// 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.Immutable;
using System.Threading;
using Microsoft.CodeAnalysis.Completion.Providers;
using Microsoft.CodeAnalysis.CSharp.Extensions;
using Microsoft.CodeAnalysis.CSharp.Extensions.ContextQuery;
using Microsoft.CodeAnalysis.CSharp.Utilities;

namespace Microsoft.CodeAnalysis.CSharp.Completion.KeywordRecommenders;

internal sealed class DynamicKeywordRecommender : IKeywordRecommender<CSharpSyntaxContext>
{
    private static bool IsValidContext(int position, CSharpSyntaxContext context, CancellationToken cancellationToken)
    {
        if (context.IsPreProcessorDirectiveContext ||
            context.IsTaskLikeTypeContext)
        {
            return false;
        }

        return IsDynamicTypeContext(position, context, cancellationToken);
    }

    public ImmutableArray<RecommendedKeyword> RecommendKeywords(int position, CSharpSyntaxContext context, CancellationToken cancellationToken)
    {
        return IsValidContext(position, context, cancellationToken)
            ? [new RecommendedKeyword("dynamic")]
            : [];
    }

    private static bool IsDynamicTypeContext(
        int position, CSharpSyntaxContext context, CancellationToken cancellationToken)
    {
        var syntaxTree = context.SyntaxTree;

        // first do quick exit check
        if (syntaxTree.IsDefinitelyNotTypeContext(position, cancellationToken))
        {
            return false;
        }

        return
            context.IsStatementContext ||
            context.IsGlobalStatementContext ||
            context.IsDefiniteCastTypeContext ||
            syntaxTree.IsPossibleCastTypeContext(position, context.LeftToken, cancellationToken) ||
            context.IsObjectCreationTypeContext ||
            context.IsGenericTypeArgumentContext ||
            context.IsFunctionPointerTypeArgumentContext ||
            context.IsIsOrAsTypeContext ||
            syntaxTree.IsDefaultExpressionContext(position, context.LeftToken) ||
            syntaxTree.IsAfterKeyword(position, SyntaxKind.ConstKeyword, cancellationToken) ||
            IsAfterRefTypeContext(context) ||
            context.IsLocalVariableDeclarationContext ||
            context.IsParameterTypeContext ||
            context.IsPossibleLambdaOrAnonymousMethodParameterTypeContext ||
            context.IsDelegateReturnTypeContext ||
            context.IsUsingAliasTypeContext ||
            context.IsPossibleTupleContext ||
            syntaxTree.IsGlobalMemberDeclarationContext(position, SyntaxKindSet.AllGlobalMemberModifiers, cancellationToken) ||
            context.IsMemberDeclarationContext(
                validModifiers: SyntaxKindSet.AllMemberModifiers,
                validTypeDeclarations: SyntaxKindSet.NonEnumTypeDeclarations,
                canBePartial: true,
                cancellationToken: cancellationToken);
    }

    private static bool IsAfterRefTypeContext(CSharpSyntaxContext context)
        => context.TargetToken.Kind() is SyntaxKind.RefKeyword or SyntaxKind.ReadOnlyKeyword &&
           context.TargetToken.Parent.IsKind(SyntaxKind.RefType);
}