// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

#nullable disable

using System.Composition;
using System.Diagnostics.CodeAnalysis;
using Microsoft.CodeAnalysis.CodeRefactorings;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Shared.Extensions;
using Microsoft.CodeAnalysis.SplitOrMergeIfStatements;
using Microsoft.CodeAnalysis.Text;

namespace Microsoft.CodeAnalysis.CSharp.SplitOrMergeIfStatements
{
    [ExportCodeRefactoringProvider(LanguageNames.CSharp, Name = PredefinedCodeRefactoringProviderNames.MergeNestedIfStatements), Shared]
    internal sealed class CSharpMergeNestedIfStatementsCodeRefactoringProvider
        : AbstractMergeNestedIfStatementsCodeRefactoringProvider
    {
        [ImportingConstructor]
        [SuppressMessage("RoslynDiagnosticsReliability", "RS0033:Importing constructor should be [Obsolete]", Justification = "Used in test code: https://github.com/dotnet/roslyn/issues/42814")]
        public CSharpMergeNestedIfStatementsCodeRefactoringProvider()
        {
        }

        protected override bool IsApplicableSpan(SyntaxNode node, TextSpan span, out SyntaxNode ifOrElseIf)
        {
            if (node is IfStatementSyntax ifStatement)
            {
                // Cases:
                // 1. Position is at a child token of an if statement with no selection (e.g. 'if' keyword, a parenthesis)
                // 2. Selection around the 'if' keyword
                // 3. Selection around the header - from 'if' keyword to the end of the condition
                // 4. Selection around the whole if statement
                if (span.Length == 0 ||
                    span.IsAround(ifStatement.IfKeyword) ||
                    span.IsAround(ifStatement.IfKeyword, ifStatement.CloseParenToken) ||
                    span.IsAround(ifStatement.IfKeyword, ifStatement))
                {
                    ifOrElseIf = ifStatement;
                    return true;
                }
            }

            if (node is ElseClauseSyntax elseClause && elseClause.Statement is IfStatementSyntax elseIfStatement)
            {
                // 5. Position is at a child token of an else clause with no selection ('else' keyword)
                // 6. Selection around the header including the 'else' keyword - from 'else' keyword to the end of the condition
                // 7. Selection from the 'else' keyword to the end of the if statement
                if (span.Length == 0 ||
                    span.IsAround(elseClause.ElseKeyword, elseIfStatement.CloseParenToken) ||
                    span.IsAround(elseClause.ElseKeyword, elseIfStatement))
                {
                    ifOrElseIf = elseIfStatement;
                    return true;
                }
            }

            ifOrElseIf = null;
            return false;
        }
    }
}
