#include <Rinternals.h>

void grad(const int n, const int p, const int q,
          const double *X,
          const double *X_diff,
          const double *Y,
          const double *V,
          const double h,
          double *G, double *loss);

SEXP grad_c(SEXP X, SEXP X_diff, SEXP Y, SEXP V, SEXP h) {
    SEXP G = PROTECT(allocMatrix(REALSXP, nrows(V), ncols(V)));
    SEXP loss = PROTECT(ScalarReal(0.0));

    grad(nrows(X), ncols(X), ncols(V),
         REAL(X), REAL(X_diff), REAL(Y), REAL(V), *REAL(h),
         REAL(G), REAL(loss));

    SEXP out = PROTECT(allocVector(VECSXP, 2));
    SET_VECTOR_ELT(out, 0, G);
    SET_VECTOR_ELT(out, 1, loss);
    SEXP names = PROTECT(allocVector(STRSXP, 2));
    SET_STRING_ELT(names, 0, mkChar("G"));
    SET_STRING_ELT(names, 1, mkChar("loss"));
    setAttrib(out, install("names"), names);

    UNPROTECT(4);
    return out;
}