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/*
 * Copyright 2017-2020 original authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package io.micronaut.management.health.indicator.discovery;

import io.micronaut.context.annotation.Requires;
import io.micronaut.core.util.StringUtils;
import io.micronaut.discovery.DiscoveryClient;
import io.micronaut.discovery.ServiceInstance;
import io.micronaut.health.HealthStatus;
import io.micronaut.management.endpoint.health.HealthEndpoint;
import io.micronaut.management.health.indicator.HealthIndicator;
import io.micronaut.management.health.indicator.HealthResult;
import jakarta.inject.Singleton;
import org.reactivestreams.Publisher;
import reactor.core.publisher.Flux;

import java.util.Collections;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.function.Function;
import java.util.stream.Collectors;
import java.util.stream.Stream;

/**
 * A health indicator for the discovery client.
 *
 * @author graemerocher
 * @since 1.0
 */
@Requires(beans = {DiscoveryClient.class, DiscoveryClientHealthIndicatorConfiguration.class})
@Singleton
@Requires(property = HealthEndpoint.PREFIX + ".discovery-client-health.enabled", defaultValue = StringUtils.TRUE, notEquals = StringUtils.FALSE)
public class DiscoveryClientHealthIndicator implements HealthIndicator {

    private final DiscoveryClient discoveryClient;

    /**
     * @param discoveryClient The Discovery client
     */
    public DiscoveryClientHealthIndicator(DiscoveryClient discoveryClient) {
        this.discoveryClient = discoveryClient;
    }

    @Override
    public Publisher getResult() {
        return Flux.from(discoveryClient.getServiceIds())
            .flatMap((Function, Publisher>) ids -> {
                List>>> serviceMap = ids.stream()
                    .map(id -> {
                        Flux> serviceList = Flux.from(discoveryClient.getInstances(id));
                        return serviceList
                            .map(serviceInstances -> Collections.singletonMap(id, serviceInstances));
                    })
                    .collect(Collectors.toList());
                Flux>> mergedServiceMap = Flux.merge(serviceMap);

                return mergedServiceMap.reduce(new LinkedHashMap>(), (allServiceMap, service) -> {
                    allServiceMap.putAll(service);
                    return allServiceMap;
                }).map(details -> {
                    HealthResult.Builder builder = HealthResult.builder(discoveryClient.getDescription(), HealthStatus.UP);
                    Stream>> entryStream = details.entrySet().stream();
                    Map value = entryStream.collect(
                        Collectors.toMap(Map.Entry::getKey, entry ->
                            entry
                                .getValue()
                                .stream()
                                .map(ServiceInstance::getURI)
                                .collect(Collectors.toList())
                        )
                    );

                    builder.details(Collections.singletonMap(
                        "services", value
                    ));
                    return builder.build();
                }).flux();
            }).onErrorResume(throwable -> {
                HealthResult.Builder builder = HealthResult.builder(discoveryClient.getDescription(), HealthStatus.DOWN);
                builder.exception(throwable);
                return Flux.just(builder.build());
            });
    }
}