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

namespace Microsoft.CodeAnalysis.CSharp.Completion.Providers;

[ExportCompletionProvider(nameof(TypeImportCompletionProvider), LanguageNames.CSharp)]
[ExtensionOrder(After = nameof(PropertySubpatternCompletionProvider))]
[Shared]
internal sealed class TypeImportCompletionProvider : AbstractTypeImportCompletionProvider<UsingDirectiveSyntax>
{
    [ImportingConstructor]
    [Obsolete(MefConstruction.ImportingConstructorMessage, error: true)]
    public TypeImportCompletionProvider()
    {
    }

    internal override string Language => LanguageNames.CSharp;

    public override bool IsInsertionTrigger(SourceText text, int characterPosition, CompletionOptions options)
        => CompletionUtilities.IsTriggerCharacter(text, characterPosition, options);

    public override ImmutableHashSet<char> TriggerCharacters { get; } = CompletionUtilities.CommonTriggerCharacters;

    protected override bool ShouldProvideCompletion(CompletionContext completionContext, SyntaxContext syntaxContext)
    {
        // In addition to the regular type contexts handled by the base provider, unimported types should be
        // offered inside `cref` documentation comments.
        return base.ShouldProvideCompletion(completionContext, syntaxContext)
            || syntaxContext is CSharpSyntaxContext { IsCrefContext: true };
    }

    protected override bool IsFinalSemicolonOfUsingOrExtern(SyntaxNode directive, SyntaxToken token)
    {
        if (token.IsKind(SyntaxKind.None) || token.IsMissing)
            return false;

        return directive switch
        {
            UsingDirectiveSyntax usingDirective => usingDirective.SemicolonToken == token,
            ExternAliasDirectiveSyntax externAliasDirective => externAliasDirective.SemicolonToken == token,
            _ => false,
        };
    }

    protected override async Task<bool> ShouldProvideParenthesisCompletionAsync(
        Document document,
        CompletionItem item,
        char? commitKey,
        CancellationToken cancellationToken)
    {
        if (commitKey is ';' or '.')
        {
            // Only consider add '()' if the type is used under object creation context
            var position = item.Span.Start;
            var syntaxTree = await document.GetRequiredSyntaxTreeAsync(cancellationToken).ConfigureAwait(false);
            var leftToken = syntaxTree.FindTokenOnLeftOfPosition(position, cancellationToken);
            return syntaxTree.IsObjectCreationTypeContext(position, leftToken, cancellationToken);
        }

        return false;
    }
}