from math import sqrt

import pytest
numpy = pytest.importorskip('numpy')
numpy.linalg = pytest.importorskip('numpy.linalg')
scipy = pytest.importorskip('scipy')
scipy.sparse = pytest.importorskip('scipy.sparse')



import networkx as nx
from networkx.testing import almost_equal

try:
    from scikits.sparse.cholmod import cholesky
    _cholesky = cholesky
except ImportError:
    _cholesky = None

if _cholesky is None:
    methods = ('tracemin_pcg', 'tracemin_lu', 'lanczos', 'lobpcg')
else:
    methods = ('tracemin_pcg', 'tracemin_chol', 'tracemin_lu', 'lanczos', 'lobpcg')


def check_eigenvector(A, l, x):
    nx = numpy.linalg.norm(x)
    # Check zeroness.
    assert not almost_equal(nx, 0)
    y = A * x
    ny = numpy.linalg.norm(y)
    # Check collinearity.
    assert almost_equal(numpy.dot(x, y), nx * ny)
    # Check eigenvalue.
    assert almost_equal(ny, l * nx)


class TestAlgebraicConnectivity(object):

    def test_directed(self):
        G = nx.DiGraph()
        for method in self._methods:
            pytest.raises(nx.NetworkXNotImplemented, nx.algebraic_connectivity,
                          G, method=method)
            pytest.raises(nx.NetworkXNotImplemented, nx.fiedler_vector, G,
                          method=method)

    def test_null_and_singleton(self):
        G = nx.Graph()
        for method in self._methods:
            pytest.raises(nx.NetworkXError, nx.algebraic_connectivity, G,
                          method=method)
            pytest.raises(nx.NetworkXError, nx.fiedler_vector, G,
                          method=method)
        G.add_edge(0, 0)
        for method in self._methods:
            pytest.raises(nx.NetworkXError, nx.algebraic_connectivity, G,
                          method=method)
            pytest.raises(nx.NetworkXError, nx.fiedler_vector, G,
                          method=method)

    def test_disconnected(self):
        G = nx.Graph()
        G.add_nodes_from(range(2))
        for method in self._methods:
            assert nx.algebraic_connectivity(G) == 0
            pytest.raises(nx.NetworkXError, nx.fiedler_vector, G,
                          method=method)
        G.add_edge(0, 1, weight=0)
        for method in self._methods:
            assert nx.algebraic_connectivity(G) == 0
            pytest.raises(nx.NetworkXError, nx.fiedler_vector, G,
                          method=method)

    def test_unrecognized_method(self):
        G = nx.path_graph(4)
        pytest.raises(nx.NetworkXError, nx.algebraic_connectivity, G,
                      method='unknown')
        pytest.raises(nx.NetworkXError, nx.fiedler_vector, G, method='unknown')

    def test_two_nodes(self):
        G = nx.Graph()
        G.add_edge(0, 1, weight=1)
        A = nx.laplacian_matrix(G)
        for method in self._methods:
            assert almost_equal(nx.algebraic_connectivity(
                G, tol=1e-12, method=method), 2)
            x = nx.fiedler_vector(G, tol=1e-12, method=method)
            check_eigenvector(A, 2, x)
        G = nx.MultiGraph()
        G.add_edge(0, 0, spam=1e8)
        G.add_edge(0, 1, spam=1)
        G.add_edge(0, 1, spam=-2)
        A = -3 * nx.laplacian_matrix(G, weight='spam')
        for method in self._methods:
            assert almost_equal(nx.algebraic_connectivity(
                G, weight='spam', tol=1e-12, method=method), 6)
            x = nx.fiedler_vector(G, weight='spam', tol=1e-12, method=method)
            check_eigenvector(A, 6, x)

    def test_abbreviation_of_method(self):
        G = nx.path_graph(8)
        A = nx.laplacian_matrix(G)
        sigma = 2 - sqrt(2 + sqrt(2))
        ac = nx.algebraic_connectivity(G, tol=1e-12, method='tracemin')
        assert almost_equal(ac, sigma)
        x = nx.fiedler_vector(G, tol=1e-12, method='tracemin')
        check_eigenvector(A, sigma, x)

