#include <stdlib.h>

#include <grass/gis.h>
#include <grass/raster.h>
#include <grass/calc.h>

/****************************************************************
graph(x, x1,y1, x2,y2, ... xn,yn)  returns y value based on graph
described by the x,y pairs.
****************************************************************/

int c_graph(int argc, int *argt)
{
    int i;

    if (argc < 3)
        return E_ARG_LO;

    if (argc % 2 == 0)
        return E_ARG_NUM;

    for (i = 0; i <= argc; i++)
        argt[i] = DCELL_TYPE;

    return 0;
}

int f_graph(int argc, const int *argt, void **args)
{
    DCELL **argz = (DCELL **)args;
    DCELL *res = argz[0];
    int n = (argc - 1) / 2;
    int i, j;

    if (argc < 3)
        return E_ARG_LO;

    if (argc % 2 == 0)
        return E_ARG_NUM;

    if (argt[0] != DCELL_TYPE)
        return E_RES_TYPE;

    for (i = 1; i <= argc; i++)
        if (argt[i] != DCELL_TYPE)
            return E_ARG_TYPE;

    for (i = 0; i < columns; i++) {
#define X(j) (argz[2 + 2 * (j) + 0][i])
#define Y(j) (argz[2 + 2 * (j) + 1][i])
#define x    (argz[1][i])

        if (IS_NULL_D(&x))
            goto null;

        for (j = 0; j < n; j++)
            if (IS_NULL_D(&X(j)))
                goto null;

        for (j = 0; j < n - 1; j++)
            if (X(j + 1) <= X(j))
                goto null;

        if (x <= X(0)) {
            if (IS_NULL_D(&Y(0)))
                goto null;
            res[i] = Y(0);
            continue;
        }

        if (x >= X(n - 1)) {
            if (IS_NULL_D(&Y(n - 1)))
                goto null;
            res[i] = Y(n - 1);
            continue;
        }

        for (j = 0; j < n - 1; j++) {
            if (x > X(j + 1))
                continue;

            if (IS_NULL_D(&Y(j)) || IS_NULL_D(&Y(j + 1)))
                goto null;

            res[i] = Y(j) + (x - X(j)) * (Y(j + 1) - Y(j)) / (X(j + 1) - X(j));

            break;
        }
#undef X
#undef Y
#undef x

        continue;

    null:
        SET_NULL_D(&res[i]);
    }

    return 0;
}

int f_graph2(int argc, const int *argt, void **args)
{
    DCELL **argz = (DCELL **)args;
    DCELL *res = argz[0];
    int n = (argc - 1) / 2;
    int i, j;

    if (argc < 3)
        return E_ARG_LO;

    if (argc % 2 == 0)
        return E_ARG_NUM;

    if (argt[0] != DCELL_TYPE)
        return E_RES_TYPE;

    for (i = 1; i <= argc; i++)
        if (argt[i] != DCELL_TYPE)
            return E_ARG_TYPE;

    for (i = 0; i < columns; i++) {
#define X(j) (argz[2 + (j) + 0][i])
#define Y(j) (argz[2 + (j) + n][i])
#define x    (argz[1][i])

        if (IS_NULL_D(&x))
            goto null;

        for (j = 0; j < n; j++)
            if (IS_NULL_D(&X(j)))
                goto null;

        for (j = 0; j < n - 1; j++)
            if (X(j + 1) <= X(j))
                goto null;

        if (x <= X(0)) {
            if (IS_NULL_D(&Y(0)))
                goto null;
            res[i] = Y(0);
            continue;
        }

        if (x >= X(n - 1)) {
            if (IS_NULL_D(&Y(n - 1)))
                goto null;
            res[i] = Y(n - 1);
            continue;
        }

        for (j = 0; j < n - 1; j++) {
            if (x > X(j + 1))
                continue;

            if (IS_NULL_D(&Y(j)) || IS_NULL_D(&Y(j + 1)))
                goto null;

            res[i] = Y(j) + (x - X(j)) * (Y(j + 1) - Y(j)) / (X(j + 1) - X(j));

            break;
        }
#undef X
#undef Y
#undef x

        continue;

    null:
        SET_NULL_D(&res[i]);
    }

    return 0;
}
