#include "tls.hpp"

#include <gnutls/gnutls.h>
#include <gnutls/x509.h>

#include <forstio/io/io_helpers.hpp>

#include <cassert>

#include <iostream>

namespace saw {

class tls::impl {
public:
	gnutls_certificate_credentials_t xcred;

public:
	impl() {
		gnutls_global_init();
		gnutls_certificate_allocate_credentials(&xcred);
		gnutls_certificate_set_x509_system_trust(xcred);
	}

	~impl() {
		gnutls_certificate_free_credentials(xcred);
		gnutls_global_deinit();
	}
};

static ssize_t forst_tls_push_func(gnutls_transport_ptr_t p, const void *data,
						 size_t size);
static ssize_t forst_tls_pull_func(gnutls_transport_ptr_t p, void *data, size_t size);

tls::tls() : impl_{heap<tls::impl>()} {}

tls::~tls() {}

tls::impl &tls::get_impl() { return *impl_; }

class tls_io_stream final : public io_stream {
private:
	own<io_stream> internal;
	gnutls_certificate_credentials_t xcred_;
	gnutls_session_t session_handle;

public:
	tls_io_stream(own<io_stream> internal_, gnutls_certificate_credentials_t xcred__, gnutls_session_t session_handle__):
		internal{std::move(internal_)},
		xcred_{xcred__},
		session_handle_{session_handle__}
	{}

	~tls_io_stream() { gnutls_bye(session_handle, GNUTLS_SHUT_RDWR); }

	error_or<size_t> read(void *buffer, size_t length) override {
		ssize_t size = gnutls_record_recv(session_handle, buffer, length);
		if (size < 0) {
			if(gnutls_error_is_fatal(size) == 0){
				return make_error<err::recoverable>("Recoverable error on read in gnutls. TODO better error msg handling");
				// Leaving proper message handling done in previous error framework
				//return recoverable_error([size](){return std::string{"Read recoverable Error "}+std::string{gnutls_strerror(size)};}, "Error read r");
			}else{
				return make_error<err::critical>("Fatal error on read in gnutls. TODO better error msg handling");
			}
		}else if(size == 0){
			return make_error<err::disconnected>();
		}

		return static_cast<size_t>(length);
	}

	conveyor<void> read_ready() override { return internal->read_ready(); }

	conveyor<void> on_read_disconnected() override {
		return internal->on_read_disconnected();
	}

	error_or<size_t> write(const void *buffer, size_t length) override {
		ssize_t size = gnutls_record_send(session_handle, buffer, length);
		if(size < 0){
			if(gnutls_error_is_fatal(size) == 0){
				return make_error<err::recoverable>("Recoverable error on write in gnutls. TODO better error msg handling");
			}else{
				return make_error<err::critical>("Fatal error on write in gnutls. TODO better error msg handling");
			}
		}

		return static_cast<size_t>(size);
	}

	conveyor<void> write_ready() override { return internal->write_ready(); }

	gnutls_session_t &session() { return session_handle; }
};

class tls_server final : public server {
private:
	own<server> internal_;
	gnutls_certificate_credentials_t xcred_;
	gnutls_session_t session_handle_;

public:
	tls_server(own<server> internal__, gnutls_certificate_credentials_t xcred__):
		internal_{std::move(internal__)}
	{}

	~tls_server() {
		gnutls_bye(session_handle_, GNUTLS_SHUT_RDWR);
		gnutls_certificate_free_credentials(xcred_);
	}

	conveyor<own<io_stream>> accept() override {
		return make_error<err::not_implemented>();
	}
};

class tls_network final : public network {
private:
	tls& tls_;
	network &internal;
public:
	tls_network(tls& tls_, network &network_);

	conveyor<own<network_address>> resolve_address(const std::string &addr, uint16_t port = 0) override;
	
	own<server> listen(network_address& address) override;

	conveyor<own<io_stream>> connect(network_address& address) override;

	own<class datagram> datagram(network_address& address) override;
};

tls_server::tls_server(own<server> srv) : internal{std::move(srv)} {}

conveyor<own<io_stream>> tls_server::accept() {
	SAW_ASSERT(internal) { return conveyor<own<io_stream>>{fix_void<own<io_stream>>{nullptr}}; }
	return internal->accept().then([](own<io_stream> stream) -> own<io_stream> {
		/// @todo handshake


		return heap<tls_io_stream>(std::move(stream));
	});
}

namespace {
/*
* Small helper for setting up the nonblocking connection handshake
*/
struct tls_client_stream_helper {
public:
	own<conveyor_feeder<own<io_stream>>> feeder;
	conveyor_sink connection_sink;
	conveyor_sink stream_reader;
	conveyor_sink stream_writer;

