// DebuggerSession.cs
//
// Author:
//   Ankit Jain <jankit@novell.com>
//   Lluis Sanchez Gual <lluis@novell.com>
//
// Copyright (c) 2008 Novell, Inc (http://www.novell.com)
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
//
//

using System;
using System.Threading;
using System.Collections.Generic;

using Mono.Debugging.Backend;
using Mono.Debugging.Evaluation;

namespace Mono.Debugging.Client
{
	public delegate void TargetEventHandler (object sender, TargetEventArgs args);
	public delegate void ProcessEventHandler (int processId);
	public delegate void ThreadEventHandler (int threadId);
	public delegate bool ExceptionHandler (Exception ex);
	public delegate string TypeResolverHandler (string identifier, SourceLocation location);
	public delegate void BreakpointTraceHandler (BreakEvent be, string trace);
	public delegate IExpressionEvaluator GetExpressionEvaluatorHandler (string extension);
	public delegate IConnectionDialog ConnectionDialogCreatorExtended (DebuggerStartInfo dsi);
	public delegate IConnectionDialog ConnectionDialogCreator ();
	
	public abstract class DebuggerSession: IDisposable
	{
		readonly Dictionary<BreakEvent, BreakEventInfo> breakpoints = new Dictionary<BreakEvent, BreakEventInfo> ();
		readonly Dictionary<string, string> resolvedExpressionCache = new Dictionary<string, string> ();
		readonly InternalDebuggerSession frontend;
		readonly object slock = new object ();
		readonly object breakpointStoreLock = new object ();
		BreakpointStore breakpointStore;
		DebuggerSessionOptions options;
		ProcessInfo[] currentProcesses;
		ThreadInfo activeThread;
		bool ownedBreakpointStore;
		bool adjustingBreakpoints;
		DebuggerTimer stepTimer;
		bool disposed;
		bool attached;

		/// <summary>
		/// Reports a debugger event
		/// </summary>
		public event EventHandler<TargetEventArgs> TargetEvent;
		
		/// <summary>
		/// Raised when the debugger resumes execution after being stopped
		/// </summary>
		public event EventHandler TargetStarted;
		
		/// <summary>
		/// Raised when the underlying debugging engine has been initialized and it is ready to start execution.
		/// </summary>
		public event EventHandler<TargetEventArgs> TargetReady;
		
		/// <summary>
		/// Raised when the debugging session is paused
		/// </summary>
		public event EventHandler<TargetEventArgs> TargetStopped;
		
		/// <summary>
		/// Raised when the execution is interrupted by an external event
		/// </summary>
		public event EventHandler<TargetEventArgs> TargetInterrupted;
		
		/// <summary>
		/// Raised when a breakpoint is hit
		/// </summary>
		public event EventHandler<TargetEventArgs> TargetHitBreakpoint;
		
		/// <summary>
		/// Raised when the execution is interrupted due to receiving a signal
		/// </summary>
		public event EventHandler<TargetEventArgs> TargetSignaled;
		
		/// <summary>
		/// Raised when the debugged process exits
		/// </summary>
		public event EventHandler<TargetEventArgs> TargetExited;
		
		/// <summary>
		/// Raised when an exception for which there is a catchpoint is thrown
		/// </summary>
		public event EventHandler<TargetEventArgs> TargetExceptionThrown;
		
		/// <summary>
		/// Raised when an exception is unhandled
		/// </summary>
		public event EventHandler<TargetEventArgs> TargetUnhandledException;
		
		/// <summary>
		/// Raised when a thread is started in the debugged process
		/// </summary>
		public event EventHandler<TargetEventArgs> TargetThreadStarted;
		
		/// <summary>
		/// Raised when a thread is stopped in the debugged process
		/// </summary>
		public event EventHandler<TargetEventArgs> TargetThreadStopped;
		
		/// <summary>
		/// Raised when the 'busy state' of the debugger changes.
		/// The debugger may switch to busy state if it is in the middle
		/// of an expression evaluation which can't be aborted.
		/// </summary>
		public event EventHandler<BusyStateEventArgs> BusyStateChanged;

		/// <summary>
		/// Raised when an assembly is loaded
		/// </summary>
		public event EventHandler<AssemblyEventArgs> AssemblyLoaded;
		
		protected DebuggerSession ()
		{
			UseOperationThread = true;
			frontend = new InternalDebuggerSession (this);
			EvaluationStats = new DebuggerStatistics ();
			StepInStats = new DebuggerStatistics ();
			StepOutStats = new DebuggerStatistics ();
			StepOverStats = new DebuggerStatistics ();
			StepInstructionStats = new DebuggerStatistics ();
			NextInstructionStats = new DebuggerStatistics ();
			LocalVariableStats = new DebuggerStatistics ();
			WatchExpressionStats = new DebuggerStatistics ();
			StackTraceStats = new DebuggerStatistics ();
			TooltipStats = new DebuggerStatistics ();
			CallStackPadUsageCounter = new UsageCounter ();
			ImmediatePadUsageCounter = new UsageCounter ();
			ThreadsPadUsageCounter = new UsageCounter ();
		}
		
		/// <summary>
		/// Releases all resource used by the <see cref="Mono.Debugging.Client.DebuggerSession"/> object.
		/// </summary>
		/// <remarks>
		/// Call <see cref="Dispose"/> when you are finished using the <see cref="Mono.Debugging.Client.DebuggerSession"/>.
		/// The <see cref="Dispose"/> method leaves the <see cref="Mono.Debugging.Client.DebuggerSession"/> in an unusable
		/// state. After calling <see cref="Dispose"/>, you must release all references to the
		/// <see cref="Mono.Debugging.Client.DebuggerSession"/> so the garbage collector can reclaim the memory that the
		/// <see cref="Mono.Debugging.Client.DebuggerSession"/> was occupying.
		/// </remarks>
		public virtual void Dispose ()
		{
			Dispatch (delegate {
				if (!disposed) {
					disposed = true;
					if (!ownedBreakpointStore)
						Breakpoints = null;
				}
			});
		}
		
		/// <summary>
		/// Gets or sets an exception handler to be invoked when an exception is raised by the debugger engine.
		/// </summary>
		/// <remarks>
		/// Notice that this handler will be used to report exceptions in the debugger, not exceptions raised
		/// in the debugged process.
		/// </remarks>
		public ExceptionHandler ExceptionHandler {
			get; set;
		}
		
		/// <summary>
		/// Gets or sets the connection dialog creator callback.
		/// </summary>
		public ConnectionDialogCreator ConnectionDialogCreator { get; set; }

