// 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.Composition;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;
using Microsoft.CodeAnalysis.Host.Mef;
using Microsoft.VisualStudio.LanguageServices.Utilities;
using VSLangProj80;
 
namespace Microsoft.VisualStudio.LanguageServices.CSharp.Utilities;
 
[ExportLanguageService(typeof(IParseOptionsChangingService), LanguageNames.CSharp), Shared]
internal sealed class CSharpParseOptionsChangingService : IParseOptionsChangingService
{
    [ImportingConstructor]
    [Obsolete(MefConstruction.ImportingConstructorMessage, error: true)]
    public CSharpParseOptionsChangingService()
    {
    }
 
    public bool CanApplyChange(ParseOptions oldOptions, ParseOptions newOptions, string? maxLangVersion)
    {
        var oldCSharpOptions = (CSharpParseOptions)oldOptions;
        var newCSharpOptions = (CSharpParseOptions)newOptions;
 
        // Currently, only changes to the LanguageVersion of parse options are supported.
        if (oldCSharpOptions.WithLanguageVersion(newCSharpOptions.SpecifiedLanguageVersion) != newOptions)
        {
            return false;
        }
 
        if (string.IsNullOrEmpty(maxLangVersion))
        {
            return true;
        }
        else if (newCSharpOptions.LanguageVersion == LanguageVersion.Preview)
        {
            // It's always fine to upgrade a project to 'preview'.  This allows users to try out new features to see
            // how well they work, while also explicitly putting them into a *known* unsupported state (that's what
            // preview is after all).  Importantly, this doesn't put them into an unrealized unsupported state (for
            // example, picking some combo of a real lang version that isn't supported with their chosen framework
            // version).
            return true;
        }
        else
        {
            Contract.ThrowIfFalse(LanguageVersionFacts.TryParse(maxLangVersion, out var parsedMaxLanguageVersion));
            return newCSharpOptions.LanguageVersion <= parsedMaxLanguageVersion;
        }
    }
 
    public void Apply(ParseOptions options, ProjectPropertyStorage storage)
    {
        var csharpOptions = (CSharpParseOptions)options;
 
        storage.SetProperty("LangVersion", nameof(CSharpProjectConfigurationProperties3.LanguageVersion),
            LanguageVersionFacts.ToDisplayString(csharpOptions.SpecifiedLanguageVersion));
    }
}