	own<tls_io_stream> stream = nullptr;
public:
	tls_client_stream_helper(own<conveyor_feeder<own<io_stream>>> f):
		feeder{std::move(f)}
	{}

	void setupTurn(){
		SAW_ASSERT(stream){
			return;
		}

		stream_reader = stream->read_ready().then([this](){
			turn();
		}).sink();

		stream_writer = stream->write_ready().then([this](){
			turn();
		}).sink();
	}

	void turn(){
		if(stream){
			// Guarantee that the receiving end is already setup
			SAW_ASSERT(feeder){
				return;
			}

			auto &session = stream->session();

			int ret;
			do {
				ret = gnutls_handshake(session);
			} while ( (ret == GNUTLS_E_AGAIN || ret == GNUTLS_E_INTERRUPTED) && gnutls_error_is_fatal(ret) == 0);

			if(gnutls_error_is_fatal(ret)){
				feeder->fail(make_error<err::critical>("Couldn't create Tls connection"));
				stream = nullptr;
			}else if(ret == GNUTLS_E_SUCCESS){
				feeder->feed(std::move(stream));
			}
		}
	}
};
}

own<server> tls_network::listen(const network_address& address) {
	gnutls_certificate_credentials_t x509_cred;
	gnutls_certificate_allocate_credentials(&x509_cred);
	auto int_srv = internal.listen(address);

	return heap<tls_server>(int_srv, x509_cred);
}

conveyor<own<io_stream>> tls_network::connect(network_address& address) {
	// Helper setups
	auto caf = new_conveyor_and_feeder<own<io_stream>>();
	own<tls_client_stream_helper> helper = heap<tls_client_stream_helper>(std::move(caf.feeder));
	tls_client_stream_helper* hlp_ptr = helper.get();
	
	// Conveyor entangled structure
	auto prim_conv = internal.connect(address).then([this, hlp_ptr, addr = address.address()](
										own<io_stream> stream) -> error_or<void> {
		io_stream* inner_stream = stream.get();
		auto tls_stream = heap<tls_io_stream>(std::move(stream));

		auto &session = tls_stream->session();

		gnutls_init(&session, GNUTLS_CLIENT);

		gnutls_server_name_set(session, GNUTLS_NAME_DNS, addr.c_str(),
							   addr.size());

		gnutls_set_default_priority(session);
		gnutls_credentials_set(session, GNUTLS_CRD_CERTIFICATE,
							   tls_.get_impl().xcred);
		gnutls_session_set_verify_cert(session, addr.c_str(), 0);

		gnutls_transport_set_ptr(session, reinterpret_cast<gnutls_transport_ptr_t>(inner_stream));
		gnutls_transport_set_push_function(session, forst_tls_push_func);
		gnutls_transport_set_pull_function(session, forst_tls_pull_func);

		// gnutls_handshake_set_timeout(session, GNUTLS_DEFAULT_HANDSHAKE_TIMEOUT);

		hlp_ptr->stream = std::move(tls_stream);
		hlp_ptr->setupTurn();
		hlp_ptr->turn();

		return void_t{};
	});

	helper->connection_sink = prim_conv.sink();

	return caf.conveyor.attach(std::move(helper));
}

own<datagram> tls_network::datagram(network_address& address){
	///@unimplemented
	return nullptr;
}

static ssize_t forst_tls_push_func(gnutls_transport_ptr_t p, const void *data,
						 size_t size) {
	io_stream *stream = reinterpret_cast<io_stream *>(p);
	if (!stream) {
		return -1;
	}

	error_or<size_t> length = stream->write(data, size);
	if (length.is_error() || !length.is_value()) {
		return -1;
	}

	return static_cast<ssize_t>(length.get_value());
}

static ssize_t forst_tls_pull_func(gnutls_transport_ptr_t p, void *data, size_t size) {
	io_stream *stream = reinterpret_cast<io_stream *>(p);
	if (!stream) {
		return -1;
	}

	error_or<size_t> length = stream->read(data, size);
	if (length.is_error() || !length.is_value()) {
		return -1;
	}

	return static_cast<ssize_t>(length.get_value());
}

tls_network::tls_network(tls& tls_, network &network) : tls_{tls_},internal{network} {}

conveyor<own<network_address>> tls_network::resolve_address(const std::string &addr,
													   uint16_t port) {
	/// @todo tls server name needed. Check validity. Won't matter later on, because gnutls should fail anyway. But
	/// it's better to find the error source sooner rather than later
	return internal.resolve_address(addr, port);
}

std::optional<own<tls_network>> setup_tls_network(network &network) {
	return std::nullopt;
}
} // namespace saw