		/// <summary>
		/// Gets or sets the connection dialog creator callback.
		/// </summary>
		public ConnectionDialogCreatorExtended ConnectionDialogCreatorExtended { get; set; }

		/// <summary>
		/// Gets or sets the breakpoint trace handler.
		/// </summary>
		/// <remarks>
		/// This handler is invoked when the value of a tracepoint has to be printed
		/// </remarks>
		public BreakpointTraceHandler BreakpointTraceHandler { get; set; }
		
		/// <summary>
		/// Gets or sets the type resolver handler.
		/// </summary>
		/// <remarks>
		/// This handler is invoked when the expression evaluator needs to resolve a type name.
		/// </remarks>
		public TypeResolverHandler TypeResolverHandler { get; set; }
		
		/// <summary>
		/// Gets or sets the an expression evaluator provider
		/// </summary>
		/// <remarks>
		/// This handler is invoked when the debugger needs to get an evaluator for a specific type of file
		/// </remarks>
		public GetExpressionEvaluatorHandler GetExpressionEvaluator { get; set; }		

		/// <summary>
		/// Gets or sets the custom break event hit handler.
		/// </summary>
		/// <remarks>
		/// This handler is invoked when a custom breakpoint is hit to determine if the debug session should
		/// continue or stop.
		/// </remarks>
		public BreakEventHitHandler CustomBreakEventHitHandler {
			get; set;
		}

		public DebuggerStatistics EvaluationStats {
			get; private set;
		}

		public DebuggerStatistics StepInStats {
			get; private set;
		}

		public DebuggerStatistics StepOutStats {
			get; private set;
		}

		public DebuggerStatistics StepOverStats {
			get; private set;
		}

		public DebuggerStatistics StepInstructionStats {
			get; private set;
		}

		public DebuggerStatistics NextInstructionStats {
			get; private set;
		}

		public DebuggerStatistics LocalVariableStats {
			get; private set;
		}

		public DebuggerStatistics WatchExpressionStats {
			get; private set;
		}

		public DebuggerStatistics StackTraceStats {
			get; private set;
		}

		public DebuggerStatistics TooltipStats {
			get; private set;
		}

		public UsageCounter CallStackPadUsageCounter {
			get; private set;
		}

		public UsageCounter ImmediatePadUsageCounter {
			get; private set;
		}

		public UsageCounter ThreadsPadUsageCounter {
			get; private set;
		}

		/// <summary>
		/// Gets or sets the breakpoint store for the debugger session.
		/// </summary>
		public BreakpointStore Breakpoints {
			get {
				lock (breakpointStoreLock) {
					if (breakpointStore == null) {
						Breakpoints = new BreakpointStore ();
						ownedBreakpointStore = true;
					}
					return breakpointStore;
				}
			}
			set {
				lock (breakpointStoreLock) {
					if (breakpointStore != null) {
						foreach (BreakEvent bp in breakpointStore) {
							RemoveBreakEvent (bp);
							NotifyBreakEventStatusChanged (bp);
						}

						breakpointStore.BreakEventAdded -= OnBreakpointAdded;
						breakpointStore.BreakEventRemoved -= OnBreakpointRemoved;
						breakpointStore.BreakEventModified -= OnBreakpointModified;
						breakpointStore.BreakEventEnableStatusChanged -= OnBreakpointStatusChanged;
						breakpointStore.CheckingReadOnly -= BreakpointStoreCheckingReadOnly;
						breakpointStore.ResetBreakpoints ();
					}

					breakpointStore = value;
					ownedBreakpointStore = false;

					if (breakpointStore != null) {
						breakpointStore.BreakEventAdded += OnBreakpointAdded;
						breakpointStore.BreakEventRemoved += OnBreakpointRemoved;
						breakpointStore.BreakEventModified += OnBreakpointModified;
						breakpointStore.BreakEventEnableStatusChanged += OnBreakpointStatusChanged;
						breakpointStore.CheckingReadOnly += BreakpointStoreCheckingReadOnly;

						if (IsConnected) {
							Dispatch (delegate {
								if (IsConnected) {
									foreach (BreakEvent bp in breakpointStore)
										AddBreakEvent (bp);
								}
							});
						}
					}
				}
			}
		}

		readonly Queue<Action> actionsQueue = new Queue<Action>();
		bool threadExecuting;

		void Dispatch (Action action)
		{
			if (UseOperationThread) {
				lock (actionsQueue) {
					actionsQueue.Enqueue (action);
					if (!threadExecuting) {
						threadExecuting = true;
						ThreadPool.QueueUserWorkItem (delegate {
							while (true) {
								Action actionToExecute = null;
								lock (actionsQueue) {
									if (actionsQueue.Count > 0) {
										actionToExecute = actionsQueue.Dequeue ();
									} else {
										threadExecuting = false;
										return;
									}
								}
								lock (slock) {
									try {
										actionToExecute ();
									} catch (Exception ex) {
										HandleException (ex);
									}
								}
							}
						});
					}
				}
			} else {
				lock (slock) {
					action ();
				}
			}
		}
		
		/// <summary>
		/// Starts a debugging session
		/// </summary>
		/// <param name='startInfo'>
		/// Startup information
		/// </param>
		/// <param name='options'>
		/// Session options
		/// </param>
		/// <exception cref='ArgumentNullException'>
		/// Is thrown when an argument passed to a method is invalid because it is <see langword="null" /> .
		/// </exception>
		public void Run (DebuggerStartInfo startInfo, DebuggerSessionOptions options)
		{
			if (startInfo == null)
				throw new ArgumentNullException (nameof (startInfo));
			if (options == null)
				throw new ArgumentNullException (nameof (options));
			
			lock (slock) {
				this.options = options;
				OnRunning ();
				Dispatch (delegate {
					try {
						OnRun (startInfo);
					} catch (Exception ex) {
						// should handle exception before raising Exit event because HandleException may ignore exceptions in Exited state
						var exceptionHandled = HandleException (ex);
						ForceExit ();
						if (!exceptionHandled)
							throw;
					}
				});
			}
		}
		
		/// <summary>
		/// Starts a debugging session by attaching the debugger to a running process
		/// </summary>
		/// <param name='proc'>
		/// Process information
		/// </param>
		/// <param name='options'>
		/// Debugging options
		/// </param>
		/// <exception cref='ArgumentNullException'>
		/// Is thrown when an argument passed to a method is invalid because it is <see langword="null" /> .
		/// </exception>
		public void AttachToProcess (ProcessInfo proc, DebuggerSessionOptions options)
		{
			if (proc == null)
				throw new ArgumentNullException (nameof (proc));
			if (options == null)
				throw new ArgumentNullException (nameof (options));
			
			lock (slock) {
				this.options = options;
				OnRunning ();
				Dispatch (delegate {
					try {
						OnAttachToProcess (proc);
						attached = true;
					} catch (Exception ex) {
						// should handle exception before raising Exit event because HandleException may ignore exceptions in Exited state
						var exceptionHandled = HandleException (ex);
						ForceExit ();
						if (!exceptionHandled)
							throw;
					}
				});
			}
		}
		
