using SimpleHttpServer.Types;
using SimpleHttpServer.Types.Exceptions;
using SimpleHttpServer.Types.ParameterConverters;
using System.Net;
using System.Numerics;
using System.Reflection;
using System.Text;
using static SimpleHttpServer.Types.EndpointInvocationInfo;

namespace SimpleHttpServer;

public sealed class HttpServer {

    public int Port { get; }

    private readonly HttpListener listener;
    private Task? listenerTask;
    private readonly Logger mainLogger;
    private readonly Logger requestLogger;
    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}/");
        mainLogger = new(LogOutputTopic.Main, conf);
        requestLogger = new(LogOutputTopic.Request, conf);
    }

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

    public async Task StopAsync(CancellationToken ctok) {
        mainLogger.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) {
                mainLogger.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<HttpEndpointAttribute>())
            .Where(x => x.Value.Any()).ToDictionary(x => x.Key, x => 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<QueryParameterInfo>();
            for (int i = expectedEndpointParameterTypes.Length; i < methodParams.Length; i++) {
                var par = methodParams[i];
                var attr = par.GetCustomAttribute<ParameterAttribute>(false);
                qparams.Add(new(
                    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)!");
                }
            }

            // stores the check attributes that are defined on the method and on the containing class
            var requiredChecks = mi.GetCustomAttributes<BaseEndpointCheckAttribute>(true).Concat(mi.DeclaringType?.GetCustomAttributes<BaseEndpointCheckAttribute>(true) ?? Enumerable.Empty<Attribute>())
                  .Where(a => a.GetType().IsAssignableTo(typeof(BaseEndpointCheckAttribute))).Cast<BaseEndpointCheckAttribute>().ToArray();

            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");
                mainLogger.Information($"Registered endpoint: '{reqMethod} {normLocation}'");
                simpleEndpointMethodInfos.Add((normLocation, reqMethod), new EndpointInvocationInfo(mi, qparams, requiredChecks));
            }
        }
    }

    /// <summary>
    /// Serves all files located in <paramref name="filesystemDirectory"/> on a website path that is relative to <paramref name="requestPath"/>, 
    /// while restricting requests to inside the local filesystem directory. Static serving has a lower priority than registering an endpoint.
    /// </summary>
    /// <param name="requestPath"></param>
    /// <param name="filesystemDirectory"></param>
    public void RegisterStaticServePath(string requestPath, string filesystemDirectory) {
        var absPath = Path.GetFullPath(filesystemDirectory);
        string npath = NormalizeUrlPath(requestPath);
        mainLogger.Information($"Registered static serve path: '{npath}' --> '{absPath}'");
        staticServePaths.Add(npath, absPath);
    }

    private readonly Dictionary<string, string> staticServePaths = new();

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

    private static string NormalizeUrlPath(string url) {
        var fwdSlashUrl = url.Replace('\\', '/');

        var segments = fwdSlashUrl.Trim('/').Split('/', StringSplitOptions.RemoveEmptyEntries).ToList();
        List<string> simplifiedSegmentsReversed = new List<string>();
        int doubleDotsEncountered = 0;
        for (int i = segments.Count - 1; i >= 0; i--) {
            var segment = segments[i];
            if (segment == ".") {
                continue; // remove single dot segments
            }
            if (segment == "..") {
                doubleDotsEncountered++; // if we encounter a doubledot, keep track of that and dont add it to the output yet
                continue;
            }
            // otherwise only keep the segment if doubleDotsEncountered > 0
            if (doubleDotsEncountered > 0) {
                doubleDotsEncountered--;
                continue;
            }
            simplifiedSegmentsReversed.Add(segment);
        }

        var rv = new StringBuilder();
        for (int i = 0; i < doubleDotsEncountered; i++) {
            rv.Append("../");
        }
        rv.AppendJoin('/', simplifiedSegmentsReversed.Reverse<string>());

        return '/' + (rv.ToString().TrimEnd('/') + (fwdSlashUrl.EndsWith('/') ? "/" : "")).TrimStart('/');
    }

    private async Task ProcessRequestAsync(HttpListenerContext ctx) {
        using RequestContext rc = new RequestContext(ctx);

