#pragma once

#include <asio.hpp>
#include <atomic>
#include <chrono>
#include <cstdint>
#include <functional>
#include <future>
#include <memory>
#include <optional>
#include <string>
#include <thread>
#include <type_traits>
#include <utility>
#include <vector>

#include "secsgem/config/loader.hpp"
#include "secsgem/endpoint.hpp"
#include "secsgem/gem/control_state.hpp"
#include "secsgem/gem/data_model.hpp"
#include "secsgem/gem/router.hpp"
#include "secsgem/gem/store/host_commands.hpp"
#include "secsgem/secs2/item.hpp"
#include "secsgem/secs2/message.hpp"

namespace secsgem::gem {

// Owns the SECS/GEM engine — io_context, the passive HSMS Server, the data
// model, the E30 control-state machine, and the Router — as one reusable
// object. It is the foundation both the demo `secs_server` app and the gRPC
// daemon build on, replacing a hand-wired main() with a class.
//
// Threading contract (unchanged from the engine's existing design): a single
// io_context thread owns the model and the connection. The outbound methods
// (set_variable / emit_event / set_alarm / clear_alarm) are safe to call from
// any thread — each posts onto the io_context, exactly like the established
// emit_* pattern. Router handlers and the command hook run on the io thread.
class EquipmentRuntime {
 public:
  struct Config {
    std::string equipment_yaml;
    std::string control_state_yaml;
    std::string process_job_yaml;
    std::string control_job_yaml;
    uint16_t port = 5000;
    std::string spool_dir;                        // empty = no persistence
    std::function<void(const std::string&)> log;  // empty = silent
  };

  explicit EquipmentRuntime(const Config& cfg);
  ~EquipmentRuntime();

  EquipmentRuntime(const EquipmentRuntime&) = delete;
  EquipmentRuntime& operator=(const EquipmentRuntime&) = delete;

  // ---- access --------------------------------------------------------------
  EquipmentDataModel& model() { return *model_; }
  const EquipmentDataModel& model() const { return *model_; }
  Router& router() { return router_; }
  ControlStateMachine& control() { return *sm_; }
  asio::io_context& io() { return io_; }
  uint16_t device_id() const { return descriptor_.device_id; }
  void log(const std::string& m) const { if (log_) log_(m); }

  // Shared-pointer / reference accessors used when wiring handlers and
  // emitters that capture the engine pieces by value (see register handlers).
  std::shared_ptr<EquipmentDataModel> model_ptr() { return model_; }
  std::shared_ptr<ControlStateMachine> control_ptr() { return sm_; }
  const config::EquipmentDescriptor& descriptor() const { return descriptor_; }
  std::shared_ptr<std::weak_ptr<Connection>> active_conn() { return active_conn_; }

  // ---- outbound: report state to the host (thread-safe; each posts) --------
  void set_variable(uint32_t vid, secs2::Item value);
  void emit_event(uint32_t ceid);
  void set_alarm(uint32_t alid);
  void clear_alarm(uint32_t alid);

  // ---- reading mutable engine state from outside the io thread -------------
  // THE standard pattern for every read of mutable state (variable values,
  // alarm activity, spool depth, ...) from gRPC/binding threads: post the
  // read onto the io thread — the model's single owner — and wait with a
  // deadline. Always truthful (no cache invalidation), and the milliseconds
  // of latency are irrelevant at SECS message rates. Returns nullopt if the
  // io thread doesn't service the post in time (not running, or stalled).
  // Requires run()/run_async(); in poll() mode there is nobody to serve the
  // post, so a same-thread caller should read the model directly instead.
  template <typename Fn>
  auto read_sync(Fn&& fn,
                 std::chrono::milliseconds timeout = std::chrono::milliseconds(2000))
      -> std::optional<std::invoke_result_t<std::decay_t<Fn>&>> {
    using R = std::invoke_result_t<std::decay_t<Fn>&>;
    auto prom = std::make_shared<std::promise<R>>();
    auto fut = prom->get_future();
    asio::post(io_, [prom, fn = std::forward<Fn>(fn)]() mutable {
      prom->set_value(fn());
    });
    if (fut.wait_for(timeout) != std::future_status::ready) return std::nullopt;
    return fut.get();
  }

  // ---- host-command behaviour hook -----------------------------------------
  void on_command(std::string rcmd, HostCommandRegistry::Handler h) {
    model_->commands.set_handler(std::move(rcmd), std::move(h));
  }

  // ---- control state -------------------------------------------------------
  // Safe from any thread: reads an atomic mirror updated by a state-machine
  // observer, so gRPC threads never touch the FSM the io thread owns.
  ControlState control_state() const { return control_state_cache_.load(std::memory_order_relaxed); }

  // Observe control-state transitions (fires on the io thread). Survives the
  // primary set_state_change_handler that register_default_handlers installs.
  // Register before run()/run_async().
  void add_control_state_observer(ControlStateMachine::StateChangeHandler h) {
    sm_->add_state_change_handler(std::move(h));
  }

  // Observe HSMS link state: fires on the io thread with true when a session
  // reaches SELECTED, false when the connection closes. Register before
  // run()/run_async(). Foundation for the daemon's WatchHealth stream.
  using LinkObserver = std::function<void(bool selected)>;
  void add_link_observer(LinkObserver h) { link_observers_.push_back(std::move(h)); }

  // Deliver a primary to the host, or spool it if there's no SELECTED session.
  // Call on the io thread (e.g. from a router handler or a posted emitter).
  // Returns false if dropped (stream not spoolable and no host).
  bool deliver_or_spool(secs2::Message msg, const std::string& what);

  // ---- lifecycle -----------------------------------------------------------
  void run();        // start accepting + run the io_context (blocks)
  void run_async();  // run the io_context on a background thread
  void poll();       // drain ready handlers without blocking (tests)
  void stop();

 private:
  void wire_connection();

  asio::io_context io_;
  std::shared_ptr<EquipmentDataModel> model_;
  std::function<void(const std::string&)> log_;
  std::shared_ptr<std::weak_ptr<Connection>> active_conn_;
  std::shared_ptr<ControlStateMachine> sm_;
  config::EquipmentDescriptor descriptor_;
  std::unique_ptr<Server> server_;
  Router router_;
  std::atomic<ControlState> control_state_cache_{ControlState::HostOffline};
  std::vector<LinkObserver> link_observers_;
  std::optional<asio::executor_work_guard<asio::io_context::executor_type>> work_;
  std::thread io_thread_;
};

}  // namespace secsgem::gem