#include "OpenSSL.hh"

#include <array>

#include <bit>

#include <cstdint>

#include <cstdio>

#include <mutex>

#include <string>

#include <utility>

#include <vector>

#ifdef _WIN32

#include <windows.h>

#include <wincrypt.h>

#else

#include <dlfcn.h>

#endif

namespace openmsx::OpenSSL {

// Opaque OpenSSL runtime types, used only by the resolved entry points

// (forward-declared here so that openMSX never needs the OpenSSL

// development headers).

struct SslCtx;

struct X509;

struct X509VerifyParam;

struct SslMethod;

struct X509StoreCtx;

struct SslInitSettings;

// Resolved OpenSSL entry points. Every member is mandatory (load() refuses

// the library when any is missing); the only exception is `version`, whose

// three name spellings differ across OpenSSL/LibreSSL and which is

// diagnostic-only.

struct OpenSSLApi {

	// init

	int (*init)(unsigned long long opts, const SslInitSettings* settings) = nullptr;

	// methods / contexts

	const SslMethod* (*tlsClientMethod)() = nullptr;

	SslCtx* (*ctxNew)(const SslMethod* method) = nullptr;

	int (*ctxSetDefaultVerifyPaths)(SslCtx* ctx) = nullptr;

	int (*ctxLoadVerifyLocations)(SslCtx* ctx, const char* caFile,

	                              const char* caPath) = nullptr;

	// sessions

	Ssl* (*newSession)(SslCtx* ctx) = nullptr;

	void (*freeSession)(Ssl* ssl) = nullptr;

	int (*setFd)(Ssl* ssl, int fd) = nullptr;

	void (*setVerify)(Ssl* ssl, int mode, void (*)(int, X509StoreCtx*)) = nullptr;

	int (*connect)(Ssl* ssl) = nullptr;

	long (*ctrl)(Ssl* ssl, int cmd, long larg, const char* parg) = nullptr;

	X509VerifyParam* (*get0Param)(const Ssl* ssl) = nullptr;

	int (*verifyParamSet1Host)(X509VerifyParam* param, const char* name,

	                           size_t namelen) = nullptr;

	// data

	int (*read)(Ssl* ssl, uint8_t* buf, int num) = nullptr;

	int (*write)(Ssl* ssl, const uint8_t* buf, int num) = nullptr;

	int (*pending)(const Ssl* ssl) = nullptr;

	int (*shutdown)(Ssl* ssl) = nullptr;

	// errors / verification

	int (*getError)(const Ssl* ssl, int ret) = nullptr;

	long (*getVerifyResult)(const Ssl* ssl) = nullptr;

	const char* (*verifyCertErrorString)(long code) = nullptr;

	X509* (*get1PeerCertificate)(const Ssl* ssl) = nullptr;

	void (*freeX509)(X509* x) = nullptr;

	unsigned long (*errGetError)() = nullptr;

	void (*errErrorStringN)(unsigned long e, char* buf, size_t len) = nullptr;

	const char* (*version)(int type) = nullptr;

};

namespace {

// ---------------------------------------------------------------------

//  Runtime library handle

// ---------------------------------------------------------------------

#ifdef _WIN32

using DllHandle = HMODULE;

DllHandle openSslLib(const char* name)

{

	return LoadLibraryA(name);

}

#else

using DllHandle = void*;

DllHandle openSslLib(const char* name)

{

	return dlopen(name, RTLD_NOW | RTLD_LOCAL);

}

#endif

#ifdef _WIN32

static constexpr std::array libraryCandidates = {

	"libssl-4-x64.dll", "libssl-4.dll",

	"libssl-3-x64.dll", "libssl-3.dll",

	"libssl-1_1-x64.dll", "libssl-1_1.dll",

	"libssl.dll"

};

