// 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.Collections.Generic;
using System.Linq;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;
using Microsoft.CodeAnalysis.CSharp.Syntax;

namespace CommunityToolkit.Mvvm.SourceGenerators;

/// <inheritdoc cref="TransitiveMembersGenerator"/>
public abstract partial class TransitiveMembersGenerator
{
    /// <summary>
    /// An <see cref="ISyntaxContextReceiver"/> that selects candidate nodes to process.
    /// </summary>
    private sealed class SyntaxReceiver : ISyntaxContextReceiver
    {
        /// <summary>
        /// The fully qualified name of the attribute type to look for.
        /// </summary>
        private readonly string attributeTypeFullName;

        /// <summary>
        /// The list of info gathered during exploration.
        /// </summary>
        private readonly List<Item> gatheredInfo = new();

        /// <summary>
        /// Initializes a new instance of the <see cref="SyntaxReceiver"/> class.
        /// </summary>
        /// <param name="attributeTypeFullName">The fully qualified name of the attribute type to look for.</param>
        public SyntaxReceiver(string attributeTypeFullName)
        {
            this.attributeTypeFullName = attributeTypeFullName;
        }

        /// <summary>
        /// Gets the collection of gathered info to process.
        /// </summary>
        public IReadOnlyCollection<Item> GatheredInfo => this.gatheredInfo;

        /// <inheritdoc/>
        public void OnVisitSyntaxNode(GeneratorSyntaxContext context)
        {
            if (context.Node is ClassDeclarationSyntax { AttributeLists: { Count: > 0 } } classDeclaration &&
                context.SemanticModel.GetDeclaredSymbol(classDeclaration) is INamedTypeSymbol classSymbol &&
                context.SemanticModel.Compilation.GetTypeByMetadataName(this.attributeTypeFullName) is INamedTypeSymbol attributeSymbol &&
                classSymbol.GetAttributes().FirstOrDefault(a => SymbolEqualityComparer.Default.Equals(a.AttributeClass, attributeSymbol)) is AttributeData attributeData &&
                attributeData.ApplicationSyntaxReference is SyntaxReference syntaxReference &&
                syntaxReference.GetSyntax() is AttributeSyntax attributeSyntax)
            {
                this.gatheredInfo.Add(new Item(classDeclaration, classSymbol, attributeSyntax, attributeData));
            }
        }

        /// <summary>
        /// A model for a group of item representing a discovered type to process.
        /// </summary>
        /// <param name="ClassDeclaration">The <see cref="ClassDeclarationSyntax"/> instance for the target class declaration.</param>
        /// <param name="ClassSymbol">The <see cref="INamedTypeSymbol"/> instance for <paramref name="ClassDeclaration"/>.</param>
        /// <param name="AttributeSyntax">The <see cref="AttributeSyntax"/> instance for the target attribute over <paramref name="ClassDeclaration"/>.</param>
        /// <param name="AttributeData">The <see cref="AttributeData"/> instance for <paramref name="AttributeSyntax"/>.</param>
        public sealed record Item(
            ClassDeclarationSyntax ClassDeclaration,
            INamedTypeSymbol ClassSymbol,
            AttributeSyntax AttributeSyntax,
            AttributeData AttributeData);
    }
}