/****************************************************************************
 *
 * MODULE:       r.buffer
 *
 * AUTHOR(S):    Michael Shapiro - CERL
 *
 * PURPOSE:      This program creates distance zones from non-zero
 *               cells in a grid layer. Distances are specified in
 *               meters (on the command-line). Window does not have to
 *               have square cells. Works both for planimetric
 *               (UTM, State Plane) and lat-long.
 *
 * COPYRIGHT:    (C) 2005 by the GRASS Development Team
 *
 *               This program is free software under the GNU General Public
 *               License (>=v2). Read the file COPYING that comes with GRASS
 *               for details.
 *
 ****************************************************************************/

#include <grass/gis.h>
#include "distance.h"
#include "local_proto.h"

static int cur_row;

int begin_distance(int row)
{
    cur_row = row;

    if (window.proj == PROJECTION_LL)
        G_set_geodesic_distance_lat1(window.north - (row + .5) * window.ns_res);

    return 0;
}

/* Determine number of columns for each distance zone
 *    (-1 means doesn't occur)
 * Returns: first zone to occur (-1 if none)
 * Note: modifies distances structure (global)
 */

int find_distances(int row)
{
    int i;
    double dist;
    double scale;
    double ns_dist;

    if (window.proj == PROJECTION_LL)
        G_set_geodesic_distance_lat2(window.north - (row + .5) * window.ns_res);

    /* if at same row, distance is constant across each cell */

    if (row == cur_row) {
        if (window.proj == PROJECTION_LL) {
            scale = 1.0 / G_geodesic_distance_lon_to_lon(0.0, window.ew_res);
            for (i = 0; i < ndist; i++) {
                distances[i].prev_ncols = (int)(scale * distances[i].dist);
                distances[i].ncols = find_ll_distance_ncols(i);
            }
        }
        else { /* note - see parse_dist.c for more info  */

            for (i = 0; i < ndist; i++)
                distances[i].ncols = distances[i].prev_ncols =
                    (int)distances[i].dist;
        }
    }
    else {
        if (window.proj == PROJECTION_LL)
            for (i = 0; i < ndist; i++)
                distances[i].ncols = find_ll_distance_ncols(i);
        else {
            i = cur_row - row;
            ns_dist = (i * i) * ns_to_ew_squared;
            for (i = 0; i < ndist; i++) {
                dist = distances[i].dist - ns_dist;
                if (dist < 0.0)
                    distances[i].ncols = -1;
                else
                    distances[i].ncols = (int)dist;
            }
        }
    }

    for (i = 0; i < ndist; i++)
        if (distances[i].ncols >= 0)
            return i;
    return -1;
}

int reset_distances(void)
{
    register int i;

    for (i = 0; i < ndist; i++)
        distances[i].ncols = distances[i].prev_ncols;

    return 0;
}

int find_ll_distance_ncols(int i)
{
    int col;
    double lon;
    register double d;
    register double dist;

    /* use the ncols from previous distances as a starting point
     * to figure the new ncols
     */

    col = distances[i].ncols - 1;
    if (col < 0)
        col = 0;
    dist = distances[i].dist;

    lon = window.ew_res * col;

    d = G_geodesic_distance_lon_to_lon(0.0, lon);
    if (d > dist) { /*backup */
        while (d > dist) {
            if (--col < 0)
                break;
            lon -= window.ew_res;
            d = G_geodesic_distance_lon_to_lon(0.0, lon);
        }
        return col;
    }
    if (d == dist)
        return col;

    while (d < dist && lon < 180.00 && col <= window.cols) {
        col++;
        lon += window.ew_res;
        d = G_geodesic_distance_lon_to_lon(0.0, lon);
    }
    return col - 1;
}
