// 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="ICommandGenerator"/>
public sealed partial class ICommandGenerator
{
    /// <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 MethodDeclarationSyntax methodDeclaration &&
                context.SemanticModel.GetDeclaredSymbol(methodDeclaration) is IMethodSymbol methodSymbol &&
                context.SemanticModel.Compilation.GetTypeByMetadataName("CommunityToolkit.Mvvm.Input.ICommandAttribute") is INamedTypeSymbol iCommandSymbol &&
                methodSymbol.GetAttributes().FirstOrDefault(a => SymbolEqualityComparer.Default.Equals(a.AttributeClass, iCommandSymbol)) is AttributeData attributeData)
            {
                this.gatheredInfo.Add(new Item(methodDeclaration.GetLeadingTrivia(), methodSymbol, attributeData));
            }
        }

        /// <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="MethodSymbol">The <see cref="IMethodSymbol"/> instance for the target method.</param>
        /// <param name="AttributeData">The <see cref="AttributeData"/> instance the method was annotated with.</param>
        public sealed record Item(SyntaxTriviaList LeadingTrivia, IMethodSymbol MethodSymbol, AttributeData AttributeData);
    }
}