// 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.

using System.Composition;
using System.Diagnostics.CodeAnalysis;
using System.Threading;
using Microsoft.CodeAnalysis.CodeRefactorings;
using Microsoft.CodeAnalysis.ConvertForToForEach;
using Microsoft.CodeAnalysis.CSharp.Extensions;
using Microsoft.CodeAnalysis.CSharp.Syntax;

namespace Microsoft.CodeAnalysis.CSharp.ConvertForToForEach;

using static CSharpSyntaxTokens;

[ExportCodeRefactoringProvider(LanguageNames.CSharp, Name = PredefinedCodeRefactoringProviderNames.ConvertForToForEach), Shared]
internal sealed class CSharpConvertForToForEachCodeRefactoringProvider :
    AbstractConvertForToForEachCodeRefactoringProvider<
        StatementSyntax,
        ForStatementSyntax,
        ExpressionSyntax,
        MemberAccessExpressionSyntax,
        TypeSyntax,
        VariableDeclaratorSyntax>
{
    [ImportingConstructor]
    [SuppressMessage("RoslynDiagnosticsReliability", "RS0033:Importing constructor should be [Obsolete]", Justification = "Used in test code: https://github.com/dotnet/roslyn/issues/42814")]
    public CSharpConvertForToForEachCodeRefactoringProvider()
    {
    }

    protected override string GetTitle()
        => CSharpFeaturesResources.Convert_to_foreach;

    protected override SyntaxList<StatementSyntax> GetBodyStatements(ForStatementSyntax forStatement)
        => forStatement.Statement is BlockSyntax block
            ? block.Statements
            : [forStatement.Statement];

    protected override bool TryGetForStatementComponents(
        ForStatementSyntax forStatement,
        out SyntaxToken iterationVariable,
        [NotNullWhen(true)] out ExpressionSyntax? initializer,
        [NotNullWhen(true)] out MemberAccessExpressionSyntax? memberAccess,
        out ExpressionSyntax? stepValueExpressionOpt,
        CancellationToken cancellationToken)
    {
        // Look for very specific forms.  Basically, only minor variations around:
        // for (var i = 0; i < expr.Lenth; i++)

        if (forStatement is { Declaration.Variables: [{ Initializer: not null } declarator], Condition.RawKind: (int)SyntaxKind.LessThanExpression, Incrementors.Count: 1 })
        {
            iterationVariable = declarator.Identifier;
            initializer = declarator.Initializer.Value;

            var binaryExpression = (BinaryExpressionSyntax)forStatement.Condition;

            // Look for:  i < expr.Length
            if (binaryExpression.Left is IdentifierNameSyntax identifierName &&
                identifierName.Identifier.ValueText == iterationVariable.ValueText &&
                binaryExpression.Right is MemberAccessExpressionSyntax right)
            {
                memberAccess = right;
                return TryGetStepValue(iterationVariable, forStatement.Incrementors[0], out stepValueExpressionOpt);
            }
        }

        iterationVariable = default;
        memberAccess = null;
        initializer = null;
        stepValueExpressionOpt = null;
        return false;
    }

    private static bool TryGetStepValue(
        SyntaxToken iterationVariable, ExpressionSyntax incrementor, out ExpressionSyntax? stepValue)
    {
        // support
        //  x++
        //  ++x
        //  x += constant_1

        ExpressionSyntax operand;
        switch (incrementor.Kind())
        {
            case SyntaxKind.PostIncrementExpression:
                operand = ((PostfixUnaryExpressionSyntax)incrementor).Operand;
                stepValue = null;
                break;

            case SyntaxKind.PreIncrementExpression:
                operand = ((PrefixUnaryExpressionSyntax)incrementor).Operand;
                stepValue = null;
                break;

            case SyntaxKind.AddAssignmentExpression:
                var assignment = (AssignmentExpressionSyntax)incrementor;
                operand = assignment.Left;
                stepValue = assignment.Right;
                break;

            default:
                stepValue = null;
                return false;
        }

        return operand is IdentifierNameSyntax identifierName &&
            identifierName.Identifier.ValueText == iterationVariable.ValueText;
    }

    protected override SyntaxNode ConvertForNode(
        ForStatementSyntax forStatement,
        TypeSyntax? typeNode,
        SyntaxToken foreachIdentifier,
        ExpressionSyntax collectionExpression,
        ITypeSymbol iterationVariableType)
    {
        typeNode ??= iterationVariableType.GenerateTypeSyntax();

        return SyntaxFactory.ForEachStatement(
            ForEachKeyword.WithTriviaFrom(forStatement.ForKeyword),
            forStatement.OpenParenToken,
            typeNode,
            foreachIdentifier,
            InKeyword,
            collectionExpression,
            forStatement.CloseParenToken,
            forStatement.Statement);
    }

    // C# has no special variable declarator forms that would cause us to not be able to convert.
    protected override bool IsValidVariableDeclarator(VariableDeclaratorSyntax firstVariable)
        => true;
}