		/// <summary>
		/// Detaches this debugging session from the debugged process
		/// </summary>
		public void Detach ()
		{
			lock (slock) {
				Dispatch (delegate {
					try {
						OnDetach ();
					}
					catch (Exception ex) {
						if (!HandleException (ex))
							throw;
					}
					finally {
						IsConnected = false;
					}
				});
			}
		}
		
		/// <summary>
		/// Gets a value indicating whether this <see cref="Mono.Debugging.Client.DebuggerSession"/> has been attached to a process using the Attach method.
		/// </summary>
		/// <value>
		/// <c>true</c> if attached to process; otherwise, <c>false</c>.
		/// </value>
		public bool AttachedToProcess {
			get { return attached; }
		}
		
		/// <summary>
		/// Gets or sets the active thread.
		/// </summary>
		/// <remarks>
		/// This property can only be used when the debugger is paused
		/// </remarks>
		public ThreadInfo ActiveThread {
			get {
				return activeThread;
			}
			set {
				lock (slock) {
					try {
						activeThread = value;
						OnSetActiveThread (activeThread.ProcessId, activeThread.Id);
					} catch (Exception ex) {
						if (!HandleException (ex))
							throw;
					}
				}
			}
		}

		void StartStepTimer (DebuggerStatistics stats)
		{
			stepTimer?.Dispose ();
			stepTimer = stats.StartTimer ();
		}

		/// <summary>
		/// Executes one line of code
		/// </summary>
		public void NextLine ()
		{
			lock (slock) {
				OnRunning ();
				Dispatch (delegate {
					StartStepTimer (StepOverStats);
					try {
						OnNextLine ();
					} catch (Exception ex) {
						ForceStop ();
						if (!HandleException (ex))
							throw;
					}
				});
			}
		}

		/// <summary>
		/// Executes one line of code, stepping into method invocations
		/// </summary>
		public void StepLine ()
		{
			lock (slock) {
				OnRunning ();
				Dispatch (delegate {
					StartStepTimer (StepInStats);
					try {
						OnStepLine ();
					} catch (Exception ex) {
						ForceStop ();
						if (!HandleException (ex))
							throw;
					}
				});
			}
		}
		
		/// <summary>
		/// Executes one low level instruction
		/// </summary>
		public void NextInstruction ()
		{
			lock (slock) {
				OnRunning ();
				Dispatch (delegate {
					StartStepTimer (NextInstructionStats);
					try {
						OnNextInstruction ();
					} catch (Exception ex) {
						ForceStop ();
						if (!HandleException (ex))
							throw;
					}
				});
			}
		}

		/// <summary>
		/// Executes one low level instruction, stepping into method invocations
		/// </summary>
		public void StepInstruction ()
		{
			lock (slock) {
				OnRunning ();
				Dispatch (delegate {
					StartStepTimer (StepInstructionStats);
					try {
						OnStepInstruction ();
					} catch (Exception ex) {
						ForceStop ();
						if (!HandleException (ex))
							throw;
					}
				});
			}
		}
		
		/// <summary>
		/// Resumes the execution of the debugger and stops when the current method is exited
		/// </summary>
		public void Finish ()
		{
			lock (slock) {
				OnRunning ();
				Dispatch (delegate {
					StartStepTimer (StepOutStats);
					try {
						OnFinish ();
					} catch (Exception ex) {
						// should handle exception before raising Exit event because HandleException may ignore exceptions in Exited state
						var exceptionHandled = HandleException (ex);
						ForceExit ();
						if (!exceptionHandled)
							throw;
					}
				});
			}
		}

		/// <summary>
		/// Sets the next statement on the active thread.
		/// </summary>
		/// <param name="fileName">File name.</param>
		/// <param name="line">Line.</param>
		/// <param name="column">Column.</param>
		public void SetNextStatement (string fileName, int line, int column)
		{
			if (fileName == null)
				throw new ArgumentNullException (nameof (fileName));

			if (fileName.Length == 0)
				throw new ArgumentException ("Path cannot be empty.", nameof (fileName));

			if (line < 1)
				throw new ArgumentOutOfRangeException (nameof (line));

			if (column < 1)
				throw new ArgumentOutOfRangeException (nameof (column));

			if (!IsConnected || IsRunning || !CanSetNextStatement)
				throw new NotSupportedException ();

			var thread = ActiveThread;

			if (thread == null)
				return;

			OnSetNextStatement (thread.Id, fileName, line, column);
		}

		/// <summary>
		/// Sets the next statement on the active thread.
		/// </summary>
		/// <param name="ilOffset">The IL offset.</param>
		public void SetNextStatement (int ilOffset)
		{
			if (ilOffset < 0)
				throw new ArgumentOutOfRangeException (nameof (ilOffset));

			if (!IsConnected || IsRunning || !CanSetNextStatement)
				throw new NotSupportedException ();

			var thread = ActiveThread;

			if (thread == null)
				return;

			OnSetNextStatement (thread.Id, ilOffset);
		}
		
		/// <summary>
		/// Returns the status of a breakpoint for this debugger session.
		/// </summary>
		public BreakEventStatus GetBreakEventStatus (BreakEvent be)
		{
			if (IsConnected) {
				lock (breakpoints) {
					if (breakpoints.TryGetValue (be, out var binfo))
						return binfo.Status;
				}
			}
			return BreakEventStatus.NotBound;
		}

