using System;
using System.Collections.Generic;
using System.IO;
using System.Security.Cryptography;
using Xunit;
using XWorld.Framework;
using XWorld.Framework.Protocol;
using XWorld.PublishTool;
using XWorld.Server.Host;
using XWorld.Server.Gateway;

namespace XWorld.Server.Gateway.Tests
{
    /// <summary>
    /// Integration tests: ServerLoop with publicKeyPem enforces signature verification end-to-end.
    /// TDD: these tests are written RED-first, then made GREEN by wiring publicKeyPem through
    /// ServerLoop ctor → GameModuleLoader.
    /// </summary>
    public class ServerLoopSignatureEnforcementTests : IDisposable
    {
        private readonly string _tempRoot;
        private readonly string _gameDir; // {tempRoot}/rps/1/

        public ServerLoopSignatureEnforcementTests()
        {
            _tempRoot = Path.Combine(Path.GetTempPath(), "sig_enforcement_" + Guid.NewGuid().ToString("N"));
            _gameDir = Path.Combine(_tempRoot, "rps", "1");
            Directory.CreateDirectory(_gameDir);

            // Copy rps/1 files from the shared TestGames root (built by build-test-games.sh)
            string src = Path.Combine(TestGames.Root, "rps", "1");
            foreach (var name in new[] { "RPS.Server.dll", "RPS.Core.dll", "game.json" })
                File.Copy(Path.Combine(src, name), Path.Combine(_gameDir, name), overwrite: true);
        }

        public void Dispose()
        {
            if (!Directory.Exists(_tempRoot)) return;
            // Unload ALCs and wait for Windows file locks to release
            for (int i = 0; i < 5; i++)
            {
                GC.Collect();
                GC.WaitForPendingFinalizers();
            }
            try { Directory.Delete(_tempRoot, true); }
            catch (UnauthorizedAccessException) { /* Windows file lock: GC will release eventually */ }
        }

        private static (string pubPem, string privPem) GenerateKeyPair()
        {
            using var rsa = RSA.Create(2048);
            return (rsa.ExportRSAPublicKeyPem(), rsa.ExportRSAPrivateKeyPem());
        }

        /// <summary>
        /// Write files.txt + files.txt.sig into _gameDir using the given private key.
        /// </summary>
        private void WriteSignature(string privPem)
        {
            var fm = new FilesManifest();
            foreach (var name in new[] { "RPS.Server.dll", "RPS.Core.dll", "game.json" })
            {
                string p = Path.Combine(_gameDir, name);
                byte[] b = File.ReadAllBytes(p);
                fm.Add(name, Md5Util.OfBytes(b), b.Length);
            }
            File.WriteAllText(Path.Combine(_gameDir, "files.txt"), fm.Render());
            File.WriteAllBytes(Path.Combine(_gameDir, "files.txt.sig"),
                ManifestSigner.Sign(fm.Digest(), privPem));
        }

        // --- helpers mirroring ServerLoopMatchmakingTests ---

        private static byte[] RpsJoinFrame()
            => FrameCodec.Encode(new Frame(Channel.Framework, (ushort)FrameworkOpcode.MatchRequest,
                new MatchRequestMsg { GameId = "rps", Version = 1 }.Encode()));

        private static List<Frame> Frames(FakeConnection c)
        {
            var list = new List<Frame>();
            foreach (var bytes in c.Sent)
                list.Add(FrameCodec.Decode(bytes));
            return list;
        }

        private static bool HasMatchFound(FakeConnection c) =>
            Frames(c).Exists(f => f.Channel == Channel.Framework && f.Opcode == (ushort)FrameworkOpcode.MatchFound);

        private static bool HasError(FakeConnection c) =>
            Frames(c).Exists(f => f.Channel == Channel.Framework && f.Opcode == (ushort)FrameworkOpcode.Error);

