function dett = mcxdettime(detp, prop, unitinmm)
%
% dett=mcxdettime(detp,prop,unitinmm)
%
% Recalculate the detected photon time using partial path data and
% optical properties (for perturbation Monte Carlo or detector readings)
%
% author: Qianqian Fang (q.fang <at> neu.edu)
%     Ruoyang Yao (yaor <at> rpi.edu)
%
% input:
%     detp: the 2nd output from mcxlab. detp must be a struct
%     prop: optical property list, as defined in the cfg.prop field of mcxlab's input
%     unitinmm: voxel edge-length in mm, should use cfg.unitinmm used to generate detp;
%           if ignored, assume to be 1 (mm)
%
% output:
%     dett: re-caculated detected photon time based on the partial path data and optical property table
%
% this file is copied from Mesh-based Monte Carlo (MMC)
%
% License: GPLv3, see http://mcx.space/ for details
%

R_C0 = 3.335640951981520e-12;   % inverse of light speed in vacuum

if (nargin < 3)
    if (isfield(detp, 'unitinmm'))
        unitinmm = detp.unitinmm;
    else
        unitinmm = 1;
    end
end

if (nargin < 2)
    if (isfield(detp, 'prop'))
        prop = detp.prop;
    else
        error('must provide input "prop"');
    end
end

medianum = size(prop, 1);
if (medianum <= 1)
    error('empty property list');
end

if (isstruct(detp))
    dett = zeros(size(detp.ppath, 1), 1);
    for i = 1:medianum - 1
        dett = dett + prop(i + 1, 4) * detp.ppath(:, i) * R_C0 * unitinmm;
    end
else
    error('the first input must be a struct with a subfield named "ppath"');
end