// 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.Threading;
using Microsoft.CodeAnalysis.Editor.EditorConfigSettings.DataProvider;
using Microsoft.VisualStudio.Shell.TableManager;
 
namespace Microsoft.VisualStudio.LanguageServices.EditorConfigSettings.Common;
 
internal abstract class SettingsSnapshotFactoryBase<T, TEntriesSnapshot> : TableEntriesSnapshotFactoryBase
    where TEntriesSnapshot : SettingsEntriesSnapshotBase<T>
{
    private readonly ISettingsProvider<T> _data;
 
    // State
    private int _currentVersionNumber;
    private int _lastSnapshotVersionNumber = -1;
    private TEntriesSnapshot? _lastSnapshot;
 
    // Disallow concurrent modification of state
    private readonly object _gate = new();
 
    public SettingsSnapshotFactoryBase(ISettingsProvider<T> data)
    {
        _data = data;
    }
 
    public override int CurrentVersionNumber => _currentVersionNumber;
 
    public override ITableEntriesSnapshot? GetCurrentSnapshot() => GetSnapshot(CurrentVersionNumber);
 
    internal void NotifyOfUpdate() => Interlocked.Increment(ref _currentVersionNumber);
 
    public override ITableEntriesSnapshot? GetSnapshot(int versionNumber)
    {
        lock (_gate)
        {
            if (versionNumber == _currentVersionNumber)
            {
                if (_lastSnapshotVersionNumber == _currentVersionNumber)
                {
                    return _lastSnapshot;
                }
                else
                {
                    var data = _data.GetCurrentDataSnapshot();
                    var snapshot = CreateSnapshot(data, _currentVersionNumber);
 
                    _lastSnapshot = snapshot;
                    _lastSnapshotVersionNumber = _currentVersionNumber;
 
                    return snapshot;
                }
            }
            else if (versionNumber < _currentVersionNumber)
            {
                // We can return null from this method.
                // This will signal to Table Control to request current snapshot.
                return null;
            }
            else // versionNumber > this.currentVersionNumber
            {
                throw new InvalidOperationException($"Invalid GetSnapshot request. Requested version: {versionNumber}. Current version: {_currentVersionNumber}");
            }
        }
    }
 
    protected abstract TEntriesSnapshot CreateSnapshot(ImmutableArray<T> data, int currentVersionNumber);
}