#nullable enable

using System;
using System.Collections.Generic;
using System.Collections.Immutable;
using System.Linq;
using System.Text;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Text;

namespace ShrinkEventBus.Generator
{
    [Generator]
    public sealed class ShrinkEventBusGenerator : IIncrementalGenerator
    {
        private const string SubscriberAttribute = "ShrinkEventBus.ShrinkEventSubscriberAttribute";
        private const string SubscribeAttribute = "ShrinkEventBus.ShrinkSubscribeAttribute";

        private static readonly DiagnosticDescriptor PartialRequired = new DiagnosticDescriptor(
            "SHRINKEVENT001", "Subscriber must be partial",
            "Subscriber type '{0}' must be partial so ShrinkEventBus can generate a reflection-free binding",
            "ShrinkEventBus", DiagnosticSeverity.Error, true);

        private static readonly DiagnosticDescriptor UnsupportedHandler = new DiagnosticDescriptor(
            "SHRINKEVENT002", "Unsupported handler signature",
            "Handler '{0}' must be void(TEvent), UniTask(TEvent), UniTask(TEvent, CancellationToken), or ValueTask(TEvent, CancellationToken)",
            "ShrinkEventBus", DiagnosticSeverity.Error, true);

        private static readonly DiagnosticDescriptor TopLevelRequired = new DiagnosticDescriptor(
            "SHRINKEVENT003", "Top-level subscriber required",
            "Subscriber type '{0}' must be top-level in the current generator version",
            "ShrinkEventBus", DiagnosticSeverity.Error, true);

        public void Initialize(IncrementalGeneratorInitializationContext context)
        {
            context.RegisterSourceOutput(context.CompilationProvider,
                static (sourceContext, compilation) =>
                {
                    if (compilation.GetTypeByMetadataName(
                            "System.Runtime.CompilerServices.ModuleInitializerAttribute") == null)
                    {
                        sourceContext.AddSource("ShrinkEventBus.ModuleInitializerAttribute.g.cs",
                            SourceText.From(
                                "namespace System.Runtime.CompilerServices { [global::System.AttributeUsage(global::System.AttributeTargets.Method, Inherited = false)] internal sealed class ModuleInitializerAttribute : global::System.Attribute { } }",
                                Encoding.UTF8));
                    }
                });

            var candidates = context.SyntaxProvider.ForAttributeWithMetadataName(
                SubscriberAttribute,
                static (node, _) => node is ClassDeclarationSyntax,
                static (syntaxContext, _) => (INamedTypeSymbol)syntaxContext.TargetSymbol);

            context.RegisterSourceOutput(candidates.Collect(), Generate);
        }

        private static void Generate(SourceProductionContext context,
            ImmutableArray<INamedTypeSymbol> candidates)
        {
            foreach (var type in candidates)
                GenerateType(context, type);
        }

        private static void GenerateType(SourceProductionContext context, INamedTypeSymbol type)
        {
            if (type.ContainingType != null)
            {
                context.ReportDiagnostic(Diagnostic.Create(TopLevelRequired,
                    type.Locations.FirstOrDefault(), type.ToDisplayString()));
                return;
            }

            var isPartial = type.DeclaringSyntaxReferences
                .Select(reference => reference.GetSyntax())
                .OfType<ClassDeclarationSyntax>()
                .Any(declaration => declaration.Modifiers.Any(SyntaxKind.PartialKeyword));
            if (!isPartial)
            {
                context.ReportDiagnostic(Diagnostic.Create(PartialRequired,
                    type.Locations.FirstOrDefault(), type.ToDisplayString()));
                return;
            }

            var handlers = new List<HandlerModel>();
            foreach (var method in type.GetMembers().OfType<IMethodSymbol>())
            {
                var attribute = method.GetAttributes().FirstOrDefault(item =>
                    item.AttributeClass?.ToDisplayString() == SubscribeAttribute);
                if (attribute == null)
                    continue;

                if (!TryCreateHandler(method, attribute, type.IsStatic, out var handler))
                {
                    context.ReportDiagnostic(Diagnostic.Create(UnsupportedHandler,
                        method.Locations.FirstOrDefault(), method.ToDisplayString()));
                    continue;
                }
                handlers.Add(handler);
            }

