using System;
using ObjCRuntime;
using Foundation;
using CoreFoundation;
using System.IO;

namespace LoadRuntimeXAML.iOS
{
    public class FileWatcher : IDisposable
    {
        public void Dispose()
        {
            StopFileMonitoring();
        }

        public FileWatcher(string filePath) : base(filePath)
        {
            Path = filePath;
            StartMonitoringFile();
        }


        private void StartMonitoringFile()
        {
            fileMonitorSource?.Cancel();
            fileMonitorSource = null;

            var stream = File.OpenRead(Path);

            int fileDescriptor = stream.SafeFileHandle.DangerousGetHandle().ToInt32();
            fileMonitorSource = new DispatchSource.VnodeMonitor(fileDescriptor, VnodeMonitorKind.Delete | VnodeMonitorKind.Extend | VnodeMonitorKind.Write, DispatchQueue.MainQueue);
            fileMonitorSource.SetEventHandler(() =>
            {
                var observedEvents = fileMonitorSource.ObservedEvents;
                Console.WriteLine("Vnode monitor event: {0} for file: {1}", observedEvents, Path);
                if (observedEvents.HasFlag(VnodeMonitorKind.Delete))
                {
                    FileDeleted();
                }

                FileChangedEvent?.Invoke(this, Path);
            });

            fileMonitorSource.SetCancelHandler(() =>
            {
                stream.Close();
            });

            fileMonitorSource.Resume();
        }
        private void StopFileMonitoring()
        {
            fileMonitorSource?.Cancel();
            fileMonitorSource = null;
        }


        private void FileDeleted()
        {
            StopFileMonitoring();

            if (File.Exists(Path))
            {
                StartMonitoringFile();
                return;
            }
            else
            {
                // Some editors delete and replace the file on save, instead of actually saving and modifying the file.
                DispatchQueue.MainQueue.DispatchAfter(new DispatchTime(DispatchTime.Now, TimeSpan.FromSeconds(0.5)), () =>
                {
                    FileDeleted();
                });
            }
        }

        private DispatchSource.VnodeMonitor fileMonitorSource;

        public string Path { get; }

        public event FileChanged FileChangedEvent;
    }
}