// Copyright (c) 2011-2016 Siegfried Pammer
// 
// 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.Linq;
using ICSharpCode.Decompiler.CSharp;
using ICSharpCode.Decompiler.IL;
using ICSharpCode.NRefactory.TypeSystem;

namespace ICSharpCode.Decompiler.IL.Transforms
{
	public class DelegateConstruction : IILTransform
	{
		ILTransformContext context;
		ITypeResolveContext decompilationContext;
		
		void IILTransform.Run(ILFunction function, ILTransformContext context)
		{
			if (!context.Settings.AnonymousMethods)
				return;
			this.context = context;
			this.decompilationContext = new SimpleTypeResolveContext(context.TypeSystem.Resolve(function.Method));
			foreach (var block in function.Descendants.OfType<Block>()) {
				for (int i = block.Instructions.Count - 1; i >= 0; i--) {
					foreach (var call in block.Instructions[i].Descendants.OfType<NewObj>()) {
						ILFunction f = TransformDelegateConstruction(call);
						if (f != null)
							call.Arguments[1].ReplaceWith(f);
					}
					
					var inst = block.Instructions[i] as IfInstruction;
					if (inst != null) {
						if (CachedDelegateInitializationWithField(inst)) {
							block.Instructions.RemoveAt(i);
							continue;
						}
						bool hasFieldStore;
						if (CachedDelegateInitializationWithLocal(inst, out hasFieldStore)) {
							block.Instructions.RemoveAt(i);
							if (hasFieldStore) {
								block.Instructions.RemoveAt(i - 1);
							}
							continue;
						}
					}
				}
			}
		}

		#region TransformDelegateConstruction
		internal static bool IsDelegateConstruction(NewObj inst, bool allowTransformed = false)
		{
			if (inst == null || inst.Arguments.Count != 2 || inst.Method.DeclaringType.Kind != TypeKind.Delegate)
				return false;
			var opCode = inst.Arguments[1].OpCode;
			
			return opCode == OpCode.LdFtn || opCode == OpCode.LdVirtFtn || (allowTransformed && opCode == OpCode.ILFunction);
		}
		
		static bool IsAnonymousMethod(ITypeDefinition decompiledTypeDefinition, IMethod method)
		{
			if (method == null || !(method.HasGeneratedName() || method.Name.Contains("$")))
				return false;
			if (!(method.IsCompilerGenerated() || IsPotentialClosure(decompiledTypeDefinition, method.DeclaringTypeDefinition)))
				return false;
			return true;
		}
		
		static bool IsPotentialClosure(ITypeDefinition decompiledTypeDefinition, ITypeDefinition potentialDisplayClass)
		{
			if (potentialDisplayClass == null || !potentialDisplayClass.IsCompilerGeneratedOrIsInCompilerGeneratedClass())
				return false;
			while (potentialDisplayClass != decompiledTypeDefinition) {
				potentialDisplayClass = potentialDisplayClass.DeclaringTypeDefinition;
				if (potentialDisplayClass == null)
					return false;
			}
			return true;
		}
		
		ILFunction TransformDelegateConstruction(NewObj value)
		{
			if (!IsDelegateConstruction(value))
				return null;
			var targetMethod = ((IInstructionWithMethodOperand)value.Arguments[1]).Method;
			if (IsAnonymousMethod(decompilationContext.CurrentTypeDefinition, targetMethod)) {
				var target = value.Arguments[0];
				var localTypeSystem = context.TypeSystem.GetSpecializingTypeSystem(new SimpleTypeResolveContext(targetMethod));
				var function = ILFunction.Read(localTypeSystem, targetMethod, context.CancellationToken);
				
				var contextPrefix = targetMethod.Name;
				foreach (ILVariable v in function.Variables.Where(v => v.Kind != VariableKind.Parameter)) {
					v.Name = contextPrefix + v.Name;
				}
				
				function.RunTransforms(CSharpDecompiler.GetILTransforms(), context, t => t is DelegateConstruction);
				function.AcceptVisitor(new ReplaceDelegateTargetVisitor(target, function.Variables.SingleOrDefault(v => v.Index == -1 && v.Kind == VariableKind.Parameter)));
				// handle nested lambdas
				((IILTransform)new DelegateConstruction()).Run(function, new ILTransformContext { Settings = context.Settings, CancellationToken = context.CancellationToken, TypeSystem = localTypeSystem });
				return function;
			}
			return null;
		}
		
