/*
 *   This example opens an NPP example file and reads a dataset with region references 
 *   VIIRS-MOD_GTM-EDR-GEO_Gran_0 under the /Data_Products/VIIRS-MOD-GTM-EDR-GEO group. 
 *   Then it finds information about the selected elements pointed by the third reference 
 *   and reads the data in.  
 *   Main illustrative functions: H5LRget_region_info, H5LRread_region
 */
#include <stdlib.h>
#include <string.h>
#include "hdf5.h"
#include "hdf5_hl.h"
#include "H5LTpublic.h"
#include "h5hl_region.h"

#define filename "GMGTO_npp_d20030125_t0657104_e0659047_b00014_c20090811150425926728_unkn_SCI.h5"
#define dsetname "/Data_Products/VIIRS-MOD-GTM-EDR-GEO/VIIRS-MOD-GTM-EDR-GEO_Gran_0"     /* dataset with region references */


int main(void)
{
    hid_t file_id; /* file identifier */
    hid_t dset_id; /* region reference dataset identifier */
    hdset_reg_ref_t ref[15]; /* array to read region references */
    herr_t status;
    hid_t dtype; /* file datatype handle */
    hid_t mtype; /* mempry datatype handle */
    size_t msize; /* size of memory datatype */
    size_t rnumelem; /* number of elements to read */
    char *rdata; /* pointer to read buffer */
    int i;
    
    /*
     * Open the NPP file.
     */
    file_id = H5Fopen(filename, H5F_ACC_RDWR, H5P_DEFAULT);
    /*
     * Open dataset and read the dataset with the region references.
     * We made an assumption that the size of the dataset is known.
     */
    dset_id = H5Dopen(file_id, dsetname, H5P_DEFAULT);
    status = H5Dread(dset_id, H5T_STD_REF_DSETREG, H5S_ALL, H5S_ALL, H5P_DEFAULT,ref); 

    /* 
     * Get datatype of the data the region reference points to.
     */
    status = H5LRget_region_info(file_id, (const hdset_reg_ref_t*)ref[2], NULL, NULL, NULL, &dtype,
				 NULL, NULL, NULL);

    /*
     * Find the corresponding type in memory and its size.
     */
    mtype = H5Tget_native_type(dtype, H5T_DIR_ASCEND);
    msize = H5Tget_size(mtype);

    /*
     * Find number of elements in the region to read.
     */
    status = H5LRread_region(file_id,(const hdset_reg_ref_t*)ref[2], mtype, &rnumelem, NULL);

    /*
     * Allocate buffer to read data in.
     */
    rdata = (char *) malloc (rnumelem * msize);
    status = H5LRread_region(file_id,(const hdset_reg_ref_t*)ref[2], mtype, NULL, rdata);

    /*
     * We need to discover an appropriate C type to print data
     */
    if ((H5T_FLOAT == H5Tget_class(mtype)) & (sizeof(float) == msize)) {
        float tmp; /* temporary variables */
        char *tmp_p;
        printf(" Number of elements pointed by a region reference is %ld \n", rnumelem);
        printf(" The first six elements are: \n");
        tmp_p = rdata;
        for (i=0; i<6; i++) {
           memcpy (&tmp, tmp_p, msize);
           printf(" %7.3f ", tmp);
           tmp_p = tmp_p + msize;
        } 
        printf("\n");
    }
    free(rdata);

    /*
     * Close dataset with region references and file.
     */
    status = H5Dclose(dset_id);
    status = H5Fclose(file_id);

    return 0;
}