/**
 * Name:
 *     subFRPSDRemapping.
 * Purpose:
 *     Calculate 9km FRP standard deviation
 * Inputs:
 *      - column and row indexes of the 3km and 9km grids.
 *      - 3km grid FRP standard deviation.
 *      - 3km grid FRP quality.
 * Output:
 *      - 9km grid FRP stndard deviation.
 * Procedure:
 *      (1) Aggregate the FRP values of the 3km grids with valid value and medium
 *          or high quality, which are centered at a given 13km grid.
 *      (2) Count the number of the 3km grids with valid value and medium or
 *          high quality.
 *      (3) Average the aggregated 3km FRP value by the number of
 *          grids.
 *      (4) Calculate 9km FRP standard deviation using individual 3km-grid FRP value and
 *          averaged 3km FRP value centered at a given 9km grid.
 *
 * @param remappingindexfile The input file that contains column and row indexes
 *        for 3km and 9km grids.
 * @param var3  The input array that contains the 3km grid FRP.
 * @param qaf3  The input array that contains the 3km grid quality.
 * @param var9  The output array that stores the remapped 9km FRP standard
 *        deviation.
 *
 */
int subFRPSDRemapping( char *remappingindexfile, float var3[], short int qaf3[],
                      float var13[])
{
    // Declare variables.
    FILE *fp;
    char buffer[MAX_LEN];
    int i, m;
    long int k;

    int nps;
    char *token;

    int i9, j9; // column index (i9) and row index (j9) for 9km data.
    int i3, j3; // column index (i3) and row index (j3) for 3km data.
    float nnp;
    float sum;

    // Initialize.
    for (i = 0; i < LAST_HOURS * grid_yt_9km * grid_xt_9km; i++)
        var9[i] = 0.0;

    // Open the grid index file.
    fp = fopen(remappingindexfile, "r");
    if (fp == NULL)
    {
        perror("Failed: ");
        return 1;
    }

      // To execute a while-loop to calculate 9km FRP value from 3km grids centerd at the 9km grid.
    while (fgets(buffer, MAX_LEN, fp))
    {
        // Remove trailing newline characters from end of string and replace it
        // with '\0'.
        buffer[strcspn(buffer, "\n")] = 0;

        // Extract 9km grid column and row indexes.
        token = strtok(buffer, ",");
        i9 = atoi(token);

        token = strtok(NULL, ",");
        j9 = grid_yt_9km - 1 - atoi(token);

        m = j9 * LAST_HOURS * grid_xt_9km + i9;

        // Extract the number of 3km grids centered at a given 9km grid.
        token = strtok(NULL, ",");
        nps = atoi(token);

        // Read lats/lons of four angle points for a given 9km grid.
        for (i = 0; i < 4; i++)
            fgets(buffer, MAX_LEN, fp);
        // Initialize.
        nnp = 0.0;
        sum = 0.0;

        // To execute a for-loop to calculate 9km grid FRP.
        for (i = 0; i < nps; i++)
        {
            // Extract 3km grid column and row indexes.
            fgets(buffer, MAX_LEN, fp);
            token = strtok(buffer, ",");
            token = strtok(NULL, ",");

            i3 = atoi(token);
            token = strtok(NULL, ",");

            j3 = atoi(token);
            k = j3 * LAST_HOURS * grid_xt_3km + i3;

            /* Aggregate 3km FRP values only for those grids with valid value
              and medium or high quality. */
            if ((qaf3[k] == 2 || qaf3[k] == 3) && var3[k] >= 0.0) //
            {
                sum = sum + var3[k];
                nnp = nnp + 1.0;
            }
        }

        // Calculate mean FRP value for 9km grid and temporarily store it to var9
        var9[m] = -1.0;
        if (nnp >= 1.0)
            var9[m] = sum / nnp;
    }

    // Close the open file stream.
    fclose(fp);

    // Re-open the grid index file.
    fp = fopen(remappingindexfile, "r");
    if (fp == NULL)
    {
        perror("Failed: ");
        return 1;
    while (fgets(buffer, MAX_LEN, fp))
    {
        buffer[strcspn(buffer, "\n")] = 0;
        token = strtok(buffer, ",");
        i9 = atoi(token);

        token = strtok(NULL, ",");
        j9 = grid_yt_9km - 1 - atoi(token);

        m = j9 * LAST_HOURS * grid_xt_9km + i9;
        token = strtok(NULL, ",");
        nps = atoi(token);
        for (i = 0; i < 4; i++)
            fgets(buffer, MAX_LEN, fp);
        nnp = 0.0;
        sum = 0.0;
        for (i = 0; i < nps; i++)
        {
            fgets(buffer, MAX_LEN, fp);
            token = strtok(buffer, ",");
            token = strtok(NULL, ",");

            i3 = atoi(token);
            token = strtok(NULL, ",");

            j3 = atoi(token);
            k = j3 * LAST_HOURS * grid_xt_3km + i3;
            if ((qaf3[k] == 2 || qaf3[k] == 3)
                && var3[k] >= 0.0 && var9[m] >= 0.0)
            {
                sum = sum + pow (var3[k] - var9[m],2);
                nnp = nnp + 1.0;
            }
        }

        // Calculate the FRP standard deviation
        var9[m] = -1.0;
        if (nnp >= 1.0)
            var13[m] = sqrt (sum / nnp) ;
    }
    // Close the open file stream.
       fclose(fp);

    return 0;
}