// Integration tests for the HSMS Connection state machine.
//
// We open a pair of connected TCP sockets on loopback, wrap one in a real
// passive Connection (the system under test), and use the other as a raw
// "peer" socket that hand-builds wire frames. This lets us assert exactly
// what bytes the Connection produces in response to specific stimuli — in
// particular the E37 §7.2 / §7.4 / §7.7 corner cases that aren't exercised
// by the happy-path demo: SelectReq while already SELECTED, DeselectReq
// while NOT_SELECTED, and Reject.req emission for unsupported SType / PType.
//
// Both ends share the same io_context, so all socket I/O on the "peer"
// side has to be async too — running an asio::read synchronously on the
// peer would block the thread that also has to drive the Connection's
// own async reads, deadlocking the test.

#include <doctest/doctest.h>

#include <asio.hpp>
#include <array>
#include <chrono>
#include <cstdint>
#include <memory>
#include <thread>
#include <utility>
#include <vector>

#include "secsgem/hsms/connection.hpp"
#include "secsgem/hsms/header.hpp"

using namespace secsgem::hsms;

namespace {

// Pair of TCP sockets connected over loopback; both ends share `io`.
struct SocketPair {
  asio::io_context io;
  asio::ip::tcp::socket a{io};   // the "system under test" side
  asio::ip::tcp::socket b{io};   // the "raw peer" side

  SocketPair() {
    asio::ip::tcp::acceptor acc(io, asio::ip::tcp::endpoint(
                                        asio::ip::address_v4::loopback(), 0));
    const auto port = acc.local_endpoint().port();

    std::error_code ec_accept;
    bool accepted = false;
    acc.async_accept(a, [&](std::error_code ec) { ec_accept = ec; accepted = true; });

    std::error_code ec_connect;
    bool connected = false;
    b.async_connect(asio::ip::tcp::endpoint(asio::ip::address_v4::loopback(), port),
                    [&](std::error_code ec) { ec_connect = ec; connected = true; });

    while (!(accepted && connected)) {
      if (io.stopped()) io.restart();
      if (io.poll() == 0) std::this_thread::sleep_for(std::chrono::milliseconds(1));
    }
    REQUIRE_FALSE(ec_accept);
    REQUIRE_FALSE(ec_connect);
  }
};

// Run the io_context until `pred()` returns true or `budget` is exhausted.
// We drain all currently-ready handlers with poll(), then sleep briefly
// before re-checking — run_one_for() can block for its full timeout even
// when ready work exists, which made earlier iterations of this helper
// look hung.
template <typename Pred>
void pump_until(asio::io_context& io, Pred pred,
                std::chrono::milliseconds budget = std::chrono::seconds(5)) {
  const auto deadline = std::chrono::steady_clock::now() + budget;
  while (!pred()) {
    if (std::chrono::steady_clock::now() > deadline) FAIL("pump_until budget exceeded");
    if (io.stopped()) io.restart();
    const std::size_t n = io.poll();
    if (n == 0) std::this_thread::sleep_for(std::chrono::milliseconds(1));
  }
}

// Async write a buffer; pumps the io_context until it completes.
void send_bytes(SocketPair& sp, std::vector<uint8_t> bytes) {
  auto buf = std::make_shared<std::vector<uint8_t>>(std::move(bytes));
  bool done = false;
  asio::async_write(sp.b, asio::buffer(*buf),
                    [buf, &done](std::error_code ec, std::size_t) {
                      REQUIRE_FALSE(ec);
                      done = true;
                    });
  pump_until(sp.io, [&] { return done; });
}

// Async read one full HSMS frame from the peer socket; pumps the io_context.
Frame recv_frame(SocketPair& sp) {
  auto lenbuf = std::make_shared<std::array<uint8_t, 4>>();
  bool len_done = false;
  asio::async_read(sp.b, asio::buffer(*lenbuf),
                   [lenbuf, &len_done](std::error_code ec, std::size_t) {
                     REQUIRE_FALSE(ec);
                     len_done = true;
                   });
  pump_until(sp.io, [&] { return len_done; });

  const uint32_t len = (uint32_t((*lenbuf)[0]) << 24) | (uint32_t((*lenbuf)[1]) << 16) |
                       (uint32_t((*lenbuf)[2]) << 8) | uint32_t((*lenbuf)[3]);
  auto payload = std::make_shared<std::vector<uint8_t>>(len);
  bool payload_done = false;
  asio::async_read(sp.b, asio::buffer(*payload),
                   [payload, &payload_done](std::error_code ec, std::size_t) {
                     REQUIRE_FALSE(ec);
                     payload_done = true;
                   });
  pump_until(sp.io, [&] { return payload_done; });
  return Frame::decode(payload->data(), payload->size());
}

Timers default_timers() {
  Timers t;
  t.linktest = std::chrono::milliseconds(0);  // disabled in tests
  return t;
}

}  // namespace

TEST_CASE("Select.req while already SELECTED returns AlreadyActive (E37 §7.2)") {
  SocketPair sp;
  auto conn = std::make_shared<Connection>(std::move(sp.a), Connection::Mode::Passive,
                                           /*device_id=*/0, default_timers());
  bool selected = false;
  conn->set_selected_handler([&] { selected = true; });
  conn->start();

