#!/usr/bin/env python3
"""
Custom form factor in DWBA.
"""
import cmath
import bornagain as ba
from bornagain import ba_plot as bp, deg, angstrom, nm


def sinc(x):
    if abs(x) == 0:
        return 1.
    return cmath.sin(x) / x


class CustomFormfactor:
    """
    A custom defined form factor.
    The particle is a prism of height H,
    with a base in form of a Greek cross ("plus" sign) with side length L.
    """

    def __init__(self, L, H):
        """ arguments and initialization for the formfactor """

        # parameters describing the form factor
        self.L = L
        self.H = H

    def formfactor(self, q:'C3'):
        """ main scattering function """

        qzhH = 0.5 * q.z() * self.H
        qxhL = 0.5 * q.x() * self.L
        qyhL = 0.5 * q.y() * self.L
        return (0.5 * self.H * self.L**2
                * cmath.exp(complex(0., 1.) * qzhH) * sinc(qzhH)
                * (sinc(0.5 * qyhL) * (sinc(qxhL) - 0.5 * sinc(0.5 * qxhL))
                   + sinc(0.5 * qxhL) * sinc(qyhL)))

    def spanZ(self, rotation):
        """ upper and lower z-positions of a custom shape """

        return ba.Span(0, self.H)


def get_sample():
    """
    Sample with particles, having a custom formfactor, on a substrate.
    """

    # materials
    vacuum = ba.RefractiveMaterial("Vacuum", 0, 0)
    material_substrate = ba.RefractiveMaterial("Substrate", 6e-6, 2e-8)
    material_particle = ba.RefractiveMaterial("Particle", 6e-4, 2e-8)

    # collection of particles
    ff = CustomFormfactor(20*nm, 15*nm)
    particle = ba.Particle(material_particle, ff)
    particle_layout = ba.ParticleLayout()
    particle_layout.addParticle(particle)
    vacuum_layer = ba.Layer(vacuum)
    vacuum_layer.addLayout(particle_layout)
    substrate_layer = ba.Layer(material_substrate)

    """ NOTE:
    Slicing of custom formfactor is not possible.
    all layers must have number of slices equal to 1.
    It is a default situation; otherwise use
    ```
    my_layer.setNumberOfSlices(1)
    ```

    Furthermore, a custom particle should not cross layer boundaries;
    that is, the z-span should be within a single layer
    """

    # assemble sample
    sample = ba.Sample()
    sample.addLayer(vacuum_layer)
    sample.addLayer(substrate_layer)
    return sample


def get_simulation(sample):
    beam = ba.Beam(1e9, 1*angstrom, 0.2*deg)
    n = 100
    det = ba.SphericalDetector(n, -1*deg, 1*deg, n, 0, 2*deg)
    simulation = ba.ScatteringSimulation(beam, sample, det)

    # Deactivate multithreading:
    # Currently BornAgain cannot access the Python interpreter
    # from a multi-threaded C++ function
    simulation.options().setNumberOfThreads(1)

    return simulation


if __name__ == '__main__':
    sample = get_sample()
    simulation = get_simulation(sample)
    result = simulation.simulate()
    plotargs = bp.parse_commandline()
    bp.plot_simulation_result(result, **plotargs)
    bp.export(**plotargs)
