import networkx as nx
import matplotlib.pyplot as plt

##--- networkx utility functions ---------


def dict2nx(aDictGraph):
    """ Converts the given dictionary representation of a graph, 
    aDictGraph, into a networkx DiGraph (directed graph) representation.   
    aDictGraph is a dictionary that maps nodes to its 
    neighbors (successors):  {node:[nodes]}
    A DiGraph object is returned.
    """
    g = nx.DiGraph()
    for node, neighbors in aDictGraph.items():
        g.add_node(node)  # in case there are nodes with no edges
        for neighbor in neighbors:
            g.add_edge(node, neighbor)
    return g


def plot_graph(aDictGraph, plotTitle):
    """  Plots a dictionary representation of a graph,
    aDictGraph, including the given plot title.
    Opens a modal plot window that will stop program execution
    until it is closed.
    """
    plt.title(plotTitle)
    nx.draw_spring(dict2nx(aDictGraph))
    plt.show()

        
#  Test code.   Uncomment the following lines to use    
#dict_graph = { 'a':['b', 'c', 'd'], 'b':['a', 'c'], 'c':['d'], 'd':['a']}    
#plot_graph(dict_graph, "A Test Graph")