// 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.
 
#nullable disable
 
using System.Collections.Immutable;
using System.Linq;
using System.Runtime.InteropServices;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.PooledObjects;
using Microsoft.VisualStudio.LanguageServices.Implementation.CodeModel.InternalElements;
using Microsoft.VisualStudio.LanguageServices.Implementation.CodeModel.Interop;
using Microsoft.VisualStudio.LanguageServices.Implementation.Interop;
 
namespace Microsoft.VisualStudio.LanguageServices.Implementation.CodeModel.Collections;
 
[ComVisible(true)]
[ComDefaultInterface(typeof(ICodeElements))]
public sealed class OverloadsCollection : AbstractCodeElementCollection
{
    internal static EnvDTE.CodeElements Create(
        CodeModelState state,
        CodeFunction parent)
    {
        var collection = new OverloadsCollection(state, parent);
        return (EnvDTE.CodeElements)ComAggregate.CreateAggregatedObject(collection);
    }
 
    private OverloadsCollection(
        CodeModelState state,
        CodeFunction parent)
        : base(state, parent)
    {
    }
 
    private ImmutableArray<EnvDTE.CodeElement> _overloads;
 
    private CodeFunction ParentElement => (CodeFunction)this.Parent;
 
    private ImmutableArray<EnvDTE.CodeElement> GetOverloads()
    {
        // Retrieving the overloads is potentially very expensive because it can force multiple FileCodeModels to be instantiated.
        // Here, we cache the result to avoid having to perform these calculations each time GetOverloads() is called.
        // This *could* be an issue because it means that an OverloadsCollection will not necessarily reflect the
        // current state of the user's code. However, because a new OverloadsCollection is created every time the Overloads
        // property is accessed on CodeFunction, consumers would hit this behavior rarely.
        if (_overloads == null)
        {
            var symbol = (IMethodSymbol)ParentElement.LookupSymbol();
 
            // Only methods and constructors can be overloaded.  However, all functions
            // can successfully return a collection of overloaded functions; if not
            // really overloaded, the collection contains just the original function.
            if (symbol.MethodKind is not MethodKind.Ordinary and
                not MethodKind.Constructor)
            {
                return [(EnvDTE.CodeElement)Parent];
            }
 
            var solution = this.Workspace.CurrentSolution;
 
            var overloadsBuilder = ArrayBuilder<EnvDTE.CodeElement>.GetInstance();
            foreach (var method in symbol.ContainingType.GetMembers(symbol.Name))
            {
                if (method.Kind != SymbolKind.Method)
                {
                    continue;
                }
 
                var location = method.Locations.FirstOrDefault(l => l.IsInSource);
                if (location != null)
                {
                    var document = solution.GetDocument(location.SourceTree);
                    if (document != null)
                    {
                        var fileCodeModelObject = this.Workspace.GetFileCodeModel(document.Id);
                        if (fileCodeModelObject != null)
                        {
                            var fileCodeModel = ComAggregate.GetManagedObject<FileCodeModel>(fileCodeModelObject);
 
                            var element = fileCodeModel.CodeElementFromPosition(location.SourceSpan.Start, EnvDTE.vsCMElement.vsCMElementFunction);
                            if (element != null)
                            {
                                overloadsBuilder.Add(element);
                            }
                        }
                    }
                }
            }
 
            _overloads = overloadsBuilder.ToImmutableAndFree();
        }
 
        return _overloads;
    }
 
    internal override Snapshot CreateSnapshot() => new CodeElementSnapshot(GetOverloads());
 
    protected override bool TryGetItemByIndex(int index, out EnvDTE.CodeElement element)
    {
        if (index >= 0 && index < GetOverloads().Length)
        {
            element = GetOverloads()[index];
            return true;
        }
 
        element = null;
        return false;
    }
 
    protected override bool TryGetItemByName(string name, out EnvDTE.CodeElement element)
    {
        element = null;
        return false;
    }
 
    public override int Count => GetOverloads().Length;
}