feat(template-folder): add TemplateFolderService.CreateFolderAsync with validation

src/ScadaLink.TemplateEngine/Services/TemplateFolderService.cs

@@ -0,0 +1,45 @@
+using ScadaLink.Commons.Entities.Templates;
+using ScadaLink.Commons.Interfaces.Repositories;
+using ScadaLink.Commons.Interfaces.Services;
+using ScadaLink.Commons.Types;
+
+namespace ScadaLink.TemplateEngine.Services;
+
+public class TemplateFolderService
+{
+    private readonly ITemplateEngineRepository _repository;
+    private readonly IAuditService _auditService;
+
+    public TemplateFolderService(ITemplateEngineRepository repository, IAuditService auditService)
+    {
+        _repository = repository ?? throw new ArgumentNullException(nameof(repository));
+        _auditService = auditService ?? throw new ArgumentNullException(nameof(auditService));
+    }
+
+    public async Task<Result<TemplateFolder>> CreateFolderAsync(
+        string name, int? parentFolderId, string user,
+        CancellationToken cancellationToken = default)
+    {
+        if (string.IsNullOrWhiteSpace(name))
+            return Result<TemplateFolder>.Failure("Folder name is required.");
+
+        if (parentFolderId.HasValue)
+        {
+            var parent = await _repository.GetFolderByIdAsync(parentFolderId.Value, cancellationToken);
+            if (parent == null)
+                return Result<TemplateFolder>.Failure($"Parent folder with ID {parentFolderId.Value} not found.");
+        }
+
+        var all = await _repository.GetAllFoldersAsync(cancellationToken);
+        if (all.Any(f => f.ParentFolderId == parentFolderId
+                         && string.Equals(f.Name, name, StringComparison.OrdinalIgnoreCase)))
+            return Result<TemplateFolder>.Failure($"A folder named '{name}' already exists at this level.");
+
+        var folder = new TemplateFolder(name) { ParentFolderId = parentFolderId };
+        await _repository.AddFolderAsync(folder, cancellationToken);
+        await _repository.SaveChangesAsync(cancellationToken);
+        await _auditService.LogAsync(user, "Create", "TemplateFolder", folder.Id.ToString(), name, folder, cancellationToken);
+
+        return Result<TemplateFolder>.Success(folder);
+    }
+}