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package org.zodic.kubernetes.leader;

import io.fabric8.kubernetes.api.model.Pod;
import io.fabric8.kubernetes.client.KubernetesClient;
import io.fabric8.kubernetes.client.Watch;
import io.fabric8.kubernetes.client.Watcher;
import io.fabric8.kubernetes.client.WatcherException;
import io.fabric8.kubernetes.client.dsl.PodResource;
import io.fabric8.kubernetes.client.internal.readiness.Readiness;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class PodReadinessWatcher implements Watcher {

    private static final Logger LOGGER = LoggerFactory.getLogger(PodReadinessWatcher.class);

    private final Object lock = new Object();

    private final String podName;

    private final KubernetesClient kubernetesClient;

    private final LeadershipController leadershipController;

    private boolean previousState;

    private Watch watch;

    public PodReadinessWatcher(String podName, KubernetesClient kubernetesClient,
        LeadershipController leadershipController) {
        this.podName = podName;
        this.kubernetesClient = kubernetesClient;
        this.leadershipController = leadershipController;
    }

    public void start() {
        if (this.watch == null) {
            synchronized (this.lock) {
                if (this.watch == null) {
                    LOGGER.debug("Starting pod readiness watcher for '{}'", this.podName);
                    PodResource podResource = this.kubernetesClient.pods().withName(this.podName);
                    this.previousState = podResource.isReady();
                    this.watch = podResource.watch(this);
                }
            }
        }
    }

    public void stop() {
        if (this.watch != null) {
            synchronized (this.lock) {
                if (this.watch != null) {
                    LOGGER.debug("Stopping pod readiness watcher for '{}'", this.podName);
                    this.watch.close();
                    this.watch = null;
                }
            }
        }
    }

    @Override
    public void eventReceived(Action action, Pod pod) {
        boolean currentState = Readiness.isPodReady(pod);
        if (this.previousState != currentState) {
            synchronized (this.lock) {
                if (this.previousState != currentState) {
                    LOGGER.debug("'{}' readiness status changed to '{}', triggering leadership update", this.podName,
                        currentState);
                    this.previousState = currentState;
                    this.leadershipController.update();
                }
            }
        }
    }

    @Override
    public void onClose(WatcherException cause) {
        if (cause != null) {
            synchronized (this.lock) {
                LOGGER.warn("Watcher stopped unexpectedly, will restart", cause);
                this.watch = null;
                start();
            }
        }
    }

}