/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */

/*

 * This file is part of the LibreOffice project.

 *

 * This Source Code Form is subject to the terms of the Mozilla Public

 * License, v. 2.0. If a copy of the MPL was not distributed with this

 * file, You can obtain one at http://mozilla.org/MPL/2.0/.

 *

 * This file incorporates work covered by the following license notice:

 *

 *   Licensed to the Apache Software Foundation (ASF) under one or more

 *   contributor license agreements. See the NOTICE file distributed

 *   with this work for additional information regarding copyright

 *   ownership. The ASF licenses this file to you under the Apache

 *   License, Version 2.0 (the "License"); you may not use this file

 *   except in compliance with the License. You may obtain a copy of

 *   the License at http://www.apache.org/licenses/LICENSE-2.0 .

 */

#include <sal/config.h>

#include <limits>

#include <string_view>

#include <ExponentialRegressionCurveCalculator.hxx>

#include <RegressionCalculationHelper.hxx>

#include <SpecialCharacters.hxx>

#include <rtl/math.hxx>

#include <rtl/ustrbuf.hxx>

using namespace ::com::sun::star;

namespace chart

{

ExponentialRegressionCurveCalculator::ExponentialRegressionCurveCalculator()

    : m_fLogSlope(std::numeric_limits<double>::quiet_NaN())

    , m_fLogIntercept(std::numeric_limits<double>::quiet_NaN())

    , m_fSign(1.0)

{

}

ExponentialRegressionCurveCalculator::~ExponentialRegressionCurveCalculator()

{}

// ____ XRegressionCurveCalculator ____

void SAL_CALL ExponentialRegressionCurveCalculator::recalculateRegression(

    const uno::Sequence< double >& aXValues,

    const uno::Sequence< double >& aYValues )

{

    RegressionCalculationHelper::tDoubleVectorPair aValues(

        RegressionCalculationHelper::cleanup(

            aXValues, aYValues,

            RegressionCalculationHelper::isValidAndYPositive()));

    m_fSign = 1.0;

    size_t nMax = aValues.first.size();

    if( nMax <= 1 ) // at least 2 points

    {

        aValues = RegressionCalculationHelper::cleanup(

                    aXValues, aYValues,

                    RegressionCalculationHelper::isValidAndYNegative());

        nMax = aValues.first.size();

        if( nMax <= 1 )

        {

            m_fLogSlope = std::numeric_limits<double>::quiet_NaN();

            m_fLogIntercept = std::numeric_limits<double>::quiet_NaN();

            m_fCorrelationCoefficient = std::numeric_limits<double>::quiet_NaN();// actual it is coefficient of determination

            return;

        }

        m_fSign = -1.0;

    }

    double fAverageX = 0.0, fAverageY = 0.0;

    double fLogIntercept = ( mForceIntercept && (m_fSign * mInterceptValue)>0 ) ? log(m_fSign * mInterceptValue) : 0.0;

    std::vector<double> yVector;

    yVector.resize(nMax, 0.0);

    size_t i = 0;

    for( i = 0; i < nMax; ++i )

    {

        double yValue = log( m_fSign *aValues.second[i] );

        if (mForceIntercept)

        {

            yValue -= fLogIntercept;

        }

        else

        {

            fAverageX += aValues.first[i];

            fAverageY += yValue;

        }

        yVector[i] = yValue;

    }

    const double fN = static_cast< double >( nMax );

    fAverageX /= fN;

    fAverageY /= fN;

    double fQx = 0.0, fQy = 0.0, fQxy = 0.0;

    for( i = 0; i < nMax; ++i )

    {

        double fDeltaX = aValues.first[i] - fAverageX;

        double fDeltaY = yVector[i] - fAverageY;

        fQx  += fDeltaX * fDeltaX;

        fQy  += fDeltaY * fDeltaY;

        fQxy += fDeltaX * fDeltaY;

    }

    m_fLogSlope = fQxy / fQx;

    m_fLogIntercept = mForceIntercept ? fLogIntercept : fAverageY - m_fLogSlope * fAverageX;

    m_fCorrelationCoefficient = fQxy / sqrt( fQx * fQy );

}

double SAL_CALL ExponentialRegressionCurveCalculator::getCurveValue( double x )

{

    if( ! ( std::isnan( m_fLogSlope ) ||

            std::isnan( m_fLogIntercept )))

    {

        return m_fSign * exp(m_fLogIntercept + x * m_fLogSlope);

    }

    return std::numeric_limits<double>::quiet_NaN();

}

uno::Sequence< geometry::RealPoint2D > SAL_CALL ExponentialRegressionCurveCalculator::getCurveValues(

    double min, double max, ::sal_Int32 nPointCount,

    const uno::Reference< chart2::XScaling >& xScalingX,

    const uno::Reference< chart2::XScaling >& xScalingY,

    sal_Bool bMaySkipPointsInCalculation )

