cosine.h

#pragma once

#include <funcy/concepts.h>
#include <funcy/util/chainer.h>

#include <cmath>

namespace funcy
{
    struct Cos : Chainer< Cos >
    {
        explicit Cos( double x = 0. ) noexcept
        {
            update( x );
        }

        void update( double x ) noexcept
        {
            sinx = ::sin( x );
            cosx = ::cos( x );
        }

        [[nodiscard]] double d0() const noexcept
        {
            return cosx;
        }

        [[nodiscard]] double d1( double dx = 1. ) const noexcept
        {
            return -sinx * dx;
        }

        [[nodiscard]] double d2( double dx = 1., double dy = 1. ) const noexcept
        {
            return -cosx * dx * dy;
        }

        [[nodiscard]] double d3( double dx = 1., double dy = 1., double dz = 1. ) const noexcept
        {
            return sinx * dx * dy * dz;
        }

    private:
        double sinx = 0, cosx = 1;
    };

    template < Function F >
    [[nodiscard]] auto cos( const F& f )
    {
        return Cos()( f );
    }
} // namespace funcy