# user interface on the DAG

# applies a new operation to the end of the graph
function push_operation!(graph::DAG, operation::Operation)
   # 1.: Add the operation to the DAG
   push!(graph.operationsToApply, operation)

   return nothing
end

# reverts the latest applied operation, essentially like a ctrl+z for
function pop_operation!(graph::DAG)
   # 1.: Remove the operation from the appliedChain of the DAG
   if !isempty(graph.operationsToApply)
      pop!(graph.operationsToApply)
   elseif !isempty(graph.appliedOperations)
      appliedOp = pop!(graph.appliedOperations)
      revert_operation!(graph, appliedOp)
   else
      error("No more operations to pop!")
   end
   return nothing
end

can_pop(graph::DAG) = !isempty(graph.operationsToApply) || !isempty(graph.appliedOperations)

# reset the graph to its initial state with no operations applied
function reset_graph!(graph::DAG)
   while (can_pop(graph))
      pop_operation!(graph)
   end

   return nothing
end