model.Utilities;
using Marco.Pms.Model.ViewModels.Employee;
using Marco.Pms.Model.ViewModels.Projects;
using Marco.Pms.Services.Helpers;
using Marco.Pms.Services.Service.ServiceInterfaces;
using MarcoBMS.Services.Helpers;
using MarcoBMS.Services.Service;
using Microsoft.CodeAnalysis;
using Microsoft.EntityFrameworkCore;
using Project = Marco.Pms.Model.Projects.Project;

namespace Marco.Pms.Services.Service
{
    public class ProjectServices : IProjectServices
    {
        private readonly IDbContextFactory<ApplicationDbContext> _dbContextFactory;
        private readonly ApplicationDbContext _context; // Keeping this for direct scoped context use where appropriate
        private readonly ILoggingService _logger;
        private readonly ProjectsHelper _projectsHelper;
        private readonly PermissionServices _permission;
        private readonly CacheUpdateHelper _cache;
        private readonly IMapper _mapper;
        public ProjectServices(
            IDbContextFactory<ApplicationDbContext> dbContextFactory,
            ApplicationDbContext context,
            ILoggingService logger,
            ProjectsHelper projectsHelper,
            PermissionServices permission,
            CacheUpdateHelper cache,
            IMapper mapper)
        {
            _dbContextFactory = dbContextFactory ?? throw new ArgumentNullException(nameof(dbContextFactory));
            _context = context ?? throw new ArgumentNullException(nameof(context));
            _logger = logger ?? throw new ArgumentNullException(nameof(logger));
            _projectsHelper = projectsHelper ?? throw new ArgumentNullException(nameof(projectsHelper));
            _permission = permission ?? throw new ArgumentNullException(nameof(permission));
            _cache = cache ?? throw new ArgumentNullException(nameof(cache));
            _mapper = mapper ?? throw new ArgumentNullException(nameof(mapper));
        }
        #region =================================================================== Project Get APIs ===================================================================

        public async Task<ApiResponse<object>> GetAllProjectsBasicAsync(Guid tenantId, Employee loggedInEmployee)
        {
            try
            {
                // Step 1: Verify the current user
                if (loggedInEmployee == null)
                {
                    return ApiResponse<object>.ErrorResponse("Unauthorized", "User could not be identified.", 401);
                }

                _logger.LogInfo("Basic project list requested by EmployeeId {EmployeeId}", loggedInEmployee.Id);

                // Step 2: Get the list of project IDs the user has access to
                List<Guid> accessibleProjectIds = await _projectsHelper.GetMyProjects(tenantId, loggedInEmployee);

                if (accessibleProjectIds == null || !accessibleProjectIds.Any())
                {
                    _logger.LogInfo("No accessible projects found for EmployeeId {EmployeeId}", loggedInEmployee.Id);
                    return ApiResponse<object>.SuccessResponse(new List<ProjectInfoVM>(), "0 records of project fetchd successfully", 200);
                }

                // Step 3: Fetch project ViewModels using the optimized, cache-aware helper
                var projectVMs = await GetProjectInfosByIdsAsync(accessibleProjectIds);

                // Step 4: Return the final list
                _logger.LogInfo("Successfully returned {ProjectCount} projects for EmployeeId {EmployeeId}", projectVMs.Count, loggedInEmployee.Id);
                return ApiResponse<object>.SuccessResponse(projectVMs, $"{projectVMs.Count} records of project fetchd successfully", 200);
            }
            catch (Exception ex)
            {
                // --- Step 5: Graceful Error Handling ---
                _logger.LogError(ex, "An unexpected error occurred in GetAllProjectsBasic for tenant {TenantId}.", tenantId);
                return ApiResponse<object>.ErrorResponse("An internal server error occurred. Please try again later.", null, 500);
            }
        }

        public async Task<ApiResponse<object>> GetAllProjectsAsync(Guid tenantId, Employee loggedInEmployee)
        {
            try
            {
                _logger.LogInfo("Starting GetAllProjects for TenantId: {TenantId}, User: {UserId}", tenantId, loggedInEmployee.Id);

                // --- Step 1: Get a list of project IDs the user can access ---
                List<Guid> projectIds = await _projectsHelper.GetMyProjects(tenantId, loggedInEmployee);
                if (!projectIds.Any())
                {
                    _logger.LogInfo("User has no assigned projects. Returning empty list.");
                    return ApiResponse<object>.SuccessResponse(new List<ProjectListVM>(), "No projects found for the current user.", 200);
                }

                // --- Step 2: Efficiently handle partial cache hits ---
                _logger.LogInfo("Attempting to fetch details for {ProjectCount} projects from cache.", projectIds.Count);

                // Fetch what we can from the cache.
                var cachedDetails = await _cache.GetProjectDetailsList(projectIds) ?? new List<ProjectMongoDB>();
                var cachedDictionary = cachedDetails.ToDictionary(p => Guid.Parse(p.Id));

                // Identify which projects are missing from the cache.
                var missingIds = projectIds.Where(id => !cachedDictionary.ContainsKey(id)).ToList();

