﻿// 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 System.Threading.Tasks;
using Microsoft.CodeAnalysis.Shared.Extensions;
using Microsoft.CodeAnalysis.Text;

namespace Microsoft.CodeAnalysis.BraceMatching
{
    internal abstract class AbstractDirectiveTriviaBraceMatcher<TDirectiveTriviaSyntax,
        TIfDirectiveTriviaSyntax, TElseIfDirectiveTriviaSyntax,
        TElseDirectiveTriviaSyntax, TEndIfDirectiveTriviaSyntax,
        TRegionDirectiveTriviaSyntax, TEndRegionDirectiveTriviaSyntax> : IBraceMatcher
            where TDirectiveTriviaSyntax : SyntaxNode
            where TIfDirectiveTriviaSyntax : TDirectiveTriviaSyntax
            where TElseIfDirectiveTriviaSyntax : TDirectiveTriviaSyntax
            where TElseDirectiveTriviaSyntax : TDirectiveTriviaSyntax
            where TEndIfDirectiveTriviaSyntax : TDirectiveTriviaSyntax
            where TRegionDirectiveTriviaSyntax : TDirectiveTriviaSyntax
            where TEndRegionDirectiveTriviaSyntax : TDirectiveTriviaSyntax
    {
        protected abstract ImmutableArray<TDirectiveTriviaSyntax> GetMatchingConditionalDirectives(TDirectiveTriviaSyntax directive, CancellationToken cancellationToken);
        protected abstract TDirectiveTriviaSyntax? GetMatchingDirective(TDirectiveTriviaSyntax directive, CancellationToken cancellationToken);
        internal abstract TextSpan GetSpanForTagging(TDirectiveTriviaSyntax directive);

        public async Task<BraceMatchingResult?> FindBracesAsync(Document document, int position, BraceMatchingOptions options, CancellationToken cancellationToken)
        {
            var root = await document.GetRequiredSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
            var token = root.FindToken(position, findInsideTrivia: true);

            if (token.Parent is not TDirectiveTriviaSyntax directive)
            {
                return null;
            }

            TDirectiveTriviaSyntax? matchingDirective = null;
            if (IsConditionalDirective(directive))
            {
                // #if/#elif/#else/#endif directive cases.
                var matchingDirectives = GetMatchingConditionalDirectives(directive, cancellationToken);
                if (matchingDirectives.Length > 0)
                    matchingDirective = matchingDirectives[(matchingDirectives.IndexOf(directive) + 1) % matchingDirectives.Length];
            }
            else
            {
                // #region/#endregion or other directive cases.
                matchingDirective = GetMatchingDirective(directive, cancellationToken);
            }

            if (matchingDirective == null)
            {
                // one line directives, that do not have a matching begin/end directive pair.
                return null;
            }

            return new BraceMatchingResult(
                LeftSpan: GetSpanForTagging(directive),
                RightSpan: GetSpanForTagging(matchingDirective));
        }

        private static bool IsConditionalDirective(TDirectiveTriviaSyntax directive)
            => directive is TIfDirectiveTriviaSyntax or
                   TElseIfDirectiveTriviaSyntax or
                   TElseDirectiveTriviaSyntax or
                   TEndIfDirectiveTriviaSyntax;
    }
}
