/**
 * Name:
 *          subCFRemapping.
 * Purpose:
 *          Calculate 9km grid cloud fraction (CF).
 * Inputs:
 *          - column and row indexes for 3km and 9km grids.
 *          - 3km grid cloud fraction.
 *          - 3km grid area.
 * Output:
 *          - 9km grid cloud fraction.
 * Procedure:
 *         (1) Aggregate the product of CF times AREA for each 3km grid.
 *         (2) Aggregate the AREA for each 3km grid.
 *         (3) Average the aggregated 3km grid CF by the aggregated area.
 *
 * @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 cloud fraction.
 * @param area3 The input array that contains the 3km grid area.
 * @param var9 The output array that stores the remapped 9km land cover types.
 *
 */

int subCFRemapping(char *remappingindexfile, int var3[], float area3[],
                   int var9[])
{
    // Declares 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 wa, wb, nnp;

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

    // Open the grid index file.
    fp = fopen(remappingindexfile, "r");
    if (fp == NULL)
    {
        perror("Failed: ");
        return 1;
    }
    // To execute a while-loop to calculate Cloud Fractor grid by 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 3km grid column and row indexes.
        token = strtok(buffer, ","); // Break the string into a series of tokens.
        i9 = atoi(token);

        token = strtok(NULL, ",");
        // Reverse 'j' index order becasue the AQM-v8 model data have oppsite order
        j9 = grid_yt_9km - 1 - atoi(token);

        m = j9 * LAST_HOURS * grid_xt_9km + i9;

        // Get 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.
        wa = 0.0;
        wb = 0.0;
        nnp = 0.0;

        // To excute a for-loop to agrregate 3km grid area.
        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;
            token = strtok(NULL, ",");

            // Aggregate variable values for those grids with valid values (>0).
            if (var3[k] > 0)
            {
                wa = wa + (float)var3[k] * area3[k]; // sum of the product of CF times area.
                wb = wb + area3[k];                  // sum of area.
                nnp = nnp + 1.0;
            }
        }

        // Calculate 9km grid Cloud Fraction.
        var9[m] = -1;
        if (nnp >= 1.0)
            var9[m] = (int)(wa / wb);
    }

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

    return 0;
}