// 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.CSharp.Syntax;
using Microsoft.CodeAnalysis.PooledObjects;
using Roslyn.Utilities;
 
namespace Microsoft.CodeAnalysis.RemoveUnnecessaryImports
{
    internal sealed class CSharpUnnecessaryImportsProvider
        : AbstractUnnecessaryImportsProvider<UsingDirectiveSyntax>
    {
        public static readonly CSharpUnnecessaryImportsProvider Instance = new();
 
        private CSharpUnnecessaryImportsProvider()
        {
        }
 
        public override ImmutableArray<UsingDirectiveSyntax> GetUnnecessaryImports(
            SemanticModel model,
            Func<SyntaxNode, bool>? predicate,
            CancellationToken cancellationToken)
        {
            var root = model.SyntaxTree.GetRoot(cancellationToken);
            predicate ??= Functions<SyntaxNode>.True;
            var diagnostics = model.GetDiagnostics(cancellationToken: cancellationToken);
 
            using var _ = ArrayBuilder<UsingDirectiveSyntax>.GetInstance(out var result);
            foreach (var diagnostic in diagnostics)
            {
                if (diagnostic.Id == "CS8019" &&
                    root.FindNode(diagnostic.Location.SourceSpan) is UsingDirectiveSyntax node && predicate(node))
                {
                    result.Add(node);
                }
            }
 
            result.RemoveDuplicates();
            return result.ToImmutableArray();
        }
    }
}