mws.backend.dotnet/application/Documents/Commands/MoveDocument.cs

using MediatR;
using mws.backend.dotnet.application.Audit;
using mws.backend.dotnet.application.Common;
using mws.backend.dotnet.application.Permissions;
using mws.backend.dotnet.domain.Documents;

namespace mws.backend.dotnet.application.Documents;

public record MoveDocumentCommand(Guid UserId, Guid DocumentId, Guid? NewParentId) : IRequest, IAuditableRequest
{
    public string Action => "Document.Move";
    public string EntityType => "Document";
    public Guid? EntityId => DocumentId;
}

public class MoveDocumentHandler(IUnitOfWork uow, IAuditContext auditContext) : IRequestHandler<MoveDocumentCommand>
{
    public async Task Handle(MoveDocumentCommand command, CancellationToken ct)
    {
        var doc = await DocumentAccess.GetDocumentForUserAsync(uow, command.UserId, command.DocumentId, ct);
        await DocumentAccess.EnsureDocumentPermissionAsync(uow, command.UserId, doc.ProjectId, PermissionAction.Edit, ct);

        if (command.NewParentId == command.DocumentId)
        {
            throw new BadRequestException("A document cannot be moved into itself");
        }

        if (command.NewParentId is { } parentId)
        {
            var parent = await uow.Documents.GetByIdAsync(parentId, ct)
                ?? throw new NotFoundException("Parent folder not found");
            if (parent.ProjectId != doc.ProjectId)
            {
                throw new BadRequestException("Parent must belong to the same project");
            }
            if (parent.Type != DocumentType.Folder)
            {
                throw new BadRequestException("Parent must be a folder");
            }

            var cursor = parent.ParentId;
            while (cursor is not null)
            {
                if (cursor == command.DocumentId)
                {
                    throw new BadRequestException("A folder cannot be moved into its own descendant");
                }
                cursor = await uow.Documents.GetParentIdAsync(cursor.Value, ct);
            }
        }

        doc.ParentId = command.NewParentId;
        doc.UpdatedAt = DateTime.UtcNow;
        doc.UpdatedBy = command.UserId;
        await uow.SaveChangesAsync(ct);

        auditContext.EntityName = doc.Title;
    }
}