using System;
using System.Collections.Generic;
using System.Configuration;
using System.IO;
using System.Linq;

namespace ConfigMonitor
{
    public class ConfigMonitor
    {
        private readonly FileSystemWatcher _watcher;
        private DateTime _lastChange;

        public ConfigMonitor(string configFilePath)
        {
            if (configFilePath == null)
            {
                throw new ArgumentNullException(nameof(configFilePath));
            }

            _lastChange = DateTime.MinValue;
            //var configFile = string.Concat(System.Reflection.Assembly.GetEntryAssembly().Location, ".config");
            if (File.Exists(configFilePath))
            {
                _watcher = new FileSystemWatcher(Path.GetDirectoryName(configFilePath), Path.GetFileName(configFilePath))
                {
                    EnableRaisingEvents = true
                };
                _watcher.Changed += Watcher_Changed;
            }
        }

        ~ConfigMonitor()
        {
            _watcher.EnableRaisingEvents = false;
            _watcher.Changed -= Watcher_Changed;
            _watcher.Dispose();    
        }

        public void Stop()
        {
            _watcher.EnableRaisingEvents = false;
            _watcher.Changed -= Watcher_Changed;
            _watcher.Dispose();
        }

        private void Watcher_Changed(object sender, FileSystemEventArgs e)
        {
            if ((DateTime.Now - _lastChange).Seconds <= 5 || IsFileLocked(e.FullPath)) return;
            var monitoredSections = ConfigurationManager.AppSettings["monitoredSections"];

            if (monitoredSections!= null)
            {
                IEnumerable<string> sections = monitoredSections.Split(new[] { ',' }, StringSplitOptions.RemoveEmptyEntries);
                if (sections.Any())
                {
                    foreach (var section in sections)
                    {
                        ConfigurationManager.RefreshSection(section);
                    }
                } 
            }
            else
            {
                ConfigurationManager.RefreshSection("appSettings");
            }
            _lastChange = DateTime.Now;
        }

        private bool IsFileLocked(string filePath)
        {
            FileStream stream = null;
            try
            {
                stream = File.OpenRead(filePath);
            }
            catch (IOException)
            {
                return true;
            }
            finally
            {
                stream?.Close();
            }
            return false;
        }
    }
}