using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Runtime.InteropServices;
using System.Text.Json.Serialization;
using Observatory.Framework;
using Observatory.Framework.Files;

namespace Observatory
{
    class LogMonitor
    {
        #region Singleton Instantiation

        public static LogMonitor GetInstance
        {
            get
            {
                return _instance.Value;
            }
        }

        private static readonly Lazy<LogMonitor> _instance = new Lazy<LogMonitor>(NewLogMonitor);

        private static LogMonitor NewLogMonitor()
        {
            return new LogMonitor();
        }

        private LogMonitor()
        {
            currentLine = new();
            journalTypes = JournalReader.PopulateEventClasses();
            InitializeWatchers(string.Empty);
        }

        #endregion

        #region Public Methods

        public void Start()
        {
            journalWatcher.EnableRaisingEvents = true;
            statusWatcher.EnableRaisingEvents = true;
            monitoring = true;
        }

        public void Stop()
        {
            journalWatcher.EnableRaisingEvents = false;
            statusWatcher.EnableRaisingEvents = false;
            monitoring = false;
        }

        public void ChangeWatchedDirectory(string path)
        {
            journalWatcher.Dispose();
            statusWatcher.Dispose();
            InitializeWatchers(path);
        }

        public bool IsMonitoring()
        {
            return monitoring;
        }

        public bool ReadAllInProgress()
        {
            return readall;
        }

        public void ReadAllJournals()
        {
            ReadAllJournals(string.Empty);
        }

        public void ReadAllJournals(string path)
        {
            readall = true;
            DirectoryInfo logDirectory = GetJournalFolder(path);
            var files = logDirectory.GetFiles("Journal.????????????.??.log");
            foreach (var file in files)
            {
                var lines = ReadAllLines(file.FullName);
                foreach (var line in lines)
                {
                    DeserializeAndInvoke(line);
                }
            }
            readall = false;
        }

        #endregion

        #region Public Events

        public event EventHandler<JournalEventArgs> JournalEntry;

        public event EventHandler<JournalEventArgs> StatusUpdate;

        #endregion



        #region Private Fields

        private FileSystemWatcher journalWatcher;
        private FileSystemWatcher statusWatcher;
        private Dictionary<string, Type> journalTypes;
        private Dictionary<string, int> currentLine;
        private bool monitoring = false;
        private bool readall = false;

        #endregion

        #region Private Methods

        private void InitializeWatchers(string path)
        {
            DirectoryInfo logDirectory = GetJournalFolder(path);

            journalWatcher = new FileSystemWatcher(logDirectory.FullName, "Journal.????????????.??.log")
            {
                NotifyFilter = NotifyFilters.LastWrite | NotifyFilters.Size | NotifyFilters.LastAccess |
                                NotifyFilters.FileName | NotifyFilters.CreationTime | NotifyFilters.DirectoryName
            };
            journalWatcher.Changed += LogChangedEvent;
            journalWatcher.Created += LogCreatedEvent;
            
            statusWatcher = new FileSystemWatcher(logDirectory.FullName, "Status.json")
            {
                NotifyFilter = NotifyFilters.LastWrite | NotifyFilters.Size | NotifyFilters.LastAccess
            };
            statusWatcher.Changed += StatusUpdateEvent;
        }

        private DirectoryInfo GetJournalFolder(string path)
        {
            DirectoryInfo logDirectory;

            if (path.Length == 0 && Properties.Core.Default.JournalFolder.Trim().Length > 0)
            {
                path = Properties.Core.Default.JournalFolder;
            }

            if (path.Length > 0)
            {
                if (Directory.Exists(path))
                {
                    logDirectory = new DirectoryInfo(path);
                }
                else
                {
                    throw new DirectoryNotFoundException($"Directory '{path}' does not exist.");
                }
            }
            else if(RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
            {
                logDirectory = new DirectoryInfo(GetSavedGamesPath() + @"\Frontier Developments\Elite Dangerous");
            }
            else if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
            {
                logDirectory = new DirectoryInfo(".");
            }
            else
            {
                throw new NotImplementedException("Current OS Platform Not Supported.");
            }

            Properties.Core.Default.JournalFolder = path;
            Properties.Core.Default.Save();

            return logDirectory;
        }

        private void DeserializeAndInvoke(string line)
        {
            var eventType = JournalUtilities.GetEventType(line);
            if (!journalTypes.ContainsKey(eventType))
            {
                eventType = "JournalBase";
            }
            
            var eventClass = journalTypes[eventType];
            MethodInfo journalRead = typeof(JournalReader).GetMethod(nameof(JournalReader.ObservatoryDeserializer));
            MethodInfo journalGeneric = journalRead.MakeGenericMethod(eventClass);
            object entry = journalGeneric.Invoke(null, new object[] { line });
            var journalEvent = new JournalEventArgs() { journalType = eventClass, journalEvent = entry };
            var handler = JournalEntry;

            handler?.Invoke(this, journalEvent);
            
        }

        private void LogChangedEvent(object source, FileSystemEventArgs eventArgs)
        {
            var fileContent = ReadAllLines(eventArgs.FullPath);

            if (currentLine[eventArgs.FullPath] == -1)
            {
                currentLine[eventArgs.FullPath] = fileContent.Count - 1;
            }

            foreach(string line in fileContent.Skip(currentLine[eventArgs.FullPath]))
            {
                DeserializeAndInvoke(line);
            }

            currentLine[eventArgs.FullPath] = fileContent.Count;
        }

        private List<string> ReadAllLines(string path)
        {
            var lines = new List<string>();
            using (StreamReader file = new StreamReader(File.Open(path, FileMode.Open, FileAccess.Read, FileShare.ReadWrite)))
            {
                while (!file.EndOfStream)
                {
                    lines.Add(file.ReadLine());
                }
            }
            return lines;
        }

        private void LogCreatedEvent(object source, FileSystemEventArgs eventArgs)
        {
            currentLine[eventArgs.FullPath] = 0;
            LogChangedEvent(source, eventArgs);
        }

        private void StatusUpdateEvent(object source, FileSystemEventArgs eventArgs)
        {
            var handler = StatusUpdate;
            var statusLines = ReadAllLines(eventArgs.FullPath);
            if (statusLines.Count > 0)
            {
                var status = JournalReader.ObservatoryDeserializer<Status>(statusLines[0]);
                handler?.Invoke(this, new JournalEventArgs() { journalType = typeof(Status), journalEvent = status });
            }
        }

        private static string GetSavedGamesPath()
        {
            if (Environment.OSVersion.Version.Major < 6) throw new NotSupportedException();
            IntPtr pathPtr = IntPtr.Zero;
            try
            {
                Guid FolderSavedGames = new Guid("4C5C32FF-BB9D-43b0-B5B4-2D72E54EAAA4");
                SHGetKnownFolderPath(ref FolderSavedGames, 0, IntPtr.Zero, out pathPtr);
                return Marshal.PtrToStringUni(pathPtr);
            }
            finally
            {
                Marshal.FreeCoTaskMem(pathPtr);
            }
        }

        [DllImport("shell32.dll", CharSet = CharSet.Auto)]
        private static extern int SHGetKnownFolderPath(ref Guid id, int flags, IntPtr token, out IntPtr path);

        #endregion
    }
}