namespace BizHawk.Analyzers;

using System.Collections.Immutable;
using System.Linq;

[DiagnosticAnalyzer(LanguageNames.CSharp)]
public sealed class FirstOrDefaultOnStructAnalyzer : DiagnosticAnalyzer
{
	private static readonly DiagnosticDescriptor DiagUseFirstOrNull = new(
		id: "BHI3100",
		title: "Call to FirstOrDefault when elements are of a value type; FirstOrNull may have been intended",
		messageFormat: "Call to FirstOrDefault when elements are of a value type; did you mean FirstOrNull?",
		category: "Usage",
		defaultSeverity: DiagnosticSeverity.Warning,
		isEnabledByDefault: true);

	public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics { get; }
		= ImmutableArray.Create(/*HawkSourceAnalyzer.DiagWTF,*/ DiagUseFirstOrNull);

	public override void Initialize(AnalysisContext context)
	{
		context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.None);
		context.EnableConcurrentExecution();
		context.RegisterCompilationStartAction(initContext =>
		{
			if (initContext.Compilation.GetTypeByMetadataName("BizHawk.Common.CollectionExtensions.CollectionExtensions") is null) return; // project does not have BizHawk.Common dependency
			var linqExtClassSym = initContext.Compilation.GetTypeByMetadataName("System.Linq.Enumerable")!;
			IMethodSymbol? firstOrDefaultNoPredSym = null;
			IMethodSymbol? firstOrDefaultWithPredSym = null;
			foreach (var sym in linqExtClassSym.GetMembers("FirstOrDefault").Cast<IMethodSymbol>())
			{
				if (sym.Parameters.Length is 2) firstOrDefaultWithPredSym = sym;
				else firstOrDefaultNoPredSym = sym;
			}
			initContext.RegisterOperationAction(
				oac =>
				{
					var operation = (IInvocationOperation) oac.Operation;
					var calledSym = operation.TargetMethod.ConstructedFrom;
					if (!(firstOrDefaultWithPredSym!.Matches(calledSym) || firstOrDefaultNoPredSym!.Matches(calledSym))) return;
					var receiverExpr = operation.Arguments[0].Syntax;
					var receiverExprType = operation.SemanticModel!.GetTypeInfo(
						(CSharpSyntaxNode) receiverExpr,
						oac.CancellationToken).ConvertedType!;
					var collectionElemType = receiverExprType switch
					{
						INamedTypeSymbol nts => nts.TypeArguments[0],
						IArrayTypeSymbol ats => ats.ElementType,
						_ => throw HawkSourceAnalyzer.ReportWTF(receiverExpr, oac, message: $"[{nameof(FirstOrDefaultOnStructAnalyzer)}] receiver parameter's effective type was of an unexpected kind (neither class/struct nor array): {receiverExprType.GetType().FullName}"),
					};
					if (collectionElemType.IsValueType) DiagUseFirstOrNull.ReportAt(operation.LocWithoutReceiver(), oac);
				},
				OperationKind.Invocation);
		});
	}
}