                // Start building the response with the items we found in the cache.
                var responseVms = _mapper.Map<List<ProjectListVM>>(cachedDictionary.Values);

                if (missingIds.Any())
                {
                    // --- Step 3: Fetch ONLY the missing items from the database ---
                    _logger.LogInfo("Cache partial MISS. Found {CachedCount}, fetching {MissingCount} projects from DB.",
                                           cachedDictionary.Count, missingIds.Count);

                    // Call our dedicated data-fetching method for the missing IDs.
                    var newMongoDetails = await FetchAndBuildProjectDetails(missingIds, tenantId);

                    if (newMongoDetails.Any())
                    {
                        // Map the newly fetched items and add them to our response list.
                        responseVms.AddRange(newMongoDetails);
                    }
                }
                else
                {
                    _logger.LogInfo("Cache HIT. All {ProjectCount} projects found in cache.", projectIds.Count);
                }

                // --- Step 4: Return the combined result ---
                _logger.LogInfo("Successfully retrieved a total of {ProjectCount} projects.", responseVms.Count);
                return ApiResponse<object>.SuccessResponse(responseVms, "Projects retrieved successfully.", 200);
            }
            catch (Exception ex)
            {
                // --- Step 5: Graceful Error Handling ---
                _logger.LogError(ex, "An unexpected error occurred in GetAllProjects for tenant {TenantId}.", tenantId);
                return ApiResponse<object>.ErrorResponse("An internal server error occurred. Please try again later.", null, 500);
            }
        }

        public async Task<ApiResponse<object>> GetProjectAsync(Guid id, Guid tenantId, Employee loggedInEmployee)
        {
            try
            {
                // --- Step 1: Run independent operations in PARALLEL ---
                // We can check permissions and fetch data at the same time to reduce latency.
                var permissionTask = _permission.HasProjectPermission(loggedInEmployee, id);

                // This helper method encapsulates the "cache-first, then database" logic.
                var projectDataTask = GetProjectDataAsync(id, tenantId);

                // Await both tasks to complete.
                await Task.WhenAll(permissionTask, projectDataTask);

                var hasPermission = await permissionTask;
                var projectVm = await projectDataTask;

                // --- Step 2: Process results sequentially ---

                // 2a. Check for permission first. Forbid() is the idiomatic way to return 403.
                if (!hasPermission)
                {
                    _logger.LogWarning("Access denied for user {UserId} on project {ProjectId}.", loggedInEmployee.Id, id);
                    return ApiResponse<object>.ErrorResponse("Access Denied.", "You do not have permission to access this project.", 403);
                }

                // 2b. Check if the project was found (either in cache or DB).
                if (projectVm == null)
                {
                    _logger.LogInfo("Project with ID {ProjectId} not found.", id);
                    return ApiResponse<object>.ErrorResponse("Project not found.", $"No project found with ID {id}.", 404);
                }

                // 2c. Success. Return the consistent ViewModel.
                _logger.LogInfo("Successfully retrieved project {ProjectId}.", id);
                return ApiResponse<object>.SuccessResponse(projectVm, "Project retrieved successfully.", 200);
            }
            catch (Exception ex)
            {
                _logger.LogError(ex, "An unexpected error occurred while getting project {ProjectId}", id);
                return ApiResponse<object>.ErrorResponse("An internal server error occurred.", null, 500);
            }
        }

        public async Task<ApiResponse<object>> GetProjectDetailsAsync(Guid id, Guid tenantId, Employee loggedInEmployee)
        {
            try
            {
                _logger.LogInfo("Details requested by EmployeeId: {EmployeeId} for ProjectId: {ProjectId}", loggedInEmployee.Id, id);

                // Step 1: Check global view project permission
                var hasViewProjectPermission = await _permission.HasPermission(PermissionsMaster.ViewProject, loggedInEmployee.Id);
                if (!hasViewProjectPermission)
                {
                    _logger.LogWarning("ViewProjects permission denied for EmployeeId: {EmployeeId}", loggedInEmployee.Id);
                    return ApiResponse<object>.ErrorResponse("Access denied", "You don't have permission to view projects", 403);
                }

                // Step 2: Check permission for this specific project
                var hasProjectPermission = await _permission.HasProjectPermission(loggedInEmployee, id);
                if (!hasProjectPermission)
                {
                    _logger.LogWarning("Project-specific access denied. EmployeeId: {EmployeeId}, ProjectId: {ProjectId}", loggedInEmployee.Id, id);
                    return ApiResponse<object>.ErrorResponse("Access denied", "You don't have access to this project", 403);
                }

                // Step 3: Fetch project with status
                var projectDetails = await _cache.GetProjectDetails(id);
                ProjectVM? projectVM = null;
                if (projectDetails == null)
                {
                    var project = await _context.Projects
                    .Include(c => c.ProjectStatus)
                    .FirstOrDefaultAsync(c => c.TenantId == tenantId && c.Id == id);

                    projectVM = _mapper.Map<ProjectVM>(project);

                    if (project != null)
                    {
                        await _cache.AddProjectDetails(project);
                    }
                }
                else
                {
                    projectVM = _mapper.Map<ProjectVM>(projectDetails);
                    if (projectVM.ProjectStatus != null)
                    {
                        projectVM.ProjectStatus.TenantId = tenantId;
                    }
                }

                if (projectVM == null)
                {
                    _logger.LogWarning("Project not found. ProjectId: {ProjectId}", id);
                    return ApiResponse<object>.ErrorResponse("Project not found", "Project not found", 404);
                }

