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

namespace Microsoft.CodeAnalysis.CSharp.Completion.KeywordRecommenders
{
    internal class VoidKeywordRecommender : AbstractSyntacticSingleKeywordRecommender
    {
        private static readonly ISet<SyntaxKind> s_validClassInterfaceRecordModifiers = new HashSet<SyntaxKind>(SyntaxFacts.EqualityComparer)
        {
            SyntaxKind.NewKeyword,
            SyntaxKind.PublicKeyword,
            SyntaxKind.ProtectedKeyword,
            SyntaxKind.InternalKeyword,
            SyntaxKind.PrivateKeyword,
            SyntaxKind.StaticKeyword,
            SyntaxKind.VirtualKeyword,
            SyntaxKind.SealedKeyword,
            SyntaxKind.OverrideKeyword,
            SyntaxKind.AbstractKeyword,
            SyntaxKind.ExternKeyword,
            SyntaxKind.UnsafeKeyword,
            SyntaxKind.AsyncKeyword
        };

        private static readonly ISet<SyntaxKind> s_validStructModifiers = new HashSet<SyntaxKind>(s_validClassInterfaceRecordModifiers, SyntaxFacts.EqualityComparer)
        {
            SyntaxKind.ReadOnlyKeyword,
        };

        public VoidKeywordRecommender()
            : base(SyntaxKind.VoidKeyword)
        {
        }

        protected override bool IsValidContext(int position, CSharpSyntaxContext context, CancellationToken cancellationToken)
        {
            var syntaxTree = context.SyntaxTree;
            return
                IsMemberReturnTypeContext(position, context, cancellationToken) ||
                context.IsGlobalStatementContext ||
                context.IsTypeOfExpressionContext ||
                syntaxTree.IsSizeOfExpressionContext(position, context.LeftToken) ||
                context.IsDelegateReturnTypeContext ||
                context.IsFunctionPointerTypeArgumentContext ||
                IsUnsafeLocalVariableDeclarationContext(context) ||
                IsUnsafeParameterTypeContext(context) ||
                IsUnsafeCastTypeContext(context) ||
                IsUnsafeDefaultExpressionContext(context) ||
                context.IsFixedVariableDeclarationContext ||
                context.SyntaxTree.IsGlobalMemberDeclarationContext(position, SyntaxKindSet.AllGlobalMemberModifiers, cancellationToken) ||
                context.SyntaxTree.IsLocalFunctionDeclarationContext(position, cancellationToken);
        }

        private static bool IsUnsafeDefaultExpressionContext(CSharpSyntaxContext context)
        {
            return
                context.TargetToken.IsUnsafeContext() &&
                context.SyntaxTree.IsDefaultExpressionContext(context.Position, context.LeftToken);
        }

        private static bool IsUnsafeCastTypeContext(CSharpSyntaxContext context)
        {
            if (context.TargetToken.IsUnsafeContext())
            {
                if (context.IsDefiniteCastTypeContext)
                {
                    return true;
                }

                var token = context.TargetToken;

                if (token.Kind() == SyntaxKind.OpenParenToken &&
                    token.Parent.IsKind(SyntaxKind.ParenthesizedExpression))
                {
                    return true;
                }
            }

            return false;
        }

        private static bool IsUnsafeParameterTypeContext(CSharpSyntaxContext context)
        {
            return
                context.TargetToken.IsUnsafeContext() &&
                context.IsParameterTypeContext;
        }

        private static bool IsUnsafeLocalVariableDeclarationContext(CSharpSyntaxContext context)
        {
            if (context.TargetToken.IsUnsafeContext())
            {
                return
                    context.IsLocalVariableDeclarationContext ||
                    context.IsStatementContext;
            }

            return false;
        }

        private static bool IsMemberReturnTypeContext(int position, CSharpSyntaxContext context, CancellationToken cancellationToken)
            => context.SyntaxTree.IsGlobalMemberDeclarationContext(position, SyntaxKindSet.AllGlobalMemberModifiers, cancellationToken) ||
                context.IsMemberDeclarationContext(validModifiers: s_validClassInterfaceRecordModifiers, validTypeDeclarations: SyntaxKindSet.ClassInterfaceRecordTypeDeclarations, canBePartial: true, cancellationToken) ||
                context.IsMemberDeclarationContext(validModifiers: s_validStructModifiers, validTypeDeclarations: SyntaxKindSet.StructOnlyTypeDeclarations, canBePartial: false, cancellationToken);
    }
}
