import pytest
import numpy as np

from ase.parallel import world
from ase.build import molecule, fcc111
from ase.build.attach import (attach, attach_randomly,
                              attach_randomly_and_broadcast)


def test_attach_molecules():
    """Attach two molecules and check that their minimal distance
    is as required"""
    m1 = molecule('C6H6')
    m2 = molecule('NH3')

    distance = 2.
    m12 = attach(m1, m2, distance)
    dmin = np.linalg.norm(m12[15].position - m12[8].position)
    assert dmin == pytest.approx(distance, 1e-8)


def test_attach_to_surface():
    """Attach a molecule to a surafce at a given distance"""
    slab = fcc111('Al', size=(3, 2, 2), vacuum=10.0)
    mol = molecule('CH4')
    
    distance = 3.
    struct = attach(slab, mol, distance, (0, 0, 1))
    dmin = np.linalg.norm(struct[10].position - struct[15].position)
    assert dmin == pytest.approx(distance, 1e-8)
   

def test_attach_randomly():
    """Attach two molecules in random orientation."""
    m1 = molecule('C6H6')
    m2 = molecule('CF4')
    distance = 2.5

    if world.size > 1:
        "Check that the coordinates are correctly distributed from master."
        rng = np.random.RandomState(world.rank)  # ensure different seed
        atoms = attach_randomly_and_broadcast(m1, m2, distance, rng)

        p0 = 1. * atoms[-1].position
        world.broadcast(p0, 0)
        for i in range(1, world.size):
            pi = 1. * atoms[-1].position
            world.broadcast(pi, i)
            assert pi == pytest.approx(p0, 1e-8)

        "Check that every core has its own structure"
        rng = np.random.RandomState(world.rank)  # ensure different seed
        atoms = attach_randomly(m1, m2, distance, rng)
        p0 = 1. * atoms[-1].position
        world.broadcast(p0, 0)
        for i in range(1, world.size):
            pi = 1. * atoms[-1].position
            world.broadcast(pi, i)
            assert pi != pytest.approx(p0, 1e-8)
    
    rng = np.random.RandomState(42)  # ensure the same seed
    pos2_ac = np.zeros((5, 3))
    N = 25
    for i in range(N):
        atoms = attach_randomly(m1, m2, distance, rng=rng)
        pos2_ac += atoms.get_positions()[12:, :]
    # the average position should be "zero" approximately
    assert (np.abs(pos2_ac / N) <= 1).all()