                // Step 4: Return result

                _logger.LogInfo("Project details fetched successfully. ProjectId: {ProjectId}", id);
                return ApiResponse<object>.SuccessResponse(projectVM, "Project details fetched successfully", 200);
            }
            catch (Exception ex)
            {
                // --- Step 5: Graceful Error Handling ---
                _logger.LogError(ex, "An unexpected error occurred in Get Project Details for project {ProjectId} for tenant {TenantId}. ", id, tenantId);
                return ApiResponse<object>.ErrorResponse("An internal server error occurred. Please try again later.", null, 500);
            }
        }

        public async Task<ApiResponse<object>> GetProjectDetailsOldAsync(Guid id, Guid tenantId, Employee loggedInEmployee)
        {
            var project = await _context.Projects
                .Where(c => c.TenantId == tenantId && c.Id == id)
                .Include(c => c.ProjectStatus)
                .SingleOrDefaultAsync();

            if (project == null)
            {
                return ApiResponse<object>.ErrorResponse("Project not found", "Project not found", 404);

            }
            else
            {
                ProjectDetailsVM vm = await GetProjectViewModel(id, project);

                OldProjectVM projectVM = new OldProjectVM();
                if (vm.project != null)
                {
                    projectVM.Id = vm.project.Id;
                    projectVM.Name = vm.project.Name;
                    projectVM.ShortName = vm.project.ShortName;
                    projectVM.ProjectAddress = vm.project.ProjectAddress;
                    projectVM.ContactPerson = vm.project.ContactPerson;
                    projectVM.StartDate = vm.project.StartDate;
                    projectVM.EndDate = vm.project.EndDate;
                    projectVM.ProjectStatusId = vm.project.ProjectStatusId;
                }
                projectVM.Buildings = new List<BuildingVM>();
                if (vm.buildings != null)
                {
                    foreach (Building build in vm.buildings)
                    {
                        BuildingVM buildVM = new BuildingVM() { Id = build.Id, Description = build.Description, Name = build.Name };
                        buildVM.Floors = new List<FloorsVM>();
                        if (vm.floors != null)
                        {
                            foreach (Floor floorDto in vm.floors.Where(c => c.BuildingId == build.Id).ToList())
                            {
                                FloorsVM floorVM = new FloorsVM() { FloorName = floorDto.FloorName, Id = floorDto.Id };
                                floorVM.WorkAreas = new List<WorkAreaVM>();

                                if (vm.workAreas != null)
                                {
                                    foreach (WorkArea workAreaDto in vm.workAreas.Where(c => c.FloorId == floorVM.Id).ToList())
                                    {
                                        WorkAreaVM workAreaVM = new WorkAreaVM() { Id = workAreaDto.Id, AreaName = workAreaDto.AreaName, WorkItems = new List<WorkItemVM>() };

                                        if (vm.workItems != null)
                                        {
                                            foreach (WorkItem workItemDto in vm.workItems.Where(c => c.WorkAreaId == workAreaDto.Id).ToList())
                                            {
                                                WorkItemVM workItemVM = new WorkItemVM() { WorkItemId = workItemDto.Id, WorkItem = workItemDto };

                                                workItemVM.WorkItem.WorkArea = new WorkArea();

                                                if (workItemVM.WorkItem.ActivityMaster != null)
                                                {
                                                    workItemVM.WorkItem.ActivityMaster.Tenant = new Tenant();
                                                }
                                                workItemVM.WorkItem.Tenant = new Tenant();

                                                double todaysAssigned = 0;
                                                if (vm.Tasks != null)
                                                {
                                                    var tasks = vm.Tasks.Where(t => t.WorkItemId == workItemDto.Id).ToList();
                                                    foreach (TaskAllocation task in tasks)
                                                    {
                                                        todaysAssigned += task.PlannedTask;
                                                    }
                                                }
                                                workItemVM.TodaysAssigned = todaysAssigned;

                                                workAreaVM.WorkItems.Add(workItemVM);
                                            }
                                        }

                                        floorVM.WorkAreas.Add(workAreaVM);
                                    }
                                }

                                buildVM.Floors.Add(floorVM);
                            }
                        }
                        projectVM.Buildings.Add(buildVM);
                    }
                }
                return ApiResponse<object>.SuccessResponse(projectVM, "Success.", 200);
            }
        }

        #endregion

        #region =================================================================== Project Manage APIs ===================================================================

        public async Task<ApiResponse<object>> CreateProjectAsync(CreateProjectDto projectDto, Guid tenantId, Employee loggedInEmployee)
        {
            // 1. Prepare data without I/O
            var loggedInUserId = loggedInEmployee.Id;
            var project = _mapper.Map<Project>(projectDto);
            project.TenantId = tenantId;

            // 2. Store it to database
            try
            {
                _context.Projects.Add(project);
                await _context.SaveChangesAsync();
            }
            catch (Exception ex)
            {
                // Log the detailed exception
                _logger.LogError(ex, "Failed to create project in database. Rolling back transaction.");
                // Return a server error as the primary operation failed
                return ApiResponse<object>.ErrorResponse("An error occurred while saving the project.", ex.Message, 500);
            }

