// Copyright (c) 2014 Daniel Grunwald
// 
// 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.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using ICSharpCode.NRefactory.Utils;
using ICSharpCode.Decompiler.CSharp;

namespace ICSharpCode.Decompiler.IL
{
	/// <summary>
	/// Represents a decoded IL instruction
	/// </summary>
	public abstract partial class ILInstruction
	{
		public readonly OpCode OpCode;
		
		protected ILInstruction(OpCode opCode)
		{
			this.OpCode = opCode;
		}
		
		protected void ValidateArgument(ILInstruction inst)
		{
			if (inst == null)
				throw new ArgumentNullException("inst");
			if (inst.ResultType == StackType.Void)
				throw new ArgumentException("Argument must not be of type void", "inst");
			Debug.Assert(!this.IsDescendantOf(inst), "ILAst must form a tree");
		}
		
		protected void ValidateChild(ILInstruction inst)
		{
			if (inst == null)
				throw new ArgumentNullException("inst");
			Debug.Assert(!this.IsDescendantOf(inst), "ILAst must form a tree");
		}
		
		[Conditional("DEBUG")]
		internal virtual void CheckInvariant()
		{
			foreach (var child in Children) {
				Debug.Assert(child.Parent == this);
				Debug.Assert(this.GetChild(child.ChildIndex) == child);
				// if child flags are invalid, parent flags must be too
				Debug.Assert(child.flags != invalidFlags || this.flags == invalidFlags);
				Debug.Assert(child.IsConnected == this.IsConnected);
				child.CheckInvariant();
			}
		}
		
		/// <summary>
		/// Gets whether this node is a descendant of <paramref name="possibleAncestor"/>.
		/// Also returns true if <c>this</c>==<paramref name="possibleAncestor"/>.
		/// </summary>
		public bool IsDescendantOf(ILInstruction possibleAncestor)
		{
			for (ILInstruction ancestor = this; ancestor != null; ancestor = ancestor.Parent) {
				if (ancestor == possibleAncestor)
					return true;
			}
			return false;
		}
		
		/// <summary>
		/// Gets the stack type of the value produced by this instruction.
		/// </summary>
		public abstract StackType ResultType { get; }
		
		internal static StackType CommonResultType(StackType a, StackType b)
		{
			if (a == StackType.I || b == StackType.I)
				return StackType.I;
			Debug.Assert(a == b);
			return a;
		}
		
		const InstructionFlags invalidFlags = (InstructionFlags)(-1);
		
		InstructionFlags flags = invalidFlags;
		
		public InstructionFlags Flags {
			get {
				if (flags == invalidFlags) {
					flags = ComputeFlags();
				}
				return flags;
			}
		}

		/// <summary>
		/// Returns whether the instruction has at least one of the specified flags.
		/// </summary>
		public bool HasFlag(InstructionFlags flags)
		{
			return (this.Flags & flags) != 0;
		}
		
		protected void InvalidateFlags()
		{
			for (ILInstruction inst = this; inst != null && inst.flags != invalidFlags; inst = inst.parent)
				inst.flags = invalidFlags;
		}
		
		protected abstract InstructionFlags ComputeFlags();
		
		/// <summary>
		/// Gets the ILRange for this instruction alone, ignoring the operands.
		/// </summary>
		public Interval ILRange;

		/// <summary>
		/// Writes the ILAst to the text output.
		/// </summary>
		public abstract void WriteTo(ITextOutput output);

		public override string ToString()
		{
			var output = new PlainTextOutput();
			WriteTo(output);
			return output.ToString();
		}
		
		/// <summary>
		/// Calls the Visit*-method on the visitor corresponding to the concrete type of this instruction.
		/// </summary>
		public abstract void AcceptVisitor(ILVisitor visitor);
		
		/// <summary>
		/// Calls the Visit*-method on the visitor corresponding to the concrete type of this instruction.
		/// </summary>
		public abstract T AcceptVisitor<T>(ILVisitor<T> visitor);
		
		/// <summary>
		/// Gets the child nodes of this instruction.
		/// </summary>
		public ChildrenCollection Children {
			get {
				return new ChildrenCollection(this);
			}
		}
		
		protected abstract int GetChildCount();
		protected abstract ILInstruction GetChild(int index);
		protected abstract void SetChild(int index, ILInstruction value);
		