#elif defined(__APPLE__)

static constexpr std::array libraryCandidates = {

	// Homebrew (Apple Silicon / Intel) and system-wide installs

	"/opt/homebrew/opt/openssl@3/lib/libssl.3.dylib",

	"/opt/homebrew/opt/[email protected]/lib/libssl.1.1.dylib",

	"/usr/local/opt/openssl@3/lib/libssl.3.dylib",

	"/usr/local/opt/[email protected]/lib/libssl.1.1.dylib",

	"/usr/local/lib/libssl.dylib",

	"/opt/homebrew/lib/libssl.dylib",

	// Generic names (default dyld search paths)

	"libssl.3.dylib", "libssl.1.1.dylib", "libssl.dylib"

};

#else

static constexpr std::array libraryCandidates = {

	// Generic names (ldconfig cache)

	"libssl.so.3", "libssl.so.1.1", "libssl.so"

};

#endif

// Resolves one exported symbol, reinterpreted to the type the caller

// expects. Returns nullptr when it is not present. All pointer types have

// the same width, so this is ABI-safe.

template<typename T>

T resolveSymbol(DllHandle lib, const char* name)

{

#ifdef _WIN32

	return std::bit_cast<T>(GetProcAddress(lib, name));

#else

	return std::bit_cast<T>(dlsym(lib, name));

#endif

}

// ---------------------------------------------------------------------

//  Trust store setup

// ---------------------------------------------------------------------

#ifdef _WIN32

// Exports the Windows system root certificates as a PEM file and loads it

// into the given context, so that the device trusts the same CAs as the

// host operating system.

bool loadWindowsTrustStore(const OpenSSLApi& api, SslCtx* ctx)

{

	// The Windows system store provides the full root CA list

	HCERTSTORE hStore = CertOpenStore(CERT_STORE_PROV_SYSTEM_A, 0, 0,

	                                  CERT_SYSTEM_STORE_CURRENT_USER,

	                                  "ROOT");

	if (!hStore) return false;

	std::array<char, MAX_PATH> tmpPath;

	std::array<char, MAX_PATH> tmpFile;

	if (!GetTempPathA(MAX_PATH, tmpPath.data())) {

		CertCloseStore(hStore, 0);

		return false;

	}

	// GetTempFileNameA creates a unique empty file in the temp directory

	if (!GetTempFileNameA(tmpPath.data(), "omsx", 0, tmpFile.data())) {

		CertCloseStore(hStore, 0);

		return false;

	}

	bool ok = false;

	if (FILE* f = fopen(tmpFile.data(), "wb"); f) {

		PCCERT_CONTEXT pCert = nullptr;

		while ((pCert = CertEnumCertificatesInStore(hStore, pCert)) != nullptr) {

			DWORD len = 0;

			if (!CryptBinaryToStringA(pCert->pbCertEncoded,

			                          pCert->cbCertEncoded,

			                          CRYPT_STRING_BASE64HEADER,

			                          nullptr, &len) || len == 0) {

				continue;

			}

			std::vector<char> buf(len);

			if (CryptBinaryToStringA(pCert->pbCertEncoded,

			                         pCert->cbCertEncoded,

			                         CRYPT_STRING_BASE64HEADER,

			                         buf.data(), &len)) {

				fwrite(buf.data(), 1, len, f);

			}

		}

		fclose(f);

		ok = api.ctxLoadVerifyLocations(ctx, tmpFile.data(), nullptr) == 1;

	}

	CertCloseStore(hStore, 0);

	DeleteFileA(tmpFile.data());

	return ok;

}

#endif

// Best-effort trust-store setup: failures only reduce what can be

// verified, they never prevent TLS, so the return values are ignored.

void setupTrustStore(const OpenSSLApi& api, SslCtx* ctx)

{

#ifdef _WIN32

	// The Windows system store provides the full root CA list

	loadWindowsTrustStore(api, ctx);

#else

	// Load the common POSIX CA bundle first: it is needed on macOS

	// (Homebrew builds do not use OpenSSL's compiled-in default paths)

	// and covers Linux distros whose bundle is not on those paths either.

