// 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.Collections.Generic;
using System.Linq;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.PooledObjects;
using Microsoft.CodeAnalysis.Rename.ConflictEngine;

namespace Microsoft.CodeAnalysis.CSharp.Rename;

internal sealed class LocalConflictVisitor : CSharpSyntaxVisitor
{
    private readonly ConflictingIdentifierTracker _tracker;
    private readonly HashSet<SyntaxNode> _containingAnonymousMethodsAndLocalFunctions = new();

    public LocalConflictVisitor(SyntaxToken tokenBeingRenamed)
    {
        _tracker = new ConflictingIdentifierTracker(tokenBeingRenamed, StringComparer.Ordinal);

        // We want to dive into the anonymous-functions/local-functions that surround the initial token being renamed
        // (so that we can actually descend to the scope that it is defined at). However, we don't need to dive any
        // deeper as more deeply nested functions can't be affected by this rename.  Specifically, inner functions 
        // get their own name scope, which does not collide with the scope of this token.
        _containingAnonymousMethodsAndLocalFunctions.AddRange(
            tokenBeingRenamed.Parent.AncestorsAndSelf().Where(n => n is AnonymousFunctionExpressionSyntax or LocalFunctionStatementSyntax));
    }

    public override void DefaultVisit(SyntaxNode node)
    {
        foreach (var child in node.ChildNodes())
            Visit(child);
    }

    public override void VisitMethodDeclaration(MethodDeclarationSyntax node)
    {
        var parameterTokens = node.ParameterList.Parameters.Select(p => p.Identifier);
        _tracker.AddIdentifiers(parameterTokens);
        Visit(node.Body);
        _tracker.RemoveIdentifiers(parameterTokens);
    }

    public override void VisitBlock(BlockSyntax node)
        => VisitBlockStatements(node, node.Statements);

    private void VisitBlockStatements(SyntaxNode node, IEnumerable<SyntaxNode> statements)
    {
        using var _ = ArrayBuilder<SyntaxToken>.GetInstance(out var tokens);

        // We want to collect any variable declarations that are in the block
        // before visiting nested statements
        foreach (var statement in statements)
        {
            if (statement is LocalDeclarationStatementSyntax declarationStatement)
            {
                foreach (var declarator in declarationStatement.Declaration.Variables)
                {
                    tokens.Add(declarator.Identifier);
                }
            }
        }

        _tracker.AddIdentifiers(tokens);
        DefaultVisit(node);
        _tracker.RemoveIdentifiers(tokens);
    }

    public override void VisitForEachStatement(ForEachStatementSyntax node)
    {
        _tracker.AddIdentifier(node.Identifier);
        Visit(node.Statement);
        _tracker.RemoveIdentifier(node.Identifier);
    }

    public override void VisitForStatement(ForStatementSyntax node)
    {
        using var _ = ArrayBuilder<SyntaxToken>.GetInstance(out var tokens);

        if (node.Declaration != null)
        {
            tokens.AddRange(node.Declaration.Variables.Select(v => v.Identifier));
        }

        _tracker.AddIdentifiers(tokens);
        Visit(node.Statement);
        _tracker.RemoveIdentifiers(tokens);
    }

    public override void VisitUsingStatement(UsingStatementSyntax node)
    {
        using var _ = ArrayBuilder<SyntaxToken>.GetInstance(out var tokens);

        if (node.Declaration != null)
        {
            tokens.AddRange(node.Declaration.Variables.Select(v => v.Identifier));
        }

        _tracker.AddIdentifiers(tokens);
        Visit(node.Statement);
        _tracker.RemoveIdentifiers(tokens);
    }

    public override void VisitCatchClause(CatchClauseSyntax node)
    {
        using var _ = ArrayBuilder<SyntaxToken>.GetInstance(out var tokens);

        if (node.Declaration != null)
        {
            tokens.Add(node.Declaration.Identifier);
        }

        _tracker.AddIdentifiers(tokens);
        Visit(node.Block);
        _tracker.RemoveIdentifiers(tokens);
    }

    public override void VisitSimpleLambdaExpression(SimpleLambdaExpressionSyntax node)
    {
        if (_containingAnonymousMethodsAndLocalFunctions.Contains(node))
            Visit(node.Body);
    }

    public override void VisitParenthesizedLambdaExpression(ParenthesizedLambdaExpressionSyntax node)
    {
        if (_containingAnonymousMethodsAndLocalFunctions.Contains(node))
            Visit(node.Body);
    }

    public override void VisitAnonymousMethodExpression(AnonymousMethodExpressionSyntax node)
    {
        if (_containingAnonymousMethodsAndLocalFunctions.Contains(node))
            Visit(node.Body);
    }

    public override void VisitLocalFunctionStatement(LocalFunctionStatementSyntax node)
    {
        if (_containingAnonymousMethodsAndLocalFunctions.Contains(node))
        {
            Visit(node.Body);
            Visit(node.ExpressionBody);
        }
    }

    public override void VisitQueryExpression(QueryExpressionSyntax node)
        => VisitQueryInternal(node.FromClause, node.Body);

    private void VisitQueryInternal(FromClauseSyntax fromClause, QueryBodySyntax body)
    {
        // This is somewhat ornery: we need to collect all the locals being introduced
        // since they're all in scope through all parts of the query.
        using var _ = ArrayBuilder<SyntaxToken>.GetInstance(out var tokens);

        if (fromClause != null)
        {
            tokens.Add(fromClause.Identifier);
        }

        foreach (var clause in body.Clauses)
        {
            switch (clause.Kind())
            {
                case SyntaxKind.FromClause:

                    tokens.Add(((FromClauseSyntax)clause).Identifier);
                    break;

                case SyntaxKind.LetClause:

                    tokens.Add(((LetClauseSyntax)clause).Identifier);
                    break;
            }
        }

        _tracker.AddIdentifiers(tokens);

        // We have to be careful that the query continuation of this query isn't visited
        // as everything there is actually an independent scope.
        if (fromClause != null)
        {
            Visit(fromClause);
        }

        foreach (var child in body.ChildNodes().Where(c => c.Kind() != SyntaxKind.QueryContinuation))
        {
            Visit(child);
        }

        _tracker.RemoveIdentifiers(tokens);

        // And now we must visit the continuation
        Visit(body.Continuation);
    }

    public override void VisitQueryContinuation(QueryContinuationSyntax node)
    {
        _tracker.AddIdentifier(node.Identifier);
        VisitQueryInternal(null, node.Body);
        _tracker.RemoveIdentifier(node.Identifier);
    }

    public override void VisitSwitchStatement(SwitchStatementSyntax node)
    {
        var statements = node.ChildNodes().Where(x => x.IsKind(SyntaxKind.SwitchSection)).SelectMany(x => x.ChildNodes());

        VisitBlockStatements(node, statements);
    }

    public IEnumerable<SyntaxToken> ConflictingTokens
    {
        get
        {
            return _tracker.ConflictingTokens;
        }
    }
}