// 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.
 
#nullable disable
 
using System;
using System.Collections.Generic;
using System.Linq;
using Microsoft.VisualStudio.Text;
using Microsoft.VisualStudio.Text.Tagging;
 
namespace Microsoft.CodeAnalysis.Editor.Implementation.Preview
{
    internal class AbstractPreviewTaggerProvider<TTag> : ITaggerProvider
            where TTag : ITag
    {
        private readonly object _key;
        private readonly TTag _tagInstance;
 
        protected AbstractPreviewTaggerProvider(object key, TTag tagInstance)
        {
            _key = key;
            _tagInstance = tagInstance;
        }
 
        public ITagger<T> CreateTagger<T>(ITextBuffer buffer) where T : ITag
            => new Tagger(buffer, _key, _tagInstance) as ITagger<T>;
 
        private class Tagger : ITagger<TTag>
        {
            private readonly ITextBuffer _buffer;
            private readonly object _key;
            private readonly TTag _tagInstance;
 
            public Tagger(ITextBuffer buffer, object key, TTag tagInstance)
            {
                _buffer = buffer;
                _key = key;
                _tagInstance = tagInstance;
            }
 
            IEnumerable<ITagSpan<TTag>> ITagger<TTag>.GetTags(NormalizedSnapshotSpanCollection spans)
                => GetTags(spans);
 
            public IEnumerable<TagSpan<TTag>> GetTags(NormalizedSnapshotSpanCollection spans)
            {
                if (_buffer.Properties.TryGetProperty(_key, out NormalizedSnapshotSpanCollection matchingSpans))
                {
                    var intersection = NormalizedSnapshotSpanCollection.Intersection(matchingSpans, spans);
 
                    return intersection.Select(s => new TagSpan<TTag>(s, _tagInstance));
                }
 
                return [];
            }
 
            public event EventHandler<SnapshotSpanEventArgs> TagsChanged = (s, e) => { };
        }
    }
}