    def test_path(self):
        G = nx.path_graph(8)
        A = nx.laplacian_matrix(G)
        sigma = 2 - sqrt(2 + sqrt(2))
        for method in self._methods:
            ac = nx.algebraic_connectivity(G, tol=1e-12, method=method)
            assert almost_equal(ac, sigma)
            x = nx.fiedler_vector(G, tol=1e-12, method=method)
            check_eigenvector(A, sigma, x)

    def test_problematic_graph_issue_2381(self):
        G = nx.path_graph(4)
        G.add_edges_from([(4, 2), (5, 1)])
        A = nx.laplacian_matrix(G)
        sigma = 0.438447187191
        for method in self._methods:
            ac = nx.algebraic_connectivity(G, tol=1e-12, method=method)
            assert almost_equal(ac, sigma)
            x = nx.fiedler_vector(G, tol=1e-12, method=method)
            check_eigenvector(A, sigma, x)

    def test_cycle(self):
        G = nx.cycle_graph(8)
        A = nx.laplacian_matrix(G)
        sigma = 2 - sqrt(2)
        for method in self._methods:
            ac = nx.algebraic_connectivity(G, tol=1e-12, method=method)
            assert almost_equal(ac, sigma)
            x = nx.fiedler_vector(G, tol=1e-12, method=method)
            check_eigenvector(A, sigma, x)

    def test_seed_argument(self):
        G = nx.cycle_graph(8)
        A = nx.laplacian_matrix(G)
        sigma = 2 - sqrt(2)
        for method in self._methods:
            ac = nx.algebraic_connectivity(G, tol=1e-12, method=method, seed=1)
            assert almost_equal(ac, sigma)
            x = nx.fiedler_vector(G, tol=1e-12, method=method, seed=1)
            check_eigenvector(A, sigma, x)

    def test_buckminsterfullerene(self):
        G = nx.Graph(
            [(1, 10), (1, 41), (1, 59), (2, 12), (2, 42), (2, 60), (3, 6),
             (3, 43), (3, 57), (4, 8), (4, 44), (4, 58), (5, 13), (5, 56),
             (5, 57), (6, 10), (6, 31), (7, 14), (7, 56), (7, 58), (8, 12),
             (8, 32), (9, 23), (9, 53), (9, 59), (10, 15), (11, 24), (11, 53),
             (11, 60), (12, 16), (13, 14), (13, 25), (14, 26), (15, 27),
             (15, 49), (16, 28), (16, 50), (17, 18), (17, 19), (17, 54),
             (18, 20), (18, 55), (19, 23), (19, 41), (20, 24), (20, 42),
             (21, 31), (21, 33), (21, 57), (22, 32), (22, 34), (22, 58),
             (23, 24), (25, 35), (25, 43), (26, 36), (26, 44), (27, 51),
             (27, 59), (28, 52), (28, 60), (29, 33), (29, 34), (29, 56),
             (30, 51), (30, 52), (30, 53), (31, 47), (32, 48), (33, 45),
             (34, 46), (35, 36), (35, 37), (36, 38), (37, 39), (37, 49),
             (38, 40), (38, 50), (39, 40), (39, 51), (40, 52), (41, 47),
             (42, 48), (43, 49), (44, 50), (45, 46), (45, 54), (46, 55),
             (47, 54), (48, 55)])
        for normalized in (False, True):
            if not normalized:
                A = nx.laplacian_matrix(G)
                sigma = 0.2434017461399311
            else:
                A = nx.normalized_laplacian_matrix(G)
                sigma = 0.08113391537997749
            for method in methods:
                try:
                    assert almost_equal(nx.algebraic_connectivity(
                        G, normalized=normalized, tol=1e-12, method=method),
                        sigma)
                    x = nx.fiedler_vector(G, normalized=normalized, tol=1e-12,
                                          method=method)
                    check_eigenvector(A, sigma, x)
                except nx.NetworkXError as e:
                    if e.args not in (('Cholesky solver unavailable.',),
                                      ('LU solver unavailable.',)):
                        raise

