// 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.Collections.Generic;
using System.Linq;
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 NewKeywordRecommender() : AbstractSyntacticSingleKeywordRecommender(SyntaxKind.NewKeyword)
{
    private static readonly ISet<SyntaxKind> s_validMemberModifiers = new HashSet<SyntaxKind>(SyntaxFacts.EqualityComparer)
        {
            SyntaxKind.AbstractKeyword,
            SyntaxKind.ExternKeyword,
            SyntaxKind.InternalKeyword,
            SyntaxKind.PublicKeyword,
            SyntaxKind.PrivateKeyword,
            SyntaxKind.ProtectedKeyword,
            SyntaxKind.ReadOnlyKeyword,
            SyntaxKind.SealedKeyword,
            SyntaxKind.StaticKeyword,
            SyntaxKind.UnsafeKeyword,
            SyntaxKind.VirtualKeyword,
            SyntaxKind.VolatileKeyword,
        };

    private static readonly ISet<SyntaxKind> ValidTypeModifiers = new HashSet<SyntaxKind>(SyntaxFacts.EqualityComparer)
        {
            SyntaxKind.AbstractKeyword,
            SyntaxKind.InternalKeyword,
            SyntaxKind.PublicKeyword,
            SyntaxKind.PrivateKeyword,
            SyntaxKind.ProtectedKeyword,
            SyntaxKind.SealedKeyword,
            SyntaxKind.StaticKeyword,
            SyntaxKind.UnsafeKeyword
        };

    protected override bool IsValidContext(int position, CSharpSyntaxContext context, CancellationToken cancellationToken)
    {
        return
            IsNewConstraintContext(context) ||
            context.IsAnyExpressionContext ||
            context.IsStatementContext ||
            context.IsGlobalStatementContext ||
            IsMemberDeclarationContext(context, cancellationToken) ||
            IsTypeDeclarationContext(context, cancellationToken);
    }

    private static bool IsTypeDeclarationContext(CSharpSyntaxContext context, CancellationToken cancellationToken)
    {
        if (context.IsTypeDeclarationContext(validModifiers: ValidTypeModifiers, validTypeDeclarations: SyntaxKindSet.ClassInterfaceStructRecordTypeDeclarations, canBePartial: false, cancellationToken: cancellationToken))
        {
            // we must be on a nested type.
            var token = context.LeftToken;
            return token.GetAncestors<TypeDeclarationSyntax>()
                .Any(t => token.SpanStart > t.OpenBraceToken.Span.End &&
                          token.Span.End < t.CloseBraceToken.SpanStart);
        }

        return false;
    }

    private static bool IsMemberDeclarationContext(CSharpSyntaxContext context, CancellationToken cancellationToken)
    {
        return
            context.SyntaxTree.IsGlobalMemberDeclarationContext(context.Position, SyntaxKindSet.AllGlobalMemberModifiers, cancellationToken) ||
            context.IsMemberDeclarationContext(
                validModifiers: s_validMemberModifiers,
                validTypeDeclarations: SyntaxKindSet.ClassInterfaceStructRecordTypeDeclarations,
                canBePartial: false,
                cancellationToken: cancellationToken);
    }

    private static bool IsNewConstraintContext(CSharpSyntaxContext context)
    {
        // cases:
        //    where T : |
        //    where T : class, |
        //    where T : Goo, |
        // note: 'new()' can't come after a 'struct' constraint.

        if (context.SyntaxTree.IsTypeParameterConstraintStartContext(context.Position, context.LeftToken))
        {
            return true;
        }

        var token = context.TargetToken;

        if (token.Kind() == SyntaxKind.CommaToken &&
            token.Parent is TypeParameterConstraintClauseSyntax constraintClause)
        {
            if (!constraintClause.Constraints
                    .OfType<ClassOrStructConstraintSyntax>()
                    .Any(c => c.ClassOrStructKeyword.Kind() == SyntaxKind.StructKeyword))
            {
                return true;
            }
        }

        return false;
    }
}