using SimpleHttpServer.Types;
using SimpleHttpServer.Types.Exceptions;
using SimpleHttpServer.Types.ParameterConverters;
using System.Net;
using System.Numerics;
using System.Reflection;

namespace SimpleHttpServer;

public sealed class HttpServer {

    public int Port { get; }

    private readonly HttpListener listener;
    private Task? listenerTask;
    private readonly Logger logger;
    private readonly SimpleHttpServerConfiguration conf;
    private bool shutdown = false;

    public HttpServer(int port, SimpleHttpServerConfiguration configuration) {
        Port = port;
        conf = configuration;
        listener = new HttpListener();
        listener.Prefixes.Add($"http://localhost:{port}/");
        logger = new(LogOutputTopic.Main, conf);
    }

    public void Start() {
        logger.Information($"Starting on port {Port}...");
        Assert(listenerTask == null, "Server was already started!");
        listener.Start();
        listenerTask = Task.Run(GetContextLoopAsync);
        logger.Information($"Ready to handle requests!");
    }

    public async Task StopAsync(CancellationToken ctok) {
        logger.Information("Stopping server...");
        Assert(listenerTask != null, "Server was not started!");
        shutdown = true;
        listener.Stop();
        await listenerTask.WaitAsync(ctok);
    }

    public async Task GetContextLoopAsync() {
        while (!shutdown) {
            try {
                var ctx = await listener.GetContextAsync();
                _ = ProcessRequestAsync(ctx);
            } catch (HttpListenerException ex) when (ex.ErrorCode == 995) { //The I/O operation has been aborted because of either a thread exit or an application request
            } catch (Exception ex) {
                logger.Fatal($"Caught otherwise uncaught exception in GetContextLoop:\n{ex}");
            }
        }
    }

    private void RegisterDefaultConverters() {
        void RegisterConverter<T>() where T : IParsable<T> {
            stringToTypeParameterConverters.Add(typeof(T), new ParsableParameterConverter<T>());
        }
        stringToTypeParameterConverters.Add(typeof(string), new StringParameterConverter());

        stringToTypeParameterConverters.Add(typeof(bool), new BoolParsableParameterConverter());
        RegisterConverter<char>();
        RegisterConverter<byte>();
        RegisterConverter<short>();
        RegisterConverter<int>();
        RegisterConverter<long>();
        RegisterConverter<Int128>();
        RegisterConverter<UInt128>();
        RegisterConverter<BigInteger>();

        RegisterConverter<sbyte>();
        RegisterConverter<ushort>();
        RegisterConverter<uint>();
        RegisterConverter<ulong>();

        RegisterConverter<Half>();
        RegisterConverter<float>();
        RegisterConverter<double>();
        RegisterConverter<decimal>();
    }

    private readonly Dictionary<(string path, string rType), EndpointInvocationInfo> simpleEndpointMethodInfos = new();
    private static readonly Type[] expectedEndpointParameterTypes = new[] { typeof(RequestContext) };
    public void RegisterEndpointsFromType<T>() {
        if (simpleEndpointMethodInfos.Count == 0)
            RegisterDefaultConverters();

        var t = typeof(T);
        foreach (var (mi, attrib) in t.GetMethods()
            .ToDictionary(x => x, x => x.GetCustomAttributes(typeof(HttpEndpointAttribute<>)))
            .Where(x => x.Value.Any()).ToDictionary(x => x.Key, x => (HttpEndpointAttribute) x.Value.Single())) {

            string GetFancyMethodName() => mi.DeclaringType!.FullName + "#" + mi.Name;

            Assert(mi.IsStatic, $"Method tagged with HttpEndpointAttribute must be static! ({GetFancyMethodName()})");
            Assert(mi.IsPublic, $"Method tagged with HttpEndpointAttribute must be public! ({GetFancyMethodName()})");

            var methodParams = mi.GetParameters();
            Assert(methodParams.Length >= expectedEndpointParameterTypes.Length);
            for (int i = 0; i < expectedEndpointParameterTypes.Length; i++) {
                Assert(methodParams[i].ParameterType.IsAssignableFrom(expectedEndpointParameterTypes[i]),
                    $"Parameter at index {i} of {GetFancyMethodName()} is of a type that cannot contain the expected type {expectedEndpointParameterTypes[i].FullName}.");
            }

