evision

#ifndef EVISION_BACKEND_CUMULATIVE_H
#define EVISION_BACKEND_CUMULATIVE_H

#include <cmath>
#include <type_traits>
#include <erl_nif.h>
#include "../../ArgInfo.hpp"
#include "../evision_mat_utils.hpp"
#include "parallel.h"

// Row-wise prefix scan (Nx.cumulative_*): op 0=sum, 1=product, 2=min, 3=max,
// accumulating left-to-right (or right-to-left when reverse). Output has the same
// shape and type as the 2D single-channel input, which the caller has already cast
// to the output type; integer sum/product use an unsigned accumulator so wraparound
// is well-defined (two's complement), matching Nx's modular semantics.
template <typename T>
static inline T evision_scan_min(T acc, T v) {
    if constexpr (std::is_floating_point<T>::value) {
        if (std::isnan(acc) || std::isnan(v)) return std::isnan(acc) ? acc : v;
    }
    return (v < acc) ? v : acc;
}

template <typename T>
static inline T evision_scan_max(T acc, T v) {
    if constexpr (std::is_floating_point<T>::value) {
        if (std::isnan(acc) || std::isnan(v)) return std::isnan(acc) ? acc : v;
    }
    return (v > acc) ? v : acc;
}

template <typename T, typename Acc>
static void evision_scan_rows(const cv::Mat &src, cv::Mat &dst, int op, bool reverse) {
    int cols = src.cols;
    evision_parallel_for(src.rows, (int64_t)src.rows * cols, EVISION_PARALLEL_SIMPLE_MIN_WORK, [&](int64_t begin, int64_t end) {
        for (int64_t row = begin; row < end; row++) {
            const T *sp = src.ptr<T>((int)row);
            T *dp = dst.ptr<T>((int)row);
            if (cols == 0) continue;
            int start = reverse ? cols - 1 : 0;
            int step = reverse ? -1 : 1;
            T running = sp[start];
            dp[start] = running;
            for (int k = 1; k < cols; k++) {
                int c = start + step * k;
                T v = sp[c];
                switch (op) {
                    case 0: running = (T)((Acc)running + (Acc)v); break;
                    case 1: running = (T)((Acc)running * (Acc)v); break;
                    case 2: running = evision_scan_min(running, v); break;
                    case 3: running = evision_scan_max(running, v); break;
                }
                dp[c] = running;
            }
        }
    });
}

// @evision c: mat_cumulative, evision_cv_mat_cumulative, 1
// @evision nif: def mat_cumulative(_opts \\ []), do: :erlang.nif_error(:undefined)
static ERL_NIF_TERM evision_cv_mat_cumulative(ErlNifEnv *env, int argc, const ERL_NIF_TERM argv[]) {
    using namespace cv;
    using namespace evision::nif;
    std::map<std::string, ERL_NIF_TERM> erl_terms;
    int nif_opts_index = 0;
    evision::nif::parse_arg(env, nif_opts_index, argv, erl_terms);

    {
        Mat src;
        int op = 0, reverse = 0;

        if (evision_to_safe(env, evision_get_kw(env, erl_terms, "src"), src, ArgInfo("src", ArgInfo::INPUT_ONLY)) &&
            evision_to_safe(env, evision_get_kw(env, erl_terms, "op"), op, ArgInfo("op", 0)) &&
            evision_to_safe(env, evision_get_kw(env, erl_terms, "reverse"), reverse, ArgInfo("reverse", 0))) {
            Mat dst(src.rows, src.cols, src.type());
            bool rev = reverse != 0;
            switch (src.depth()) {
                case CV_8U:  evision_scan_rows<uint8_t, uint32_t>(src, dst, op, rev); break;
                case CV_8S:  evision_scan_rows<int8_t, uint32_t>(src, dst, op, rev); break;
                case CV_16U: evision_scan_rows<uint16_t, uint32_t>(src, dst, op, rev); break;
                case CV_16S: evision_scan_rows<int16_t, uint32_t>(src, dst, op, rev); break;
                case CV_32S: evision_scan_rows<int32_t, uint32_t>(src, dst, op, rev); break;
                case CV_32U: evision_scan_rows<uint32_t, uint32_t>(src, dst, op, rev); break;
                case CV_64S: evision_scan_rows<int64_t, uint64_t>(src, dst, op, rev); break;
                case CV_64U: evision_scan_rows<uint64_t, uint64_t>(src, dst, op, rev); break;
                case CV_32F: evision_scan_rows<float, float>(src, dst, op, rev); break;
                case CV_64F: evision_scan_rows<double, double>(src, dst, op, rev); break;
                default: return evision::nif::error(env, "mat_cumulative: unsupported depth");
            }
            return evision_from(env, dst);
        }
    }

    return enif_make_badarg(env);
}

#endif // EVISION_BACKEND_CUMULATIVE_H