# In the previous model, we used Credit Leading/Following to capture PAYG credit behaviors. Credit Leading basically meant "use your local credit and POST to accessories"

SketchSystems.spec

# In the previous model, we used Credit Leading/Following to capture PAYG credit behaviors. Credit Leading basically meant "use your local credit and POST to accessories"
# and Credit Following meant "be POSTed to by a Leader". The addition of "unlocked" complicated the model due to scenarios where accessories would need to use local credit
# but had no accessories of their own. The concept of a "credit origin" can handle this case, where Leading and Following are now specific cases. When the Credit Origin
# Self, it means "use your local credit"; when it is "External" it means "be POSTed to by an external source".

PAYG Credit Resource Behavior with NXC Links and Credit Origin

  # Initial state
  Credit origin is Self*
    # 'local credit' is what the 'nxp' interface reports for PAYG credit (what it was last updated to by a Nexus message, either keycode or channel)
    new link made -> Change credit origin?
    # let lower layers handle whether or not commanded devices exist (controller, no linked accessories case) / can exist (accessory case)
    any other link event -> Use local credit and update commanded devices
  
  Change credit origin?
    In controller role for new link? -> Credit origin is Self
    In accessory role for new link? -> Credit origin is External
    
  Credit origin is External
    No links -> 0 credit
    Has links but none new -> Use commanded credit
    Unlink -> 0 credit
    New link -> Use commanded credit

  Use local credit and update commanded devices
    Link event -> Credit origin is Self
  
  0 credit
  Use commanded credit

SketchSystems_prototype.js

function render(model){
  let current_state_name = model.active_states[0].name;
  return $("h1",
           {style: {color: "darkBlue"}},
           `The current state is: ${current_state_name}`);
}