// 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;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.CodeAnalysis.Collections;
using Microsoft.CodeAnalysis.Text.Shared.Extensions;
using Microsoft.VisualStudio.Text;
using Roslyn.Utilities;
 
namespace Microsoft.CodeAnalysis.Editor.Tagging;
 
internal partial class AbstractAsynchronousTaggerProvider<TTag>
{
    private partial class TagSource
    {
        public event EventHandler<SnapshotSpanEventArgs>? TagsChanged;
 
        private void OnTagsChangedForBuffer(
            ICollection<KeyValuePair<ITextBuffer, DiffResult>> changes, bool highPriority)
        {
            // Can be called from any thread.  Just filters out changes that aren't for our buffer and adds to the right
            // queue to actually notify interested parties.
 
            foreach (var change in changes)
            {
                if (change.Key != _subjectBuffer)
                    continue;
 
                // Removed tags are always treated as high pri, so we can clean their stale
                // data out from the ui immediately.
                _highPriTagsChangedQueue.AddWork(change.Value.Removed);
 
                // Added tags are run at the requested priority.
                var addedTagsQueue = highPriority ? _highPriTagsChangedQueue : _normalPriTagsChangedQueue;
                addedTagsQueue.AddWork(change.Value.Added);
            }
        }
 
        private ValueTask ProcessTagsChangedAsync(
            ImmutableSegmentedList<NormalizedSnapshotSpanCollection> snapshotSpans, CancellationToken cancellationToken)
        {
            var tagsChanged = this.TagsChanged;
            if (tagsChanged == null)
                return ValueTaskFactory.CompletedTask;
 
            foreach (var collection in snapshotSpans)
            {
                if (collection.Count == 0)
                    continue;
 
                var snapshot = collection.First().Snapshot;
 
                // Coalesce the spans if there are a lot of them.
                var coalesced = collection.Count > CoalesceDifferenceCount
                    ? new NormalizedSnapshotSpanCollection(snapshot.GetSpanFromBounds(collection.First().Start, collection.Last().End))
                    : collection;
 
                _dataSource.BeforeTagsChanged(snapshot);
 
                foreach (var span in coalesced)
                    tagsChanged(this, new SnapshotSpanEventArgs(span));
            }
 
            return ValueTaskFactory.CompletedTask;
        }
    }
}