// 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.Diagnostics.CodeAnalysis;
using System.Linq;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using static CommunityToolkit.Mvvm.SourceGenerators.Diagnostics.DiagnosticDescriptors;

namespace CommunityToolkit.Mvvm.SourceGenerators;

/// <summary>
/// A source generator for the <c>ObservableObjectAttribute</c> type.
/// </summary>
[Generator]
public sealed class ObservableObjectGenerator : TransitiveMembersGenerator
{
    /// <summary>
    /// Initializes a new instance of the <see cref="ObservableObjectGenerator"/> class.
    /// </summary>
    public ObservableObjectGenerator()
        : base("CommunityToolkit.Mvvm.ComponentModel.ObservableObjectAttribute")
    {
    }

    /// <inheritdoc/>
    protected override DiagnosticDescriptor TargetTypeErrorDescriptor => ObservableObjectGeneratorError;

    /// <inheritdoc/>
    protected override bool ValidateTargetType(
        GeneratorExecutionContext context,
        AttributeData attributeData,
        ClassDeclarationSyntax classDeclaration,
        INamedTypeSymbol classDeclarationSymbol,
        [NotNullWhen(false)] out DiagnosticDescriptor? descriptor)
    {
        INamedTypeSymbol iNotifyPropertyChangedSymbol = context.Compilation.GetTypeByMetadataName("System.ComponentModel.INotifyPropertyChanged")!;
        INamedTypeSymbol iNotifyPropertyChangingSymbol = context.Compilation.GetTypeByMetadataName("System.ComponentModel.INotifyPropertyChanging")!;

        // Check if the type already implements INotifyPropertyChanged...
        if (classDeclarationSymbol.AllInterfaces.Any(i => SymbolEqualityComparer.Default.Equals(i, iNotifyPropertyChangedSymbol)))
        {
            descriptor = DuplicateINotifyPropertyChangedInterfaceForObservableObjectAttributeError;

            return false;
        }

        // ...or INotifyPropertyChanging
        if (classDeclarationSymbol.AllInterfaces.Any(i => SymbolEqualityComparer.Default.Equals(i, iNotifyPropertyChangingSymbol)))
        {
            descriptor = DuplicateINotifyPropertyChangingInterfaceForObservableObjectAttributeError;

            return false;
        }

        descriptor = null;

        return true;
    }
}