		/// <summary>
		/// Returns a status message of a breakpoint for this debugger session.
		/// </summary>
		public string GetBreakEventStatusMessage (BreakEvent be)
		{
			if (IsConnected) {
				lock (breakpoints) {
					if (breakpoints.TryGetValue (be, out var binfo)) {
						if (binfo.StatusMessage != null)
							return binfo.StatusMessage;
						switch (binfo.Status) {
						case BreakEventStatus.BindError: return "The breakpoint could not be bound";
						case BreakEventStatus.Bound: return "";
						case BreakEventStatus.Disconnected: return "";
						case BreakEventStatus.Invalid: return "The breakpoint location is invalid. Perhaps the source line does " +
							"not contain any statements, or the source does not correspond to the current binary";
						case BreakEventStatus.NotBound: return "The breakpoint could not yet be bound to a valid location";
						}
					}
				}
			}
			return "The breakpoint will not currently be hit";
		}
		
		void AddBreakEvent (BreakEvent be)
		{
			try {
				var eventInfo = OnInsertBreakEvent (be);
				if (eventInfo == null)
					throw new InvalidOperationException ("OnInsertBreakEvent can't return a null value. If the breakpoint can't be bound or is invalid, a BreakEventInfo with the corresponding status must be returned");
				lock (breakpoints) {
					breakpoints [be] = eventInfo;
				}
				eventInfo.AttachSession (this, be);
			} catch (Exception ex) {
				string msg;
				
				if (be is FunctionBreakpoint)
					msg = "Could not set breakpoint at location '" + ((FunctionBreakpoint) be).FunctionName + ":" + ((FunctionBreakpoint) be).Line + "'";
				else if (be is Breakpoint)
					msg = "Could not set breakpoint at location '" + ((Breakpoint) be).FileName + ":" + ((Breakpoint) be).Line + "'";
				else
					msg = "Could not set catchpoint for exception '" + ((Catchpoint) be).ExceptionName + "'";
				
				msg += " (" + ex.Message + ")";
				OnDebuggerOutput (false, msg + "\n");
				HandleException (ex);
			}
		}

		bool RemoveBreakEvent (BreakEvent be)
		{
			BreakEventInfo binfo = null;
			lock (breakpoints) {
				if (!breakpoints.TryGetValue (be, out binfo))
					return true;

				breakpoints.Remove (be);
			}

			if (binfo != null) {
				try {
					OnRemoveBreakEvent (binfo);
				} catch (Exception ex) {
					if (IsConnected)
						OnDebuggerOutput (false, ex.Message);
					HandleException (ex);
					return false;
				}
			}

			return true;
		}

		void UpdateBreakEventStatus (BreakEvent be)
		{
			BreakEventInfo binfo = null;
			lock (breakpoints) {
				if (!breakpoints.TryGetValue (be, out binfo))
					return;
			}

			try {
				OnEnableBreakEvent (binfo, be.Enabled);
			} catch (Exception ex) {
				if (IsConnected)
					OnDebuggerOutput (false, ex.Message);
				HandleException (ex);
			}
		}
		
		void UpdateBreakEvent (BreakEvent be)
		{
			BreakEventInfo binfo;
			lock (breakpoints) {
				if (!breakpoints.TryGetValue (be, out binfo))
					return;
			}

			OnUpdateBreakEvent (binfo);
		}
		
		void OnBreakpointAdded (object s, BreakEventArgs args)
		{
			if (adjustingBreakpoints)
				return;

			if (IsConnected) {
				Dispatch (delegate {
					if (IsConnected)
						AddBreakEvent (args.BreakEvent);
				});
			}
		}
		
		void OnBreakpointRemoved (object s, BreakEventArgs args)
		{
			if (adjustingBreakpoints)
				return;

			if (IsConnected) {
				Dispatch (delegate {
					if (IsConnected)
						RemoveBreakEvent (args.BreakEvent);
				});
			}
		}
		
		void OnBreakpointModified (object s, BreakEventArgs args)
		{
			if (IsConnected) {
				Dispatch (delegate {
					if (IsConnected)
						UpdateBreakEvent (args.BreakEvent);
				});
			}
		}
		
		void OnBreakpointStatusChanged (object s, BreakEventArgs args)
		{
			if (IsConnected) {
				Dispatch (delegate {
					if (IsConnected)
						UpdateBreakEventStatus (args.BreakEvent);
				});
			}
		}

		void BreakpointStoreCheckingReadOnly (object sender, ReadOnlyCheckEventArgs e)
		{
			e.SetReadOnly (!AllowBreakEventChanges);
		}
		
		/// <summary>
		/// Gets the debugger options object
		/// </summary>
		public DebuggerSessionOptions Options {
			get { return options; }
		}
		
		/// <summary>
		/// Gets or sets the evaluation options.
		/// </summary>
		public EvaluationOptions EvaluationOptions {
			get { return options.EvaluationOptions; }
			set { options.EvaluationOptions = value; }
		}
		
		/// <summary>
		/// Resumes the execution of the debugger
		/// </summary>
		public void Continue ()
		{
			lock (slock) {
				OnRunning ();
				Dispatch (delegate {
					try {
						OnContinue ();
					} catch (Exception ex) {
						ForceStop ();
						if (!HandleException (ex))
							throw;
					}
				});
			}
		}
		
		/// <summary>
		/// Pauses the execution of the debugger
		/// </summary>
		public void Stop ()
		{
			Dispatch (delegate {
				try {
					OnStop ();
				} catch (Exception ex) {
					if (!HandleException (ex))
						throw;
				}
			});
		}
		
		/// <summary>
		/// Stops the execution of the debugger by killing the debugged process
		/// </summary>
		public void Exit ()
		{
			Dispatch (delegate {
				try {
					OnExit ();
				} catch (Exception ex) {
					if (!HandleException (ex))
						throw;
				}
			});
		}

		/// <summary>
		/// Gets a value indicating whether the debuggee is currently connected
		/// </summary>
		public bool IsConnected {
			get; private set;
		}
		
		/// <summary>
		/// Gets a value indicating whether the debuggee is currently running (not paused by the debugger)
		/// </summary>
		public bool IsRunning {
			get; private set;
		}

		/// <summary>
		/// Gets a value indicating whether the debuggee has exited.
		/// </summary>
		public bool HasExited {
			get; protected set;
		}
		
		/// <summary>
		/// Gets a list of all processes
		/// </summary>
		/// <remarks>
		/// This method can only be used when the debuggee is stopped by the debugger
		/// </remarks>
		public ProcessInfo[] GetProcesses ()
		{
			lock (slock) {
				if (currentProcesses == null) {
					currentProcesses = OnGetProcesses ();
					foreach (var process in currentProcesses)
						process.Attach (this);
				}
				return currentProcesses;
			}
		}
		
		/// <summary>
		/// Gets or sets the output writer callback.
		/// </summary>
		/// <remarks>
		/// This callback is invoked to print debuggee output
		/// </remarks>
		public OutputWriterDelegate OutputWriter {
			get; set;
		}
		
		/// <summary>
		/// Gets or sets the log writer.
		/// </summary>
		/// <remarks>
		/// This callback is invoked to print debugger log messages
		/// </remarks>
		public OutputWriterDelegate LogWriter {
			get; set;
		}

