/*
 * Copyright 2014-2018 the original author or 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
 *
 *     http://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 de.codecentric.boot.admin.server.web;

import de.codecentric.boot.admin.server.domain.entities.Instance;
import de.codecentric.boot.admin.server.domain.values.BuildVersion;
import de.codecentric.boot.admin.server.domain.values.StatusInfo;
import de.codecentric.boot.admin.server.eventstore.InstanceEventPublisher;
import de.codecentric.boot.admin.server.notify.ServicesList;
import de.codecentric.boot.admin.server.services.InstanceRegistry;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.http.codec.ServerSentEvent;
import org.springframework.web.bind.annotation.DeleteMapping;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.ResponseBody;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;
import reactor.util.function.Tuple2;
import reactor.util.function.Tuples;

import java.time.Duration;
import java.time.Instant;
import java.util.*;

import static java.util.Comparator.naturalOrder;
import static java.util.stream.Collectors.toList;
import static java.util.stream.Collectors.toMap;

/**
 * REST controller for controlling registration of managed instances.
 */
@AdminController
@ResponseBody
public class ApplicationsController {
    private static final Logger log = LoggerFactory.getLogger(ApplicationsController.class);
    private static final ServerSentEvent<?> PING = ServerSentEvent.builder().comment("ping").build();
    private static final Flux<ServerSentEvent<?>> PING_FLUX = Flux.interval(Duration.ZERO, Duration.ofSeconds(10L))
        .map(tick -> PING);
    private final InstanceRegistry registry;
    private final InstanceEventPublisher eventPublisher;

    public ApplicationsController(InstanceRegistry registry, InstanceEventPublisher eventPublisher) {
        this.registry = registry;
        this.eventPublisher = eventPublisher;
    }

    @Autowired
    private ServicesList servicesList;


    @GetMapping(path = "/applications", produces = MediaType.APPLICATION_JSON_VALUE)
    public Flux<Application> applications() {
        Flux<Application> applicationFlux = registry.getInstances()
            .filter(Instance::isRegistered)
            .groupBy(instance -> instance.getRegistration().getName())
            .flatMap(grouped -> toApplication(grouped.key(), grouped));

        List<String> appNames = new ArrayList<>();

        applicationFlux.subscribe(application -> appNames.add(application.getName()));

        for (String appName : minus(servicesList.getServices(),appNames)) {
            Application group = new Application(appName.toUpperCase());
            group.setStatus("OFFINE");
            group.setInstances(Collections.emptyList());
            applicationFlux = applicationFlux.concatWithValues(group);
        }

        return applicationFlux;
    }

    /**
     * 求两数组的差集
     *
     * @param arr1 模板数组
     * @param arr2 比较数组
     * @return
     */
    public static String[] minus(List<String> arr1, List<String> arr2) {
        LinkedList<String> list = new LinkedList<>();
        LinkedList<String> history = new LinkedList<>();

        for (String str : arr1) {
            if (!list.contains(str.toUpperCase())) {
                list.add(str.toUpperCase());
            }
        }
        for (String str : arr2) {
            list.remove(str.toUpperCase());
        }

        String[] result = {};
        return list.toArray(result);
    }

    @GetMapping(path = "/applications", produces = MediaType.TEXT_EVENT_STREAM_VALUE)
    public Flux<ServerSentEvent<Application>> applicationsStream() {
        return Flux.from(eventPublisher)
            .flatMap(event -> registry.getInstance(event.getInstance()))
            .map(this::getApplicationForInstance)
            .flatMap(group -> toApplication(group.getT1(), group.getT2()))
            .map(application -> ServerSentEvent.builder(application).build())
            .mergeWith(ping());
    }

    @DeleteMapping(path = "/applications/{name}")
    public Mono<ResponseEntity<Void>> unregister(@PathVariable("name") String name) {
        log.debug("Unregister application with name '{}'", name);
        return registry.getInstances(name)
            .flatMap(instance -> registry.deregister(instance.getId()))
            .collectList()
            .map(
                deregistered -> !deregistered.isEmpty() ? ResponseEntity.noContent().build() : ResponseEntity
                    .notFound()
                    .build());
    }

    protected Tuple2<String, Flux<Instance>> getApplicationForInstance(Instance instance) {
        String name = instance.getRegistration().getName();
        return Tuples.of(name, registry.getInstances(name).filter(Instance::isRegistered));
    }

    protected Mono<Application> toApplication(String name, Flux<Instance> instances) {
        return instances.collectList().map(instanceList -> {
            Application group = new Application(name);
            group.setInstances(instanceList);
            group.setBuildVersion(getBuildVersion(instanceList));
            Tuple2<String, Instant> status = getStatus(instanceList);
            group.setStatus(status.getT1());
            group.setStatusTimestamp(status.getT2());
            return group;
        });
    }

    protected BuildVersion getBuildVersion(List<Instance> instances) {
        List<BuildVersion> versions = instances.stream()
            .map(Instance::getBuildVersion)
            .filter(Objects::nonNull)
            .distinct()
            .sorted()
            .collect(toList());
        if (versions.isEmpty()) {
            return null;
        } else if (versions.size() == 1) {
            return versions.get(0);
        } else {
            return BuildVersion.valueOf(versions.get(0) + " ... " + versions.get(versions.size() - 1));
        }
    }

    protected Tuple2<String, Instant> getStatus(List<Instance> instances) {
        //TODO: Correct is just a second readmodel for groups
        Map<String, Instant> statusWithTime = instances.stream()
            .collect(toMap(instance -> instance.getStatusInfo().getStatus(),
                Instance::getStatusTimestamp, this::getMax));
        if (statusWithTime.size() == 1) {
            Map.Entry<String, Instant> e = statusWithTime.entrySet().iterator().next();
            return Tuples.of(e.getKey(), e.getValue());
        }

        if (statusWithTime.containsKey(StatusInfo.STATUS_UP)) {
            Instant oldestNonUp = statusWithTime.entrySet()
                .stream()
                .filter(e -> !StatusInfo.STATUS_UP.equals(e.getKey()))
                .map(Map.Entry::getValue)
                .min(naturalOrder())
                .orElse(Instant.EPOCH);
            Instant latest = getMax(oldestNonUp, statusWithTime.getOrDefault(StatusInfo.STATUS_UP, Instant.EPOCH));
            return Tuples.of(StatusInfo.STATUS_RESTRICTED, latest);
        }

        return statusWithTime.entrySet()
            .stream()
            .min(Map.Entry.comparingByKey(StatusInfo.severity()))
            .map(e -> Tuples.of(e.getKey(), e.getValue()))
            .orElse(Tuples.of(StatusInfo.STATUS_UNKNOWN, Instant.EPOCH));
    }

    private Instant getMax(Instant t1, Instant t2) {
        return t1.compareTo(t2) >= 0 ? t1 : t2;
    }

    @SuppressWarnings("unchecked")
    private static <T> Flux<ServerSentEvent<T>> ping() {
        return (Flux<ServerSentEvent<T>>) (Flux) PING_FLUX;
    }

    @lombok.Data
    public static class Application {
        private final String name;
        private BuildVersion buildVersion;
        private String status;
        private Instant statusTimestamp;
        private List<Instance> instances;
    }
}