    _methods = methods


class TestSpectralOrdering(object):

    def test_nullgraph(self):
        for graph in (nx.Graph, nx.DiGraph, nx.MultiGraph, nx.MultiDiGraph):
            G = graph()
            pytest.raises(nx.NetworkXError, nx.spectral_ordering, G)

    def test_singleton(self):
        for graph in (nx.Graph, nx.DiGraph, nx.MultiGraph, nx.MultiDiGraph):
            G = graph()
            G.add_node('x')
            assert nx.spectral_ordering(G) == ['x']
            G.add_edge('x', 'x', weight=33)
            G.add_edge('x', 'x', weight=33)
            assert nx.spectral_ordering(G) == ['x']

    def test_unrecognized_method(self):
        G = nx.path_graph(4)
        pytest.raises(nx.NetworkXError, nx.spectral_ordering, G,
                      method='unknown')

    def test_three_nodes(self):
        G = nx.Graph()
        G.add_weighted_edges_from([(1, 2, 1), (1, 3, 2), (2, 3, 1)],
                                  weight='spam')
        for method in self._methods:
            order = nx.spectral_ordering(G, weight='spam', method=method)
            assert set(order) == set(G)
            assert set([1, 3]) in (set(order[:-1]), set(order[1:]))
        G = nx.MultiDiGraph()
        G.add_weighted_edges_from([(1, 2, 1), (1, 3, 2), (2, 3, 1), (2, 3, 2)])
        for method in self._methods:
            order = nx.spectral_ordering(G, method=method)
            assert set(order) == set(G)
            assert set([2, 3]) in (set(order[:-1]), set(order[1:]))

    def test_path(self):
        # based on setup_class numpy is installed if we get here
        from numpy.random import shuffle
        path = list(range(10))
        shuffle(path)
        G = nx.Graph()
        nx.add_path(G, path)
        for method in self._methods:
            order = nx.spectral_ordering(G, method=method)
            assert order in [path, list(reversed(path))]

    def test_seed_argument(self):
        # based on setup_class numpy is installed if we get here
        from numpy.random import shuffle
        path = list(range(10))
        shuffle(path)
        G = nx.Graph()
        nx.add_path(G, path)
        for method in self._methods:
            order = nx.spectral_ordering(G, method=method, seed=1)
            assert order in [path, list(reversed(path))]

    def test_disconnected(self):
        G = nx.Graph()
        nx.add_path(G, range(0, 10, 2))
        nx.add_path(G, range(1, 10, 2))
        for method in self._methods:
            order = nx.spectral_ordering(G, method=method)
            assert set(order) == set(G)
            seqs = [list(range(0, 10, 2)), list(range(8, -1, -2)),
                    list(range(1, 10, 2)), list(range(9, -1, -2))]
            assert order[:5] in seqs
            assert order[5:] in seqs

    def test_cycle(self):
        path = list(range(10))
        G = nx.Graph()
        nx.add_path(G, path, weight=5)
        G.add_edge(path[-1], path[0], weight=1)
        A = nx.laplacian_matrix(G).todense()
        for normalized in (False, True):
            for method in methods:
                try:
                    order = nx.spectral_ordering(G, normalized=normalized,
                                                 method=method)
                except nx.NetworkXError as e:
                    if e.args not in (('Cholesky solver unavailable.',),
                                      ('LU solver unavailable.',)):
                        raise
                else:
                    if not normalized:
                        assert order in [[1, 2, 0, 3, 4, 5, 6, 9, 7, 8],
                                         [8, 7, 9, 6, 5, 4, 3, 0, 2, 1]]
                    else:
                        assert order in [[1, 2, 3, 0, 4, 5, 9, 6, 7, 8],
                                         [8, 7, 6, 9, 5, 4, 0, 3, 2, 1]]

    _methods = methods