            // 3. Perform non-critical side-effects (caching, notifications) concurrently
            try
            {
                // These operations do not depend on each other, so they can run in parallel.
                Task cacheAddDetailsTask = _cache.AddProjectDetails(project);
                Task cacheClearListTask = _cache.ClearAllProjectIdsByPermissionId(PermissionsMaster.ManageProject);

                // Await all side-effect tasks to complete in parallel
                await Task.WhenAll(cacheAddDetailsTask, cacheClearListTask);
            }
            catch (Exception ex)
            {
                // The project was created successfully, but a side-effect failed.
                // Log this as a warning, as the primary operation succeeded. Don't return an error to the user.
                _logger.LogError(ex, "Project {ProjectId} was created, but a post-creation side-effect (caching/notification) failed. ", project.Id);
            }

            // 4. Return a success response to the user as soon as the critical data is saved.
            return ApiResponse<object>.SuccessResponse(_mapper.Map<ProjectDto>(project), "Project created successfully.", 200);
        }

        /// <summary>
        /// Updates an existing project's details.
        /// This endpoint is secure, handles concurrency, and performs non-essential tasks in the background.
        /// </summary>
        /// <param name="id">The ID of the project to update.</param>
        /// <param name="updateProjectDto">The data to update the project with.</param>
        /// <returns>An ApiResponse confirming the update or an appropriate error.</returns>
        public async Task<ApiResponse<object>> UpdateProjectAsync(Guid id, UpdateProjectDto updateProjectDto, Guid tenantId, Employee loggedInEmployee)
        {
            try
            {
                // --- Step 1: Fetch the Existing Entity from the Database ---
                // This is crucial to avoid the data loss bug. We only want to modify an existing record.
                var existingProject = await _context.Projects
                    .Where(p => p.Id == id && p.TenantId == tenantId)
                    .SingleOrDefaultAsync();

                // 1a. Existence Check
                if (existingProject == null)
                {
                    _logger.LogWarning("Attempt to update non-existent project with ID {ProjectId} by user {UserId}.", id, loggedInEmployee.Id);
                    return ApiResponse<object>.ErrorResponse("Project not found.", $"No project found with ID {id}.", 404);
                }

                // 1b. Security Check
                var hasPermission = await _permission.HasProjectPermission(loggedInEmployee, id);
                if (!hasPermission)
                {
                    _logger.LogWarning("Access DENIED for user {UserId} attempting to update project {ProjectId}.", loggedInEmployee.Id, id);
                    return ApiResponse<object>.ErrorResponse("Access Denied.", "You do not have permission to modify this project.", 403);
                }

                // --- Step 2: Apply Changes and Save ---
                // Map the changes from the DTO onto the entity we just fetched from the database.
                // This only modifies the properties defined in the mapping, preventing data loss.
                _mapper.Map(updateProjectDto, existingProject);

                // Mark the entity as modified (if your mapping doesn't do it automatically).
                _context.Entry(existingProject).State = EntityState.Modified;

                try
                {
                    await _context.SaveChangesAsync();
                    _logger.LogInfo("Successfully updated project {ProjectId} by user {UserId}.", id, loggedInEmployee.Id);
                }
                catch (DbUpdateConcurrencyException ex)
                {
                    // --- Step 3: Handle Concurrency Conflicts ---
                    // This happens if another user modified the project after we fetched it.
                    _logger.LogError(ex, "Concurrency conflict while updating project {ProjectId} ", id);
                    return ApiResponse<object>.ErrorResponse("Conflict occurred.", "This project has been modified by someone else. Please refresh and try again.", 409);
                }

                // --- Step 4: Perform Side-Effects (Fire and Forget) ---
                // Create a DTO of the updated project to pass to background tasks.
                var projectDto = _mapper.Map<ProjectDto>(existingProject);

                // 4a. Update Cache
                await UpdateCacheInBackground(existingProject);

                // --- Step 5: Return Success Response Immediately ---
                // The client gets a fast response without waiting for caching or SignalR.
                return ApiResponse<object>.SuccessResponse(projectDto, "Project updated successfully.", 200);
            }
            catch (Exception ex)
            {
                // --- Step 6: Graceful Error Handling for Unexpected Errors ---
                _logger.LogError(ex, "An unexpected error occurred while updating project {ProjectId} ", id);
                return ApiResponse<object>.ErrorResponse("An internal server error occurred.", null, 500);
            }
        }

        #endregion

        #region =================================================================== Project Allocation APIs ===================================================================

        /// <summary>
        /// Retrieves a list of employees for a specific project.
        /// This method is optimized to perform all filtering and mapping on the database server.
        /// </summary>
        /// <param name="projectId">The ID of the project.</param>
        /// <param name="includeInactive">Whether to include employees from inactive allocations.</param>
        /// <param name="tenantId">The ID of the current tenant.</param>
        /// <param name="loggedInEmployee">The current authenticated employee (used for permission checks).</param>
        /// <returns>An ApiResponse containing a list of employees or an error.</returns>
        public async Task<ApiResponse<object>> GetEmployeeByProjectIdAsync(Guid? projectId, bool includeInactive, Guid tenantId, Employee loggedInEmployee)
        {
            // --- Step 1: Input Validation ---
            if (projectId == null)
            {
                _logger.LogWarning("GetEmployeeByProjectID called with a null projectId.");
                // 400 Bad Request is more appropriate for invalid input than 404 Not Found.
                return ApiResponse<object>.ErrorResponse("Project ID is required.", "Invalid Input Parameter", 400);
            }

