#!/usr/bin/python

current_sequence=""
previous_sequences=[]
dict={}

class Sequence:
    ''' implement sequence in interface xml'''
    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_step(self, st):
        ''' set current step based on input step name'''
        self.current_step = self.steps.index(st)

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

def previous():
    global current_sequence
    cur_seq = dict[current_sequence]
    if cur_seq.current_step:
        cur_seq.current_step -= 1
        return cur_seq.steps[cur_seq.current_step]
    # current sequence already in first step
    elif previous_sequences:
        current_sequence = previous_sequences.pop()
        cur_seq = dict[current_sequence]
        return cur_seq.steps[cur_seq.current_step]

def next():
    global current_sequence
    cur_seq = dict[current_sequence]
    if cur_seq.current_step < len(cur_seq.steps)-1:
        cur_seq.current_step += 1
        return cur_seq.steps[cur_seq.current_step]
    # current sequence already in last step
    elif previous_sequences:
        current_sequence = previous_sequences.pop()
        cur_seq = dict[current_sequence]
        return cur_seq.steps[cur_seq.current_step]