        /// <summary>
        /// Signed module + correct public key → 2 players receive MatchFound (verification passes).
        /// </summary>
        [Fact]
        public void SignedModule_WithCorrectKey_PlayersGetMatchFound()
        {
            var (pubPem, privPem) = GenerateKeyPair();
            WriteSignature(privPem);

            // Large matchTimeoutTicks so the 2 humans match by player-count before any AI fill
            var loop = new ServerLoop(_tempRoot, new ConsoleLogger("[sig-ok]"),
                reconnectWindowTicks: 100, matchTimeoutTicks: 10000, publicKeyPem: pubPem);

            var c1 = new FakeConnection(1);
            var c2 = new FakeConnection(2);

            loop.Submit(new ConnectCommand { PlayerId = 1, Connection = c1 });
            loop.Submit(new ConnectCommand { PlayerId = 2, Connection = c2 });
            loop.Submit(new FrameCommand { PlayerId = 1, Frame = FrameCodec.Decode(RpsJoinFrame()) });
            loop.Submit(new FrameCommand { PlayerId = 2, Frame = FrameCodec.Decode(RpsJoinFrame()) });

            // One DrainAndTick: both players enqueued → matchmaker sees count=2 >= playerCount=2
            // → forms match → CreateRoomForSeats → GameModuleLoader.Load (verifies signature: OK)
            // → room created → both players receive MatchFound
            loop.DrainAndTick(1f);

            Assert.True(HasMatchFound(c1), "c1 should receive MatchFound when signature is valid");
            Assert.True(HasMatchFound(c2), "c2 should receive MatchFound when signature is valid");
        }

        /// <summary>
        /// Tampered module + correct public key → signature verification fails during CreateRoom
        /// → CreateRoomForSeats catches and sends Error to players → neither gets MatchFound.
        /// </summary>
        [Fact]
        public void TamperedModule_WithKey_PlayersGetErrorNotMatchFound()
        {
            var (pubPem, privPem) = GenerateKeyPair();
            WriteSignature(privPem);

            // Tamper RPS.Core.dll: flip first byte → md5 changes → manifest md5 check fails
            string coreDll = Path.Combine(_gameDir, "RPS.Core.dll");
            byte[] bytes = File.ReadAllBytes(coreDll);
            bytes[0] ^= 0xFF;
            File.WriteAllBytes(coreDll, bytes);

            // Large matchTimeoutTicks so 2 humans match before AI fill
            var loop = new ServerLoop(_tempRoot, new ConsoleLogger("[sig-bad]"),
                reconnectWindowTicks: 100, matchTimeoutTicks: 10000, publicKeyPem: pubPem);

            var c1 = new FakeConnection(1);
            var c2 = new FakeConnection(2);

            loop.Submit(new ConnectCommand { PlayerId = 1, Connection = c1 });
            loop.Submit(new ConnectCommand { PlayerId = 2, Connection = c2 });
            loop.Submit(new FrameCommand { PlayerId = 1, Frame = FrameCodec.Decode(RpsJoinFrame()) });
            loop.Submit(new FrameCommand { PlayerId = 2, Frame = FrameCodec.Decode(RpsJoinFrame()) });

            // One DrainAndTick: match forms → CreateRoomForSeats → GameModuleLoader.Load
            // (detects tampered dll via md5 mismatch) → throws → caught by CreateRoomForSeats
            // → sends Error (code=1) to both real players
            loop.DrainAndTick(1f);

            // Primary invariant: no MatchFound (room was never created)
            Assert.False(HasMatchFound(c1), "c1 must NOT receive MatchFound for a tampered module");
            Assert.False(HasMatchFound(c2), "c2 must NOT receive MatchFound for a tampered module");

            // Secondary invariant: at least one player receives an Error frame
            // (CreateRoomForSeats sends Error to all realPids on load failure)
            Assert.True(HasError(c1) || HasError(c2),
                "At least one player should receive an Error frame when module load fails");
        }
    }
}