		/// <summary>
		/// Gets or sets the debug writer.
		/// </summary>
		/// <remarks>
		/// This callback is invoked to print debugge messages
		/// called via System.Diagnostics.Debugger.Log
		/// </remarks>
		public DebugWriterDelegate DebugWriter {
			get; set;
		}
		
		/// <summary>
		/// Gets the disassembly of a source code file
		/// </summary>
		/// <returns>
		/// An array of AssemblyLine, with one element for each source code line that could be disassembled
		/// </returns>
		/// <param name='file'>
		/// The file.
		/// </param>
		/// <remarks>
		/// This method can only be used when the debuggee is stopped by the debugger
		/// </remarks>
		public AssemblyLine[] DisassembleFile (string file)
		{
			lock (slock) {
				return OnDisassembleFile (file);
			}
		}
		
		public string ResolveExpression (string expression, string file, int line, int column, int endLine, int endColumn)
		{
			return ResolveExpression (expression, new SourceLocation (null, file, line, column, endLine, endColumn, null, null));
		}
		
		public virtual string ResolveExpression (string expression, SourceLocation location)
		{
			var key = expression + " " + location;

			if (!resolvedExpressionCache.TryGetValue (key, out var resolved)) {
				try {
					resolved = OnResolveExpression (expression, location);
				} catch (Exception ex) {
					OnDebuggerOutput (true, "Error while resolving expression: " + ex.Message);
				}
				resolvedExpressionCache [key] = resolved;
			}

			return resolved ?? expression;
		}
		
		/// <summary>
		/// Stops the execution of background evaluations being done by the debugger
		/// </summary>
		/// <remarks>
		/// This method can only be used when the debuggee is stopped by the debugger
		/// </remarks>
		public void CancelAsyncEvaluations ()
		{
			if (UseOperationThread) {
				ThreadPool.QueueUserWorkItem (delegate {
					OnCancelAsyncEvaluations ();
				});
			} else
				OnCancelAsyncEvaluations ();
		}

		/// <summary>
		/// Gets a value indicating whether there are background evaluations being done by the debugger
		/// which can be cancelled.
		/// </summary>
		/// <remarks>
		/// This method can only be used when the debuggee is stopped by the debugger
		/// </remarks>
		public virtual bool CanCancelAsyncEvaluations {
			get { return false; }
		}
		
		/// <summary>
		/// Override to stop the execution of background evaluations being done by the debugger
		/// </summary>
		protected virtual void OnCancelAsyncEvaluations ()
		{
		}
		
		readonly Dictionary<string, IExpressionEvaluator> evaluators = new Dictionary<string, IExpressionEvaluator> ();
		readonly ExpressionEvaluator defaultResolver = new NRefactoryExpressionEvaluator ();

		internal IExpressionEvaluator FindExpressionEvaluator (StackFrame frame)
		{
			if (GetExpressionEvaluator == null)
				return null;

			var fileName = frame.SourceLocation?.FileName;
			if (string.IsNullOrEmpty (fileName))
				return null;

			var extension = System.IO.Path.GetExtension (fileName);
			if (evaluators.TryGetValue (extension, out var result))
				return result;

			result = GetExpressionEvaluator (extension);
			evaluators[extension] = result;

			return result;
		}

		public ExpressionEvaluator GetEvaluator (StackFrame frame)
		{
			var result = FindExpressionEvaluator (frame);
			if (result == null)
				return defaultResolver;
			return result.Evaluator;
		}
		
		protected void RaiseStopEvent ()
		{
			TargetEvent?.Invoke (this, new TargetEventArgs (TargetEventType.TargetStopped));
		}

		/// <summary>
		/// Called when an expression needs to be resolved
		/// </summary>
		/// <param name='expression'>
		/// The expression
		/// </param>
		/// <param name='location'>
		/// The source code location
		/// </param>
		/// <returns>
		/// The resolved expression
		/// </returns>
		protected virtual string OnResolveExpression (string expression, SourceLocation location)
		{
			var resolver = defaultResolver;
			if (GetExpressionEvaluator != null)
				resolver = GetExpressionEvaluator(System.IO.Path.GetExtension(location.FileName))?.Evaluator ?? defaultResolver;

			return resolver.Resolve(this, location, expression);
		}
		
		internal protected string ResolveIdentifierAsType (string identifier, SourceLocation location)
		{
			if (TypeResolverHandler != null)
				return TypeResolverHandler (identifier, location);

			return null;
		}
		
		internal ThreadInfo[] GetThreads (long processId)
		{
			lock (slock) {
				var threads = OnGetThreads (processId);
				foreach (var thread in threads)
					thread.Attach (this);
				return threads;
			}
		}
		
		internal Backtrace GetBacktrace (long processId, long threadId)
		{
			lock (slock) {
				var bt = OnGetThreadBacktrace (processId, threadId);
				if (bt != null)
					bt.Attach (this);
				return bt;
			}
		}

		internal long GetElapsedTime (long processId, long threadId)
		{
			lock (slock) {
				return OnGetElapsedTime (processId, threadId);
			}
		}

		void ForceStop ()
		{
			var args = new TargetEventArgs (TargetEventType.TargetStopped);
			OnTargetEvent (args);
		}
		
		void ForceExit ()
		{
			var args = new TargetEventArgs (TargetEventType.TargetExited);
			OnTargetEvent (args);
		}
		
		internal protected void OnTargetEvent (TargetEventArgs args)
		{
			currentProcesses = null;
			
			if (args.Process != null)
				args.Process.Attach (this);
			if (args.Thread != null)
				args.Thread.Attach (this);
			if (args.Backtrace != null)
				args.Backtrace.Attach (this);

