#!/usr/local/bin/python3

from typing import List, Mapping

class Node:
    name: str
    deps: List[str] = []

    def __init__(self, name: str, deps: List[str] = []):
        self.name = name
        self.deps = deps


class Nodes:
    nodes: Mapping[str, Node] = []

    def __init__(self, nodes: List[str]):
        self.nodes = nodes

data = Nodes(nodes={
    'a': Node(name='a', deps=['b']),
    'b': Node(name='b', deps=['a']),
})

def dep_resolve(name: str, resolved: List[str], unresolved: List[str) -> None:
    unresolved.append(name)
    node = data.nodes[name]
    for edge in node.deps:
        print(edge)
        if edge not in resolved:
            if edge in unresolved:
                raise Exception('Circular reference detected: %s -> %s' % (name, edge))
            dep_resolve(edge, resolved, unresolved)
    resolved.append(name)
    unresolved.remove(name)


resolved = []
dep_resolve('b', resolved, [])