// 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 PartialTypeCollection : AbstractCodeElementCollection
{
    internal static EnvDTE.CodeElements Create(
        CodeModelState state,
        AbstractCodeType parent)
    {
        var collection = new PartialTypeCollection(state, parent);
        return (EnvDTE.CodeElements)ComAggregate.CreateAggregatedObject(collection);
    }
 
    private PartialTypeCollection(
        CodeModelState state,
        AbstractCodeType parent)
        : base(state, parent)
    {
    }
 
    private ImmutableArray<EnvDTE.CodeElement> _parts;
 
    private AbstractCodeType ParentType => (AbstractCodeType)this.Parent;
 
    private ImmutableArray<EnvDTE.CodeElement> GetParts()
    {
        // Retrieving the parts 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 GetParts() is called.
        // This *could* be an issue because it means that a PartialTypeCollection will not necessarily reflect the
        // current state of the user's code. However, because a new PartialTypeCollection is created every time the Parts
        // property is accessed on CodeClass, CodeStruct or CodeInterface, consumers would hit this behavior rarely.
        if (_parts == null)
        {
            var partsBuilder = ArrayBuilder<EnvDTE.CodeElement>.GetInstance();
 
            var solution = this.Workspace.CurrentSolution;
            var symbol = ParentType.LookupSymbol();
 
            foreach (var location in symbol.Locations.Where(l => l.IsInSource))
            {
                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, ParentType.Kind);
                        if (element != null)
                        {
                            partsBuilder.Add(element);
                        }
                    }
                }
            }
 
            _parts = partsBuilder.ToImmutableAndFree();
        }
 
        return _parts;
    }
 
    internal override Snapshot CreateSnapshot() => new CodeElementSnapshot(GetParts());
 
    protected override bool TryGetItemByIndex(int index, out EnvDTE.CodeElement element)
    {
        var parts = GetParts();
        if (index < parts.Length)
        {
            element = parts[index];
            return true;
        }
 
        element = null;
        return false;
    }
 
    protected override bool TryGetItemByName(string name, out EnvDTE.CodeElement element)
    {
        foreach (var part in GetParts())
        {
            if (part.Name == name)
            {
                element = part;
                return true;
            }
        }
 
        element = null;
        return false;
    }
 
    public override int Count => GetParts().Length;
}