// 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;
using System.Linq;
using System.Threading;
using Microsoft.CodeAnalysis.CodeStyle;
using Microsoft.CodeAnalysis.CSharp.Extensions;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.CSharp.Utilities;
using Microsoft.CodeAnalysis.PooledObjects;
using Microsoft.CodeAnalysis.Simplification;
using Roslyn.Utilities;

namespace Microsoft.CodeAnalysis.CSharp.Simplification;

internal sealed partial class CSharpMiscellaneousReducer : AbstractCSharpReducer
{
    private static readonly ObjectPool<IReductionRewriter> s_pool = new(
        () => new Rewriter(s_pool));

    private static readonly Func<ParameterSyntax, SemanticModel, SimplifierOptions, CancellationToken, SyntaxNode> s_simplifyParameter = SimplifyParameter;

    public CSharpMiscellaneousReducer() : base(s_pool)
    {
    }

    protected override bool IsApplicable(CSharpSimplifierOptions options)
       => true;

    private static bool CanRemoveTypeFromParameter(
        ParameterSyntax parameterSyntax,
        SemanticModel semanticModel,
        CancellationToken cancellationToken)
    {
        // We reduce any the parameters that are contained inside ParameterList
        if (parameterSyntax.IsParentKind(SyntaxKind.ParameterList) &&
            parameterSyntax.Parent.IsParentKind(SyntaxKind.ParenthesizedLambdaExpression))
        {
            if (parameterSyntax.Type != null)
            {
                var annotation = new SyntaxAnnotation();
                var newParameterSyntax = parameterSyntax.WithType(null).WithAdditionalAnnotations(annotation);

                var oldLambda = parameterSyntax.FirstAncestorOrSelf<ParenthesizedLambdaExpressionSyntax>();
                var newLambda = oldLambda.ReplaceNode(parameterSyntax, newParameterSyntax);
                var speculationAnalyzer = new SpeculationAnalyzer(oldLambda, newLambda, semanticModel, cancellationToken);
                newParameterSyntax = (ParameterSyntax)speculationAnalyzer.ReplacedExpression.GetAnnotatedNodesAndTokens(annotation).First();

                var oldSymbol = semanticModel.GetDeclaredSymbol(parameterSyntax, cancellationToken);
                var newSymbol = speculationAnalyzer.SpeculativeSemanticModel.GetDeclaredSymbol(newParameterSyntax, cancellationToken);
                if (oldSymbol != null &&
                    newSymbol != null &&
                    Equals(oldSymbol.Type, newSymbol.Type))
                {
                    return !speculationAnalyzer.ReplacementChangesSemantics();
                }
            }
        }

        return false;
    }

    private static SyntaxNode SimplifyParameter(
        ParameterSyntax node,
        SemanticModel semanticModel,
        SimplifierOptions options,
        CancellationToken cancellationToken)
    {
        if (CanRemoveTypeFromParameter(node, semanticModel, cancellationToken))
        {
            var newParameterSyntax = node.WithType(null);
            newParameterSyntax = SimplificationHelpers.CopyAnnotations(node, newParameterSyntax).WithoutAnnotations(Simplifier.Annotation);
            return newParameterSyntax;
        }

        return node;
    }

    private static readonly Func<ParenthesizedLambdaExpressionSyntax, SemanticModel, SimplifierOptions, CancellationToken, SyntaxNode> s_simplifyParenthesizedLambdaExpression = SimplifyParenthesizedLambdaExpression;

    private static SyntaxNode SimplifyParenthesizedLambdaExpression(
        ParenthesizedLambdaExpressionSyntax parenthesizedLambda,
        SemanticModel semanticModel,
        SimplifierOptions options,
        CancellationToken cancellationToken)
    {
        if (parenthesizedLambda.ParameterList != null &&
            parenthesizedLambda.ParameterList.Parameters.Count == 1)
        {
            var parameter = parenthesizedLambda.ParameterList.Parameters.First();
            if (CanRemoveTypeFromParameter(parameter, semanticModel, cancellationToken))
            {
                var newParameterSyntax = parameter.WithType(null);
                var newSimpleLambda = SyntaxFactory.SimpleLambdaExpression(
                    parenthesizedLambda.AsyncKeyword,
                    newParameterSyntax.WithTrailingTrivia(parenthesizedLambda.ParameterList.GetTrailingTrivia()),
                    parenthesizedLambda.ArrowToken,
                    parenthesizedLambda.Body);

                return SimplificationHelpers.CopyAnnotations(parenthesizedLambda, newSimpleLambda).WithoutAnnotations(Simplifier.Annotation);
            }
        }

        return parenthesizedLambda;
    }

    private static readonly Func<BlockSyntax, SemanticModel, CSharpSimplifierOptions, CancellationToken, SyntaxNode> s_simplifyBlock = SimplifyBlock;

    private static SyntaxNode SimplifyBlock(
        BlockSyntax node,
        SemanticModel semanticModel,
        CSharpSimplifierOptions options,
        CancellationToken cancellationToken)
    {
        if (node.Statements.Count != 1)
        {
            return node;
        }

        if (!CanHaveEmbeddedStatement(node.Parent))
        {
            return node;
        }

        switch (options.PreferBraces.Value)
        {
            case PreferBracesPreference.Always:
            default:
                return node;

            case PreferBracesPreference.WhenMultiline:
                // Braces are optional in several scenarios for 'when_multiline', but are only automatically removed
                // in a subset of cases where all of the following are met:
                //
                // 1. This is an 'if' statement
                // 1. The 'if' statement does not have an 'else' clause and is not part of a larger 'if'/'else if'/'else' sequence
                // 2. The 'if' statement is not considered multiline
                if (!node.Parent.IsKind(SyntaxKind.IfStatement))
                {
                    // Braces are only removed for 'if' statements
                    return node;
                }

                if (node.Parent?.Parent is (kind: SyntaxKind.IfStatement or SyntaxKind.ElseClause))
                {
                    // Braces are not removed from more complicated 'if' sequences
                    return node;
                }

                if (!FormattingRangeHelper.AreTwoTokensOnSameLine(node.Statements[0].GetFirstToken(), node.Statements[0].GetLastToken()))
                {
                    // Braces are not removed when the embedded statement is multiline
                    return node;
                }

                if (!FormattingRangeHelper.AreTwoTokensOnSameLine(node.Parent.GetFirstToken(), node.GetFirstToken().GetPreviousToken()))
                {
                    // Braces are not removed when the part of the 'if' statement preceding the embedded statement
                    // is multiline.
                    return node;
                }

                break;

            case PreferBracesPreference.None:
                break;
        }

        return node.Statements[0];
    }

    private static bool CanHaveEmbeddedStatement(SyntaxNode node)
    {
        if (node != null)
        {
            switch (node.Kind())
            {
                case SyntaxKind.IfStatement:
                case SyntaxKind.ElseClause:
                case SyntaxKind.ForStatement:
                case SyntaxKind.ForEachStatement:
                case SyntaxKind.ForEachVariableStatement:
                case SyntaxKind.WhileStatement:
                case SyntaxKind.DoStatement:
                case SyntaxKind.UsingStatement:
                case SyntaxKind.LockStatement:
                    return true;
            }
        }

        return false;
    }
}