#pragma once

#include <cstdint>
#include <functional>
#include <optional>
#include <string>
#include <vector>

#include "secsgem/gem/handler_slot.hpp"

namespace secsgem::gem {

// E30 §6.2 Control State Model.
enum class ControlState {
  EquipmentOffline,
  AttemptOnline,
  HostOffline,
  OnlineLocal,
  OnlineRemote,
};

const char* control_state_name(ControlState s);
std::optional<ControlState> parse_control_state(const std::string& s);
bool is_online(ControlState s);

enum class ControlEvent {
  OperatorSwitchOnline,
  OperatorSwitchOffline,
  OperatorSwitchLocal,
  OperatorSwitchRemote,
  AttemptComplete,
  AttemptFailed,
  HostRequestOnline,
  HostRequestOffline,
};

const char* control_event_name(ControlEvent e);
std::optional<ControlEvent> parse_control_event(const std::string& s);

enum class OnlineAck : uint8_t {
  Accept = 0,
  NotAccept = 1,
  AlreadyOnline = 2,
};

enum class OfflineAck : uint8_t {
  Accept = 0,
};

enum class CommAck : uint8_t {
  Accept = 0,
  Denied = 1,
};

// One row of the control-state transition table (E30 §6.2 + extensions).
// `to` and `then` are both optional: a row may produce no transition (e.g.
// host_request_online while already OnlineRemote — ack only); a row may also
// chain straight through the transient AttemptOnline state via `then`.
// `ack_code` is the raw uint8_t carried by S1F18 (ONLACK) or S1F16 (OFLACK);
// its interpretation depends on the triggering event.
struct ControlTransition {
  ControlState from;
  ControlEvent on;
  std::optional<ControlState> to;
  std::optional<ControlState> then;
  std::optional<uint8_t> ack_code;
};

// Pure data table — no behaviour. Lookup is first-match on (from, on).
class ControlTransitionTable {
 public:
  void add(ControlTransition row);
  const ControlTransition* find(ControlState from, ControlEvent on) const;
  std::size_t size() const { return rows_.size(); }
  const std::vector<ControlTransition>& rows() const { return rows_; }

  // Built-in default table, matching data/control_state.yaml exactly.
  // Used by tests so they don't depend on the YAML file being present.
  static ControlTransitionTable default_table();

 private:
  std::vector<ControlTransition> rows_;
};

// The E30 control state machine, driven by a transition table. All
// behavioural rules live in the table; this class is just the engine.
class ControlStateMachine {
 public:
  using StateChangeHandler =
      std::function<void(ControlState from, ControlState to, ControlEvent trigger)>;

  ControlStateMachine();
  explicit ControlStateMachine(ControlTransitionTable table,
                               ControlState initial = ControlState::HostOffline);

  ControlState state() const { return state_; }
  bool online() const { return is_online(state_); }

  // Replaces the primary handler (legacy single-slot semantics).
  void set_state_change_handler(StateChangeHandler h) { on_change_ = std::move(h); }
  // Appends an observer that survives set_state_change_handler calls.
  void add_state_change_handler(StateChangeHandler h) { on_change_.add(std::move(h)); }

  // Operator actions. Return true if a transition (or self-ack) was found.
  bool operator_online();
  bool operator_offline();
  bool operator_local();
  bool operator_remote();

  // Host requests. Return the ack code from the matching table row.
  OnlineAck on_host_request_online();
  OfflineAck on_host_request_offline();

 private:
  // Apply the matching row (if any) for (state_, event); returns the row.
  const ControlTransition* fire(ControlEvent on);
  void transition(ControlState next, ControlEvent trigger);

  ControlTransitionTable table_;
  ControlState state_;
  HandlerSlot<ControlState, ControlState, ControlEvent> on_change_;
};

}  // namespace secsgem::gem