using System.Text.RegularExpressions;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp.Syntax;

namespace I2R.Endpoints.Generator;

[Generator]
public class EndpointGenerator : ISourceGenerator
{
    private const string SourceGenereatedComment = "// Generated by I2R.Endpoints, probably smart to leave it be";

    public void Initialize(GeneratorInitializationContext context) {
        context.RegisterForSyntaxNotifications(() => new EndpointFinder());
    }

    public void Execute(GeneratorExecutionContext context) {
        var endpointClasses = ((EndpointFinder) context.SyntaxReceiver)?.Endpoints;
        if (endpointClasses == null) {
            context.ReportDiagnostic(CreateDebugDiagnostic("no endpoints were found"));
            return;
        }

        foreach (var info in endpointClasses.Select(GetEndpointInfoFromClass)) {
            context.AddSource(info.GeneratedFileName, info.IsSynchronous ? GetSyncSource(info) : GetAsyncSource(info));
        }
    }

    private static Diagnostic CreateDebugDiagnostic(string message) {
        var descriptor = new DiagnosticDescriptor("debug", "Debug", message, "debug", DiagnosticSeverity.Warning, true);
        return Diagnostic.Create(descriptor, null, "");
    }

    private class EndpointInfo
    {
        public string BaseEndpointClassName { get; set; }
        public bool IsSynchronous { get; set; }
        public string GeneratedFileName { get; set; }
    }

    public static bool IsSyncEndpoint(string name) {
        return name.StartsWith("SyncEndpoint");
    }

    public static bool IsAyncEndpoint(string name) {
        return name.StartsWith("AsyncEndpoint");
    }

    private static EndpointInfo GetEndpointInfoFromClass(ClassDeclarationSyntax classDeclarationSyntax) {
        var baseType = classDeclarationSyntax.BaseList?.Types.FirstOrDefault();
        if (baseType == default) {
            return default;
        }

        var fullTypeName = baseType.Type.ToString();
        var className = Regex.Match(fullTypeName, "(!?<).+?(?=>)").Value.Replace("<", "");
        return new EndpointInfo() {
            BaseEndpointClassName = className,
            IsSynchronous = IsSyncEndpoint(baseType.ToString()),
            GeneratedFileName = className + ".endpoints.g.cs"
        };
    }

    private static string GetSyncSource(EndpointInfo info) {
        return $@"
{SourceGenereatedComment}
namespace {typeof(EndpointGenerator).Namespace};
public static partial class SyncEndpoint<T{info.BaseEndpointClassName}>
{{
    public static class Req<TRequest>
    {{
        public abstract class Res<TResponse> : {info.BaseEndpointClassName}
        {{
            public abstract TResponse Handle(
                TRequest request
            );
        }}

        public abstract class NoRes : {info.BaseEndpointClassName}
        {{
            public abstract void Handle(
                TRequest request
            );
        }}
    }}

    public static class NoReq
    {{
        public abstract class Res<TResponse> : {info.BaseEndpointClassName}
        {{
            public abstract TResponse Handle();
        }}

        public abstract class NoRes : {info.BaseEndpointClassName}
        {{
            public abstract void Handle();
        }}
    }}
}}
";
    }

    private static string GetAsyncSource(EndpointInfo info) {
        return $@"
{SourceGenereatedComment}
namespace {typeof(EndpointGenerator).Namespace};
public static partial class AsyncEndpoint<T>
{{
    public static class Req<TRequest>
    {{
        public abstract class Res<TResponse> : {info.BaseEndpointClassName}
        {{
            public abstract Task<TResponse> HandleAsync(
                TRequest request,
                CancellationToken cancellationToken = default
            );
        }}

        public abstract class NoRes : {info.BaseEndpointClassName}
        {{
            public abstract Task HandleAsync(
                TRequest request,
                CancellationToken cancellationToken = default
            );
        }}
    }}

    public static class NoReq
    {{
        public abstract class Res<TResponse> : {info.BaseEndpointClassName}
        {{
            public abstract Task<TResponse> HandleAsync(
                CancellationToken cancellationToken = default
            );
        }}

        public abstract class NoRes : {info.BaseEndpointClassName}
        {{
            public abstract Task HandleAsync(
                CancellationToken cancellationToken = default
            );
        }}
    }}
}}
";
    }
}