			EventHandler<TargetEventArgs> evnt = null;
			switch (args.Type) {
			case TargetEventType.ExceptionThrown:
				lock (slock) {
					IsRunning = false;
					args.IsStopEvent = true;
				}
				evnt = TargetExceptionThrown;
				break;
			case TargetEventType.TargetExited:
				lock (slock) {
					IsRunning = false;
					IsConnected = false;
					HasExited = true;
				}
				evnt = TargetExited;
				break;
			case TargetEventType.TargetHitBreakpoint:
				lock (slock) {
					IsRunning = false;
					args.IsStopEvent = true;
				}
				evnt = TargetHitBreakpoint;
				break;
			case TargetEventType.TargetInterrupted:
				lock (slock) {
					IsRunning = false;
					args.IsStopEvent = true;
				}
				evnt = TargetInterrupted;
				break;
			case TargetEventType.TargetSignaled:
				lock (slock) {
					IsRunning = false;
					args.IsStopEvent = true;
				}
				evnt = TargetSignaled;
				break;
			case TargetEventType.TargetStopped:
				lock (slock) {
					IsRunning = false;
					args.IsStopEvent = true;
				}
				evnt = TargetStopped;
				break;
			case TargetEventType.UnhandledException:
				lock (slock) {
					IsRunning = false;
					args.IsStopEvent = true;
				}
				evnt = TargetUnhandledException;
				break;
			case TargetEventType.TargetReady:
				evnt = TargetReady;
				break;
			case TargetEventType.ThreadStarted:
				evnt = TargetThreadStarted;
				break;
			case TargetEventType.ThreadStopped:
				evnt = TargetThreadStopped;
				break;
			}
			// Set activeThread only when event is IsStopEvent(stopping execution)
			// otherwise ThreadDeath(as example) event can set activeThread to dying thread
			// resulting in invalid activeThread being set while process is paused.
			// This happens often when using ThreadPool because after breakpoint is hit and
			// process is paused threadpool kills threads since they are not in use...
			if (args.Thread != null && args.IsStopEvent)
				activeThread = args.Thread;

			if (HasExited || args.IsStopEvent) {
				var timer = Interlocked.Exchange (ref stepTimer, null);
				if (timer != null) {
					timer.Stop (true);
					timer.Dispose ();
				}
			}

			evnt?.Invoke (this, args);

			TargetEvent?.Invoke (this, args);
		}
		
		internal void OnRunning ()
		{
			IsRunning = true;
			TargetStarted?.Invoke (this, EventArgs.Empty);
		}
		
		internal protected void OnStarted ()
		{
			OnStarted (null);
		}
		
		internal protected virtual void OnStarted (ThreadInfo t)
		{
			if (HasExited)
				return;

			OnTargetEvent (new TargetEventArgs (TargetEventType.TargetReady) { Thread = t });

			lock (slock) {
				if (!HasExited) {
					IsConnected = true;
					if (breakpointStore != null) {
						foreach (BreakEvent bp in breakpointStore)
							AddBreakEvent (bp);
					}
				}
			}
		}
		
		internal protected void OnTargetOutput (bool isStderr, string text)
		{
			OutputWriter?.Invoke (isStderr, text);
		}
		
		internal protected void OnDebuggerOutput (bool isStderr, string text)
		{
			LogWriter?.Invoke (isStderr, text);
		}

		internal protected void OnTargetDebug (int level, string category, string message)
		{
			var writer = DebugWriter;

			if (writer != null) {
				writer (level, category, message);
			} else {
				OnDebuggerOutput (false, string.Format ("[{0}:{1}] {2}", level, category, message));
			}
		}

		internal protected void OnAssemblyLoaded (string assemblyLocation)
		{
			AssemblyLoaded?.Invoke (this, new AssemblyEventArgs (assemblyLocation));
		}
		
		internal protected void SetBusyState (BusyStateEventArgs args)
		{
			BusyStateChanged?.Invoke (this, args);
		}
		
		/// <summary>
		/// Tries to bind all unbound breakpoints of a source file
		/// </summary>
		/// <param name='fullFilePath'>
		/// Source file path
		/// </param>
		/// <remarks>
		/// This method can be called by a subclass to ask the debugger session to attempt
		/// to bind all unbound breakpoints defined on the given file. This method could
		/// be called, for example, when a new assembly that contains this file is loaded
		/// into memory. It is not necessary to use this method if the subclass keeps
		/// track of unbound breakpoints by itself.
		/// </remarks>
		internal protected void BindSourceFileBreakpoints (string fullFilePath)
		{
			Dictionary<BreakEvent, BreakEventInfo> breakpointsCopy;
			StringComparer comparer;

			if (System.IO.Path.DirectorySeparatorChar == '\\')
				comparer = StringComparer.InvariantCultureIgnoreCase;
			else
				comparer = StringComparer.InvariantCulture;

			lock (breakpoints) {
				// Make a copy of the breakpoints table since it can be modified while iterating
				breakpointsCopy = new Dictionary<BreakEvent, BreakEventInfo> (breakpoints);
			}

			foreach (var bps in breakpointsCopy) {
				if (bps.Key is Breakpoint bp && comparer.Compare (System.IO.Path.GetFullPath (bp.FileName), fullFilePath) == 0)
					RetryEventBind (bps.Value);
			}
		}
		
		void RetryEventBind (BreakEventInfo binfo)
		{
			// Try inserting the breakpoint again
			var be = binfo.BreakEvent;

			try {
				binfo = OnInsertBreakEvent (be);
				if (binfo == null)
					throw new InvalidOperationException ("OnInsertBreakEvent can't return a null value. If the breakpoint can't be bound or is invalid, a BreakEventInfo with the corresponding status must be returned");
				lock (breakpoints) {
					breakpoints [be] = binfo;
				}
				binfo.AttachSession (this, be);
			} catch (Exception ex) {
				if (be is Breakpoint bp)
					OnDebuggerOutput (false, "Could not set breakpoint at location '" + bp.FileName + ":" + bp.Line + " (" + ex.Message + ")\n");
				else
					OnDebuggerOutput (false, "Could not set catchpoint for exception '" + ((Catchpoint)be).ExceptionName + "' (" + ex.Message + ")\n");
				HandleException (ex);
			}
		}
		
		/// <summary>
		/// Unbinds all bound breakpoints of a source file
		/// </summary>
		/// <param name='fullFilePath'>
		/// The source file path
		/// </param>
		/// <remarks>
		/// This method can be called by a subclass to ask the debugger session to
		/// unbind all bound breakpoints defined on the given file. This method could
		/// be called, for example, when an assembly that contains this file is unloaded
		/// from memory. It is not necessary to use this method if the subclass keeps
		/// track of unbound breakpoints by itself.
		/// </remarks>
		internal protected void UnbindSourceFileBreakpoints (string fullFilePath)
		{
			var toUpdate = new List<BreakEventInfo> ();

			lock (breakpoints) {
				foreach (var bps in breakpoints) {
					if (bps.Key is Breakpoint bp && bps.Value.Status == BreakEventStatus.Bound) {
						if (System.IO.Path.GetFullPath (bp.FileName) == fullFilePath)
							toUpdate.Add (bps.Value);
					}
				}

				foreach (var be in toUpdate)
					breakpoints.Remove (be.BreakEvent);
			}

			foreach (var be in toUpdate)
				NotifyBreakEventStatusChanged (be.BreakEvent);
		}
		
		internal void NotifyBreakEventStatusChanged (BreakEvent be)
		{
			var s = GetBreakEventStatus (be);
			if (s == BreakEventStatus.BindError || s == BreakEventStatus.Invalid)
				OnDebuggerOutput (true, GetBreakEventErrorMessage (be) + ": " + GetBreakEventStatusMessage (be) + "\n");
			Breakpoints.NotifyStatusChanged (be);
		}
		
		static string GetBreakEventErrorMessage (BreakEvent be)
		{
			if (be is Breakpoint bp)
				return string.Format ("Could not insert breakpoint at '{0}:{1}'", bp.FileName, bp.Line);

			var cp = (Catchpoint) be;

			return string.Format ("Could not enable catchpoint for exception '{0}'", cp.ExceptionName);
		}
		
