com.github.rahulsom.grooves.queries.internal.Utils Maven / Gradle / Ivy

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package com.github.rahulsom.grooves.queries.internal;

import com.github.rahulsom.grooves.api.AggregateType;
import com.github.rahulsom.grooves.api.events.BaseEvent;
import com.github.rahulsom.grooves.api.events.DeprecatedBy;
import com.github.rahulsom.grooves.api.snapshots.internal.BaseSnapshot;
import rx.Observable;

import java.util.List;
import java.util.function.Supplier;
import java.util.stream.Collector;
import java.util.stream.Collectors;

/**
 * Utility objects and methods to help with Queries.
 *
 * @author Rahul Somasunderam
 */
public class Utils {

    private static final Collector JOIN_EVENT_IDS =
            Collectors.joining(", ");

    private static final Collector JOIN_EVENTS =
            Collectors.joining(",\n    ", "[\n    ", "\n]");

    private Utils() {
    }

    /**
     * Returns a snapshot or redirects to its deprecator.
     *
     * @param redirect           Whether a redirect is desirable
     * @param events             The sequence of events
     * @param it                 The snapshot
     * @param redirectedSnapshot A computation for the redirected snapshot
     * @param         The type of the snapshot
     * @param            The type of the event
     *
     * @return An observable of a snapshot.
     */
    public static <
            SnapshotT extends BaseSnapshot,
            EventT extends BaseEvent
            > Observable returnOrRedirect(
            boolean redirect, List events, SnapshotT it,
            Supplier> redirectedSnapshot) {
        final EventT lastEvent =
                events.isEmpty() ? null : events.get(events.size() - 1);

        return it.getDeprecatedByObservable()
                .flatMap(deprecatedBy -> {
                    final boolean redirectToDeprecator =
                            lastEvent != null
                                    && lastEvent instanceof DeprecatedBy
                                    && redirect;

                    return redirectToDeprecator ?
                            redirectedSnapshot.get() :
                            Observable.just(it);

                })
                .defaultIfEmpty(it);

    }

    /**
     * Computes forward only events. This could mean cancelling out events with their reverts
     * within a list, or sometimes, invoking the supplier of fallback events to get events.
     *
     * @param events                    The sequence of events
     * @param executor                  The executor to use for processing events
     * @param fallbackSnapshotAndEvents The fallback supplier
     * @param               The type of Aggregate
     * @param                 The type of Event Id
     * @param                   The type of Event
     * @param              The type of Snapshot Id
     * @param                The type of Snapshot
     *
     * @return an observable of forward only events
     */
    public static <
            AggregateT extends AggregateType,
            EventIdT,
            EventT extends BaseEvent,
            SnapshotIdT,
            SnapshotT extends BaseSnapshot
            > Observable getForwardOnlyEvents(
            List events,
            Executor executor,
            Supplier>>> fallbackSnapshotAndEvents) {
        return executor.applyReverts(Observable.from(events))
                .toList()
                .map(Observable::just)
                .onErrorReturn(throwable -> executor
                        .applyReverts(
                                fallbackSnapshotAndEvents.get()
                                        .flatMap(it -> Observable.from(it.getSecond()))
                        )
                        .toList()
                )
                .flatMap(it -> it)
                .flatMap(Observable::from);
    }

    /**
     * Turns a list of events into a readable log style string.
     *
     * @param events   The list of events
     * @param  The type of events
     *
     * @return A String representation of events
     */
    public static  String stringifyEvents(List events) {
        return events.stream()
                .map(EventT::toString)
                .collect(Utils.JOIN_EVENTS);
    }

    /**
     * Turns a list of events into a readable list of ids.
     *
     * @param events   The list of events
     * @param  The type of events
     *
     * @return A String representation of events
     */
    public static  String stringifyEventIds(List events) {
        return events.stream()
                .map(i -> i.getId().toString())
                .collect(Utils.JOIN_EVENT_IDS);
    }

}