// 
// ConstantConditionIssue.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.Collections.Generic;
using ICSharpCode.NRefactory.Refactoring;

namespace ICSharpCode.NRefactory.CSharp.Refactoring
{
	[IssueDescription("Condition is always 'true' or always 'false'",
		Description = "Condition is always 'true' or always 'false'.",
		Category = IssueCategories.CodeQualityIssues,
		Severity = Severity.Warning)]
	public class ConstantConditionIssue : GatherVisitorCodeIssueProvider
	{
		protected override IGatherVisitor CreateVisitor(BaseRefactoringContext context)
		{
			return new GatherVisitor(context);
		}

		class GatherVisitor : GatherVisitorBase<ConstantConditionIssue>
		{
			public GatherVisitor(BaseRefactoringContext ctx)
				: base(ctx)
			{
			}

			public override void VisitConditionalExpression(ConditionalExpression conditionalExpression)
			{
				base.VisitConditionalExpression(conditionalExpression);

				CheckCondition(conditionalExpression.Condition);
			}

			public override void VisitIfElseStatement(IfElseStatement ifElseStatement)
			{
				base.VisitIfElseStatement(ifElseStatement);

				CheckCondition(ifElseStatement.Condition);
			}

			public override void VisitWhileStatement(WhileStatement whileStatement)
			{
				base.VisitWhileStatement(whileStatement);

				CheckCondition(whileStatement.Condition);
			}

			public override void VisitDoWhileStatement(DoWhileStatement doWhileStatement)
			{
				base.VisitDoWhileStatement(doWhileStatement);

				CheckCondition(doWhileStatement.Condition);
			}

			public override void VisitForStatement(ForStatement forStatement)
			{
				base.VisitForStatement(forStatement);

				CheckCondition(forStatement.Condition);
			}

			void CheckCondition(Expression condition)
			{
				if (condition is PrimitiveExpression)
					return;

				var resolveResult = ctx.Resolve(condition);
				if (!(resolveResult.IsCompileTimeConstant && resolveResult.ConstantValue is bool))
					return;

				var value = (bool)resolveResult.ConstantValue;
				var conditionalExpr = condition.Parent as ConditionalExpression;
				var ifElseStatement = condition.Parent as IfElseStatement;
				var valueStr = value.ToString().ToLowerInvariant();

				CodeAction action;
				if (conditionalExpr != null) {
					var replaceExpr = value ? conditionalExpr.TrueExpression : conditionalExpr.FalseExpression;
					action = new CodeAction(
						string.Format(ctx.TranslateString("Replace '?:' with '{0}' branch"), valueStr),
						script => script.Replace(conditionalExpr, replaceExpr.Clone()),
						condition);
				} else if (ifElseStatement != null) {
					action = new CodeAction(
						string.Format(ctx.TranslateString("Replace 'if' with '{0}' branch"), valueStr),
						script => {
							var statement = value ? ifElseStatement.TrueStatement : ifElseStatement.FalseStatement;
							var blockStatement = statement as BlockStatement;
							if (statement.IsNull || (blockStatement != null && blockStatement.Statements.Count == 0)) {
								script.Remove(ifElseStatement);
								return;
							}

							TextLocation start, end;
							if (blockStatement != null) {
								start = blockStatement.Statements.FirstOrNullObject().StartLocation;
								end = blockStatement.Statements.LastOrNullObject().EndLocation;
							} else {
								start = statement.StartLocation;
								end = statement.EndLocation;
							}
							RemoveText(script, ifElseStatement.StartLocation, start);
							RemoveText(script, end, ifElseStatement.EndLocation);
							script.FormatText(ifElseStatement.Parent);
						}, condition);
				} else {
					action = new CodeAction(
						string.Format(ctx.TranslateString("Replace expression with '{0}'"), valueStr),
						script => script.Replace(condition, new PrimitiveExpression(value)), 
						condition
					);
				}
				AddIssue(new CodeIssue(condition, string.Format(ctx.TranslateString("Condition is always '{0}'"), valueStr), 
					new [] { action }));
			}

			void RemoveText(Script script, TextLocation start, TextLocation end)
			{
				var startOffset = script.GetCurrentOffset(start);
				var endOffset = script.GetCurrentOffset(end);
				if (startOffset < endOffset)
					script.RemoveText(startOffset, endOffset - startOffset);
			}
		}
	}
}
