﻿// 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;
using Microsoft.CodeAnalysis.Completion.Providers;
using Microsoft.CodeAnalysis.CSharp.Extensions.ContextQuery;

namespace Microsoft.CodeAnalysis.CSharp.Completion.KeywordRecommenders
{
    internal abstract partial class AbstractSyntacticSingleKeywordRecommender : IKeywordRecommender<CSharpSyntaxContext>
    {
        public readonly SyntaxKind KeywordKind;
        private readonly bool _isValidInPreprocessorContext;

        private readonly ImmutableArray<RecommendedKeyword> _keywordPriorityRecommendedKeywords;
        private readonly ImmutableArray<RecommendedKeyword> _defaultPriorityRecommendedKeywords;

        /// <summary>
        /// Matching priority for the provided item when <see cref="ShouldPreselect"/> returns <see langword="false"/>.
        /// </summary>
        protected virtual int DefaultMatchPriority => MatchPriority.Default;

        protected virtual int PreselectMatchPriority => SymbolMatchPriority.Keyword;

        protected AbstractSyntacticSingleKeywordRecommender(
            SyntaxKind keywordKind,
            bool isValidInPreprocessorContext = false,
            bool shouldFormatOnCommit = false)
        {
            KeywordKind = keywordKind;
            _isValidInPreprocessorContext = isValidInPreprocessorContext;

            _keywordPriorityRecommendedKeywords = ImmutableArray.Create(
                new RecommendedKeyword(SyntaxFacts.GetText(keywordKind),
                shouldFormatOnCommit: shouldFormatOnCommit,
                matchPriority: PreselectMatchPriority));
            _defaultPriorityRecommendedKeywords = ImmutableArray.Create(
                new RecommendedKeyword(SyntaxFacts.GetText(keywordKind),
                shouldFormatOnCommit: shouldFormatOnCommit,
                matchPriority: DefaultMatchPriority));
        }

        protected abstract bool IsValidContext(int position, CSharpSyntaxContext context, CancellationToken cancellationToken);

        public ImmutableArray<RecommendedKeyword> RecommendKeywords(
            int position,
            CSharpSyntaxContext context,
            CancellationToken cancellationToken)
        {
            var syntaxKind = RecommendKeyword(position, context, cancellationToken);
            if (!syntaxKind.HasValue)
                return ImmutableArray<RecommendedKeyword>.Empty;

            return ShouldPreselect(context, cancellationToken)
                ? _keywordPriorityRecommendedKeywords
                : _defaultPriorityRecommendedKeywords;
        }

        protected virtual bool ShouldPreselect(CSharpSyntaxContext context, CancellationToken cancellationToken) => false;

        private SyntaxKind? RecommendKeyword(int position, CSharpSyntaxContext context, CancellationToken cancellationToken)
        {
            // NOTE: The collector ensures that we're not in "NonUserCode" like comments, strings, inactive code
            // for perf reasons.
            if (!_isValidInPreprocessorContext &&
                context.IsPreProcessorDirectiveContext)
            {
                return null;
            }

            return IsValidContext(position, context, cancellationToken) ? KeywordKind : null;
        }

        internal TestAccessor GetTestAccessor() => new(this);

        internal readonly struct TestAccessor(AbstractSyntacticSingleKeywordRecommender recommender)
        {
            private readonly AbstractSyntacticSingleKeywordRecommender _recommender = recommender;

            public ImmutableArray<RecommendedKeyword> RecommendKeywords(int position, CSharpSyntaxContext context)
                => _recommender.RecommendKeywords(position, context, CancellationToken.None);
        }
    }
}