		#region ChildrenCollection + ChildrenEnumerator
		public struct ChildrenCollection : IReadOnlyList<ILInstruction>
		{
			readonly ILInstruction inst;
			
			internal ChildrenCollection(ILInstruction inst)
			{
				Debug.Assert(inst != null);
				this.inst = inst;
			}
			
			public int Count {
				get { return inst.GetChildCount(); }
			}
			
			public ILInstruction this[int index] {
				get { return inst.GetChild(index); }
			}
			
			public ChildrenEnumerator GetEnumerator()
			{
				return new ChildrenEnumerator(inst);
			}
			
			IEnumerator<ILInstruction> IEnumerable<ILInstruction>.GetEnumerator()
			{
				return GetEnumerator();
			}
			
			System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
			{
				return GetEnumerator();
			}
		}
		
		#if DEBUG
		int activeEnumerators;
		
		[Conditional("DEBUG")]
		internal void StartEnumerator()
		{
			activeEnumerators++;
		}
		
		[Conditional("DEBUG")]
		internal void StopEnumerator()
		{
			Debug.Assert(activeEnumerators > 0);
			activeEnumerators--;
		}
		#endif
		
		[Conditional("DEBUG")]
		internal void AssertNoEnumerators()
		{
			#if DEBUG
			Debug.Assert(activeEnumerators == 0);
			#endif
		}
		
		/// <summary>
		/// Enumerator over the children of an ILInstruction.
		/// Warning: even though this is a struct, it is invalid to copy:
		/// the number of constructor calls must match the number of dispose calls.
		/// </summary>
		public struct ChildrenEnumerator : IEnumerator<ILInstruction>
		{
			ILInstruction inst;
			readonly int end;
			int pos;
			
			public ChildrenEnumerator(ILInstruction inst)
			{
				Debug.Assert(inst != null);
				this.inst = inst;
				this.pos = -1;
				this.end = inst.GetChildCount();
				#if DEBUG
				inst.StartEnumerator();
				#endif
			}
			
			public ILInstruction Current {
				get {
					return inst.GetChild(pos);
				}
			}

			public bool MoveNext()
			{
				return ++pos < end;
			}

			public void Dispose()
			{
				#if DEBUG
				if (inst != null) {
					inst.StopEnumerator();
					inst = null;
				}
				#endif
			}
			
			object System.Collections.IEnumerator.Current {
				get { return this.Current; }
			}
			
			void System.Collections.IEnumerator.Reset()
			{
				pos = -1;
			}
		}
		#endregion
		
		/// <summary>
		/// Replaces this ILInstruction with the given replacement instruction.
		/// </summary>
		public void ReplaceWith(ILInstruction replacement)
		{
			Debug.Assert(parent.GetChild(ChildIndex) == this);
			if (replacement == this)
				return;
			parent.SetChild(ChildIndex, replacement);
		}
		
		/// <summary>
		/// Returns all descendants of the ILInstruction in post-order.
		/// </summary>
		/// <remarks>
		/// Within a loop 'foreach (var node in inst.Descendants)', it is illegal to
		/// add or remove from the child collections of node's ancestors, as those are
		/// currently being enumerated.
		/// Note that it is valid to modify node's children as those were already previously visited.
		/// As a special case, it is also allowed to replace node itself with another node.
		/// </remarks>
		public IEnumerable<ILInstruction> Descendants {
			get {
				// Copy of TreeTraversal.PostOrder() specialized for ChildrenEnumerator
				Stack<ChildrenEnumerator> stack = new Stack<ChildrenEnumerator>();
				ChildrenEnumerator enumerator = new ChildrenEnumerator(this);
				try {
					while (true) {
						while (enumerator.MoveNext()) {
							var element = enumerator.Current;
							stack.Push(enumerator);
							enumerator = new ChildrenEnumerator(element);
						}
						enumerator.Dispose();
						if (stack.Count > 0) {
							enumerator = stack.Pop();
							yield return enumerator.Current;
						} else {
							break;
						}
					}
				} finally {
					enumerator.Dispose();
					while (stack.Count > 0) {
						stack.Pop().Dispose();
					}
				}
			}
		}
		
		/// <summary>
		/// Attempts inlining from the inline context into this instruction.
		/// </summary>
		/// <param name="flagsBefore">Combined instruction flags of the instructions
		/// that the instructions getting inlined would get moved over.</param>
		/// <param name="context">The inline context providing the values on the evaluation stack.</param>
		/// <returns>
		/// Returns the modified ILInstruction after inlining is complete.
		/// Note that inlining modifies the AST in-place, so this method usually returns <c>this</c>
		/// (unless <c>this</c> should be replaced by another node)
		/// </returns>
		/// <remarks>
		/// Inlining from an inline context representing the actual evaluation stack
		/// is equivalent to phase-1 execution of the instruction.
		/// </remarks>
		internal abstract ILInstruction Inline(InstructionFlags flagsBefore, IInlineContext context);