            _logger.LogInfo("Fetching employees for ProjectID: {ProjectId}, IncludeInactive: {IncludeInactive}", projectId, includeInactive);

            try
            {
                // --- CRITICAL: Security Check  ---
                // Before fetching data, you MUST verify the user has permission to see it.
                // This is a placeholder for your actual permission logic.
                var hasProjectPermission = await _permission.HasProjectPermission(loggedInEmployee, projectId.Value);
                var hasAllEmployeePermission = await _permission.HasPermission(PermissionsMaster.ViewAllEmployees, loggedInEmployee.Id);
                var hasviewTeamPermission = await _permission.HasPermission(PermissionsMaster.ViewTeamMembers, loggedInEmployee.Id);

                if (!(hasProjectPermission && (hasAllEmployeePermission || hasviewTeamPermission)))
                {
                    _logger.LogWarning("Access DENIED for user {UserId} on project {ProjectId}.", loggedInEmployee.Id, projectId);
                    return ApiResponse<object>.ErrorResponse("Access Denied.", "You do not have permission to view this project's team.", 403);
                }

                // --- Step 2: Build a Single, Efficient IQueryable ---
                // We start with the base query and conditionally add filters before executing it.
                // This avoids code duplication and is highly performant.
                var employeeQuery = _context.ProjectAllocations
                    .Where(pa => pa.ProjectId == projectId && pa.TenantId == tenantId);

                // Conditionally apply the filter for active allocations.
                if (!includeInactive)
                {
                    employeeQuery = employeeQuery.Where(pa => pa.IsActive);
                }

                // --- Step 3: Project Directly to the ViewModel on the Database Server ---
                // This is the most significant performance optimization.
                // Instead of fetching full Employee entities, we select only the data needed for the EmployeeVM.
                // AutoMapper's ProjectTo is perfect for this, as it translates the mapping configuration into an efficient SQL SELECT statement.
                var resultVM = await employeeQuery
                    .Where(pa => pa.Employee != null) // Safety check for data integrity
                    .Select(pa => pa.Employee)        // Navigate to the Employee entity
                    .ProjectTo<EmployeeVM>(_mapper.ConfigurationProvider) // Let AutoMapper generate the SELECT
                    .ToListAsync();

                _logger.LogInfo("Successfully fetched {EmployeeCount} employees for project {ProjectId}.", resultVM.Count, projectId);

                // Note: The original mapping loop is now completely gone, replaced by the single efficient query above.

                return ApiResponse<object>.SuccessResponse(resultVM, "Successfully fetched the list of employees for the selected project.", 200);
            }
            catch (Exception ex)
            {
                // --- Step 4: Graceful Error Handling ---
                _logger.LogError(ex, "An error occurred while fetching employees for project {ProjectId}. ", projectId);
                return ApiResponse<object>.ErrorResponse("An internal server error occurred.", "Database Query Failed", 500);
            }
        }

        /// <summary>
        /// Retrieves project allocation details for a specific project.
        /// This method is optimized for performance and includes security checks.
        /// </summary>
        /// <param name="projectId">The ID of the project.</param>
        /// <param name="tenantId">The ID of the current tenant.</param>
        /// <param name="loggedInEmployee">The current authenticated employee for permission checks.</param>
        /// <returns>An ApiResponse containing allocation details or an appropriate error.</returns>
        public async Task<ApiResponse<object>> GetProjectAllocationAsync(Guid? projectId, Guid tenantId, Employee loggedInEmployee)
        {
            // --- Step 1: Input Validation ---
            if (projectId == null)
            {
                _logger.LogWarning("GetProjectAllocation called with a null projectId.");
                return ApiResponse<object>.ErrorResponse("Project ID is required.", "Invalid Input Parameter", 400);
            }

            _logger.LogInfo("Fetching allocations for ProjectID: {ProjectId} for user {UserId}", projectId, loggedInEmployee.Id);

            try
            {
                // --- Step 2: Security and Existence Checks ---
                // Before fetching data, you MUST verify the user has permission to see it.
                // This is a placeholder for your actual permission logic.
                var hasPermission = await _permission.HasProjectPermission(loggedInEmployee, projectId.Value);
                if (!hasPermission)
                {
                    _logger.LogWarning("Access DENIED for user {UserId} on project {ProjectId}.", loggedInEmployee.Id, projectId);
                    return ApiResponse<object>.ErrorResponse("Access Denied.", "You do not have permission to view this project's team.", 403);
                }

                // --- Step 3: Execute a Single, Optimized Database Query ---
                // This query projects directly to a new object on the database server, which is highly efficient.
                var allocations = await _context.ProjectAllocations
                    // Filter down to the relevant records first.
                    .Where(pa => pa.ProjectId == projectId && pa.TenantId == tenantId && pa.Employee != null)
                    // Project directly to the final shape. This tells EF Core which columns to select.
                    // The redundant .Include() is removed as EF Core infers the JOIN from this Select.
                    .Select(pa => new
                    {
                        // Fields from ProjectAllocation
                        ID = pa.Id,
                        pa.EmployeeId,
                        pa.ProjectId,
                        pa.AllocationDate,
                        pa.ReAllocationDate,
                        pa.IsActive,