		/// <summary>
		/// Reports an unhandled exception in the debugger
		/// </summary>
		/// <returns>
		/// True if the debugger engine handles the exception. False otherwise.
		/// </returns>
		/// <param name='ex'>
		/// The exception
		/// </param>
		/// <remarks>
		/// This method can be used by subclasses to report errors in the debugger that must be reported
		/// to the user.
		/// </remarks>
		protected virtual bool HandleException (Exception ex)
		{
			if (ExceptionHandler != null)
				return ExceptionHandler (ex);

			return false;
		}
		
		internal void AdjustBreakpointLocation (Breakpoint b, int newLine, int newColumn)
		{
			lock (slock) {
				lock (breakpoints) {
					try {
						adjustingBreakpoints = true;
						Breakpoints.AdjustBreakpointLine (b, newLine, newColumn);
					} finally {
						adjustingBreakpoints = false;
					}
				}
			}
		}

		/// <summary>
		/// When set, operations such as OnRun, OnAttachToProcess, OnStepLine, etc, are run in
		/// a background thread, so it will not block the caller of the corresponding public methods.
		/// </summary>
		protected bool UseOperationThread { get; set; }
		
		/// <summary>
		/// Called to start the execution of the debugger
		/// </summary>
		/// <param name='startInfo'>
		/// Startup information
		/// </param>
		protected abstract void OnRun (DebuggerStartInfo startInfo);
		
		/// <summary>
		/// Called to attach the debugger to a running process
		/// </summary>
		/// <param name='processId'>
		/// Process identifier.
		/// </param>
		protected abstract void OnAttachToProcess (long processId);

		/// <summary>
		/// Called to attach the debugger to a running process
		/// </summary>
		/// <param name='processInfo'>
		/// Process identifier.
		/// </param>
		protected virtual void OnAttachToProcess (ProcessInfo processInfo)
		{
			OnAttachToProcess (processInfo.Id);
		}

		/// <summary>
		/// Called to detach the debugging session from the running process
		/// </summary>
		protected abstract void OnDetach ();
		
		/// <summary>
		/// Called when the active thread has to be changed
		/// </summary>
		/// <param name='processId'>
		/// Process identifier.
		/// </param>
		/// <param name='threadId'>
		/// Thread identifier.
		/// </param>
		/// <remarks>
		/// This method can only be called when the debuggee is stopped by the debugger
		/// </remarks>
		protected abstract void OnSetActiveThread (long processId, long threadId);
		
		/// <summary>
		/// Called when the debug session has to be paused
		/// </summary>
		protected abstract void OnStop ();
		
		/// <summary>
		/// Called when the target process has to be exited
		/// </summary>
		protected abstract void OnExit ();
		
		
		/// <summary>
		/// Called to step one source code line
		/// </summary>
		/// <remarks>
		/// This method can only be called when the debuggee is stopped by the debugger
		/// </remarks>
		protected abstract void OnStepLine ();

		/// <summary>
		/// Called to step one source line, but step over method calls
		/// </summary>
		/// <remarks>
		/// This method can only be called when the debuggee is stopped by the debugger
		/// </remarks>
		protected abstract void OnNextLine ();

		/// <summary>
		/// Called to step one instruction
		/// </summary>
		/// <remarks>
		/// This method can only be called when the debuggee is stopped by the debugger
		/// </remarks>
		protected abstract void OnStepInstruction ();

		/// <summary>
		/// Called to step one instruction, but step over method calls
		/// </summary>
		/// <remarks>
		/// This method can only be called when the debuggee is stopped by the debugger
		/// </remarks>
		protected abstract void OnNextInstruction ();

		/// <summary>
		/// Called to continue execution until leaving the current method
		/// </summary>
		/// <remarks>
		/// This method can only be called when the debuggee is stopped by the debugger
		/// </remarks>
		protected abstract void OnFinish ();

		/// <summary>
		/// Called to resume execution
		/// </summary>
		/// <remarks>
		/// This method can only be called when the debuggee is stopped by the debugger
		/// </remarks>
		protected abstract void OnContinue ();

		/// <summary>
		/// Checks whether or not the debugger supports setting the next statement to use when the debugger is resumed.
		/// </summary>
		/// <remarks>
		/// This method is generally used to determine whether or not UI menu items should be shown.
		/// </remarks>
		/// <value><c>true</c> if the debugger supports setting the next statement to use when the debugger is resumed; otherwise, <c>false</c>.</value>
		public virtual bool CanSetNextStatement {
			get { return false; }
		}

		/// <summary>
		/// Sets the next statement to be executed when the debugger is resumed.
		/// </summary>
		/// <remarks>
		/// This method can only be called when the debuggee is stopped by the debugger.
		/// </remarks>
		protected virtual void OnSetNextStatement (long threadId, string fileName, int line, int column)
		{
			throw new NotSupportedException ();
		}

		/// <summary>
		/// Sets the next statement to be executed when the debugger is resumed.
		/// </summary>
		/// <remarks>
		/// This method can only be called when the debuggee is stopped by the debugger.
		/// </remarks>
		protected virtual void OnSetNextStatement (long threadId, int ilOffset)
		{
			throw new NotSupportedException ();
		}
		
		//breakpoints etc

		/// <summary>
		/// Called to insert a new breakpoint or catchpoint
		/// </summary>
		/// <param name='breakEvent'>
		/// The break event.
		/// </param>
		/// <remarks>
		/// Implementations of this method must: (1) create (and return) an instance of BreakEventInfo
		/// (or a subclass of it). (2) Attempt to activate a breakpoint at the location
		/// specified in breakEvent. If the breakpoint cannot be activated at the time this
		/// method is called, it is the responsibility of the DebuggerSession subclass
		/// to attempt it later on.
		/// The BreakEventInfo object can be used to change the status of the breakpoint,
		/// update the hit point, etc.
		/// </remarks>
		protected abstract BreakEventInfo OnInsertBreakEvent (BreakEvent breakEvent);
		
