// 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.Threading;
using Microsoft.CodeAnalysis.CSharp.Extensions.ContextQuery;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.CSharp.Utilities;
using Microsoft.CodeAnalysis.Shared.Extensions;

namespace Microsoft.CodeAnalysis.CSharp.Completion.KeywordRecommenders;

internal sealed class PrivateKeywordRecommender() : AbstractSyntacticSingleKeywordRecommender(SyntaxKind.PrivateKeyword)
{
    protected override bool IsValidContext(int position, CSharpSyntaxContext context, CancellationToken cancellationToken)
    {
        return
            (context.IsGlobalStatementContext && context.SyntaxTree.IsScript()) ||
            IsValidContextForAccessor(context) ||
            IsValidContextForType(context, cancellationToken) ||
            IsValidContextForMember(context, cancellationToken);
    }

    private static bool IsValidContextForAccessor(CSharpSyntaxContext context)
    {
        if (context.TargetToken.IsAccessorDeclarationContext<PropertyDeclarationSyntax>(context.Position) ||
            context.TargetToken.IsAccessorDeclarationContext<IndexerDeclarationSyntax>(context.Position))
        {
            return CheckPreviousAccessibilityModifiers(context);
        }

        return false;
    }

    private static bool IsValidContextForMember(CSharpSyntaxContext context, CancellationToken cancellationToken)
    {
        if (context.SyntaxTree.IsGlobalMemberDeclarationContext(context.Position, SyntaxKindSet.AllGlobalMemberModifiers, cancellationToken) ||
            context.IsMemberDeclarationContext(validModifiers: SyntaxKindSet.AllMemberModifiers, validTypeDeclarations: SyntaxKindSet.NonEnumTypeDeclarations, canBePartial: false, cancellationToken: cancellationToken))
        {
            var modifiers = context.PrecedingModifiers;

            // can't have private + abstract/virtual/override/sealed
            if (modifiers.Contains(SyntaxKind.AbstractKeyword) ||
                modifiers.Contains(SyntaxKind.VirtualKeyword) ||
                modifiers.Contains(SyntaxKind.OverrideKeyword) ||
                modifiers.Contains(SyntaxKind.SealedKeyword))
            {
                return false;
            }

            return CheckPreviousAccessibilityModifiers(context);
        }

        return false;
    }

    private static bool IsValidContextForType(CSharpSyntaxContext context, CancellationToken cancellationToken)
    {
        if (context.IsTypeDeclarationContext(validModifiers: SyntaxKindSet.AllTypeModifiers, validTypeDeclarations: SyntaxKindSet.NonEnumTypeDeclarations, canBePartial: false, cancellationToken: cancellationToken))
        {
            // private things can't be in namespaces.
            var typeDecl = context.ContainingTypeDeclaration;
            if (typeDecl == null)
            {
                return false;
            }

            return CheckPreviousAccessibilityModifiers(context);
        }

        return false;
    }

    private static bool CheckPreviousAccessibilityModifiers(CSharpSyntaxContext context)
    {
        // We can show up after 'protected'.
        var precedingModifiers = context.PrecedingModifiers;
        return
            !precedingModifiers.Contains(SyntaxKind.FileKeyword) &&
            !precedingModifiers.Contains(SyntaxKind.PublicKeyword) &&
            !precedingModifiers.Contains(SyntaxKind.InternalKeyword) &&
            !precedingModifiers.Contains(SyntaxKind.PrivateKeyword);
    }
}