import java.util.Calendar;
import java.util.Date;

import com.amazonaws.regions.Regions;
import com.amazonaws.services.cloudwatch.AmazonCloudWatch;
import com.amazonaws.services.cloudwatch.AmazonCloudWatchClientBuilder;
import com.amazonaws.services.cloudwatch.model.GetMetricStatisticsRequest;
import com.amazonaws.services.cloudwatch.model.GetMetricStatisticsResult;
import com.amazonaws.services.cloudwatch.model.StandardUnit;
import com.amazonaws.services.cloudwatch.model.Dimension;
import com.amazonaws.services.cloudwatch.model.Datapoint;

public class RDSInfo {
    private final long GB;
    private Calendar calendar;
    private Date endTime;
    private Date startTime;
    private String dbIdentifier;
    private Regions region;

    public RDSInfo() {
        this.GB = 1024L * 1024L * 1024L;
        this.calendar = Calendar.getInstance();
        this.endTime = this.calendar.getTime();
        this.calendar.add(Calendar.MINUTE, -5);
        this.startTime = this.calendar.getTime();
        this.dbIdentifier = "dbIdentifier";
        this.region = Regions.EU_WEST_1;
    }

    public void getRDSFreeSpace() {
        Dimension dim = new Dimension()
            .withName("DBInstanceIdentifier")
            .withValue(this.dbIdentifier);

        final AmazonCloudWatch cw = AmazonCloudWatchClientBuilder.standard()
                                        .withRegion(this.region)
                                        .build();

        GetMetricStatisticsRequest req = new GetMetricStatisticsRequest()
            .withNamespace("AWS/RDS")
            .withMetricName("FreeStorageSpace")
            .withStatistics("Average")
            .withStartTime(this.startTime)
            .withEndTime(this.endTime)
            .withDimensions(this.dim)
            .withPeriod(300);

        GetMetricStatisticsResult res = cw.getMetricStatistics(req);

        for (Datapoint dp : res.getDatapoints()) {
            double freespaceGigs = dp.getAverage() / this.GB;
            System.out.println(String.format("RDS Free Space: %.2f GB", freespaceGigs));
        }
    }
}