	// Best effort: when the file is missing, the default paths below may

	// still work.

	api.ctxLoadVerifyLocations(ctx, "/etc/ssl/cert.pem", nullptr);

#endif

	// The library's compiled-in default paths (e.g. /etc/ssl/certs on

	// Linux); on macOS Homebrew builds this fails, but the bundle above

	// was already loaded.

	api.ctxSetDefaultVerifyPaths(ctx);

}

// Shared client context, created once on first use

SslCtx* getSharedContext(const OpenSSLApi& api)

{

	static std::once_flag flag;

	static SslCtx* ctx = nullptr;

	std::call_once(flag, [&api] {

		// TLS_client_method and SSL_CTX_new are mandatory entry points

		ctx = api.ctxNew(api.tlsClientMethod());

		if (ctx) {

			setupTrustStore(api, ctx);

		}

	});

	return ctx;

}

// ---------------------------------------------------------------------

//  Symbol resolution

// ---------------------------------------------------------------------

static constexpr unsigned long OPENSSL_INIT_LOAD_SSL_STRINGS = 0x00200000UL;

static constexpr unsigned long OPENSSL_INIT_LOAD_CRYPTO_STRINGS = 0x00000001UL;

template<typename T>

T resolve(DllHandle lib, const char* name)

{

	return resolveSymbol<T>(lib, name);

}

// Tries the SSL library first, then the crypto library: the X509/ERR

// entry points live in libcrypto (GetProcAddress does not search DLL

// dependencies, so on Windows the crypto library must be loaded too)

template<typename T>

T resolveAny(DllHandle lib, DllHandle crypto, const char* name)

{

	if (auto p = resolveSymbol<T>(lib, name)) {

		return p;

	}

	if (crypto) {

		if (auto p = resolveSymbol<T>(crypto, name)) {

			return p;

		}

	}

	return nullptr;

}

// Name of the libcrypto DLL that belongs to a libssl DLL

std::string cryptoNameFor(std::string n)

{

	if (auto pos = n.find("libssl"); pos != std::string::npos) {

		n.replace(pos, 6, "libcrypto");

	}

	return n;

}

bool openLibrary(DllHandle& sslLib, DllHandle& cryptoLib)

{

	for (const char* name : libraryCandidates) {

		if (auto h = openSslLib(name)) {

			sslLib = h;

			// Load the matching libcrypto as well: the X509/ERR entry

			// points are exported by libcrypto, and GetProcAddress does

			// not search DLL dependencies (best effort; the TLS session

			// functions themselves all live in libssl).

			std::string cryptoName = cryptoNameFor(name);

			if (auto ch = openSslLib(cryptoName.c_str())) {

				cryptoLib = ch;

			}

			return true;

		}

	}

	return false;

}

bool resolveSymbols(OpenSSLApi& api, DllHandle sslLib, DllHandle cryptoLib)

{

	// All entry points are mandatory (except the OPENSSL_version name

	// spellings at the end, which are diagnostic-only). Each entry point

	// is resolved and checked immediately, so none can be forgotten and

	// missing ones are visible right where they are queried. This

	// requires OpenSSL >= 1.1 or LibreSSL >= 3.5.

	api.init = resolve<decltype(api.init)>(sslLib, "OPENSSL_init_ssl");

	if (!api.init) return false;

	api.tlsClientMethod = resolve<decltype(api.tlsClientMethod)>(sslLib, "TLS_client_method");

	if (!api.tlsClientMethod) return false;

	api.ctxNew = resolve<decltype(api.ctxNew)>(sslLib, "SSL_CTX_new");

	if (!api.ctxNew) return false;

	api.ctxSetDefaultVerifyPaths = resolve<decltype(api.ctxSetDefaultVerifyPaths)>(sslLib, "SSL_CTX_set_default_verify_paths");

	if (!api.ctxSetDefaultVerifyPaths) return false;

