// -*- c++ -*-
/*****************************************************************************/
// Copyright (c) Illumina 2008
// Author: Richard Shaw
//
// This software is covered by the "Illumina Genome Analyzer Software
// License Agreement" and the "Illumina Source Code License Agreement",
// and certain third party copyright/licenses, and any user of this
// source file is bound by the terms therein (see accompanying files
// Illumina_Genome_Analyzer_Software_License_Agreement.pdf and
// Illumina_Source_Code_License_Agreement.pdf and third party
// copyright/license notices).
/*****************************************************************************/

#ifndef INFO_CALC_H
#define INFO_CALC_H

/*****************************************************************************/

#include <cassert>
#include "common/MathCompatibility.hh"

/*****************************************************************************/

class Info_Calc
{
 public:
    /** It is up to the user to guard against pointless instantiation,
        i.e. with a total_freq of 0, to avoid repeated checks in pointless
        calls of the operator() method.
    */
    Info_Calc(unsigned int total_freq)
        : my_total_freq(total_freq), my_entropy(0.0) {
        assert(total_freq > 0);
    }

    ~Info_Calc() { }

    void operator()(const unsigned int freq) {
        if (freq > 0) {
            const double prob((1.0 * freq) / my_total_freq);
            my_entropy += (prob * log(prob));
        }
    }

    double info_val() {
        return ((((my_entropy * our_to_base2) + our_prior_entropy) / 2.0)
                * my_total_freq);
    }

private:
    unsigned int my_total_freq;
    double my_entropy;

    static const float our_prior_entropy;
    static const float our_to_base2;
};

/*****************************************************************************/

const float Info_Calc::our_prior_entropy(2.0);
const float Info_Calc::our_to_base2(1.0 / log(2.0));

/*****************************************************************************/

#endif // ! INFO_CALC_H

/*****************************************************************************/