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package org.apache.james.dlp.eventsourcing.aggregates;

import java.util.List;
import java.util.Optional;
import java.util.Set;
import java.util.stream.Stream;

import org.apache.james.dlp.api.DLPConfigurationItem;
import org.apache.james.dlp.api.DLPRules;
import org.apache.james.dlp.eventsourcing.events.ConfigurationItemsAdded;
import org.apache.james.dlp.eventsourcing.events.ConfigurationItemsRemoved;
import org.apache.james.eventsourcing.Event;
import org.apache.james.eventsourcing.EventId;
import org.apache.james.eventsourcing.eventstore.History;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Sets;

public class DLPDomainConfiguration {

    public static DLPDomainConfiguration load(DLPAggregateId aggregateId, History history) {
        return new DLPDomainConfiguration(aggregateId, history);
    }

    private static class State {

        static State initial() {
            return new State(ImmutableSet.of());
        }

        final ImmutableSet rules;

        private State(ImmutableSet rules) {
            this.rules = rules;
        }

        State add(List toAdd) {
            ImmutableSet union = Stream.concat(this.rules.stream(), toAdd.stream()).collect(ImmutableSet.toImmutableSet());
            return new State(union);
        }

        State remove(List toRemove) {
            ImmutableSet filtered = rules.stream().filter(rule -> !toRemove.contains(rule)).collect(ImmutableSet.toImmutableSet());
            return new State(filtered);
        }
    }

    private final DLPAggregateId aggregateId;
    private final History history;
    private State state;

    private DLPDomainConfiguration(DLPAggregateId aggregateId, History history) {
        this.aggregateId = aggregateId;
        this.state = State.initial();
        history.getEventsJava().forEach(this::apply);
        this.history = history;
    }

    public DLPRules retrieveRules() {
        return new DLPRules(ImmutableList.copyOf(state.rules));
    }

    public List clear() {
        ImmutableList rules = retrieveRules().getItems();
        if (!rules.isEmpty()) {
            ImmutableList events = ImmutableList.of(new ConfigurationItemsRemoved(aggregateId, history.getNextEventId(), rules));
            events.forEach(this::apply);
            return events;
        } else {
            return ImmutableList.of();
        }
    }

    public List store(DLPRules updatedRules) {
        ImmutableSet existingRules = retrieveRules().getItems().stream().collect(ImmutableSet.toImmutableSet());
        ImmutableSet updatedRulesSet = ImmutableSet.copyOf(updatedRules);

        Optional removedRulesEvent = generateRemovedRulesEvent(existingRules, updatedRulesSet);
        Optional addedRulesEvent = generateAddedRulesEvent(existingRules, updatedRulesSet, computeNextEventId(removedRulesEvent));

        ImmutableList events = Stream
            .of(removedRulesEvent, addedRulesEvent)
            .flatMap(Optional::stream)
            .collect(ImmutableList.toImmutableList());

        events.forEach(this::apply);
        return events;
    }

    private EventId computeNextEventId(Optional removedRulesEvent) {
        return removedRulesEvent
            .map(Event::eventId)
            .map(EventId::next)
            .orElseGet(history::getNextEventId);
    }

    private Optional generateRemovedRulesEvent(ImmutableSet existingRules, ImmutableSet updateRulesSet) {
        Set removedRules = Sets.difference(existingRules, updateRulesSet);
        if (!removedRules.isEmpty()) {
            return Optional.of(new ConfigurationItemsRemoved(aggregateId, history.getNextEventId(), removedRules));
        }
        return Optional.empty();
    }

    private Optional generateAddedRulesEvent(Set existingRules, Set updateRulesSet, EventId nextEventId) {
        Set addedRules = Sets.difference(updateRulesSet, existingRules);
        if (!addedRules.isEmpty()) {
            return Optional.of(new ConfigurationItemsAdded(aggregateId, nextEventId, addedRules));
        }
        return Optional.empty();
    }

    private void apply(Event event) {
        if (event instanceof ConfigurationItemsAdded) {
            state = state.add(((ConfigurationItemsAdded) event).getRules());
        }
        if (event instanceof ConfigurationItemsRemoved) {
            state = state.remove(((ConfigurationItemsRemoved) event).getRules());
        }
    }

}