// 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 System.Threading;
using System.Threading.Tasks;
using Microsoft.CodeAnalysis.Completion;
using Microsoft.CodeAnalysis.CSharp.Completion.Providers;
using Microsoft.CodeAnalysis.Host;
using Microsoft.CodeAnalysis.Host.Mef;
using Microsoft.CodeAnalysis.Shared.Extensions;
using Microsoft.CodeAnalysis.Shared.TestHooks;
using Microsoft.CodeAnalysis.Text;

namespace Microsoft.CodeAnalysis.CSharp.Completion;

internal sealed class CSharpCompletionService : CommonCompletionService
{
    [ExportLanguageServiceFactory(typeof(CompletionService), LanguageNames.CSharp), Shared]
    [method: ImportingConstructor]
    [method: Obsolete(MefConstruction.ImportingConstructorMessage, error: true)]
    internal sealed class Factory(IAsynchronousOperationListenerProvider listenerProvider) : ILanguageServiceFactory
    {
        private readonly IAsynchronousOperationListenerProvider _listenerProvider = listenerProvider;

        [Obsolete(MefConstruction.FactoryMethodMessage, error: true)]
        public ILanguageService CreateLanguageService(HostLanguageServices languageServices)
            => new CSharpCompletionService(languageServices.LanguageServices.SolutionServices, _listenerProvider);
    }

    private CompletionRules _latestRules = CompletionRules.Default;

    private CSharpCompletionService(SolutionServices services, IAsynchronousOperationListenerProvider listenerProvider)
        : base(services, listenerProvider)
    {
    }

    public override string Language => LanguageNames.CSharp;

    public override TextSpan GetDefaultCompletionListSpan(SourceText text, int caretPosition)
        => CompletionUtilities.GetCompletionItemSpan(text, caretPosition);

    internal override CompletionRules GetRules(CompletionOptions options)
    {
        var enterRule = options.EnterKeyBehavior;
        var snippetRule = options.SnippetsBehavior;

        // Although EnterKeyBehavior is a per-language setting, the meaning of an unset setting (Default) differs between C# and VB
        // In C# the default means Never to maintain previous behavior
        if (enterRule == EnterKeyRule.Default)
        {
            enterRule = EnterKeyRule.Never;
        }

        if (snippetRule == SnippetsRule.Default)
        {
            snippetRule = SnippetsRule.AlwaysInclude;
        }

        // use interlocked + stored rules to reduce # of times this gets created when option is different than default
        var newRules = _latestRules.WithDefaultEnterKeyRule(enterRule)
                                   .WithSnippetsRule(snippetRule);

        Interlocked.Exchange(ref _latestRules, newRules);

        return newRules;
    }

    internal override async Task<bool> IsSpeculativeTypeParameterContextAsync(Document document, int position, CancellationToken cancellationToken)
    {
        var syntaxTree = await document.GetRequiredSyntaxTreeAsync(cancellationToken).ConfigureAwait(false);

        // Because it's less likely the user wants to type a (undeclared) type parameter when they are inside a method body, treating them so
        // might intefere with user intention. For example, while it's fine to provide a speculative `T` item in a statement context,
        // since typing 2 characters would filter it out, but for selection, we don't want to soft-select item `TypeBuilder`after `TB`
        // is typed in the example below (as if user want to add `TBuilder` to method declaration later):
        //
        // class C
        // {
        //     void M()
        //     {
        //         TB$$
        //     }
        return CompletionUtilities.IsSpeculativeTypeParameterContext(syntaxTree, position, semanticModel: null, includeStatementContexts: false, cancellationToken);
    }
}