            Assert(mi.ReturnType == typeof(Task), $"Return type of {GetFancyMethodName()} is not {typeof(Task)}!");


            var qparams = new List<(string, (Type type, bool isOptional))>();
            for (int i = expectedEndpointParameterTypes.Length; i < methodParams.Length; i++) {
                var par = methodParams[i];
                var attr = par.GetCustomAttribute<ParameterAttribute>(false);
                qparams.Add((attr?.Name ?? par.Name ?? throw new ArgumentException($"C# variable name of parameter at index {i} of method {GetFancyMethodName()} is null!"),
                    (par.ParameterType, attr?.IsOptional ?? false)));

                if (!stringToTypeParameterConverters.ContainsKey(par.ParameterType)) {
                    throw new MissingParameterConverterException($"Parameter converter for type {par.ParameterType} has not been registered (yet)!");
                }
            }

            foreach (var location in attrib.Locations) {
                var normLocation = NormalizeUrlPath(location);
                int idx = normLocation.IndexOf('{');
                if (idx >= 0) {
                    // this path contains path parameters
                    throw new NotImplementedException("Path parameters are not yet implemented!");
                }

                var reqMethod = Enum.GetName(attrib.RequestMethod) ?? throw new ArgumentException("Request method was undefined");
                simpleEndpointMethodInfos.Add((normLocation, reqMethod), new EndpointInvocationInfo(mi, qparams));
            }
        }
    }

    private readonly Dictionary<Type, IParameterConverter> stringToTypeParameterConverters = new();

    private string NormalizeUrlPath(string url) => '/' + url.TrimStart('/');

    private async Task ProcessRequestAsync(HttpListenerContext ctx) {
        using RequestContext rc = new RequestContext(ctx);
        try {
            var decUri = WebUtility.UrlDecode(ctx.Request.RawUrl)!; // TODO add path escape countermeasures+unittests
            var splitted = NormalizeUrlPath(decUri).Split('?', 2, StringSplitOptions.None);
            var path = WebUtility.UrlDecode(splitted.First());


            if (simpleEndpointMethodInfos.TryGetValue((path, ctx.Request.HttpMethod.ToUpperInvariant()), out var endpointInvocationInfo)) {
                var mi = endpointInvocationInfo.methodInfo;
                var qparams = endpointInvocationInfo.queryParameters;
                var args = splitted.Length == 2 ? splitted[1] : null;

                var parsedQParams = new Dictionary<string, string>();
                var convertedQParamValues = new object[qparams.Count + 1];

                // TODO add authcheck here

                if (args != null) {
                    var queryStringArgs = args.Split('&', StringSplitOptions.None);
                    foreach (var queryKV in queryStringArgs) {
                        var queryKVSplitted = queryKV.Split('=');
                        if (queryKVSplitted.Length != 2) {
                            rc.SetStatusCodeAndDispose(HttpStatusCode.BadRequest, "Malformed request URL parameters");
                            return;
                        }
                        if (!parsedQParams.TryAdd(WebUtility.UrlDecode(queryKVSplitted[0]), WebUtility.UrlDecode(queryKVSplitted[1]))) {
                            rc.SetStatusCodeAndDispose(HttpStatusCode.BadRequest, "Duplicate request URL parameters");
                            return;
                        }
                    }

                    for (int i = 0; i < qparams.Count;) {
                        var (qparamName, qparamInfo) = qparams[i];
                        i++;

                        if (parsedQParams.TryGetValue(qparamName, out var qparamValue)) {
                            if (stringToTypeParameterConverters[qparamInfo.type].TryConvertFromString(qparamValue, out object objRes)) {
                                convertedQParamValues[i] = objRes;
                            } else {
                                rc.SetStatusCodeAndDispose(HttpStatusCode.BadRequest);
                                return;
                            }
                        } else {
                            if (qparamInfo.isOptional) {
                                convertedQParamValues[i] = null!;
                            } else {
                                rc.SetStatusCodeAndDispose(HttpStatusCode.BadRequest, $"Missing required query parameter {qparamName}");
                                return;
                            }
                        }
                    }
                }
                convertedQParamValues[0] = rc;

                await (Task) (mi.Invoke(null, convertedQParamValues) ?? throw new NullReferenceException("Website func returned null unexpectedly"));
            } else {
                // invoke 404
                await HandleDefaultErrorPageAsync(rc, 404);
            }

        } catch (Exception ex) {
            await HandleDefaultErrorPageAsync(rc, 500);
            logger.Fatal($"Caught otherwise uncaught exception while ProcessingRequest:\n{ex}");
        }
    }


    private static async Task HandleDefaultErrorPageAsync(RequestContext ctx, int errorCode) {
        await ctx.WriteLineToRespAsync($"""
            <body>
            <h1>Oh no, an error occurred!</h1>
            <p>Code: {errorCode}</p>
            </body>
            """);
    }
}