  // First Select.req: should be answered with Ok (status=0) and transition
  // the connection into SELECTED.
  send_bytes(sp, Frame(Header::control(SType::SelectReq, /*sys=*/1)).encode());
  Frame rsp1 = recv_frame(sp);
  CHECK(rsp1.header.stype == SType::SelectRsp);
  CHECK(rsp1.header.byte3 == static_cast<uint8_t>(SelectStatus::Ok));
  pump_until(sp.io, [&] { return selected; });

  // Second Select.req while already SELECTED: must reply AlreadyActive (1)
  // and must NOT re-fire the selected handler.
  selected = false;
  send_bytes(sp, Frame(Header::control(SType::SelectReq, /*sys=*/2)).encode());
  Frame rsp2 = recv_frame(sp);
  CHECK(rsp2.header.stype == SType::SelectRsp);
  CHECK(rsp2.header.byte3 == static_cast<uint8_t>(SelectStatus::AlreadyActive));
  CHECK_FALSE(selected);

  conn->close("test done");
}

TEST_CASE("Deselect.req while NOT_SELECTED returns NotEstablished (E37 §7.4)") {
  SocketPair sp;
  auto conn = std::make_shared<Connection>(std::move(sp.a), Connection::Mode::Passive,
                                           /*device_id=*/0, default_timers());
  conn->start();

  send_bytes(sp, Frame(Header::control(SType::DeselectReq, /*sys=*/1)).encode());
  Frame rsp = recv_frame(sp);
  CHECK(rsp.header.stype == SType::DeselectRsp);
  CHECK(rsp.header.byte3 == static_cast<uint8_t>(DeselectStatus::NotEstablished));
  CHECK(conn->state() == Connection::State::NotSelected);

  conn->close("test done");
}

TEST_CASE("Unsupported SType triggers Reject.req(StypeNotSupported) (E37 §7.7)") {
  SocketPair sp;
  auto conn = std::make_shared<Connection>(std::move(sp.a), Connection::Mode::Passive,
                                           /*device_id=*/0, default_timers());
  conn->start();

  // Standalone Header doesn't let us produce an unknown SType via the
  // constructors, so we build the wire bytes by hand.
  std::vector<uint8_t> bad = {0x00, 0x00, 0x00, 0x0A,
                              // header: session=0xFFFF, byte2=0, byte3=0,
                              // ptype=0, stype=10, sys=5
                              0xFF, 0xFF, 0x00, 0x00, 0x00, 0x0A,
                              0x00, 0x00, 0x00, 0x05};
  send_bytes(sp, std::move(bad));

  Frame rej = recv_frame(sp);
  CHECK(rej.header.stype == SType::RejectReq);
  CHECK(rej.header.system_bytes == 5);
  CHECK(rej.header.byte2 == 10);  // offending SType echoed in byte2
  CHECK(rej.header.byte3 == static_cast<uint8_t>(RejectReason::StypeNotSupported));

  conn->close("test done");
}

TEST_CASE("Non-zero PType triggers Reject.req(PtypeNotSupported) (E37 §7.7)") {
  SocketPair sp;
  auto conn = std::make_shared<Connection>(std::move(sp.a), Connection::Mode::Passive,
                                           /*device_id=*/0, default_timers());
  conn->start();

  // Linktest.req-like frame but with PType=7 (unsupported).
  std::vector<uint8_t> bad = {0x00, 0x00, 0x00, 0x0A,
                              0xFF, 0xFF, 0x00, 0x00,
                              /*ptype=*/0x07, /*stype=LinktestReq*/0x05,
                              0x00, 0x00, 0x00, 0x09};
  send_bytes(sp, std::move(bad));

  Frame rej = recv_frame(sp);
  CHECK(rej.header.stype == SType::RejectReq);
  CHECK(rej.header.system_bytes == 9);
  CHECK(rej.header.byte2 == 7);  // offending PType echoed in byte2
  CHECK(rej.header.byte3 == static_cast<uint8_t>(RejectReason::PtypeNotSupported));

  conn->close("test done");
}

TEST_CASE("Data frame while NOT_SELECTED triggers Reject.req(EntityNotSelected)") {
  SocketPair sp;
  auto conn = std::make_shared<Connection>(std::move(sp.a), Connection::Mode::Passive,
                                           /*device_id=*/0, default_timers());
  conn->start();

  // Primary S1F1 W=1 before selecting — equipment must Reject with
  // EntityNotSelected.  Construct via the header API: Data with an empty
  // body is a valid wire frame.
  Frame data(Header::data_message(/*session=*/1, /*stream=*/1, /*function=*/1,
                                  /*reply_expected=*/true, /*sys=*/42));
  send_bytes(sp, data.encode());

  Frame rej = recv_frame(sp);
  CHECK(rej.header.stype == SType::RejectReq);
  CHECK(rej.header.byte3 == static_cast<uint8_t>(RejectReason::EntityNotSelected));

  conn->close("test done");
}