// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.

using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp.Extensions;
using Microsoft.CodeAnalysis.CSharp.Symbols;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Shared.Extensions;
using Microsoft.CodeAnalysis.Simplification;
using Microsoft.CodeAnalysis.CSharp;
using ICSharpCode.NRefactory6.CSharp;

namespace MonoDevelop.CSharp.CodeRefactorings.InlineTemporary
{
	internal partial class InlineTemporaryCodeRefactoringProvider
	{
		/// <summary>
		/// This class handles rewriting initializer expressions that refer to the variable
		/// being initialized into a simpler form.  For example, in "int x = x = 1", we want to
		/// get just "1" back as the initializer.
		/// </summary>
		private class InitializerRewriter : CSharpSyntaxRewriter
		{
			private readonly SemanticModel _semanticModel;
			private readonly ILocalSymbol _localSymbol;
			private readonly ExpressionSyntax _initializer;

			private InitializerRewriter(ExpressionSyntax initializer, ILocalSymbol localSymbol, SemanticModel semanticModel)
			{
				_semanticModel = semanticModel;
				_localSymbol = localSymbol;
				_initializer = initializer;
			}

			private bool IsReference(SimpleNameSyntax name)
			{
				if (name.Identifier.ValueText != _localSymbol.Name)
				{
					return false;
				}

				var symbol = _semanticModel.GetSymbolInfo(name).Symbol;
				return symbol != null
					&& symbol.Equals(_localSymbol);
			}

			public override SyntaxNode VisitAssignmentExpression(AssignmentExpressionSyntax node)
			{
				// Note - leave this as SyntaxNode for now, we might have already re-written it
				var newNode = base.VisitAssignmentExpression(node);

				if (newNode.Kind() == SyntaxKind.SimpleAssignmentExpression)
				{
					// It's okay to just look at the text, since we're explicitly looking for an
					// identifier standing alone, and we know we're in a local's initializer.
					// The text can only bind to the initializer.
					var assignment = (AssignmentExpressionSyntax)newNode;
					var name = assignment.Left.Kind() == SyntaxKind.IdentifierName
						? (IdentifierNameSyntax)assignment.Left
						: null;

					if (name != null && IsReference(name))
					{
						return assignment.Right;
					}
				}

				return newNode;
			}

			public override SyntaxNode VisitIdentifierName(IdentifierNameSyntax node)
			{
				if (IsReference(node))
				{
					var assignmentExpression = node.Parent as AssignmentExpressionSyntax;
					if (assignmentExpression != null)
					{
						if (assignmentExpression.IsCompoundAssignExpression() &&
							assignmentExpression.Left == node)
						{
							return node.Update(node.Identifier.WithAdditionalAnnotations(CreateConflictAnnotation()));
						}
					}
				}

				return base.VisitIdentifierName(node);
			}

			public override SyntaxNode VisitParenthesizedExpression(ParenthesizedExpressionSyntax node)
			{
				var newNode = base.VisitParenthesizedExpression(node);

				if (node != newNode && newNode.Kind() == SyntaxKind.ParenthesizedExpression)
				{
					return newNode.WithAdditionalAnnotations(Simplifier.Annotation);
				}

				return newNode;
			}

			public static ExpressionSyntax Visit(ExpressionSyntax initializer, ILocalSymbol local, SemanticModel semanticModel)
			{
				var simplifier = new InitializerRewriter(initializer, local, semanticModel);
				return (ExpressionSyntax)simplifier.Visit(initializer);
			}
		}
	}
}