#pragma once

#include <string>
#include <stdexcept> // std::runtime_error
#include <opencv2/opencv.hpp> // all opencv header
// TODO: add openmp support

namespace hdrplus
{

template <typename T>
cv::Mat box_filter_2x2( cv::Mat src_image )
{
    // https://stackoverflow.com/questions/34042112/opencv-mat-data-member-access
    const T* src_image_ptr = (T*)src_image.data;
    int src_height = src_image.size().height;
    int src_width  = src_image.size().width;
    int src_step   = src_image.step1();

    if ( src_height % 2 != 0 || src_width % 2 != 0 )
    {
        throw std::runtime_error( std::string( __FILE__ ) + "::" + __func__ + " source image need to have size multiplier of 2\n" );
    }

    cv::Mat dst_image( src_height / 2, src_width / 2, src_image.type() );
    T* dst_image_ptr = (T*)dst_image.data;
    //int dst_height = dst_image.size().height;
    //int dst_width  = dst_image.size().width;
    int dst_step = dst_image.step1();

    // -03 should be enough to optimize below code
    for ( int row_i = 0; row_i < src_height; row_i += 2 )
    {
        for ( int col_i = 0; col_i < src_width; col_i += 2 )
        {
            T box_sum = src_image_ptr[ ( row_i + 0 ) * src_step + col_i + 0 ] + \
                        src_image_ptr[ ( row_i + 0 ) * src_step + col_i + 1 ] + \
                        src_image_ptr[ ( row_i + 1 ) * src_step + col_i + 0 ] + \
                        src_image_ptr[ ( row_i + 1 ) * src_step + col_i + 1 ];
            T box_avg = ( box_sum + T(3) ) / 4; // take ceiling
            dst_image_ptr[ ( row_i / 2 ) * dst_step + ( col_i / 2 ) ] = box_avg;
        }
    }

    // cv::Mat internally use reference count. Will not copy by value here
    return dst_image;
}

} // namespace hdrplus