// <copyright file="FileChangeNotificationSystem.cs" company="Microsoft">
//   Copyright (c) 2009 Microsoft Corporation.  All rights reserved.
// </copyright>
using System;
using System.Runtime.Caching.Hosting;
using System.Runtime.Caching.Resources;
using System.Collections;
using System.IO;
using System.Security;
using System.Security.Permissions;

namespace System.Runtime.Caching {
    internal sealed class FileChangeNotificationSystem : IFileChangeNotificationSystem {
        private Hashtable _dirMonitors;
        private object _lock;

        internal class DirectoryMonitor {
            internal FileSystemWatcher Fsw;
        }

        internal class FileChangeEventTarget {
            private string _fileName;
            private OnChangedCallback _onChangedCallback;
            private FileSystemEventHandler _changedHandler;
            private ErrorEventHandler _errorHandler;
            private RenamedEventHandler _renamedHandler;
            
            private static bool EqualsIgnoreCase(string s1, string s2) {
                if (String.IsNullOrEmpty(s1) && String.IsNullOrEmpty(s2)) {
                    return true;
                }
                if (String.IsNullOrEmpty(s1) || String.IsNullOrEmpty(s2)) {
                    return false;
                }
                if(s2.Length != s1.Length) {
                    return false;
                }
                return 0 == string.Compare(s1, 0, s2, 0, s2.Length, StringComparison.OrdinalIgnoreCase);
            }

            private void OnChanged(Object sender, FileSystemEventArgs e) {
                if (EqualsIgnoreCase(_fileName, e.Name)) {
                    _onChangedCallback(null);
                }
            }

            private void OnError(Object sender, ErrorEventArgs e) {
                _onChangedCallback(null);
            }
            
            private void OnRenamed(Object sender, RenamedEventArgs e) {
                if (EqualsIgnoreCase(_fileName, e.Name) || EqualsIgnoreCase(_fileName, e.OldName)) {
                    _onChangedCallback(null);
                }
            }
            
            internal FileSystemEventHandler ChangedHandler { get { return _changedHandler; } }
            internal ErrorEventHandler ErrorHandler { get { return _errorHandler; } }
            internal RenamedEventHandler RenamedHandler { get { return _renamedHandler; } }
            
            internal FileChangeEventTarget(string fileName, OnChangedCallback onChangedCallback) {
                _fileName = fileName;
                _onChangedCallback = onChangedCallback;
                _changedHandler = new FileSystemEventHandler(this.OnChanged);
                _errorHandler = new ErrorEventHandler(this.OnError);
                _renamedHandler = new RenamedEventHandler(this.OnRenamed);
            }
        }

        internal FileChangeNotificationSystem() {
            _dirMonitors = Hashtable.Synchronized(new Hashtable(StringComparer.OrdinalIgnoreCase)); 
            _lock = new object();
        }

        [SecuritySafeCritical]
        [PermissionSet(SecurityAction.Assert, Unrestricted = true)]
        void IFileChangeNotificationSystem.StartMonitoring(string filePath, OnChangedCallback onChangedCallback, out Object state, out DateTimeOffset lastWriteTime, out long fileSize) {
            if (filePath == null) {
                throw new ArgumentNullException("filePath");
            }
            if (onChangedCallback == null) {
                throw new ArgumentNullException("onChangedCallback");
            }
            FileInfo fileInfo = new FileInfo(filePath);
            string dir = Path.GetDirectoryName(filePath);
            DirectoryMonitor dirMon = _dirMonitors[dir] as DirectoryMonitor;
            if (dirMon == null) {
                lock (_lock) {
                    dirMon = _dirMonitors[dir] as DirectoryMonitor;
                    if (dirMon == null) {
                        dirMon = new DirectoryMonitor();
                        dirMon.Fsw = new FileSystemWatcher(dir);
                        dirMon.Fsw.NotifyFilter = NotifyFilters.FileName 
                                                  | NotifyFilters.DirectoryName 
                                                  | NotifyFilters.CreationTime 
                                                  | NotifyFilters.Size 
                                                  | NotifyFilters.LastWrite 
                                                  | NotifyFilters.Security;
                        dirMon.Fsw.EnableRaisingEvents = true;
                    }
                    _dirMonitors[dir] = dirMon;
                }
            }
            
            FileChangeEventTarget target = new FileChangeEventTarget(fileInfo.Name, onChangedCallback);

            lock (dirMon) {
                dirMon.Fsw.Changed += target.ChangedHandler;
                dirMon.Fsw.Created += target.ChangedHandler;
                dirMon.Fsw.Deleted += target.ChangedHandler;
                dirMon.Fsw.Error += target.ErrorHandler;
                dirMon.Fsw.Renamed += target.RenamedHandler;
            }

            state = target;
            lastWriteTime = File.GetLastWriteTime(filePath);
            fileSize = (fileInfo.Exists) ? fileInfo.Length : -1;
        }

        [SecuritySafeCritical]
        [PermissionSet(SecurityAction.Assert, Unrestricted = true)]
        void IFileChangeNotificationSystem.StopMonitoring(string filePath, Object state) {
            if (filePath == null) {
                throw new ArgumentNullException("filePath");
            }
            if (state == null) {
                throw new ArgumentNullException("state");
            }
            FileChangeEventTarget target = state as FileChangeEventTarget;
            if (target == null) {
                throw new ArgumentException(R.Invalid_state,"state");
            }
            string dir = Path.GetDirectoryName(filePath);
            DirectoryMonitor dirMon = _dirMonitors[dir] as DirectoryMonitor;
            if (dirMon != null) {
                lock (dirMon) {
                    dirMon.Fsw.Changed -= target.ChangedHandler;
                    dirMon.Fsw.Created -= target.ChangedHandler;
                    dirMon.Fsw.Deleted -= target.ChangedHandler;
                    dirMon.Fsw.Error -= target.ErrorHandler;
                    dirMon.Fsw.Renamed -= target.RenamedHandler;
                }
            }
        }
    }
}