# Source code for PyMca5.PyMcaPhysics.xrf.CoherentScattering

    #/*##########################################################################
    #
    # The PyMca X-Ray Fluorescence Toolkit
    #
    # Copyright (c) 2004-2014 European Synchrotron Radiation Facility
    #
    # This file is part of the PyMca X-ray Fluorescence Toolkit developed at
    # the ESRF by the Software group.
    #
    # Permission is hereby granted, free of charge, to any person obtaining a copy
    # of this software and associated documentation files (the "Software"), to deal
    # in the Software without restriction, including without limitation the rights
    # to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
    # copies of the Software, and to permit persons to whom the Software is
    # furnished to do so, subject to the following conditions:
    #
    # The above copyright notice and this permission notice shall be included in
    # all copies or substantial portions of the Software.
    #
    # THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    # IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    # FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
    # AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    # LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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    #############################################################################*/
    __author__ = "V.A. Sole - ESRF Data Analysis"
    __contact__ = "sole@esrf.fr"
    __license__ = "MIT"
    __copyright__ = "European Synchrotron Radiation Facility, Grenoble, France"
    import os
    import numpy
    from PyMca5.PyMcaIO import ConfigDict
    from PyMca5 import PyMcaDataDir

    dirmod = PyMcaDataDir.PYMCA_DATA_DIR
    ffile = os.path.join(dirmod, "attdata")
    ffile = os.path.join(ffile, "atomsf.dict")
    if not os.path.exists(ffile):
        #freeze does bad things with the path ...
        dirmod = os.path.dirname(dirmod)
        ffile = os.path.join(dirmod, "attdata")
        ffile = os.path.join(ffile, "atomsf.dict")
        if not os.path.exists(ffile):
            if dirmod.lower().endswith(".zip"):
                dirmod = os.path.dirname(dirmod)
                ffile = os.path.join(dirmod, "attdata")
                ffile = os.path.join(ffile, "atomsf.dict")
        if not os.path.exists(ffile):
            print("Cannot find file ", ffile)
            raise IOError("Cannot find file %s" % ffile)
    COEFFICIENTS = ConfigDict.ConfigDict()
    COEFFICIENTS.read(ffile)
    KEVTOANG = 12.39852000
    R0 = 2.82E-13 #electron radius in cm

    def getElementFormFactor(ele, theta, energy):
        """
        Usage:
            getFormFactor(ele,theta, energy):

        ele   - Element
        theta - Scattering angle or array of scattering angles in degrees
        energy- Photon Energy in keV

        This routine calculates the atomic form factor in electron units using
        a four gaussians approximation
        """
        wavelength = KEVTOANG / energy
        x = numpy.sin(theta*(numpy.pi/360.0)) / wavelength
        x = x * x
        c0= COEFFICIENTS[ele]['c'][0]
        c = COEFFICIENTS[ele]['c'][1:]
        b = COEFFICIENTS[ele]['b']
        return c0 + (c[0] * numpy.exp(-b[0]*x)) + \
                      (c[1] * numpy.exp(-b[1]*x)) + \
                      (c[2] * numpy.exp(-b[2]*x)) + \
                      (c[3] * numpy.exp(-b[3]*x))

    def getElementCoherentDifferentialCrossSection(ele, theta, energy, p1=None):
        if p1 is None:
            p1=0.0
        if (p1 > 1.0) or (p1 < -1):
            raise ValueError(\
            "Invalid degree of linear polarization respect to the scattering plane")
        thetasin2 = pow(numpy.sin(theta*numpy.pi/180.0),2)
        return (1.0+ 0.5 *(p1-1.0) * thetasin2) * \
               pow(R0*getElementFormFactor(ele, theta, energy),2)

    if __name__ == "__main__":
        import sys
        if len(sys.argv) >  3:
            ele   = sys.argv[1]
            theta = float(sys.argv[2])
            energy= float(sys.argv[3])
            print(getElementFormFactor(ele, theta, energy))
        else:
            print("Usage:")
            print("python CoherentScattering.py Element Theta(deg) Energy(kev)")