from itertools import chain

import pytest

import networkx as nx


class TestIsSemiconnected:
    def test_undirected(self):
        pytest.raises(nx.NetworkXNotImplemented, nx.is_semiconnected, nx.Graph())
        pytest.raises(nx.NetworkXNotImplemented, nx.is_semiconnected, nx.MultiGraph())

    def test_empty(self):
        pytest.raises(nx.NetworkXPointlessConcept, nx.is_semiconnected, nx.DiGraph())
        pytest.raises(
            nx.NetworkXPointlessConcept, nx.is_semiconnected, nx.MultiDiGraph()
        )

    def test_single_node_graph(self):
        G = nx.DiGraph()
        G.add_node(0)
        assert nx.is_semiconnected(G)

    def test_path(self):
        G = nx.path_graph(100, create_using=nx.DiGraph())
        assert nx.is_semiconnected(G)
        G.add_edge(100, 99)
        assert not nx.is_semiconnected(G)

    def test_cycle(self):
        G = nx.cycle_graph(100, create_using=nx.DiGraph())
        assert nx.is_semiconnected(G)
        G = nx.path_graph(100, create_using=nx.DiGraph())
        G.add_edge(0, 99)
        assert nx.is_semiconnected(G)

    def test_tree(self):
        G = nx.DiGraph()
        G.add_edges_from(
            chain.from_iterable([(i, 2 * i + 1), (i, 2 * i + 2)] for i in range(100))
        )
        assert not nx.is_semiconnected(G)

    def test_dumbbell(self):
        G = nx.cycle_graph(100, create_using=nx.DiGraph())
        G.add_edges_from((i + 100, (i + 1) % 100 + 100) for i in range(100))
        assert not nx.is_semiconnected(G)  # G is disconnected.
        G.add_edge(100, 99)
        assert nx.is_semiconnected(G)

    def test_alternating_path(self):
        G = nx.DiGraph(
            chain.from_iterable([(i, i - 1), (i, i + 1)] for i in range(0, 100, 2))
        )
        assert not nx.is_semiconnected(G)