                        // Fields from the joined Employee table (no null checks needed due to the 'Where' clause)
                        FirstName = pa.Employee!.FirstName,
                        LastName = pa.Employee.LastName,
                        MiddleName = pa.Employee.MiddleName,

                        // Simplified JobRoleId logic: Use the allocation's role if it exists, otherwise fall back to the employee's default role.
                        JobRoleId = pa.JobRoleId ?? pa.Employee.JobRoleId
                    })
                    .ToListAsync();

                _logger.LogInfo("Successfully fetched {AllocationCount} allocations for project {ProjectId}.", allocations.Count, projectId);

                return ApiResponse<object>.SuccessResponse(allocations, "Project allocations retrieved successfully.", 200);
            }
            catch (Exception ex)
            {
                // --- Step 4: Graceful Error Handling ---
                // Log the full exception for debugging, but return a generic, safe error message.
                _logger.LogError(ex, "An error occurred while fetching allocations for project {ProjectId}.", projectId);
                return ApiResponse<object>.ErrorResponse("An internal server error occurred.", "Database query failed.", 500);
            }
        }

        //public async Task<ApiResponse<object>> ManageAllocation(List<ProjectAllocationDot> projectAllocationDot, Guid tenantId, Employee loggedInEmployee)
        //{
        //    if (projectAllocationDot != null)
        //    {
        //        List<object>? result = new List<object>();
        //        List<Guid> employeeIds = new List<Guid>();
        //        List<Guid> projectIds = new List<Guid>();

        //        foreach (var item in projectAllocationDot)
        //        {
        //            try
        //            {
        //                //ProjectAllocation projectAllocation = item.ToProjectAllocationFromProjectAllocationDto(tenantId);
        //                ProjectAllocation projectAllocation = item.ToProjectAllocationFromProjectAllocationDto(tenantId);
        //                ProjectAllocation? projectAllocationFromDb = await _context.ProjectAllocations.Where(c => c.EmployeeId == projectAllocation.EmployeeId
        //                && c.ProjectId == projectAllocation.ProjectId
        //                && c.ReAllocationDate == null
        //                && c.TenantId == tenantId).SingleOrDefaultAsync();

        //                if (projectAllocationFromDb != null)
        //                {
        //                    _context.ProjectAllocations.Attach(projectAllocationFromDb);

        //                    if (item.Status)
        //                    {
        //                        projectAllocationFromDb.JobRoleId = projectAllocation.JobRoleId; ;
        //                        projectAllocationFromDb.IsActive = true;
        //                        _context.Entry(projectAllocationFromDb).Property(e => e.JobRoleId).IsModified = true;
        //                        _context.Entry(projectAllocationFromDb).Property(e => e.IsActive).IsModified = true;
        //                    }
        //                    else
        //                    {
        //                        projectAllocationFromDb.ReAllocationDate = DateTime.Now;
        //                        projectAllocationFromDb.IsActive = false;
        //                        _context.Entry(projectAllocationFromDb).Property(e => e.ReAllocationDate).IsModified = true;
        //                        _context.Entry(projectAllocationFromDb).Property(e => e.IsActive).IsModified = true;

        //                        employeeIds.Add(projectAllocation.EmployeeId);
        //                        projectIds.Add(projectAllocation.ProjectId);
        //                    }
        //                    await _context.SaveChangesAsync();
        //                    var result1 = new
        //                    {
        //                        Id = projectAllocationFromDb.Id,
        //                        EmployeeId = projectAllocation.EmployeeId,
        //                        JobRoleId = projectAllocation.JobRoleId,
        //                        IsActive = projectAllocation.IsActive,
        //                        ProjectId = projectAllocation.ProjectId,
        //                        AllocationDate = projectAllocation.AllocationDate,
        //                        ReAllocationDate = projectAllocation.ReAllocationDate,
        //                        TenantId = projectAllocation.TenantId
        //                    };
        //                    result.Add(result1);
        //                }
        //                else
        //                {
        //                    projectAllocation.AllocationDate = DateTime.Now;
        //                    projectAllocation.IsActive = true;
        //                    _context.ProjectAllocations.Add(projectAllocation);
        //                    await _context.SaveChangesAsync();

        //                    employeeIds.Add(projectAllocation.EmployeeId);
        //                    projectIds.Add(projectAllocation.ProjectId);
        //                }
        //                await _cache.ClearAllProjectIds(item.EmpID);

        //            }
        //            catch (Exception ex)
        //            {
        //                return ApiResponse<object>.ErrorResponse(ex.Message, ex, 400);
        //            }
        //        }

        //        return ApiResponse<object>.SuccessResponse(result, "Data saved successfully", 200);

        //    }
        //    return ApiResponse<object>.ErrorResponse("Invalid details.", "Work Item Details are not valid.", 400);

        //}

        #endregion

        #region =================================================================== Helper Functions ===================================================================

