/**
 * {@link Event} represents an event that happened in Flink for reporting, e.g. a completed
 * checkpoint or a restart.
 */
@Experimental
public interface Event {

    static EventBuilder builder(Class<?> classScope, String name) {
        return new EventBuilder(classScope, name);
    }

    /** The timestamp for when the event happened or was observed, in milliseconds. */
    long getObservedTsMillis();

    /** The name of the event. */
    String getName();

    /** The scope of the event, typically the fully qualified name of the emitting class. */
    String getClassScope();

    /** Textual description of the event. */
    String getBody();

    /** Severity of the event, e.g. DEBUG, INFO, ... */
    String getSeverity();

    /**
     * Additional attributes for the event. Currently, returned values can be of type String, Long
     * or Double, however more types can be added in the future.
     */
    Map<String, Object> getAttributes();
}

/** Builder used to construct {@link Event}. See {@link Event#builder(Class, String)}. */
@Experimental
public class EventBuilder {
    ...
    
    // Ctors
    public EventBuilder(Class<?> classScope, String name) {...}
    public EventBuilder(String classScope, String name) {...}
    public EventBuilder(Class<?> classScope) {...}
    public EventBuilder() {...}

    /** Sets the timestamp for when the event happened or was observed, in milliseconds. */
    public EventBuilder setObservedTsMillis(long observedTsMillis) {...}

    /** Sets the name of the event. */
    public EventBuilder setName(String name) {...}

    /** Sets the scope of the event, typically the fully qualified name of the emitting class. */
    public EventBuilder setClassScope(String classScope) {...}

    /** Sets the textual description of the event. */
    public EventBuilder setBody(String body) {...}

    /** Sets the severity of the event, e.g. DEBUG, INFO, ... */
    public EventBuilder setSeverity(String severity) {...}

    /** Additional attribute to be attached to this {@link Event}. */
    public EventBuilder setAttribute(String key, String value) {...}

    /** Additional attribute to be attached to this {@link Event}. */
    public EventBuilder setAttribute(String key, long value) {...}

    /** Additional attribute to be attached to this {@link Event}. */
    public EventBuilder setAttribute(String key, double value) {...}

    public String getName() {...}

    /** Builds the specified instance. */
    public Event build(Map<String, String> additionalVariables) {...}
    public Event build() {...}
}

@Experimental
public interface EventReporter extends Reporter {
    
    /** Report the given event. */
    void notifyOfAddedEvent(Event event);
}

/** Parent interface to all reporters, defining their common lifecycle. */
@public
public interface Reporter {

    /** Configures this reporter. */
    void open(MetricConfig config);

    /** Closes this reporter. Should be used to close channels, streams and release resources. */
    void close();
}

/**
 * {@link EventReporter} factory.
 *
 * <p>Event reporters that can be instantiated with a factory automatically qualify for being loaded
 * as a plugin, so long as the reporter jar is self-contained (excluding Flink dependencies) and
 * contains a {@code META-INF/services/org.apache.flink.events.reporter.EventReporterFactory} file
 * containing the qualified class name of the factory.
 */
@Experimental
public interface EventReporterFactory {
    /**
     * Creates a new event reporter.
     *
     * @param properties configured properties for the reporter
     * @return created metric reporter
     */
    EventReporter createEventReporter(Properties properties);
}

@Public
public interface MetricGroup {

    @Experimental
    default void addEvent(EventBuilder eventBuilder) {}
    
    (...)
}