	api.ctxLoadVerifyLocations = resolve<decltype(api.ctxLoadVerifyLocations)>(sslLib, "SSL_CTX_load_verify_locations");

	if (!api.ctxLoadVerifyLocations) return false;

	api.newSession = resolve<decltype(api.newSession)>(sslLib, "SSL_new");

	if (!api.newSession) return false;

	api.freeSession = resolve<decltype(api.freeSession)>(sslLib, "SSL_free");

	if (!api.freeSession) return false;

	api.setFd = resolve<decltype(api.setFd)>(sslLib, "SSL_set_fd");

	if (!api.setFd) return false;

	api.setVerify = resolve<decltype(api.setVerify)>(sslLib, "SSL_set_verify");

	if (!api.setVerify) return false;

	api.connect = resolve<decltype(api.connect)>(sslLib, "SSL_connect");

	if (!api.connect) return false;

	api.ctrl = resolve<decltype(api.ctrl)>(sslLib, "SSL_ctrl");

	if (!api.ctrl) return false;

	api.get0Param = resolve<decltype(api.get0Param)>(sslLib, "SSL_get0_param");

	if (!api.get0Param) return false;

	api.verifyParamSet1Host = resolveAny<decltype(api.verifyParamSet1Host)>(sslLib, cryptoLib, "X509_VERIFY_PARAM_set1_host");

	if (!api.verifyParamSet1Host) return false;

	api.read = resolve<decltype(api.read)>(sslLib, "SSL_read");

	if (!api.read) return false;

	api.write = resolve<decltype(api.write)>(sslLib, "SSL_write");

	if (!api.write) return false;

	api.pending = resolve<decltype(api.pending)>(sslLib, "SSL_pending");

	if (!api.pending) return false;

	api.shutdown = resolve<decltype(api.shutdown)>(sslLib, "SSL_shutdown");

	if (!api.shutdown) return false;

	api.getError = resolve<decltype(api.getError)>(sslLib, "SSL_get_error");

	if (!api.getError) return false;

	api.getVerifyResult = resolve<decltype(api.getVerifyResult)>(sslLib, "SSL_get_verify_result");

	if (!api.getVerifyResult) return false;

	api.verifyCertErrorString = resolveAny<decltype(api.verifyCertErrorString)>(sslLib, cryptoLib, "X509_verify_cert_error_string");

	if (!api.verifyCertErrorString) return false;

	api.get1PeerCertificate = resolve<decltype(api.get1PeerCertificate)>(sslLib, "SSL_get1_peer_certificate");

	if (!api.get1PeerCertificate) return false;

	api.freeX509 = resolveAny<decltype(api.freeX509)>(sslLib, cryptoLib, "X509_free");

	if (!api.freeX509) return false;

	api.errGetError = resolveAny<decltype(api.errGetError)>(sslLib, cryptoLib, "ERR_get_error");

	if (!api.errGetError) return false;

	api.errErrorStringN = resolveAny<decltype(api.errErrorStringN)>(sslLib, cryptoLib, "ERR_error_string_n");

	if (!api.errErrorStringN) return false;

	// Diagnostic-only: the version function is not mandatory and has

	// different name spellings across OpenSSL/LibreSSL.

	api.version = resolveAny<decltype(api.version)>(sslLib, cryptoLib, "OPENSSL_version");

	if (!api.version) {

		// LibreSSL exports the version function with this exact name

		api.version = resolveAny<decltype(api.version)>(sslLib, cryptoLib, "OpenSSL_version");

	}

	if (!api.version) {

		api.version = resolveAny<decltype(api.version)>(sslLib, cryptoLib, "SSLeay_version");

	}

	// Initialize the library (idempotent in OpenSSL >= 1.1)

	if (api.init(OPENSSL_INIT_LOAD_SSL_STRINGS |

	             OPENSSL_INIT_LOAD_CRYPTO_STRINGS, nullptr) != 1) {

		return false;

	}

	return true;

