using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace InstallMonitor
{
    public class LogReader
    {
        private CancellationTokenSource _cts;
        private ConfigService _configService;
        private long _lastPosition = 0;
        private int _retryCount = 0;
        public LogReader(ConfigService config, CancellationTokenSource cts)
        {
            _configService = config;
            _cts = cts;
        }
        
        public string Directory => _configService.Settings.LogFileDirectory;
        public string FilePattern => _configService.Settings.LogFileNamePattern;
        public int MaxRetries => _configService.Settings.MaxRetries;
        public int RetryTimeout => _configService.Settings.RetryTimeout;
        public string LogFile { get; private set; } = string.Empty;

        public event EventHandler? InternalError;
        public event EventHandler? ReadLine;
        public event EventHandler? StreamOpen;
        public event EventHandler? AwaitLine;
        public event EventHandler? TaskFailed;

        private void FindLogFile() 
        {
            var file = new DirectoryInfo(Directory)
            .GetFiles(FilePattern)
            .OrderByDescending(f => f.Name)
            .FirstOrDefault();

            if (file != null)
            {
                LogFile = file.FullName;
            }

            if (!File.Exists(LogFile))
                throw new IOException("Datei nicht gefunden");

        }

        public async Task ReadLogAsync() 
        {
            while (!_cts.Token.IsCancellationRequested) 
            {
                try 
                {
                    FindLogFile();

                    using var fs = new FileStream(LogFile, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
                    using var reader = new StreamReader(fs, System.Text.Encoding.UTF8, true);

                    StreamOpened();

                    if (_lastPosition == 0)
                    {
                        string? line;
                        while ((line = await reader.ReadLineAsync()) != null)
                        {
                            LineRead(line);
                        }
                        _lastPosition = fs.Position;
                    }

                    while (!_cts.IsCancellationRequested)
                    {
                        fs.Seek(_lastPosition, SeekOrigin.Begin);

                        string? line;
                        while ((line = await reader.ReadLineAsync()) != null)
                        {
                            LineRead(line);
                        }

                        _lastPosition = fs.Position;
                        await Task.Delay(200, _cts.Token);

                        LineAwaited();
                    }
                }
                catch (OperationCanceledException ex) { }
                catch (Exception ex) when (_retryCount < MaxRetries)
                {
                    InternalErrorCaught($"Versuch: ({_retryCount + 1}/{MaxRetries}) - {ex.Message}");
                    _retryCount++;
                    await Task.Delay(RetryTimeout, _cts.Token);
                }
                catch (Exception ex) 
                {
                    TaskHasFailed($"Versuch: (no more retries) - {ex.Message}");
                    break;
                }
            }
        }

        public void StreamOpened() 
        {
            _retryCount = 0;

            var handle = StreamOpen;
            if(handle != null)
                handle.Invoke(null, EventArgs.Empty);
        }

        public void LineRead(string line)
        {
            var handle = ReadLine;
            if (handle != null)
                handle.Invoke(line, EventArgs.Empty);
        }

        public void LineAwaited()
        {
            var handle = AwaitLine;
            if (handle != null)
                handle.Invoke(null, EventArgs.Empty);
        }

        public void InternalErrorCaught(string message)
        {
            var handle = InternalError;
            if (handle != null)
                handle.Invoke(message, EventArgs.Empty);
        }

        public void TaskHasFailed(string message)
        {
            var handle = InternalError;
            if (handle != null)
                handle.Invoke(message, EventArgs.Empty);
        }
    }
}