public interface Metric {}

/** Gauge calculates a specific value at a point in time. */
@Public
public interface Gauge<T> {

    /**
     * Calculates and returns the measured value.
     *
     * @return calculated value
     */
    T getValue();
}

/** A Counter is a metric measured by incrementing and decrementing. */
@Public
public interface Counter extends Metric {

    /** Increment the current count by 1. */
    void inc();

    /**
     * Increment the current count by the given value.
     *
     * @param n value to increment the current count by
     */
    void inc(long n);

    /** Decrement the current count by 1. */
    void dec();

    /**
     * Decrement the current count by the given value.
     *
     * @param n value to decrement the current count by
     */
    void dec(long n);

    /**
     * Returns the current count.
     *
     * @return current count
     */
    long getCount();
}

/** The histogram allows to record values, get the current count of recorded values and create
 * histogram statistics for the currently seen elements.*/
@Public
public interface Histogram extends Metric {

    /**
     * Update the histogram with the given value.
     *
     * @param value Value to update the histogram with
     */
    void update(long value);

    /**
     * Get the count of seen elements.
     *
     * @return Count of seen elements
     */
    long getCount();

    /**
     * Create statistics for the currently recorded elements.
     *
     * @return Statistics about the currently recorded elements
     */
    HistogramStatistics getStatistics();

	interface HistogramStatistics {
    	/**
     	* Return the number of values that the statistics computation is based on.
     	*/
    	int size();

    	/** Returns the mean value of the histogram observations. */
    	double mean();

    	/** Returns the standard deviation of the histogram distribution. */
    	double stdDev();

    	/** Returns the maximum value of the histogram observations. */
    	long max();

    	/** Returns the minimum value of the histogram observations. */
    	long min();

    	/**
     	* Returns the percentile value based on the histogram statistics.
     	*
     	* @param percentile percentile point in double. E.g., 0.75 means 75 percentile. It is up to the
     	*     implementation to decide what valid percentile points are supported.
     	* @return Value for the given percentile
     	*/
    	long percentile(double percentile);
  } 
}

public class Metrics {

    /** The metrics reporters container. */
  	private final List<MetricsReporter> reporters = new ArrayList<>();

	/** The metrics group. */  
	private final List<MetricGroup> metricGroups = new ArrayList<>();   

	/** Add a metrics reporter. */
	public void addReporter(MetricsReporter reporter) {};

	/** Add a metric group. */
	public void addGroup(MetricGroup group) {};

	/** Get metrics reporters. */
	public List<MetricsReporter> getReporters() {};

	/** Get metric groups. */
	public List<MetricGroup> getMetricGroups() {};
}

public interface MetricGroup {
   /** Register gauge metric. */
 	public void gauge(String name, Gauge gauge) {}

	/** Register counter metric. */
	public void counter(String name, Counter counter) {}

	/** Register histogram metric. */
	public void histogram(String name, Histogram counter) {}
}

public interface MetricsReporter {
	/** Configure reporter after instantiating it.*/
     void open();

    /** Closes this reporter. */
    void close();

	/** Report the current measurements. This method is called periodically by the Metrics. */
	void report();
}

public class CommitMetrics {
	private final String LAST_COMMIT_DURATION_METRIC = "lastCommitDuration";
	...

    private final Map<Integer, BucketMetricGroup> bucketMetricGroups = new HashMap<>();
    private final Map<BinaryRow, PartitionMetricGroup> partitionMetricGroups = new HashMap<>();
    private final MetricGroup genericMetricGroup;

	private void registerGenericCommitMetrics() {   
		group.gauge(LAST_COMMIT_DURATION_METRIC, new CommitDurationGauge());
		...
	}

 	private void registerTaggedCommitMetrics() {
		if(isNewBucket()) {
			registerTaggedMetrics();
		}

	 	if(isNewBucket()) {
			registerTaggedMetrics();
		}
	}
}

public class ScanMetrics {
	private final String LAST_SCAN_SKIPPED_MANIFESTS_METRIC = "lastScanSkippedManifests";
	...
 	
	private final Map<Integer, BucketMetricGroup> bucketMetricGroups = new HashMap<>();
    private final Map<BinaryRow, PartitionMetricGroup> partitionMetricGroups = new HashMap<>();

 	private void registerTaggedScanMetrics() {
		if(isNewBucket()) {
			registerTaggedMetrics();
		}

	 	if(isNewPartition()) {
			registerTaggedMetrics();
		}
	}       
}

public class CompactionMetrics {

	private final String LAST_TABLE_FILES_COMPACTED_BEFORE_METRIC = "lastTableFilesCompactedBefore";
 	...
 	
	private final Map<Integer, BucketMetricGroup> bucketMetricGroups = new HashMap<>();
    private final Map<BinaryRow, PartitionMetricGroup> partitionMetricGroups = new HashMap<>();

 	private void registerTaggedCompactionMetrics() {
		if(isNewBucket()) {
			registerTaggedMetrics();
		}

	 	if(isNewPartition()) {
			registerTaggedMetrics();
		}
	}
}