		class ReplaceDelegateTargetVisitor : ILVisitor
		{
			readonly ILVariable thisVariable;
			readonly ILInstruction target;
			
			public ReplaceDelegateTargetVisitor(ILInstruction target, ILVariable thisVariable)
			{
				this.target = target;
				this.thisVariable = thisVariable;
			}
			
			protected override void Default(ILInstruction inst)
			{
				foreach (var child in inst.Children) {
					child.AcceptVisitor(this);
				}
			}
			
			protected internal override void VisitLdLoc(LdLoc inst)
			{
				if (inst.MatchLdLoc(thisVariable)) {
					inst.ReplaceWith(target.Clone());
					return;
				}
				base.VisitLdLoc(inst);
			}
		}
		#endregion

		bool CachedDelegateInitializationWithField(IfInstruction inst)
		{
			// if (comp(ldsfld CachedAnonMethodDelegate == ldnull) {
			//     stsfld CachedAnonMethodDelegate(DelegateConstruction)
			// }
			// ... one usage of CachedAnonMethodDelegate ...
			// =>
			// ... one usage of DelegateConstruction ...
			Block trueInst = inst.TrueInst as Block;
			var condition = inst.Condition as Comp;
			if (condition == null || trueInst == null || trueInst.Instructions.Count != 1 || !inst.FalseInst.MatchNop())
				return false;
			IField field, field2;
			ILInstruction value;
			var storeInst = trueInst.Instructions[0];
			if (!condition.Left.MatchLdsFld(out field) || !condition.Right.MatchLdNull())
				return false;
			if (!storeInst.MatchStsFld(out value, out field2) || !field.Equals(field2) || !field.IsCompilerGeneratedOrIsInCompilerGeneratedClass())
				return false;
			if (!IsDelegateConstruction(value as NewObj, true))
				return false;
			var nextInstruction = inst.Parent.Children.ElementAtOrDefault(inst.ChildIndex + 1);
			if (nextInstruction == null)
				return false;
			var usages = nextInstruction.Descendants.Where(i => i.MatchLdsFld(field)).ToArray();
			if (usages.Length != 1)
				return false;
			usages[0].ReplaceWith(value);
			return true;
		}

		bool CachedDelegateInitializationWithLocal(IfInstruction inst, out bool hasFieldStore)
		{
			// [stloc v(ldsfld CachedAnonMethodDelegate)]
			// if (comp(ldloc v == ldnull) {
			//     stloc v(DelegateConstruction)
			//     [stsfld CachedAnonMethodDelegate(v)]
			// }
			// ... one usage of v ...
			// =>
			// ... one usage of DelegateConstruction ...
			Block trueInst = inst.TrueInst as Block;
			var condition = inst.Condition as Comp;
			hasFieldStore = false;
			if (condition == null || trueInst == null || (trueInst.Instructions.Count != 1 && trueInst.Instructions.Count != 2) || !inst.FalseInst.MatchNop())
				return false;
			ILVariable v;
			ILInstruction value, value2;
			var storeInst = trueInst.Instructions[0];
			var optionalFieldStore = trueInst.Instructions.ElementAtOrDefault(1);
			if (!condition.Left.MatchLdLoc(out v) || !condition.Right.MatchLdNull())
				return false;
			if (!storeInst.MatchStLoc(v, out value))
				return false;
			if (optionalFieldStore != null) {
				IField field, field2;
				if (!optionalFieldStore.MatchStsFld(out value2, out field) || !value2.MatchLdLoc(v) || !field.IsCompilerGeneratedOrIsInCompilerGeneratedClass())
					return false;
				var storeBeforeIf = inst.Parent.Children.ElementAtOrDefault(inst.ChildIndex - 1) as StLoc;
				if (storeBeforeIf == null || storeBeforeIf.Variable != v || !storeBeforeIf.Value.MatchLdsFld(out field2) || !field.Equals(field2))
					return false;
				hasFieldStore = true;
			}
			if (!IsDelegateConstruction(value as NewObj, true))
				return false;
			var nextInstruction = inst.Parent.Children.ElementAtOrDefault(inst.ChildIndex + 1);
			if (nextInstruction == null)
				return false;
			var usages = nextInstruction.Descendants.OfType<LdLoc>().Where(i => i.Variable == v).ToArray();
			if (usages.Length != 1)
				return false;
			usages[0].ReplaceWith(value);
			return true;
		}
	}
}