}

static constexpr int SSL_VERIFY_NONE = 0x00;

static constexpr int SSL_VERIFY_PEER = 0x01;

static constexpr int SSL_ERROR_WANT_READ = 2;

static constexpr int SSL_ERROR_WANT_WRITE = 3;

static constexpr int SSL_ERROR_ZERO_RETURN = 6;

static constexpr int SSL_CTRL_SET_TLSEXT_HOSTNAME = 55;

static constexpr long TLSEXT_NAMETYPE_HOST_NAME = 0;

static constexpr int OPENSSL_VERSION = 0;

// X509 verify error codes (used to map to TCP-IP UNAPI close reasons)

static constexpr long X509_V_OK = 0;

static constexpr long X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT = 2;

static constexpr long X509_V_ERR_CERT_NOT_YET_VALID = 9;

static constexpr long X509_V_ERR_CERT_HAS_EXPIRED = 10;

static constexpr long X509_V_ERR_DEPTH_ZERO_SELF_SIGNED_CERT = 18;

static constexpr long X509_V_ERR_SELF_SIGNED_CERT_IN_CHAIN = 19;

static constexpr long X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT_LOCALLY = 20;

static constexpr long X509_V_ERR_UNABLE_TO_VERIFY_LEAF_SIGNATURE = 21;

static constexpr long X509_V_ERR_CERT_REVOKED = 23;

static constexpr long X509_V_ERR_INVALID_CA = 24;

static constexpr long X509_V_ERR_CERT_UNTRUSTED = 27;

static constexpr long X509_V_ERR_CERT_REJECTED = 28;

static constexpr long X509_V_ERR_HOSTNAME_MISMATCH = 62;

} // namespace

// ---------------------------------------------------------------------

//  OpenSSL public interface

// ---------------------------------------------------------------------

LibHandle::LibHandle()

	: api(std::make_unique<OpenSSLApi>())

{

}

LibHandle::~LibHandle() = default;

LibHandle* load()

{

	static LibHandle singleton;

	static std::once_flag flag;

	std::call_once(flag, [] {

		// The handles are only needed during symbol resolution; the

		// loaded libraries stay resident for the process lifetime.

		DllHandle sslLib = nullptr;

		DllHandle cryptoLib = nullptr;

		if (openLibrary(sslLib, cryptoLib)) {

			singleton.loaded = resolveSymbols(*singleton.api, sslLib, cryptoLib);

			singleton.libHandle = sslLib;

			singleton.cryptoHandle = cryptoLib;

		}

	});

	return singleton.loaded ? &singleton : nullptr;

}

SessionHandle::SessionHandle(Ssl* ssl_, const OpenSSLApi* api_)

	: ssl(ssl_)

	, api(api_)

{

}

SessionHandle::SessionHandle(SessionHandle&& other) noexcept

	: ssl(std::exchange(other.ssl, nullptr))

	, api(other.api)

{

}

SessionHandle& SessionHandle::operator=(SessionHandle&& other) noexcept

{

	if (this != &other) {

		release();

		ssl = std::exchange(other.ssl, nullptr);

		api = other.api;

	}

	return *this;

}

SessionHandle::~SessionHandle()

{

	release();

}

void SessionHandle::release() noexcept

{

	if (!ssl) return;

	// Best-effort shutdown: the peer may already be gone

	api->shutdown(ssl);

	api->freeSession(ssl);

	ssl = nullptr;

}

HandshakeResult SessionHandle::handshake() const

{

	int r = api->connect(ssl);

	if (r == 1) return HandshakeType::Done;

	int e = api->getError(ssl, r);

	if (e == SSL_ERROR_WANT_READ) return HandshakeType::NeedRead;

	if (e == SSL_ERROR_WANT_WRITE) return HandshakeType::NeedWrite;

	// Real error: capture the OpenSSL error code now, before any other

	// OpenSSL call can overwrite the error queue (mirrors serial::ErrorCode).

	return std::unexpected(ErrorCode{api->errGetError()});