Implementation

public class TerminateCourseService : ITerminateCourseService
{
 
  public IVisaTerminationWorkflowService _visaTerminationWorkflow { get; set; }
  public TerminateCourseService()
  {
  }
  
  public ITerminationWorkflowService GetTerminationWorkflow(TerminationReason terminationReason) // because IVisaTerminationWorkflowService inherit from ITerminationWorkflowService
  {
      ITerminationWorkflowService terminationWorkflow = null;
      switch (terminationReason)
      {
          case TerminationReason.VisaCategory:
          case TerminationReason.VisaRenewal:
              terminationWorkflow = _visaTerminationWorkflow;
              break;
      }
      return terminationWorkflow;
  }
  
  public async Task<ServiceResponse<bool>> UpdateVevoStatusWorktray(TerminationReason terminationReason)
  {
      Func<Task<bool>> func = async delegate
      {
          var terminationWorkflow = GetTerminationWorkflow(terminationReason);
          //Trigger the related workflow terminatin process
          var triggerRequestDataDTO = new TriggerRequestDataDTO()
          {
              //IsOnshore = process.IsOnshore,
              TerminateCourseProcessId = process.ProcessRequest_Id,
              TriggerSource = TriggerSource.VevoStatusWorktrayItem,
              WorktrayItemId = vevoStatusDTO.WorkTrayId
          };
          await terminationWorkflow.Trigger(triggerRequestDataDTO);
          return true;
      };
      return await ExecuteAsync(func);
  }
}

parent-child class stucture

***Parent class
public abstract class AbstractTerminationWorkflowService : ITerminationWorkflowService
{
    protected readonly IProcessRequestStatusChangeService<TerminateCourseProcessRequest> _processRequestStatusChangeService;

    public Lazy<IServicesExternalApiConnector> _externalServiceConnector { get; set; }

    public AbstractTerminationWorkflowService(IProcessRequestStatusChangeService<TerminateCourseProcessRequest> processRequestStatusChangeService)
    {
        _processRequestStatusChangeService = processRequestStatusChangeService;
    }
    
    public virtual async Task<bool> Trigger(TriggerRequestDataDTO triggerRequestData)
    {
        throw new NotImplementedException();
    }

    public virtual async Task<DateTime?> GetTriggerDate(ProcessRequest processRequest, CreateTerminateCourseDTO createTerminateCourseDTO)
    {
        throw new NotImplementedException();
    }

    public virtual async Task<bool> TerminateCourseProcessCreated(Guid terminateCourseProcessId)
    {
        throw new NotImplementedException();
    }
    
    protected async Task AddWorktrayItemToSchool(Guid terminationProcessRequestId, string studentNumber) // this is equal to private method here
    {
        throw new NotImplementedException();
    }
}

***Parent class interface
public interface ITerminationWorkflowService
{
    Task<bool> Trigger(TriggerRequestDataDTO triggerRequestData)
    Task<DateTime?> GetTriggerDate(ProcessRequest processRequest, CreateTerminateCourseDTO createTerminateCourseDTO);
    Task<bool> TerminateCourseProcessCreated(Guid terminateCourseProcessId);
}

***Child class
public class VisaTerminationWorkflowService : AbstractTerminationWorkflowService, IVisaTerminationWorkflowService
{       

    public VisaTerminationWorkflowService(IProcessRequestStatusChangeService<TerminateCourseProcessRequest> processRequestStatusChangeService)
    : base(processRequestStatusChangeService) // inherite service from parent


    public override async Task<bool> Trigger(TriggerRequestDataDTO triggerRequestData)
    {
        return await base.Trigger(triggerRequestData);
    }
    
    public override async Task<DateTime?> GetTriggerDate(ProcessRequest processRequest, CreateTerminateCourseDTO createTerminateCourseDTO)
    {
        // use same method in parent class declared in parent interface
        return await base.GetTriggerDate(processRequest, createTerminateCourseDTO);
    }
    
    // use method in the body
    public override async Task<bool> TerminateCourseProcessCreated(Guid terminateCourseProcessId)
    {
        // can directly use protected method from parent class 
        AddWorktrayItemToSchool(terminationProcessRequestId, studentNumber)
        
        var triggerRequestDataDTO = new TriggerRequestDataDTO()
        {
            TerminateCourseProcessId = terminateCourseProcessId,
            TriggerSource = TriggerSource.Expulsion
        };
        return true
    }
}

*** Child class interface
public interface IVisaTerminationWorkflowService : ITerminationWorkflowService
{
}