        /// <summary>
        /// Retrieves a list of ProjectInfoVMs by their IDs, using an efficient partial cache-hit strategy.
        /// It fetches what it can from the cache (as ProjectMongoDB), gets the rest from the 
        /// database (as Project), updates the cache, and returns a unified list of ViewModels.
        /// </summary>
        /// <param name="projectIds">The list of project IDs to retrieve.</param>
        /// <returns>A list of ProjectInfoVMs.</returns>
        private async Task<List<ProjectInfoVM>> GetProjectInfosByIdsAsync(List<Guid> projectIds)
        {
            // --- Step 1: Fetch from Cache ---
            // The cache returns a list of MongoDB documents for the projects it found.
            var cachedMongoDocs = await _cache.GetProjectDetailsList(projectIds) ?? new List<ProjectMongoDB>();
            var finalViewModels = _mapper.Map<List<ProjectInfoVM>>(cachedMongoDocs);

            _logger.LogDebug("Cache hit for {CacheCount} of {TotalCount} projects.", finalViewModels.Count, projectIds.Count);

            // --- Step 2: Identify Missing Projects ---
            // If we found everything in the cache, we can return early.
            if (finalViewModels.Count == projectIds.Count)
            {
                return finalViewModels;
            }

            var cachedIds = cachedMongoDocs.Select(p => p.Id).ToHashSet(); // Assuming ProjectMongoDB has an Id
            var missingIds = projectIds.Where(id => !cachedIds.Contains(id.ToString())).ToList();

            // --- Step 3: Fetch Missing from Database ---
            if (missingIds.Any())
            {
                _logger.LogDebug("Cache miss for {MissingCount} projects. Querying database.", missingIds.Count);

                var projectsFromDb = await _context.Projects
                    .Where(p => missingIds.Contains(p.Id))
                    .AsNoTracking() // Use AsNoTracking for read-only query performance
                    .ToListAsync();

                if (projectsFromDb.Any())
                {
                    // Map the newly fetched projects (from SQL) to their ViewModel
                    var vmsFromDb = _mapper.Map<List<ProjectInfoVM>>(projectsFromDb);
                    finalViewModels.AddRange(vmsFromDb);

                    // --- Step 4: Update Cache with Missing Items in a new scope ---
                    _logger.LogDebug("Updating cache with {DbCount} newly fetched projects.", projectsFromDb.Count);
                    await _cache.AddProjectDetailsList(projectsFromDb);
                }
            }

            return finalViewModels;
        }

        private async Task<ProjectDetailsVM> GetProjectViewModel(Guid? id, Project project)
        {
            ProjectDetailsVM vm = new ProjectDetailsVM();

            // List<Building> buildings = _unitOfWork.Building.GetAll(c => c.ProjectId == id).ToList();
            List<Building> buildings = await _context.Buildings.Where(c => c.ProjectId == id).ToListAsync();
            List<Guid> idList = buildings.Select(o => o.Id).ToList();
            // List<Floor> floors = _unitOfWork.Floor.GetAll(c => idList.Contains(c.Id)).ToList();
            List<Floor> floors = await _context.Floor.Where(c => idList.Contains(c.BuildingId)).ToListAsync();
            idList = floors.Select(o => o.Id).ToList();
            //List<WorkArea> workAreas = _unitOfWork.WorkArea.GetAll(c => idList.Contains(c.Id), includeProperties: "WorkItems,WorkItems.ActivityMaster").ToList();

            List<WorkArea> workAreas = await _context.WorkAreas.Where(c => idList.Contains(c.FloorId)).ToListAsync();

            idList = workAreas.Select(o => o.Id).ToList();
            List<WorkItem> workItems = await _context.WorkItems.Include(c => c.WorkCategoryMaster).Where(c => idList.Contains(c.WorkAreaId)).Include(c => c.ActivityMaster).ToListAsync();
            //  List <WorkItem> workItems = _unitOfWork.WorkItem.GetAll(c => idList.Contains(c.WorkAreaId), includeProperties: "ActivityMaster").ToList();
            idList = workItems.Select(t => t.Id).ToList();
            List<TaskAllocation> tasks = await _context.TaskAllocations.Where(t => idList.Contains(t.WorkItemId) && t.AssignmentDate.Date == DateTime.UtcNow.Date).ToListAsync();
            vm.project = project;
            vm.buildings = buildings;
            vm.floors = floors;
            vm.workAreas = workAreas;
            vm.workItems = workItems;
            vm.Tasks = tasks;
            return vm;
        }

        /// <summary>
        /// Fetches project details from the database for a given list of project IDs and assembles them into MongoDB models.
        /// This method encapsulates the optimized, parallel database queries.
        /// </summary>
        /// <param name="projectIdsToFetch">The list of project IDs to fetch.</param>
        /// <param name="tenantId">The current tenant ID for filtering.</param>
        /// <returns>A list of fully populated ProjectMongoDB objects.</returns>
        private async Task<List<ProjectListVM>> FetchAndBuildProjectDetails(List<Guid> projectIdsToFetch, Guid tenantId)
        {
            // Task to get base project details for the MISSING projects
            var projectsTask = Task.Run(async () =>
            {
                using var context = _dbContextFactory.CreateDbContext();
                return await context.Projects.AsNoTracking()
                    .Where(p => projectIdsToFetch.Contains(p.Id) && p.TenantId == tenantId)
                    .ToListAsync();
            });

