% GET_GAS_TRANS returns transmission of a solid for a given energy (range)
%   formula...              chemical formula
%   energy...               single value in keV or energy range in keV
%   thickness...            thickness in cm
%   (optional) press...     pressure in Torr (default 30)
%   (optional) tempr...     temperature in Kelvin (default 295)
%   (optional) npts...      number of points
%   (optional) plot...      set to 1 for plotting
%
%   returns 
%       trans...            (energy in keV, transmission)
%       req_press...        pressure
%
%   examples:
%   get_gas_trans('Air', 8.7, 2)
%   get_gas_trans('CO2', [11.2 24], 20, 30, 100)
%
%   03/2017

%*-----------------------------------------------------------------------*
%|                                                                       |
%|  Except where otherwise noted, this work is licensed under a          |
%|  Creative Commons Attribution-NonCommercial-ShareAlike 4.0            |
%|  International (CC BY-NC-SA 4.0) license.                             |
%|                                                                       |
%|  Copyright (c) 2017 by Paul Scherrer Institute (http://www.psi.ch)    |
%|                                                                       |
%|       Author: CXS group, PSI                                          |
%*-----------------------------------------------------------------------*
% You may use this code with the following provisions:
%
% If the code is fully or partially redistributed, or rewritten in another
%   computing language this notice should be included in the redistribution.
%
% If this code, or subfunctions or parts of it, is used for research in a 
%   publication or if it is fully or partially rewritten for another 
%   computing language the authors and institution should be acknowledged 
%   in written form in the publication: “Data processing was carried out 
%   using the “cSAXS matlab package” developed by the CXS group,
%   Paul Scherrer Institut, Switzerland.” 
%   Variations on the latter text can be incorporated upon discussion with 
%   the CXS group if needed to more specifically reflect the use of the package 
%   for the published work.
%
% A publication that focuses on describing features, or parameters, that
%    are already existing in the code should be first discussed with the
%    authors.
%   
% This code and subroutines are part of a continuous development, they 
%    are provided “as they are” without guarantees or liability on part
%    of PSI or the authors. It is the user responsibility to ensure its 
%    proper use and the correctness of the results.

function [ trans, req_press ] = get_gas_trans( formula, energy, thickness, varargin )

% check pressure
if nargin < 4
    press = 30;
else
    press = varargin{1};
end

% check temperature
if nargin < 5
    tempr = 295;
else
    tempr = varargin{2};
end

% check specified number of points
if nargin < 6
    npts = 99;
else
    npts = varargin{3}-1;
end

% check if plotting is requested
if nargin < 7
    plot_trans = false;
else
    plot_trans = varargin{4};
end

% default compounds
switch lower(formula)
    case lower('Air')
        formula = 'N1.562O.42C.0003Ar.0094';
    case lower('Methane')
        formula = 'C1H4';
    case lower('P-10')
        formula = 'Ar.9C.1H.4';
    case lower('Propane')
        formula = 'C3H8';
end

% convert to keV
energy = energy * 1000;

if size(energy) ==1
    emin = energy-1;
    emax = energy+1;
    npts = 2;
    req_range = false;
elseif size(energy,2) == 2
    emin = energy(1);
    emax = energy(2);
    req_range = true;
else
    error('Only one specific energy or an energy range is supported.')
    
end

% check the energy range
if emin < 30 || emax > 30000
    error('Energies must be in the range 0.03 keV to 30 keV.')
end

% request the data
server = 'http://henke.lbl.gov/';
req = sprintf('Material=Enter+Formula&Formula=%s&Press=%f&Temp=%f&Path=%f&Scan=Energy&Min=%d&Max=%d&Npts=%d&Plot=Linear&Output=Plot', formula, press, tempr, thickness, emin, emax, npts);
data_req = webwrite('http://henke.lbl.gov/cgi-bin/gastrn.pl', req);

% find and read dat file
f_pos = strfind(data_req, '/tmp');
data_req = strsplit(data_req(f_pos(1):end), '.');
data = webread([server data_req{1} '.dat']);

% split data by line breaks
data = strsplit(data, '\n');

% extract density
req_press = data{1};
req_press = strsplit(req_press, '=');
req_press = strsplit(req_press{2}, ' ');
req_press = str2double(req_press{1});

%keyboard

% output
if npts==2 && ~req_range
    trans = zeros(1,2);
    req_trans = data{4};
    req_trans = strsplit(req_trans,' ');
    trans(1,1) = str2double(req_trans{2})/1000;
    trans(1,2) = str2double(req_trans{3});
else
    trans = zeros(npts+1,2);
    for i=1:npts+1
        req_trans = data{i+2};
        req_trans = strsplit(req_trans,' ');
        trans(i,1) = str2double(req_trans{2})/1000;
        trans(i,2) = str2double(req_trans{3});
    end
end

% plot transmission
if plot_trans
    if ~req_range
        fprintf('Requested plot for a single point.')
    end
    figure(76);
    plot(trans(:,1), trans(:,2))
    ylabel('transmission')
    xlabel('energy in keV')
    grid on;
    
end

end