// 
// UnreachableCodeIssue.cs
// 
// Author:
//      Mansheng Yang <lightyang0@gmail.com>
// 
// Copyright (c) 2012 Mansheng Yang <lightyang0@gmail.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.Collections.Generic;
using ICSharpCode.NRefactory.CSharp.Analysis;
using System.Linq;
using ICSharpCode.NRefactory.Refactoring;

namespace ICSharpCode.NRefactory.CSharp.Refactoring
{
	[IssueDescription ("Code is unreachable",
						Description = "Code is unreachable.",
						Category = IssueCategories.Redundancies,
						Severity = Severity.Warning,
						IssueMarker = IssueMarker.GrayOut)]
	public class UnreachableCodeIssue : ICodeIssueProvider
	{
		public IEnumerable<CodeIssue> GetIssues (BaseRefactoringContext context)
		{
			return new GatherVisitor (context).GetIssues ();
		}

		class GatherVisitor : GatherVisitorBase<UnreachableCodeIssue>
		{
			HashSet<AstNode> unreachableNodes;

			public GatherVisitor (BaseRefactoringContext ctx)
				: base (ctx)
			{
				unreachableNodes = new HashSet<AstNode> ();
			}

			public override void VisitMethodDeclaration (MethodDeclaration methodDeclaration)
			{
				StatementIssueCollector.Collect (this, methodDeclaration.Body);

				base.VisitMethodDeclaration (methodDeclaration);
			}

			public override void VisitLambdaExpression (LambdaExpression lambdaExpression)
			{
				var blockStatement = lambdaExpression.Body as BlockStatement;
				if (blockStatement != null)
					StatementIssueCollector.Collect (this, blockStatement);

				base.VisitLambdaExpression (lambdaExpression);
			}

			public override void VisitAnonymousMethodExpression (AnonymousMethodExpression anonymousMethodExpression)
			{
				StatementIssueCollector.Collect (this, anonymousMethodExpression.Body);

				base.VisitAnonymousMethodExpression (anonymousMethodExpression);
			}

			public override void VisitConditionalExpression (ConditionalExpression conditionalExpression)
			{
				var resolveResult = ctx.Resolve (conditionalExpression.Condition);
				if (resolveResult.ConstantValue is bool) {
					var condition = (bool)resolveResult.ConstantValue;
					Expression resultExpr, unreachableExpr;
					if (condition) {
						resultExpr = conditionalExpression.TrueExpression;
						unreachableExpr = conditionalExpression.FalseExpression;
					} else {
						resultExpr = conditionalExpression.FalseExpression;
						unreachableExpr = conditionalExpression.TrueExpression;
					}
					unreachableNodes.Add (unreachableExpr);

					AddIssue (unreachableExpr, ctx.TranslateString ("Remove unreachable code"),
						script => script.Replace (conditionalExpression, resultExpr.Clone ()));
				}
				base.VisitConditionalExpression (conditionalExpression);
			}

			protected override void VisitChildren (AstNode node)
			{
				// skip unreachable nodes
				if (!unreachableNodes.Contains (node))
					base.VisitChildren (node);
			}

			class StatementIssueCollector : DepthFirstAstVisitor
			{
				GatherVisitor visitor;
				ReachabilityAnalysis reachability;
				HashSet<Statement> collectedStatements;

				private StatementIssueCollector (GatherVisitor visitor, ReachabilityAnalysis reachability)
				{
					collectedStatements = new HashSet<Statement> ();
					this.visitor = visitor;
					this.reachability = reachability;
				}

				public static void Collect (GatherVisitor visitor, BlockStatement body)
				{
					if (body.IsNull)
						return;
					var reachability = visitor.ctx.CreateReachabilityAnalysis (body);

					var collector = new StatementIssueCollector (visitor, reachability);
					collector.VisitBlockStatement (body);
				}

				protected override void VisitChildren (AstNode node)
				{
					var statement = node as Statement;
					if (statement == null || !AddStatement (statement))
						base.VisitChildren (node);
				}

				bool AddStatement(Statement statement)
				{
					if (reachability.IsReachable (statement))
						return false;
					if (collectedStatements.Contains (statement))
						return true;
					var prevEnd = statement.GetPrevNode (n => !(n is NewLineNode)).EndLocation;

					// group multiple continuous statements into one issue
					var start = statement.StartLocation;
					collectedStatements.Add (statement);
					visitor.unreachableNodes.Add (statement);
					while (statement.GetNextSibling (s => s is Statement) != null) {
						statement = (Statement)statement.GetNextSibling (s => s is Statement);
						collectedStatements.Add (statement);
						visitor.unreachableNodes.Add (statement);
					}
					var end = statement.EndLocation;

					var removeAction = new CodeAction (visitor.ctx.TranslateString ("Remove unreachable code"),
						script =>
						{
							var startOffset = script.GetCurrentOffset (prevEnd);
							var endOffset = script.GetCurrentOffset (end);
							script.RemoveText (startOffset, endOffset - startOffset);
						}, collectedStatements.First().StartLocation, collectedStatements.Last().EndLocation);
					var commentAction = new CodeAction(visitor.ctx.TranslateString("Comment unreachable code"),
						script =>
					{
						var startOffset = script.GetCurrentOffset(prevEnd);
						script.InsertText(startOffset, Environment.NewLine + "/*");
						var endOffset = script.GetCurrentOffset(end);
						script.InsertText(endOffset, Environment.NewLine + "*/");
					}, collectedStatements.First().StartLocation, collectedStatements.Last().EndLocation);
					var actions = new [] { removeAction, commentAction };
					visitor.AddIssue (start, end, visitor.ctx.TranslateString ("Code is unreachable"), actions);
					return true;
				}

				// skip lambda and anonymous method
				public override void VisitLambdaExpression (LambdaExpression lambdaExpression)
				{
				}

				public override void VisitAnonymousMethodExpression (
					AnonymousMethodExpression anonymousMethodExpression)
				{
				}
			}
		}
	}
}
