// 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.Diagnostics;
using Microsoft.CodeAnalysis.Options;
using Roslyn.Utilities;
 
namespace Microsoft.VisualStudio.LanguageServices.Implementation.Options;
 
/// <summary>
/// Stores values of options read from global options and values set to these options.
/// Not thread safe.
/// </summary>
internal sealed class OptionStore : IOptionsReader
{
    public readonly IGlobalOptionService GlobalOptions;
 
    public event EventHandler<OptionKey2>? OptionChanged;
 
    /// <summary>
    /// Cached values read from global options.
    /// </summary>
    private ImmutableDictionary<OptionKey2, object?> _globalValues;
 
    /// <summary>
    /// Updated values.
    /// </summary>
    private ImmutableDictionary<OptionKey2, object?> _updatedValues;
 
    public OptionStore(IGlobalOptionService globalOptions)
    {
        GlobalOptions = globalOptions;
 
        _globalValues = ImmutableDictionary<OptionKey2, object?>.Empty;
        _updatedValues = ImmutableDictionary<OptionKey2, object?>.Empty;
    }
 
    public void Clear()
    {
        _globalValues = ImmutableDictionary<OptionKey2, object?>.Empty;
        _updatedValues = ImmutableDictionary<OptionKey2, object?>.Empty;
    }
 
    public ImmutableArray<(OptionKey2 key, object? oldValue, object? newValue)> GetChangedOptions()
        => _updatedValues.SelectAsArray(entry => (entry.Key, _globalValues[entry.Key], entry.Value));
 
    bool IOptionsReader.TryGetOption<T>(OptionKey2 optionKey, out T value)
    {
        value = (T)GetOption(optionKey)!;
        return true;
    }
 
    public T GetOption<T>(Option2<T> option)
        => (T)GetOption(new OptionKey2(option))!;
 
    public T GetOption<T>(PerLanguageOption2<T> option, string language)
        => (T)GetOption(new OptionKey2(option, language))!;
 
    public T GetOption<T>(IOption2 option, string? language)
    {
        Debug.Assert(option.IsPerLanguage == language is not null);
        return (T)GetOption(new OptionKey2(option, language))!;
    }
 
    private object? GetOption(OptionKey2 optionKey)
    {
        if (_updatedValues.TryGetValue(optionKey, out var value))
        {
            return value;
        }
 
        if (_globalValues.TryGetValue(optionKey, out value))
        {
            return value;
        }
 
        value = GlobalOptions.GetOption<object?>(optionKey);
        _globalValues = _globalValues.Add(optionKey, value);
        return value;
    }
 
    public void SetOption<T>(Option2<T> option, T value)
        => SetOption(new OptionKey2(option), value);
 
    public void SetOption<T>(PerLanguageOption2<T> option, string language, T value)
        => SetOption(new OptionKey2(option, language), value);
 
    public void SetOption(IOption2 option, string? language, object? value)
    {
        Debug.Assert(option.IsPerLanguage == language is not null);
        SetOption(new OptionKey2(option, language), value);
    }
 
    private void SetOption(OptionKey2 optionKey, object? value)
    {
        var currentValue = GetOption(optionKey);
        if (!Equals(value, currentValue))
        {
            _updatedValues = _updatedValues.SetItem(optionKey, value);
            OptionChanged?.Invoke(this, optionKey);
        }
    }
}