#!/usr/bin/python

class Sequence:
    ''' implement sequence in interface xml'''
    dict={}

    def __init__(self, xml_node):
        self.steps = [ s.attributes["name"].value for s in xml_node.childNodes
                 if s.nodeType == s.ELEMENT_NODE and s.nodeName == "widget" ]
        self.current_step = 0

    def set_current_step(self, st):
        ''' set current step based on input step name'''
        self.current_step = self.steps.index(st)

    @staticmethod
    def set_current_sequence(name):
        Sequence.current_sequence = Sequence.dict[name]

    @staticmethod
    def current():
        return (Sequence.current_sequence, Sequence.current_sequence.steps[Sequence.current_sequence.current_step])

    @staticmethod
    def previous():
        if Sequence.current_sequence.current_step:
            Sequence.current_sequence.current_step -= 1
            return Sequence.current_sequence.steps[Sequence.current_sequence.current_step]

    @staticmethod
    def next():
        if Sequence.current_sequence.current_step < len(Sequence.current_sequence.steps)-1:
            Sequence.current_sequence.current_step += 1
            return Sequence.current_sequence.steps[Sequence.current_sequence.current_step]

def construct(xml_root):
    ''' construct Sequence's static members'''
    for s in xml_root.childNodes:
        if s.nodeType == s.ELEMENT_NODE and s.nodeName == "sequence":
            Sequence.dict[s.attributes["name"].value] = Sequence(s)