            var subscriber = type.GetAttributes().First(item =>
                item.AttributeClass?.ToDisplayString() == SubscriberAttribute);
            var defaultBus = ReadString(subscriber, "DefaultBus");
            var source = type.IsStatic
                ? BuildStaticSource(type, handlers, defaultBus)
                : BuildSource(type, handlers, defaultBus);
            var hint = type.ToDisplayString().Replace('.', '_').Replace('+', '_') + ".ShrinkEvents.g.cs";
            context.AddSource(hint, SourceText.From(source, Encoding.UTF8));
        }

        private static bool TryCreateHandler(IMethodSymbol method, AttributeData attribute,
            bool staticSubscriber,
            out HandlerModel model)
        {
            model = default;
            if (method.IsStatic != staticSubscriber || method.Parameters.Length == 0 || method.Parameters.Length > 2)
                return false;

            var eventType = method.Parameters[0].Type.ToDisplayString(SymbolDisplayFormat.FullyQualifiedFormat);
            var returnType = method.ReturnType.ToDisplayString();
            var isSync = method.ReturnsVoid && method.Parameters.Length == 1;
            var isValueTask = returnType == "System.Threading.Tasks.ValueTask" &&
                              method.Parameters.Length == 2 &&
                              method.Parameters[1].Type.ToDisplayString() == "System.Threading.CancellationToken";
            var isUniTask = returnType == "Cysharp.Threading.Tasks.UniTask";
            var isUniTaskLegacy = isUniTask && method.Parameters.Length == 1;
            var isUniTaskCancelable = isUniTask && method.Parameters.Length == 2 &&
                                      method.Parameters[1].Type.ToDisplayString() == "System.Threading.CancellationToken";
            if (!isSync && !isValueTask && !isUniTaskLegacy && !isUniTaskCancelable)
                return false;

            var bindingMethod = isSync
                ? "Subscribe"
                : isUniTaskLegacy ? "SubscribeAsyncLegacy" : "SubscribeAsync";

            model = new HandlerModel(
                method.Name,
                eventType,
                bindingMethod,
                ReadString(attribute, "Bus"),
                ReadInt(attribute, "Priority", 2),
                ReadInt(attribute, "NumericPriority", 0),
                ReadBool(attribute, "ReceiveCanceled", false));
            return true;
        }

        private static string BuildSource(INamedTypeSymbol type, IReadOnlyList<HandlerModel> handlers,
            string defaultBus)
        {
            var builder = new StringBuilder();
            builder.AppendLine("// <auto-generated />");
            builder.AppendLine("#nullable enable");
            if (!type.ContainingNamespace.IsGlobalNamespace)
            {
                builder.Append("namespace ").Append(type.ContainingNamespace.ToDisplayString()).AppendLine();
                builder.AppendLine("{");
            }

            var accessibility = type.DeclaredAccessibility switch
            {
                Accessibility.Public => "public ",
                Accessibility.Internal => "internal ",
                _ => string.Empty
            };
            builder.Append("    ").Append(accessibility).Append("partial class ")
                .Append(type.Name).AppendLine(" : global::ShrinkEventBus.IShrinkGeneratedSubscriber");
            builder.AppendLine("    {");
            builder.AppendLine("        global::System.IDisposable global::ShrinkEventBus.IShrinkGeneratedSubscriber.AttachGenerated(");
            builder.AppendLine("            global::ShrinkEventBus.IShrinkBusResolver resolver,");
            builder.AppendLine("            global::ShrinkEventBus.ShrinkBusKey? defaultBus)");
            builder.AppendLine("        {");
            builder.AppendLine("            var binding = new global::ShrinkEventBus.ShrinkEventBinding();");

            foreach (var handler in handlers)
            {
                var bus = string.IsNullOrWhiteSpace(handler.Bus) ? defaultBus : handler.Bus;
                builder.Append("            binding.Add(global::ShrinkEventBus.ShrinkGeneratedBinding.")
                    .Append(handler.BindingMethod).Append('<').Append(handler.EventType).AppendLine(">(");
                builder.Append("                resolver, defaultBus, ")
                    .Append(ToLiteral(bus)).AppendLine(", this,");
                builder.Append("                this.").Append(handler.MethodName)
                    .Append(", (global::ShrinkEventBus.ShrinkEventPriority)")
                    .Append(handler.Priority).Append(", ").Append(handler.NumericPriority).Append(", ")
                    .Append(handler.ReceiveCanceled ? "true" : "false").AppendLine("));");
            }

            builder.AppendLine("            return binding;");
            builder.AppendLine("        }");
            builder.AppendLine("    }");
            if (!type.ContainingNamespace.IsGlobalNamespace)
                builder.AppendLine("}");
            return builder.ToString();
        }

