"""
Tests for second order centrality.
"""

import pytest
np = pytest.importorskip('numpy')
scipy = pytest.importorskip('scipy')

import networkx as nx
from networkx.testing import almost_equal


class TestSecondOrderCentrality(object):

    def test_empty(self):
        with pytest.raises(nx.NetworkXException):
            G = nx.empty_graph()
            nx.second_order_centrality(G)

    def test_non_connected(self):
        with pytest.raises(nx.NetworkXException):
            G = nx.Graph()
            G.add_node(0)
            G.add_node(1)
            nx.second_order_centrality(G)

    def test_non_negative_edge_weights(self):
        with pytest.raises(nx.NetworkXException):
            G = nx.path_graph(2)
            G.add_edge(0, 1, weight=-1)
            nx.second_order_centrality(G)

    def test_one_node_graph(self):
        """Second order centrality: single node"""
        G = nx.Graph()
        G.add_node(0)
        G.add_edge(0, 0)
        assert nx.second_order_centrality(G)[0] == 0

    def test_P3(self):
        """Second order centrality: line graph, as defined in paper"""
        G = nx.path_graph(3)
        b_answer = {0: 3.741, 1: 1.414, 2: 3.741}

        b = nx.second_order_centrality(G)

        for n in sorted(G):
            assert almost_equal(b[n], b_answer[n], places=2)

    def test_K3(self):
        """Second order centrality: complete graph, as defined in paper"""
        G = nx.complete_graph(3)
        b_answer = {0: 1.414, 1: 1.414, 2: 1.414}

        b = nx.second_order_centrality(G)

        for n in sorted(G):
            assert almost_equal(b[n], b_answer[n], places=2)

    def test_ring_graph(self):
        """Second order centrality: ring graph, as defined in paper"""
        G = nx.cycle_graph(5)
        b_answer = {0: 4.472, 1: 4.472, 2: 4.472,
                    3: 4.472, 4: 4.472}

        b = nx.second_order_centrality(G)

        for n in sorted(G):
            assert almost_equal(b[n], b_answer[n], places=2)