gistfile1.java

public interface UICommand
{
   public UICommandID getId();

   public void initializeUI(UIContext context) throws Exception;

   public void validate(UIValidationContext context);

   public Result execute(UIContext context) throws Exception;
   
   //leaning TOWARDS list<string>
   //public List<UIInpu<?>t> complete(UIInput<?> value);
   public List<String> complete(UIInput<?> value);
}

public class FooCommand implements UICommand
{
   @Inject
   private UIInput<File> f1;
   @Inject
   private UIInput<String> f2;
   @Inject
   private UIInput<List<File>> arguments;

   @Override
   public UICommandID getId()
   {
      return new SimpleUICommandID("foo", "Do some foo");
   }

   @Override
   public void initializeUI(UIContext context) throws Exception
   {
      f1.setLabel("config-file");
      f1.setRequired(true);
      context.getUIBuilder().add(f1);
      f2.setLabel("value");
      f2.setRequired(false);
      context.getUIBuilder().add(f2);
      
      arguments.setLabel(""); //no labal means its an argument afaik
      arguments.setRequired(true);
      context.getUIBuilder().add(arguments);
   }

   @Override
   public void validate(UIValidationContext context)
   {
   }

   @Override
   public Result execute(UIContext context) throws Exception
   {
      //ignore result for now
      return Results.success("boo");
   }
   
   //I would argue that List<String> would be easier for the user, but List<UIInput<?>> will also work
   //public List<UIInput<?>> complete(UIInput<?> value) {
    public List<String> complete(UIInput<?> value)
     if(value.getName().equals(f1.getName())
       return configFileCompletion(value.getValue());
     else if(value.getName().equals(f2.getName())
       return valueCompletion(value.getValue());
     else if(value.getName().equals(arguments.getName())
       return argumentsCompletion(value.getValue());     
     else
       return null;
   }
   
   private List<String> configFileCompletion(String configValue) {
     //blabla
   } 
   ...
   private List<String> argumentsCompletion(List<File> configValue) {
     //this would not be needed in the final version as æsh would
     //recognize arguments set as Files and use the "default" filehandler.
   }
   
}