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/*-------------------------------------------------------------------------
 *
 * Copyright (c) 2014, PostgreSQL Global Development Group
 *
 *
 *-------------------------------------------------------------------------
 */
package org.postgresql.hostchooser;

import static java.lang.System.currentTimeMillis;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.postgresql.util.HostSpec;

/**
 * Keeps track of HostSpec targets in a global map.
 */
public class GlobalHostStatusTracker {
    private static final Map hostStatusMap = new HashMap();

    /**
     * Store the actual observed host status. 
     *
     * @param hostSpec The host whose status is known.
     * @param hostStatus Latest known status for the host.
     */
    public static void reportHostStatus(HostSpec hostSpec, HostStatus hostStatus) {
        long now = currentTimeMillis();
        synchronized (hostStatusMap) {
            HostSpecStatus oldStatus = hostStatusMap.get(hostSpec);
            if (oldStatus == null || updateStatusFromTo(oldStatus.status, hostStatus)) {
                hostStatusMap.put(hostSpec, new HostSpecStatus(hostSpec, hostStatus, now));
            }
        }
    }

    private static boolean updateStatusFromTo(HostStatus oldStatus, HostStatus newStatus) {
        if (oldStatus == null) {
            return true;
        }
        if (newStatus == HostStatus.ConnectOK) {
            return oldStatus != HostStatus.Master && oldStatus != HostStatus.Slave;
        }
        return true;
    }

    /**
     * Returns a list of candidate hosts that have the required targetServerType.
     *
     * @param hostSpecs The potential list of hosts.
     * @param targetServerType The required target server type.
     * @param hostRecheckMillis How stale information is allowed.
     * @return candidate hosts to connect to.
     */
    static List getCandidateHosts(HostSpec[] hostSpecs, HostRequirement targetServerType, long hostRecheckMillis) {
        List candidates = new ArrayList(hostSpecs.length);
        long latestAllowedUpdate = currentTimeMillis() - hostRecheckMillis;
        synchronized (hostStatusMap) {
            for (HostSpec hostSpec : hostSpecs) {
                HostSpecStatus hostInfo = hostStatusMap.get(hostSpec);
                // return null status wrapper if if the current value is not known or is too old
                if (hostInfo == null || hostInfo.lastUpdated < latestAllowedUpdate) {
                    hostInfo = new HostSpecStatus(hostSpec, null, Long.MAX_VALUE);
                }
                // candidates are nodes we do not know about and the nodes with correct type
                if (hostInfo.status == null || targetServerType.allowConnectingTo(hostInfo.status)) {
                    candidates.add(hostInfo);
                }
            }
        }
        return candidates;
    }

    /**
     * Immutable structure of known status of one HostSpec.
     */
    static class HostSpecStatus {
        final HostSpec host;
        final HostStatus status;
        final long lastUpdated;

        HostSpecStatus(HostSpec host, HostStatus hostStatus, long lastUpdated) {
            this.host = host;
            this.status = hostStatus;
            this.lastUpdated = lastUpdated;
        }

        @Override
        public String toString() {
            return host.toString() + '=' + status;
        }
    }
}