OnPluginUnloaded

using System.Linq;
using System;
using System.Collections.Generic;
using Newtonsoft.Json;
using Oxide.Core;
using Oxide.Core.Plugins;

namespace Oxide.Plugins
{
    [Info("Dependency Watcher", "RustPluginGenerator", "1.0.0")]
    [Description("Watches key companion plugins and records when they are unloaded.")]
    public class DependencyWatcher : RustPlugin
    {
        private const string PermAdmin = "dependencywatcher.admin";

        private PluginConfig config;
        private readonly Dictionary<string, DateTime> lastUnload = new Dictionary<string, DateTime>(StringComparer.OrdinalIgnoreCase);

        private class PluginConfig
        {
            [JsonProperty("Watched plugin names")]
            public List<string> WatchedPlugins = new List<string> { "Economics", "ServerRewards", "PermissionsManager" };
        }

        protected override void LoadDefaultConfig() => config = new PluginConfig();

        protected override void LoadConfig()
        {
            base.LoadConfig();
            try
            {
                config = Config.ReadObject<PluginConfig>();
                if (config == null) throw new Exception();
            }
            catch
            {
                PrintWarning("Configuration file is invalid, using defaults");
                LoadDefaultConfig();
            }
            SaveConfig();
        }

        protected override void SaveConfig() => Config.WriteObject(config);

        protected override void LoadDefaultMessages()
        {
            lang.RegisterMessages(new Dictionary<string, string>
            {
                ["NoPermission"] = "You do not have permission to use this command.",
                ["NoWatched"] = "No plugins are being watched.",
                ["Header"] = "Watched plugins:",
                ["Line"] = "{0} - {1}",
                ["Loaded"] = "loaded",
                ["UnloadedAt"] = "last unloaded at {0} UTC",
                ["Cleared"] = "Unload records cleared."
            }, this);
        }

        private string Msg(string key, string userId = null, params object[] args) => string.Format(lang.GetMessage(key, this, userId), args);

        private void Init()
        {
            permission.RegisterPermission(PermAdmin, this);
        }

        private void OnPluginUnloaded(Plugin plugin)
        {
            if (plugin == null || string.IsNullOrEmpty(plugin.Name)) return;
            if (!config.WatchedPlugins.Contains(plugin.Name)) return;

            lastUnload[plugin.Name] = DateTime.UtcNow;

            foreach (var player in BasePlayer.activePlayerList)
            {
                if (player != null && permission.UserHasPermission(player.UserIDString, PermAdmin))
                    player.ChatMessage(Msg("Line", player.UserIDString, plugin.Name, Msg("UnloadedAt", player.UserIDString, DateTime.UtcNow.ToString("HH:mm:ss"))));
            }
        }

        [ChatCommand("depwatch")]
        private void CmdDepwatch(BasePlayer player, string command, string[] args)
        {
            if (player == null) return;
            if (!permission.UserHasPermission(player.UserIDString, PermAdmin))
            {
                player.ChatMessage(Msg("NoPermission", player.UserIDString));
                return;
            }

            if (args.Length > 0 && args[0].Equals("clear", StringComparison.OrdinalIgnoreCase))
            {
                lastUnload.Clear();
                player.ChatMessage(Msg("Cleared", player.UserIDString));
                return;
            }

            if (config.WatchedPlugins.Count == 0)
            {
                player.ChatMessage(Msg("NoWatched", player.UserIDString));
                return;
            }

            player.ChatMessage(Msg("Header", player.UserIDString));
            foreach (var name in config.WatchedPlugins)
            {
                string state;
                DateTime stamp;
                if (lastUnload.TryGetValue(name, out stamp))
                    state = Msg("UnloadedAt", player.UserIDString, stamp.ToString("yyyy-MM-dd HH:mm:ss"));
                else
                    state = Msg("Loaded", player.UserIDString);

                player.ChatMessage(Msg("Line", player.UserIDString, name, state));
            }
        }
    }
}