		/// <summary>
		/// Called when a breakpoint has been removed.
		/// </summary>
		/// <param name='eventInfo'>
		/// The breakpoint
		/// </param>
		/// <remarks>
		/// Implementations of this method should remove or disable the breakpoint
		/// in the debugging engine.
		/// </remarks>
		protected abstract void OnRemoveBreakEvent (BreakEventInfo eventInfo);

		/// <summary>
		/// Called when information about a breakpoint has changed
		/// </summary>
		/// <param name='eventInfo'>
		/// The break event
		/// </param>
		/// <remarks>
		/// This method is called when some information about the breakpoint changes.
		/// Notice that the file and line of a breakpoint or the exception name of
		/// a catchpoint can't be modified. Changes of the Enabled property are
		/// notified by calling OnEnableBreakEvent. 
		/// </remarks>
		protected abstract void OnUpdateBreakEvent (BreakEventInfo eventInfo);
		
		/// <summary>
		/// Called when a break event is enabled or disabled
		/// </summary>
		/// <param name='eventInfo'>
		/// The break event
		/// </param>
		/// <param name='enable'>
		/// The new status
		/// </param>
		protected abstract void OnEnableBreakEvent (BreakEventInfo eventInfo, bool enable);
		
		/// <summary>
		/// Queried when the debugger session has to check if changes in breakpoints are allowed or not
		/// </summary>
		/// <value>
		/// <c>true</c> if break event changes are allowed; otherwise, <c>false</c>.
		/// </value>
		/// <remarks>
		/// This property should return false if at the time it is invoked the debugger engine doesn't support
		/// adding, removing or doing changes in breakpoints.
		/// </remarks>
		protected virtual bool AllowBreakEventChanges { get { return true; } }
		
		/// <summary>
		/// Called to get a list of the threads of a process
		/// </summary>
		/// <param name='processId'>
		/// Process identifier.
		/// </param>
		/// <remarks>
		/// This method can only be called when the debuggee is stopped by the debugger
		/// </remarks>
		protected abstract ThreadInfo[] OnGetThreads (long processId);
		
		/// <summary>
		/// Called to get a list of all debugee processes
		/// </summary>
		/// <remarks>
		/// This method can only be called when the debuggee is stopped by the debugger
		/// </remarks>
		protected abstract ProcessInfo[] OnGetProcesses ();
		
		/// <summary>
		/// Called to get the backtrace of a thread
		/// </summary>
		/// <param name='processId'>
		/// Process identifier.
		/// </param>
		/// <param name='threadId'>
		/// Thread identifier.
		/// </param>
		/// <remarks>
		/// This method can only be called when the debuggee is stopped by the debugger
		/// </remarks>
		protected abstract Backtrace OnGetThreadBacktrace (long processId, long threadId);

		/// <summary>
		/// Called to get the elapsedTime of last step of a thread in milliseconds
		/// </summary>
		/// <param name='processId'>
		/// Process identifier.
		/// </param>
		/// <param name='threadId'>
		/// Thread identifier.
		/// </param>
		/// <remarks>
		/// This method can only be called when the debuggee is stopped by the debugger
		/// This method will return -1 if time measurement is not available
		/// </remarks>
		protected virtual long OnGetElapsedTime (long processId, long threadId)
		{
			return -1;
		}

		/// <summary>
		/// Called to gets the disassembly of a source code file
		/// </summary>
		/// <returns>
		/// An array of AssemblyLine, with one element for each source code line that could be disassembled
		/// </returns>
		/// <param name='file'>
		/// The file.
		/// </param>
		/// <remarks>
		/// This method can only be used when the debuggee is stopped by the debugger
		/// </remarks>
		protected virtual AssemblyLine[] OnDisassembleFile (string file)
		{
			return null;
		}

		internal T WrapDebuggerObject<T> (T obj) where T:class,IDebuggerBackendObject
		{
			return obj != null ? OnWrapDebuggerObject (obj) : null;
		}

		/// <summary>
		/// Called for every object that is obtained from the debugger engine.
		/// Subclasses may want to create wrappers for some of those objects
		/// </summary>
		protected virtual T OnWrapDebuggerObject<T> (T obj) where T:class,IDebuggerBackendObject
		{
			return obj;
		}

		protected IDebuggerSessionFrontend Frontend {
			get {
				return frontend;
			}
		}

		protected virtual void OnFetchFrames (ThreadInfo[] threads)
		{
		}

		/// <summary>
		/// Calling this method is optional.
		/// It's usefull to call this method so underlying debugger can optimize speed of fetching multiple frames on <paramref name="threads"/>.
		/// </summary>
		/// <param name="threads">Array of threads to fetch frames.</param>
		public void FetchFrames (ThreadInfo[] threads)
		{
			OnFetchFrames (threads);
		}
	}
	
	class InternalDebuggerSession: IDebuggerSessionFrontend
	{
		readonly DebuggerSession session;
		
		public InternalDebuggerSession (DebuggerSession session)
		{
			this.session = session;
		}
		
		public void NotifyTargetEvent (TargetEventArgs args)
		{
			session.OnTargetEvent (args);
		}

		public void NotifyTargetOutput (bool isStderr, string text)
		{
			session.OnTargetOutput (isStderr, text);
		}
		
		public void NotifyDebuggerOutput (bool isStderr, string text)
		{
			session.OnDebuggerOutput (isStderr, text);
		}
		
		public void NotifyStarted (ThreadInfo t)
		{
			session.OnStarted (t);
		}
		
		public void NotifyStarted ()
		{
			session.OnStarted ();
		}
		
		public void BindSourceFileBreakpoints (string fullFilePath)
		{
			session.BindSourceFileBreakpoints (fullFilePath);
		}

		public void UnbindSourceFileBreakpoints (string fullFilePath)
		{
			session.UnbindSourceFileBreakpoints (fullFilePath);
		}
	}

	public delegate void OutputWriterDelegate (bool isStderr, string text);
	public delegate void DebugWriterDelegate (int level, string category, string message);

	public class BusyStateEventArgs: EventArgs
	{
		public bool IsBusy { get; internal set; }
		
		public string Description { get; internal set; }

		public EvaluationContext EvaluationContext { get; internal set; }
	}
	
	public interface IConnectionDialog : IDisposable
	{
		event EventHandler UserCancelled;
		
		//message may be null in which case the dialog should construct a default
		void SetMessage (DebuggerStartInfo dsi, string message, bool listening, int attemptNumber);
	}
}