        // TODO add path escape countermeasure-unittests
        var splitted = (ctx.Request.RawUrl ?? "").Split('?', 2, StringSplitOptions.None);
        var reqPath = NormalizeUrlPath(WebUtility.UrlDecode(splitted.First()));
        string requestMethod = ctx.Request.HttpMethod.ToUpperInvariant();
        bool wasStaticlyServed = false;

        void LogRequest() {
            requestLogger.Information($"{rc.ListenerContext.Response.StatusCode} {(wasStaticlyServed ? "static" : "endpnt")} {requestMethod} {ctx.Request.Url}");
        }
        try {

            if (simpleEndpointMethodInfos.TryGetValue((reqPath, requestMethod), 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];

                // run the checks to see if the client is allowed to make this request
                if (!endpointInvocationInfo.CheckAll(rc.ListenerContext.Request)) { // if any check failed return Forbidden
                    await HandleDefaultErrorPageAsync(rc, HttpStatusCode.Forbidden, "Client is not allowed to access this resource");
                    return;
                }

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

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

                        if (parsedQParams.TryGetValue(qparam.Name, out var qparamValue)) {
                            if (stringToTypeParameterConverters[qparam.Type].TryConvertFromString(qparamValue, out object objRes)) {
                                convertedQParamValues[i] = objRes;
                            } else {
                                await HandleDefaultErrorPageAsync(rc, HttpStatusCode.BadRequest);
                                return;
                            }
                        } else {
                            if (qparam.IsOptional) {
                                convertedQParamValues[i] = null!;
                            } else {
                                await HandleDefaultErrorPageAsync(rc, HttpStatusCode.BadRequest, $"Missing required query parameter {qparam.Name}");
                                return;
                            }
                        }
                    }
                }
                convertedQParamValues[0] = rc;
                rc.ParsedParameters = parsedQParams.AsReadOnly();

                await (Task) (mi.Invoke(null, convertedQParamValues) ?? throw new NullReferenceException("Website func returned null unexpectedly"));
            } else {
                if (requestMethod == "GET")
                    foreach (var (k, v) in staticServePaths) {
                        if (reqPath.StartsWith(k)) { // do a static serve
                            wasStaticlyServed = true;
                            var relativeStaticReqPath = reqPath[k.Length..];
                            var staticResponsePath = Path.GetFullPath(Path.Join(v, relativeStaticReqPath.TrimStart('/')));

                            if (Path.GetRelativePath(v, staticResponsePath).Contains("..")) {
                                requestLogger.Warning($"Blocked GET request to {reqPath} as somehow the target file does not lie inside the static serve folder? Are you using symlinks?");
                                await HandleDefaultErrorPageAsync(rc, HttpStatusCode.NotFound);
                                return;
                            }

                            if (File.Exists(staticResponsePath)) {
                                rc.SetStatusCode(HttpStatusCode.OK);
                                if (staticResponsePath.EndsWith(".svg")) {
                                    rc.ListenerContext.Response.AddHeader("Content-Type", "image/svg+xml");
                                }
                                using var f = File.OpenRead(staticResponsePath);
                                await f.CopyToAsync(rc.ListenerContext.Response.OutputStream);
                            } else {
                                await HandleDefaultErrorPageAsync(rc, HttpStatusCode.NotFound);
                            }
                            return;
                        }
                    }

                // invoke 404
                await HandleDefaultErrorPageAsync(rc, 404);
            }

        } catch (Exception ex) {
            await HandleDefaultErrorPageAsync(rc, 500);
            mainLogger.Fatal($"Caught otherwise uncaught exception while ProcessingRequest:\n{ex}");
        } finally {
            try { await rc.RespWriter.FlushAsync(); } catch (ObjectDisposedException) { }
            rc.ListenerContext.Response.Close();
            LogRequest();
        }
    }

    private static async Task HandleDefaultErrorPageAsync(RequestContext ctx, HttpStatusCode errorCode, string? statusDescription = null) => await HandleDefaultErrorPageAsync(ctx, (int) errorCode, statusDescription);

    private static async Task HandleDefaultErrorPageAsync(RequestContext ctx, int errorCode, string? statusDescription = null) {
        ctx.SetStatusCode(errorCode);
        string desc = statusDescription != null ? $"\r\n{statusDescription}" : "";
        await ctx.WriteLineToRespAsync($"""
            <body>
            <h1>Oh no, an error occurred!</h1>
            <p>Code: {errorCode}</p>{desc}
            </body>
            """);
        try {
            if (statusDescription == null) {
                await ctx.SetStatusCodeAndDisposeAsync(errorCode);
            } else {
                await ctx.SetStatusCodeAndDisposeAsync(errorCode, statusDescription);
            }
        } catch (ObjectDisposedException) { }
    }
}