de.melnichuk.events.Events Maven / Gradle / Ivy
package de.melnichuk.events;
import java.util.*;
import java.util.stream.Collectors;
public class Events {
/**
* holds samples of different resolution.
*
* key is the increment (aka. resolution)
* value is the list of length {@code threshold} holding samples.
*/
private final Map> history = new HashMap<>();
/**
* default behaviour ist to pick the first item assuming first==newest
*/
private SamplingStrategy samplingStrategy = LinkedList::getFirst;
/**
* max number of items in a list holding samples.
*/
private final int threshold;
/**
* items stored for sampling strategy to work with
*/
private LinkedList itemBacklog = new LinkedList<>();
/**
* number of items to remember for sampling strategy to work with
*/
private int itemBacklogCount = 10;
/**
* number of items processed.
*/
private long count;
public Events(int threshold, int... increments) {
this.threshold = threshold;
Arrays.stream(increments).forEach(i -> history.put(i, new LinkedList<>()));
}
public void process(T item) {
try {
doProcess(item);
} finally {
count++;
}
}
private void doProcess(T item) {
addItemToList(item, itemBacklog, itemBacklogCount);
// select list of samples with matching increment
final List>> matchingIncrementsAndSamples = history.entrySet().stream()
.filter(incrementAndSamples -> count % incrementAndSamples.getKey() == 0)
.collect(Collectors.toList());
if (!matchingIncrementsAndSamples.isEmpty()) {
final T sample = samplingStrategy.getSample(itemBacklog);
matchingIncrementsAndSamples.stream()
.map(incrementAndSamples -> incrementAndSamples.getValue())
.forEach(samples -> {
addItemToList(sample, samples, threshold);
});
}
}
private void addItemToList(final T event, final LinkedList samples, final int threshold) {
samples.addFirst(event);
if (samples.size() > threshold) {
samples.removeLast();
}
}
public Map> getHistory() {
return history;
}
}