using System;
using System.IO;
using System.Runtime.CompilerServices;
using System.Security.Cryptography;
using Xunit;
using XWorld.PublishTool;
using XWorld.Server.Host;

namespace XWorld.Server.Host.Tests
{
    /// <summary>
    /// 设计§7：服务端加载时签名验证测试（TDD RED→GREEN）。
    /// 验证 GameModuleLoader 在配置公钥时执行签名+md5 校验，未配置时跳过（向后兼容）。
    /// </summary>
    public class GameModuleSignatureTests : IDisposable
    {
        private readonly string _tempRoot;
        private readonly string _gameDir; // {tempRoot}/rps/1/

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

            // 从已构建的 TestGames/rps/1 复制 3 个文件
            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))
            {
                // Windows 下 ALC 加载的 DLL 可能还被锁住；先做 GC 等待释放，再删除
                for (int i = 0; i < 5; i++)
                {
                    GC.Collect();
                    GC.WaitForPendingFinalizers();
                }
                try { Directory.Delete(_tempRoot, true); }
                catch (UnauthorizedAccessException) { /* Windows 文件锁：测试结束后 GC 会最终释放；不影响测试结果 */ }
            }
        }

        // 生成签名 fixture 并写入 files.txt + files.txt.sig
        private static (string pubPem, string privPem) GenerateKeyPair()
        {
            using var rsa = RSA.Create(2048);
            return (rsa.ExportRSAPublicKeyPem(), rsa.ExportRSAPrivateKeyPem());
        }

        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));
        }

        [Fact]
        public void Load_WithValidSignature_Succeeds()
        {
            var (pubPem, privPem) = GenerateKeyPair();
            WriteSignature(privPem);

            var module = new GameModuleLoader(pubPem).Load(_tempRoot, "rps", 1);

            Assert.NotNull(module);
            Assert.Equal("rps", module.GameId);
            Assert.Equal(1, module.Version);
            var room = module.CreateRoom();
            Assert.NotNull(room);

            // 卸载 ALC，释放 Windows 文件锁，以便 Dispose() 能清理临时目录
            room = null;
            module.Unload();
            GC.Collect();
            GC.WaitForPendingFinalizers();
        }

        [Fact]
        public void Load_TamperedDll_Rejected()
        {
            var (pubPem, privPem) = GenerateKeyPair();
            WriteSignature(privPem);

            // 篡改 RPS.Core.dll 的一个字节，md5 随之改变
            string coreDll = Path.Combine(_gameDir, "RPS.Core.dll");
            byte[] bytes = File.ReadAllBytes(coreDll);
            bytes[0] ^= 0xFF; // 翻转首字节
            File.WriteAllBytes(coreDll, bytes);

            var ex = Assert.ThrowsAny<Exception>(() =>
                new GameModuleLoader(pubPem).Load(_tempRoot, "rps", 1));
            Assert.Contains("md5", ex.Message, StringComparison.OrdinalIgnoreCase);
        }

        [Fact]
        public void Load_WrongKey_Rejected()
        {
            var (_, privPem) = GenerateKeyPair();
            WriteSignature(privPem);

            // 用另一组密钥的公钥验证 → 签名不符
            var (wrongPubPem, _) = GenerateKeyPair();

            var ex = Assert.ThrowsAny<Exception>(() =>
                new GameModuleLoader(wrongPubPem).Load(_tempRoot, "rps", 1));
            Assert.Contains("签名", ex.Message, StringComparison.OrdinalIgnoreCase);
        }

        [Fact]
        public void Load_MissingSignature_WhenKeyConfigured_Rejected()
        {
            var (pubPem, _) = GenerateKeyPair();
            // 故意不写 files.txt.sig（签名文件缺失）

            var ex = Assert.ThrowsAny<Exception>(() =>
                new GameModuleLoader(pubPem).Load(_tempRoot, "rps", 1));
            Assert.Contains("签名", ex.Message, StringComparison.OrdinalIgnoreCase);
        }

        [Fact]
        public void Load_NoKeyConfigured_SkipsVerification()
        {
            // 不配置公钥，使用无签名的原始 TestGames/rps/1 目录
            // 向后兼容：无公钥时跳过验证，正常加载
            var module = new GameModuleLoader().Load(TestGames.Root, "rps", 1);

            Assert.NotNull(module);
            Assert.Equal("rps", module.GameId);
            var room = module.CreateRoom();
            Assert.NotNull(room);
        }

        [Fact]
        public void Load_TamperedGameJson_Rejected()
        {
            // 构建签名 fixture（与其他测试相同方式）
            var (pubPem, privPem) = GenerateKeyPair();
            WriteSignature(privPem);

            // 篡改 game.json：追加一个空格，改变其 md5，使清单 md5 校验失败
            File.AppendAllText(Path.Combine(_gameDir, "game.json"), " ");

            Assert.ThrowsAny<Exception>(() =>
                new GameModuleLoader(pubPem).Load(_tempRoot, "rps", 1));
        }

        [Fact]
        public void Load_TamperedManifestWithoutResign_Rejected()
        {
            // 构建签名 fixture
            var (pubPem, privPem) = GenerateKeyPair();
            WriteSignature(privPem);

            // 攻击者篡改 RPS.Core.dll 一字节，并重算其 md5 写回 files.txt，
            // 但没有私钥无法重签 files.txt.sig → 验签时发现 Digest 与 sig 不符 → 拒绝
            string coreDll = Path.Combine(_gameDir, "RPS.Core.dll");
            byte[] bytes = File.ReadAllBytes(coreDll);
            bytes[0] ^= 0xFF;
            File.WriteAllBytes(coreDll, bytes);

            // 重算被篡改 DLL 的 md5，重写 files.txt（files.txt.sig 保持不变）
            string newMd5 = Md5Util.OfFile(coreDll);
            var fm = FilesManifest.Parse(File.ReadAllText(Path.Combine(_gameDir, "files.txt")));
            fm.Entries["RPS.Core.dll"].Md5 = newMd5;
            File.WriteAllText(Path.Combine(_gameDir, "files.txt"), fm.Render());

            Assert.ThrowsAny<Exception>(() =>
                new GameModuleLoader(pubPem).Load(_tempRoot, "rps", 1));
        }
    }
}