            // Task to get team sizes for the MISSING projects
            var teamSizesTask = Task.Run(async () =>
            {
                using var context = _dbContextFactory.CreateDbContext();
                return await context.ProjectAllocations.AsNoTracking()
                    .Where(pa => pa.TenantId == tenantId && projectIdsToFetch.Contains(pa.ProjectId) && pa.IsActive)
                    .GroupBy(pa => pa.ProjectId)
                    .Select(g => new { ProjectId = g.Key, Count = g.Count() })
                    .ToDictionaryAsync(x => x.ProjectId, x => x.Count);
            });

            // Task to get work summaries for the MISSING projects
            var workSummariesTask = Task.Run(async () =>
            {
                using var context = _dbContextFactory.CreateDbContext();
                return await context.WorkItems.AsNoTracking()
                    .Where(wi => wi.TenantId == tenantId &&
                                 wi.WorkArea != null &&
                                 wi.WorkArea.Floor != null &&
                                 wi.WorkArea.Floor.Building != null &&
                                 projectIdsToFetch.Contains(wi.WorkArea.Floor.Building.ProjectId))
                    .GroupBy(wi => wi.WorkArea!.Floor!.Building!.ProjectId)
                    .Select(g => new { ProjectId = g.Key, PlannedWork = g.Sum(i => i.PlannedWork), CompletedWork = g.Sum(i => i.CompletedWork) })
                    .ToDictionaryAsync(x => x.ProjectId);
            });

            // Await all parallel tasks to complete
            await Task.WhenAll(projectsTask, teamSizesTask, workSummariesTask);

            var projects = await projectsTask;
            var teamSizes = await teamSizesTask;
            var workSummaries = await workSummariesTask;

            // Proactively update the cache with the items we just fetched.
            _logger.LogInfo("Updating cache with {NewItemCount} newly fetched projects.", projects.Count);
            await _cache.AddProjectDetailsList(projects);

            // This section would build the full ProjectMongoDB objects, similar to your AddProjectDetailsList method.
            // For brevity, assuming you have a mapper or a builder for this. Here's a simplified representation:
            var mongoDetailsList = new List<ProjectListVM>();
            foreach (var project in projects)
            {
                // This is a placeholder for the full build logic from your other methods.
                // In a real scenario, you would fetch all hierarchy levels (buildings, floors, etc.)
                // for the `projectIdsToFetch` and build the complete MongoDB object.
                var mongoDetail = _mapper.Map<ProjectListVM>(project);
                mongoDetail.Id = project.Id;
                mongoDetail.TeamSize = teamSizes.GetValueOrDefault(project.Id, 0);
                if (workSummaries.TryGetValue(project.Id, out var summary))
                {
                    mongoDetail.PlannedWork = summary.PlannedWork;
                    mongoDetail.CompletedWork = summary.CompletedWork;
                }
                mongoDetailsList.Add(mongoDetail);
            }

            return mongoDetailsList;
        }

        /// <summary>
        /// Private helper to encapsulate the cache-first data retrieval logic.
        /// </summary>
        /// <returns>A ProjectDetailVM if found, otherwise null.</returns>
        private async Task<Project?> GetProjectDataAsync(Guid projectId, Guid tenantId)
        {
            // --- Cache First ---
            _logger.LogDebug("Attempting to fetch project {ProjectId} from cache.", projectId);
            var cachedProject = await _cache.GetProjectDetails(projectId);
            if (cachedProject != null)
            {
                _logger.LogInfo("Cache HIT for project {ProjectId}.", projectId);
                // Map from the cache model (e.g., ProjectMongoDB) to the response ViewModel.
                return _mapper.Map<Project>(cachedProject);
            }

            // --- Database Second (on Cache Miss) ---
            _logger.LogInfo("Cache MISS for project {ProjectId}. Fetching from database.", projectId);
            var dbProject = await _context.Projects
                .AsNoTracking() // Use AsNoTracking for read-only queries.
                .Where(p => p.Id == projectId && p.TenantId == tenantId)
                .SingleOrDefaultAsync();

            if (dbProject == null)
            {
                return null; // The project doesn't exist.
            }

            // --- Proactively Update Cache ---
            // The next request for this project will now be a cache hit.
            try
            {
                // Map the DB entity to the cache model (e.g., ProjectMongoDB) before caching.
                await _cache.AddProjectDetails(dbProject);
                _logger.LogInfo("Updated cache with project {ProjectId}.", projectId);
            }
            catch (Exception ex)
            {
                _logger.LogError(ex, "Failed to update cache for project {ProjectId} : ", projectId);
            }

            // Map from the database entity to the response ViewModel.
            return dbProject;
        }

        // Helper method for background cache update
        private async Task UpdateCacheInBackground(Project project)
        {
            try
            {
                // This logic can be more complex, but the idea is to update or add.
                var demo = await _cache.UpdateProjectDetailsOnly(project);
                if (!demo)
                {
                    await _cache.AddProjectDetails(project);
                }
                _logger.LogInfo("Background cache update succeeded for project {ProjectId}.", project.Id);
            }
            catch (Exception ex)
            {
                _logger.LogError(ex, "Background cache update failed for project {ProjectId} ", project.Id);
            }
        }

        #endregion
    }
}