        private static string BuildStaticSource(INamedTypeSymbol type,
            IReadOnlyList<HandlerModel> handlers, string defaultBus)
        {
            var builder = new StringBuilder();
            builder.AppendLine("// <auto-generated />");
            builder.AppendLine("#nullable enable");
            if (!type.ContainingNamespace.IsGlobalNamespace)
            {
                builder.Append("namespace ").Append(type.ContainingNamespace.ToDisplayString()).AppendLine();
                builder.AppendLine("{");
            }

            var accessibility = type.DeclaredAccessibility switch
            {
                Accessibility.Public => "public ",
                Accessibility.Internal => "internal ",
                _ => string.Empty
            };
            builder.Append("    ").Append(accessibility).Append("static partial class ")
                .Append(type.Name).AppendLine();
            builder.AppendLine("    {");
            builder.AppendLine("        [global::System.Runtime.CompilerServices.ModuleInitializer]");
            builder.AppendLine("        internal static void ShrinkEventBus_RegisterStaticBindings()");
            builder.AppendLine("        {");
            for (var i = 0; i < handlers.Count; i++)
            {
                var bus = string.IsNullOrWhiteSpace(handlers[i].Bus) ? defaultBus : handlers[i].Bus;
                builder.Append("            global::ShrinkEventBus.ShrinkStaticBindingRegistry.Register(")
                    .Append("global::ShrinkEventBus.ShrinkBusKey.Parse(")
                    .Append(ToLiteral(bus)).Append("), ShrinkEventBus_Bind_").Append(i).AppendLine(");");
            }
            builder.AppendLine("        }");

            for (var i = 0; i < handlers.Count; i++)
            {
                var handler = handlers[i];
                var bus = string.IsNullOrWhiteSpace(handler.Bus) ? defaultBus : handler.Bus;
                builder.Append("        private static global::System.IDisposable ShrinkEventBus_Bind_")
                    .Append(i).AppendLine("(global::ShrinkEventBus.IShrinkBusResolver resolver)");
                builder.AppendLine("        {");
                builder.Append("            return global::ShrinkEventBus.ShrinkGeneratedBinding.")
                    .Append(handler.BindingMethod).Append('<').Append(handler.EventType).AppendLine(">(");
                builder.Append("                resolver, null, ").Append(ToLiteral(bus))
                    .AppendLine(", null,");
                builder.Append("                ").Append(handler.MethodName)
                    .Append(", (global::ShrinkEventBus.ShrinkEventPriority)")
                    .Append(handler.Priority).Append(", ").Append(handler.NumericPriority).Append(", ")
                    .Append(handler.ReceiveCanceled ? "true" : "false").AppendLine(");");
                builder.AppendLine("        }");
            }

            builder.AppendLine("    }");
            if (!type.ContainingNamespace.IsGlobalNamespace)
                builder.AppendLine("}");
            return builder.ToString();
        }

        private static string ReadString(AttributeData attribute, string name)
        {
            foreach (var pair in attribute.NamedArguments)
            {
                if (pair.Key == name)
                    return pair.Value.Value as string ?? string.Empty;
            }
            return string.Empty;
        }

        private static int ReadInt(AttributeData attribute, string name, int defaultValue)
        {
            foreach (var pair in attribute.NamedArguments)
            {
                if (pair.Key == name && pair.Value.Value != null)
                    return Convert.ToInt32(pair.Value.Value);
            }
            return defaultValue;
        }

        private static bool ReadBool(AttributeData attribute, string name, bool defaultValue)
        {
            foreach (var pair in attribute.NamedArguments)
            {
                if (pair.Key == name && pair.Value.Value is bool value)
                    return value;
            }
            return defaultValue;
        }

        private static string ToLiteral(string value) => SymbolDisplay.FormatLiteral(value ?? string.Empty, true);

        private readonly struct HandlerModel
        {
            public HandlerModel(string methodName, string eventType, string bindingMethod, string bus,
                int priority, int numericPriority, bool receiveCanceled)
            {
                MethodName = methodName;
                EventType = eventType;
                BindingMethod = bindingMethod;
                Bus = bus;
                Priority = priority;
                NumericPriority = numericPriority;
                ReceiveCanceled = receiveCanceled;
            }

            public string MethodName { get; }
            public string EventType { get; }
            public string BindingMethod { get; }
            public string Bus { get; }
            public int Priority { get; }
            public int NumericPriority { get; }
            public bool ReceiveCanceled { get; }
        }
    }
}