// Copyright (c) AlphaSierraPapa for the SharpDevelop Team (for details please see \doc\copyright.txt)
// This code is distributed under MIT X11 license (for details please see \doc\license.txt)

using System;
using System.Linq;
using Decompiler.Transforms;
using ICSharpCode.NRefactory.CSharp;
using ICSharpCode.NRefactory.CSharp.PatternMatching;
using Mono.Cecil;

namespace Decompiler.Transforms
{
	/// <summary>
	/// Finds the expanded form of using statements using pattern matching and replaces it with a UsingStatement.
	/// </summary>
	public class UsingStatementTransform : IAstTransform
	{
		static readonly AstNode usingVarDeclPattern = new VariableDeclarationStatement {
			Type = new AnyNode("type").ToType(),
			Variables = {
				new NamedNode(
					"variable",
					new VariableInitializer {
						Initializer = new AnyNode().ToExpression()
					}
				).ToVariable()
			}
		};
		static readonly AstNode simpleVariableDefinition = new VariableDeclarationStatement {
			Type = new AnyNode().ToType(),
			Variables = {
				new VariableInitializer() // any name but no initializer
			}
		};
		static readonly AstNode usingTryCatchPattern = new TryCatchStatement {
			TryBlock = new AnyNode("body").ToBlock(),
			FinallyBlock = new BlockStatement {
				Statements = {
					new Choice {
						{ "valueType",
							new ExpressionStatement(new NamedNode("ident", new IdentifierExpression()).ToExpression().Invoke("Dispose"))
						},
						{ "referenceType",
							new IfElseStatement {
								Condition = new BinaryOperatorExpression(
									new NamedNode("ident", new IdentifierExpression()).ToExpression(),
									BinaryOperatorType.InEquality,
									new NullReferenceExpression()
								),
								TrueStatement = new BlockStatement {
									Statements = {
										new ExpressionStatement(new Backreference("ident").ToExpression().Invoke("Dispose"))
									}
								}
							}
						}
					}.ToStatement()
				}
			}
		};
		
		public void Run(AstNode compilationUnit)
		{
			foreach (AstNode node in compilationUnit.Descendants.ToArray()) {
				Match m1 = usingVarDeclPattern.Match(node);
				if (m1 == null) continue;
				AstNode tryCatch = node.NextSibling;
				while (simpleVariableDefinition.Match(tryCatch) != null)
					tryCatch = tryCatch.NextSibling;
				Match m2 = usingTryCatchPattern.Match(tryCatch);
				if (m2 == null) continue;
				if (m1.Get<VariableInitializer>("variable").Single().Name == m2.Get<IdentifierExpression>("ident").Single().Identifier) {
					if (m2.Has("valueType")) {
						// if there's no if(x!=null), then it must be a value type
						TypeReference tr = m1.Get<AstType>("type").Single().Annotation<TypeReference>();
						if (tr == null || !tr.IsValueType)
							continue;
					}
					BlockStatement body = m2.Get<BlockStatement>("body").Single();
					tryCatch.ReplaceWith(
						new UsingStatement {
							ResourceAcquisition = node.Detach(),
							EmbeddedStatement = body.Detach()
						});
				}
			}
		}
	}
}