/*
 ****************************************************************************
 *
 * MODULE:       gis library
 * AUTHOR(S):    Andreas Lange - andreas.lange@rhein-main.de
 *               Paul Kelly - paul-grass@stjohnspoint.co.uk
 * PURPOSE: 	 provide functions for reading datum parameters from the
 *               location database.     
 * COPYRIGHT:    (C) 2000, 2003 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.
 *
 *****************************************************************************/

#define DATUMTABLE "/etc/datum.table"

#include <unistd.h>
#include <string.h>
#include <ctype.h>
#include <stdlib.h>

#include <grass/gis.h>
#include <grass/glocale.h>

static struct table
{
    char *name;   /* Short Name / acronym of map datum */
    char *descr;  /* Long Name for map datum */
    char *ellps;  /* acronym for ellipsoid used with this datum */
    double dx;    /* delta x */
    double dy;    /* delta y */
    double dz;    /* delta z */
} *table;

static int size;
static int count = -1;

static int compare_table_names(const void *, const void *);
static void read_datum_table(void);

int 
G_get_datum_by_name(const char *name)
{
    int i;

    read_datum_table();

    for (i = 0; i < count; i++)
	if (G_strcasecmp(name, table[i].name) == 0)
	    return i;

    return -1;
}

char *
G_datum_name(int n)
{
    read_datum_table();

    if (n < 0 || n >= count) 
	return NULL; 

    return table[n].name;
}

char *
G_datum_description(int n)
{ 
    read_datum_table();
  
    if (n < 0 || n >= count)
	return NULL;

    return table[n].descr;
}

char *
G_datum_ellipsoid(int n)
{
    read_datum_table();

    if (n < 0 || n >= count)
	return NULL;

    return table[n].ellps;
}

/***********************************************************
 *  G_get_datumparams_from_projinfo(projinfo, datumname, params)
 *     struct Key_Value *projinfo Set of key_value pairs containing
 *                       projection information in PROJ_INFO file
 *                       format
 *     char *datumname   Pointer into which a string containing
 *                       the datum name (if present) will be
 *                       placed.
 *     char *params      Pointer into which a string containing
 *                       the datum parameters (if present) will
 *                       be placed.
 *
 *  Extract the datum transformation-related parameters from a 
 *  set of general PROJ_INFO parameters.
 *  This function can be used to test if a location set-up 
 *  supports datum transformation.
 *  
 *  returns: -1 error or no datum information found, 
 *           1 only datum name found, 2 params found
 ************************************************************/

int G_get_datumparams_from_projinfo(const struct Key_Value *projinfo, 
				    char *datumname, char *params)
{
    int returnval = -1;
   
    if( NULL != G_find_key_value("datum", projinfo) )
    {
        sprintf(datumname, G_find_key_value("datum", projinfo));
        returnval = 1;
    }
          
    if( G_find_key_value("datumparams", projinfo) != NULL )
    {
        sprintf(params, G_find_key_value("datumparams", projinfo));
        returnval = 2;
    }
    else if( G_find_key_value("nadgrids", projinfo) != NULL )
    {
        sprintf(params, "nadgrids=%s", G_find_key_value("nadgrids", projinfo));
        returnval = 2;
    }
    else if( G_find_key_value("towgs84", projinfo) != NULL )
    {
        sprintf(params, "towgs84=%s", G_find_key_value("towgs84", projinfo));
        returnval = 2;
    }
    else if( G_find_key_value("dx", projinfo) != NULL
	  && G_find_key_value("dy", projinfo) != NULL
	  && G_find_key_value("dz", projinfo) != NULL ) 
    {
        sprintf(params, "towgs84=%s,%s,%s",
	        G_find_key_value("dx", projinfo),
	      	G_find_key_value("dy", projinfo),
	       	G_find_key_value("dz", projinfo) );
        returnval = 2;
    }

    return returnval;
   
}

static void
read_datum_table(void) 
{
    FILE *fd;
    char file[1024];
    char buf[1024];
    int line;

    if (count >= 0)
        return;

    count = 0;

    sprintf(file, "%s%s", G_gisbase(), DATUMTABLE);

    fd = fopen(file, "r");
    if (!fd)
    {
        G_warning(_("unable to open datum table file: %s"), file);
        return;
    }

    for (line = 1; G_getl2(buf, sizeof(buf), fd); line++)
    {
        char name[100], descr[100], ellps[100];
        struct table *t;

        G_strip(buf);
        if (*buf == '\0' || *buf == '#')
            continue;

        if (count >= size)
        {
            size += 50;
            table = G_realloc(table, size * sizeof(struct table));
        }

        t = &table[count];

        if (sscanf(buf, "%s \"%99[^\"]\" %s dx=%lf dy=%lf dz=%lf",
                   name, descr, ellps, &t->dx, &t->dy, &t->dz) != 6)
        {
            G_warning(_("error in datum table file, line %d"), line);
            continue;
        }

        t->name  = G_store (name);
        t->descr = G_store (descr);
        t->ellps = G_store (ellps);

        count++;
    }
 
    qsort(table, count, sizeof(struct table), compare_table_names);
}

static int
compare_table_names(const void *aa, const void *bb)
{
    const struct table *a = aa;
    const struct table *b = bb;

    return G_strcasecmp(a->name, b->name);
}
