using System;
using System.IO;
using System.Runtime.InteropServices;
using System.Text;

namespace MSCO
{
    /// <summary>
    /// HTTPS-Abruf über Windows (WinHTTP). Unitys WWW in My Summer Car (Unity 5.0) kann nur TLS 1.0,
    /// heutige Server verlangen TLS 1.2+. WinHTTP nutzt die TLS-Version des Betriebssystems
    /// (unter Proton/Wine über GnuTLS). Blockierend - nur in einem Hintergrund-Thread aufrufen.
    /// </summary>
    public static class WinHttp
    {
        public static string Get(string url, int timeoutMs, out string error)
        {
            error = null;
            IntPtr session = IntPtr.Zero, connect = IntPtr.Zero, request = IntPtr.Zero;
            try
            {
                var uri = new Uri(url);
                bool secure = uri.Scheme == "https";

                session = WinHttpOpen("MSCO/" + MSCO.ModVersion, AccessTypeDefaultProxy, null, null, 0);
                if (session == IntPtr.Zero) return Fail(out error, "WinHttpOpen");
                WinHttpSetTimeouts(session, timeoutMs, timeoutMs, timeoutMs, timeoutMs);

                // Ältere Windows-Versionen haben TLS 1.2 nicht standardmäßig an - ausdrücklich erlauben
                int protocols = ProtocolTls12 | ProtocolTls13;
                if (!WinHttpSetOption(session, OptionSecureProtocols, ref protocols, 4))
                {
                    protocols = ProtocolTls12;
                    WinHttpSetOption(session, OptionSecureProtocols, ref protocols, 4);
                }

                connect = WinHttpConnect(session, uri.Host, (ushort)uri.Port, 0);
                if (connect == IntPtr.Zero) return Fail(out error, "WinHttpConnect");

                request = WinHttpOpenRequest(connect, "GET", uri.PathAndQuery, null, null, IntPtr.Zero, secure ? FlagSecure : 0);
                if (request == IntPtr.Zero) return Fail(out error, "WinHttpOpenRequest");

                if (!WinHttpSendRequest(request, null, 0, IntPtr.Zero, 0, 0, IntPtr.Zero)) return Fail(out error, "WinHttpSendRequest");
                if (!WinHttpReceiveResponse(request, IntPtr.Zero)) return Fail(out error, "WinHttpReceiveResponse");

                int status = 0, size = 4;
                WinHttpQueryHeaders(request, QueryStatusCode | QueryFlagNumber, null, ref status, ref size, IntPtr.Zero);
                if (status != 0 && status != 200)
                {
                    error = "HTTP " + status;
                    return null;
                }

                using (var body = new MemoryStream())
                {
                    var buffer = new byte[16 * 1024];
                    while (true)
                    {
                        int read;
                        if (!WinHttpReadData(request, buffer, buffer.Length, out read)) return Fail(out error, "WinHttpReadData");
                        if (read == 0) break;
                        body.Write(buffer, 0, read);
                        if (body.Length > 4 * 1024 * 1024) { error = "Response too large"; return null; }
                    }
                    return Encoding.UTF8.GetString(body.ToArray());
                }
            }
            catch (Exception e)
            {
                error = e.Message;
                return null;
            }
            finally
            {
                if (request != IntPtr.Zero) WinHttpCloseHandle(request);
                if (connect != IntPtr.Zero) WinHttpCloseHandle(connect);
                if (session != IntPtr.Zero) WinHttpCloseHandle(session);
            }
        }

        static string Fail(out string error, string step)
        {
            int code = Marshal.GetLastWin32Error();
            error = step + " failed (" + code + (code == 12175 ? ", secure connection failed" : code == 12002 ? ", timeout" : code == 12029 ? ", cannot connect" : "") + ")";
            return null;
        }

        const int AccessTypeDefaultProxy = 0;
        const int FlagSecure = 0x00800000;
        const int OptionSecureProtocols = 84;
        const int ProtocolTls12 = 0x00000800;
        const int ProtocolTls13 = 0x00002000;
        const int QueryStatusCode = 19;
        const int QueryFlagNumber = 0x20000000;

        [DllImport("winhttp.dll", SetLastError = true, CharSet = CharSet.Unicode)]
        static extern IntPtr WinHttpOpen(string agent, int accessType, string proxy, string bypass, int flags);

        [DllImport("winhttp.dll", SetLastError = true)]
        static extern bool WinHttpSetTimeouts(IntPtr handle, int resolve, int connect, int send, int receive);

        [DllImport("winhttp.dll", SetLastError = true)]
        static extern bool WinHttpSetOption(IntPtr handle, int option, ref int value, int length);

        [DllImport("winhttp.dll", SetLastError = true, CharSet = CharSet.Unicode)]
        static extern IntPtr WinHttpConnect(IntPtr session, string server, ushort port, int reserved);

        [DllImport("winhttp.dll", SetLastError = true, CharSet = CharSet.Unicode)]
        static extern IntPtr WinHttpOpenRequest(IntPtr connect, string verb, string path, string version, string referrer,
                                                IntPtr acceptTypes, int flags);

        [DllImport("winhttp.dll", SetLastError = true, CharSet = CharSet.Unicode)]
        static extern bool WinHttpSendRequest(IntPtr request, string headers, int headersLength, IntPtr optional,
                                              int optionalLength, int totalLength, IntPtr context);

        [DllImport("winhttp.dll", SetLastError = true)]
        static extern bool WinHttpReceiveResponse(IntPtr request, IntPtr reserved);

        [DllImport("winhttp.dll", SetLastError = true, CharSet = CharSet.Unicode)]
        static extern bool WinHttpQueryHeaders(IntPtr request, int infoLevel, string name, ref int buffer, ref int bufferLength, IntPtr index);

        [DllImport("winhttp.dll", SetLastError = true)]
        static extern bool WinHttpReadData(IntPtr request, byte[] buffer, int toRead, out int read);

        [DllImport("winhttp.dll", SetLastError = true)]
        static extern bool WinHttpCloseHandle(IntPtr handle);
    }
}