{

    if( bMaySkipPointsInCalculation &&

        isLinearScaling( xScalingX ) &&

        isLogarithmicScaling( xScalingY ))

    {

        // optimize result

        uno::Sequence< geometry::RealPoint2D > aResult{ { min, getCurveValue( min ) },

                                                        { max, getCurveValue( max ) } };

        return aResult;

    }

    return RegressionCurveCalculator::getCurveValues( min, max, nPointCount, xScalingX, xScalingY, bMaySkipPointsInCalculation );

}

OUString ExponentialRegressionCurveCalculator::ImplGetRepresentation(

    const uno::Reference< util::XNumberFormatter >& xNumFormatter,

    sal_Int32 nNumberFormatKey, sal_Int32* pFormulaMaxWidth /* = nullptr */ ) const

{

    double fIntercept = exp(m_fLogIntercept);

    bool bHasSlope = !rtl::math::approxEqual( exp(m_fLogSlope), 1.0 );

    bool bHasLogSlope = !rtl::math::approxEqual( fabs(m_fLogSlope), 1.0 );

    bool bHasIntercept = !rtl::math::approxEqual( fIntercept, 1.0 ) && fIntercept != 0.0;

    OUStringBuffer aBuf( mYName + " = " );

    sal_Int32 nLineLength = aBuf.getLength();

    sal_Int32 nValueLength=0;

    if ( pFormulaMaxWidth && *pFormulaMaxWidth > 0 )

    {          // count characters different from coefficients

        sal_Int32 nCharMin = nLineLength + 10 + mXName.getLength();  // 10 = "exp( ", " x )" + 2 extra characters

        if ( m_fSign < 0.0 )

            nCharMin += 2;

        if ( fIntercept == 0.0 || ( !bHasSlope && m_fLogIntercept != 0.0 ) )

            nCharMin += 3; // " + " special case where equation is written exp( a + b x )

        if ( ( bHasIntercept || fIntercept == 0.0 || ( !bHasSlope && m_fLogIntercept != 0.0 ) ) &&

               bHasLogSlope )

            nValueLength = ( *pFormulaMaxWidth - nCharMin ) / 2;

        else

            nValueLength = *pFormulaMaxWidth - nCharMin;

        if ( nValueLength <= 0 )

            nValueLength = 1;

    }

                    // temporary buffer

    OUStringBuffer aTmpBuf("");

        // if nValueLength not calculated then nullptr

    sal_Int32* pValueLength = nValueLength ? &nValueLength : nullptr;

    if ( m_fSign < 0.0 )

        aTmpBuf.append( OUStringChar(aMinusSign) + " " );

    if ( bHasIntercept )

    {

        OUString aValueString = getFormattedString( xNumFormatter, nNumberFormatKey, fIntercept, pValueLength );

        if ( aValueString != "1" )  // aValueString may be rounded to 1 if nValueLength is small

        {

            aTmpBuf.append( aValueString + " " );

            addStringToEquation( aBuf, nLineLength, aTmpBuf, pFormulaMaxWidth );

            aTmpBuf.truncate();

        }

    }

    aTmpBuf.append( "exp( " );

    if ( !bHasIntercept )

    {

        if ( fIntercept == 0.0 ||  // underflow, a true zero is impossible

           ( !bHasSlope && m_fLogIntercept != 0.0 ) )   // show logarithmic output, if intercept and slope both are near one

        {                                               // otherwise drop output of intercept, which is 1 here

            OUString aValueString = getFormattedString( xNumFormatter, nNumberFormatKey, m_fLogIntercept, pValueLength );

            if ( aValueString != "0" )  // aValueString may be rounded to 0 if nValueLength is small

            {

                aTmpBuf.append( aValueString ).append( (m_fLogSlope < 0.0) ? std::u16string_view(u" ") : std::u16string_view(u" + ") );

            }

        }

    }

    if ( m_fLogSlope < 0.0 )

        aTmpBuf.append( OUStringChar(aMinusSign) + " " );

    if ( bHasLogSlope )

    {

        OUString aValueString = getFormattedString( xNumFormatter, nNumberFormatKey, fabs(m_fLogSlope), pValueLength );

        if ( aValueString != "1" )  // aValueString may be rounded to 1 if nValueLength is small

        {

            aTmpBuf.append( aValueString + " " );

        }

    }

    aTmpBuf.append( mXName + " )");

    addStringToEquation( aBuf, nLineLength, aTmpBuf, pFormulaMaxWidth );

    return aBuf.makeStringAndClear();

}

} //  namespace chart

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