// 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="ObservablePropertyGenerator"/>
public sealed partial class ObservablePropertyGenerator
{
    /// <summary>
    /// An <see cref="ISyntaxContextReceiver"/> that selects candidate nodes to process.
    /// </summary>
    private sealed class SyntaxReceiver : ISyntaxContextReceiver
    {
        /// <summary>
        /// The list of info gathered during exploration.
        /// </summary>
        private readonly List<Item> gatheredInfo = new();

        /// <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 FieldDeclarationSyntax { AttributeLists: { Count: > 0 } } fieldDeclaration &&
                context.SemanticModel.Compilation.GetTypeByMetadataName("CommunityToolkit.Mvvm.ComponentModel.ObservablePropertyAttribute") is INamedTypeSymbol attributeSymbol)
            {
                SyntaxTriviaList leadingTrivia = fieldDeclaration.GetLeadingTrivia();

                foreach (VariableDeclaratorSyntax variableDeclarator in fieldDeclaration.Declaration.Variables)
                {
                    if (context.SemanticModel.GetDeclaredSymbol(variableDeclarator) is IFieldSymbol fieldSymbol &&
                        fieldSymbol.GetAttributes().Any(a => SymbolEqualityComparer.Default.Equals(a.AttributeClass, attributeSymbol)))
                    {
                        this.gatheredInfo.Add(new Item(leadingTrivia, fieldSymbol));
                    }
                }
            }
        }

        /// <summary>
        /// A model for a group of item representing a discovered type to process.
        /// </summary>
        /// <param name="LeadingTrivia">The leading trivia for the field declaration.</param>
        /// <param name="FieldSymbol">The <see cref="IFieldSymbol"/> instance for the target field.</param>
        public sealed record Item(SyntaxTriviaList LeadingTrivia, IFieldSymbol FieldSymbol);
    }
}