// Copyright © 2019, Oracle and/or its affiliates. All rights reserved.
//
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License, version 2.0, as
// published by the Free Software Foundation.
//
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//
// Without limiting anything contained in the foregoing, this file,
// which is part of MySQL Connector/NET, is also subject to the
// Universal FOSS Exception, version 1.0, a copy of which can be found at
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// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
// See the GNU General Public License, version 2.0, for more details.
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using MySql.Data.MySqlClient;
using System;
using System.Collections.Generic;
using Sog.Properties;

namespace MySql.Data.Failover
{
    /// <summary>
    /// Manages the hosts available for client side failover using the Random Failover method.
    /// The Random Failover method attempts to connect to the hosts specified in the list randomly until all the hosts have been attempted.
    /// </summary>
    internal class RandomFailoverGroup : FailoverGroup
    {
        /// <summary>
        /// The initial host taken from the list.
        /// </summary>
        private FailoverServer _initialHost;

        /// <summary>
        /// The host for the current connection attempt.
        /// </summary>
        private FailoverServer _currentHost;

        /// <summary>
        /// Random object to get the next host.
        /// </summary>
        private readonly Random rnd = new Random();


        public RandomFailoverGroup(List<FailoverServer> hosts) : base(hosts) { }

        /// <summary>
        /// Sets the initial active host.
        /// </summary>
        protected internal override void SetInitialActiveServer()
        {
            if (this.Hosts == null || this.Hosts.Count == 0)
            {
                throw new MySqlException(Resources.Replication_NoAvailableServer);
            }

            var initialIndex = this.rnd.Next(this.Hosts.Count);
            this._initialHost = this.Hosts[initialIndex];

            this._initialHost.IsActive = true;
            this._initialHost.Attempted = true;
            this._activeHost = this._initialHost;
            this._currentHost = this._activeHost;
        }

        /// <summary>
        /// Determines the next host.
        /// </summary>
        /// <returns>A <see cref="FailoverServer"/> object that represents the next available host.</returns>
        protected internal override FailoverServer GetNextHost()
        {
            if (this.Hosts == null || this.Hosts?.Count == 0)
            {
                throw new MySqlException(Resources.Replication_NoAvailableServer);
            }

            this.Hosts.Find(h => h.Host == this._currentHost.Host && h.Port == this._currentHost.Port).IsActive = false;
            var notAttemptedHosts = this.Hosts.FindAll(h => h.Attempted == false);

            if (notAttemptedHosts.Count > 0)
            {
                this._activeHost = notAttemptedHosts[this.rnd.Next(notAttemptedHosts.Count)];
                this._activeHost.IsActive = true;
                this._activeHost.Attempted = true;
                this._currentHost = this._activeHost;
            }
            else
            {
                this._activeHost = this._initialHost;
            }

            return this._activeHost;
        }
    }
}