// 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.Immutable;
using System.ComponentModel.Composition;
using Microsoft.CodeAnalysis.Completion;
using Microsoft.CodeAnalysis.Host.Mef;

namespace Microsoft.CodeAnalysis.Editor.Implementation.IntelliSense.AsyncCompletion;

[Export]
internal sealed class RecentItemsManager
{
    private const int MaxMRUSize = 10;

    /// <summary>
    /// Guard for <see cref="RecentItems"/>
    /// </summary>
    private readonly object _mruUpdateLock = new();

    [ImportingConstructor]
    [Obsolete(MefConstruction.ImportingConstructorMessage, error: true)]
    public RecentItemsManager()
    {
    }

    private ImmutableArray<string> RecentItems { get; set; } = [];

    public void MakeMostRecentItem(CompletionItem item)
    {
        lock (_mruUpdateLock)
        {
            var items = RecentItems;
            items = items.Remove(item.FilterText);

            if (items.Length == MaxMRUSize)
            {
                // Remove the least recent item.
                items = items.RemoveAt(0);
            }

            RecentItems = items.Add(item.FilterText);
        }
    }

    public int GetRecentItemIndex(CompletionItem item)
    {
        return RecentItems.IndexOf(item.FilterText);
    }
}
