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 * to you under the Apache License, Version 2.0 (the            *
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package org.apache.james.queue.rabbitmq.view.cassandra.configuration;

import java.util.List;
import java.util.Optional;

import org.apache.james.eventsourcing.AggregateId;
import org.apache.james.eventsourcing.Event;
import org.apache.james.eventsourcing.eventstore.History;

import com.google.common.base.Preconditions;
import com.google.common.collect.ImmutableList;

class ConfigurationAggregate {

    private static class State {

        private static State initial() {
            return new State(Optional.empty());
        }

        private Optional<CassandraMailQueueViewConfiguration> maybeConfiguration;

        State(Optional<CassandraMailQueueViewConfiguration> maybeConfiguration) {
            Preconditions.checkNotNull(maybeConfiguration);
            this.maybeConfiguration = maybeConfiguration;
        }

        State set(CassandraMailQueueViewConfiguration configuration) {
            return new State(Optional.of(configuration));
        }

    }

    static ConfigurationAggregate load(AggregateId aggregateId, History history) {
        return new ConfigurationAggregate(aggregateId, history);
    }

    private static final List<? extends Event> EMPTY_EVENTS = ImmutableList.of();

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

    ConfigurationAggregate(AggregateId aggregateId, History history) {
        this.aggregateId = aggregateId;
        this.history = history;
        this.state = State.initial();

        history.getEvents().forEach(this::apply);
    }

    List<? extends Event> registerConfiguration(CassandraMailQueueViewConfiguration configuration) {
        boolean isSame = state.maybeConfiguration.map(configuration::equals).orElse(false);
        if (isSame) {
            return EMPTY_EVENTS;
        }

        state.maybeConfiguration.ifPresent(oldConfiguration -> oldConfiguration.validateConfigurationChange(configuration));

        return ImmutableList.of(new ConfigurationChanged(
            aggregateId,
            history.getNextEventId(),
            configuration));
    }

    Optional<CassandraMailQueueViewConfiguration> getCurrentConfiguration() {
        return state.maybeConfiguration;
    }

    private void apply(Event event) {
        if (event instanceof ConfigurationChanged) {
            ConfigurationChanged configurationChanged = (ConfigurationChanged) event;

            state = state.set(configurationChanged.getConfiguration());
        }
    }
}