		/// <summary>
		/// Transforms the evaluation stack 'pop' and 'peek' instructions into local copy.
		/// </summary>
		internal abstract void TransformStackIntoVariables(TransformStackIntoVariablesState state);
		
		/// <summary>
		/// Number of parents that refer to this instruction and are connected to the root.
		/// Usually is 0 for unconnected nodes and 1 for connected nodes, but may temporarily increase to 2
		/// when the ILAst is re-arranged (e.g. within SetChildInstruction).
		/// </summary>
		byte refCount;
		
		internal void AddRef()
		{
			if (refCount++ == 0) {
				Connected();
			}
		}
		
		internal void ReleaseRef()
		{
			Debug.Assert(refCount > 0);
			if (--refCount == 0) {
				Disconnected();
			}
		}
		
		/// <summary>
		/// Gets whether this ILInstruction is connected to the root node of the ILAst.
		/// </summary>
		protected bool IsConnected {
			get { return refCount > 0; }
		}
		
		/// <summary>
		/// Called after the ILInstruction was connected to the root node of the ILAst.
		/// </summary>
		protected virtual void Connected()
		{
			foreach (var child in Children)
				child.AddRef();
		}
		
		/// <summary>
		/// Called after the ILInstruction was disconnected from the root node of the ILAst.
		/// </summary>
		protected virtual void Disconnected()
		{
			foreach (var child in Children)
				child.ReleaseRef();
		}
		
		ILInstruction parent;
		
		/// <summary>
		/// Gets the parent of this ILInstruction.
		/// </summary>
		public ILInstruction Parent {
			get { return parent; }
		}
		
		/// <summary>
		/// Gets the index of this node in the Parent.Children collection.
		/// </summary>
		public int ChildIndex { get; internal set; }
		
		/// <summary>
		/// Replaces a child of this ILInstruction.
		/// </summary>
		/// <param name="childPointer">Reference to the field holding the child</param>
		/// <param name="newValue">New child</param>
		/// <param name="index">Index of the field in the Children collection</param>
		protected internal void SetChildInstruction(ref ILInstruction childPointer, ILInstruction newValue, int index)
		{
			ILInstruction oldValue = childPointer;
			Debug.Assert(this is Return || oldValue == GetChild(index));
			if (oldValue == newValue)
				return;
			childPointer = newValue;
			if (newValue != null) {
				newValue.parent = this;
				newValue.ChildIndex = index;
			}
			if (refCount > 0) {
				// The new value may be a subtree of the old value.
				// We first call AddRef(), then ReleaseRef() to prevent the subtree
				// that stays connected from receiving a Disconnected() notification followed by a Connected() notification.
				if (newValue != null)
					newValue.AddRef();
				if (oldValue != null)
					oldValue.ReleaseRef();
			}
			InvalidateFlags();
		}
		
		/// <summary>
		/// Called when a new child is added to a InstructionCollection.
		/// </summary>
		protected internal void InstructionCollectionAdded(ILInstruction newChild)
		{
			Debug.Assert(GetChild(newChild.ChildIndex) == newChild);
			Debug.Assert(!this.IsDescendantOf(newChild), "ILAst must form a tree");
			newChild.parent = this;
			if (refCount > 0)
				newChild.AddRef();
		}
		
		/// <summary>
		/// Called when a child is removed from a InstructionCollection.
		/// </summary>
		protected internal void InstructionCollectionRemoved(ILInstruction oldChild)
		{
			if (refCount > 0)
				oldChild.ReleaseRef();
		}
		
		/// <summary>
		/// Called when a series of add/remove operations on the InstructionCollection is complete.
		/// </summary>
		protected internal virtual void InstructionCollectionUpdateComplete()
		{
			InvalidateFlags();
		}
		
		/// <summary>
		/// Creates a deep clone of the ILInstruction.
		/// </summary>
		public abstract ILInstruction Clone();
		
		/// <summary>
		/// Creates a shallow clone of the ILInstruction.
		/// </summary>
		/// <remarks>
		/// Like MemberwiseClone(), except that the new instruction starts as disconnected.
		/// </remarks>
		protected ILInstruction ShallowClone()
		{
			ILInstruction inst = (ILInstruction)MemberwiseClone();
			// reset refCount and parent so that the cloned instruction starts as disconnected
			inst.refCount = 0;
			inst.parent = null;
			inst.flags = invalidFlags;
			#if DEBUG
			inst.activeEnumerators = 0;
			#endif
			return inst;
		}
	}
}