#include "secsgem/gem/ept_state.hpp"

namespace secsgem::gem {

static_assert(static_cast<uint8_t>(EptState::NonScheduledTime)    == 0);
static_assert(static_cast<uint8_t>(EptState::ScheduledDowntime)   == 1);
static_assert(static_cast<uint8_t>(EptState::UnscheduledDowntime) == 2);
static_assert(static_cast<uint8_t>(EptState::Engineering)         == 3);
static_assert(static_cast<uint8_t>(EptState::Standby)             == 4);
static_assert(static_cast<uint8_t>(EptState::Productive)          == 5);

const char* ept_state_name(EptState s) {
  switch (s) {
    case EptState::NonScheduledTime:    return "NonScheduledTime";
    case EptState::ScheduledDowntime:   return "ScheduledDowntime";
    case EptState::UnscheduledDowntime: return "UnscheduledDowntime";
    case EptState::Engineering:         return "Engineering";
    case EptState::Standby:             return "Standby";
    case EptState::Productive:          return "Productive";
    case EptState::NoState:             return "NoState";
  }
  return "?";
}

std::optional<EptState> parse_ept_state(const std::string& s) {
  if (s == "NonScheduledTime")    return EptState::NonScheduledTime;
  if (s == "ScheduledDowntime")   return EptState::ScheduledDowntime;
  if (s == "UnscheduledDowntime") return EptState::UnscheduledDowntime;
  if (s == "Engineering")         return EptState::Engineering;
  if (s == "Standby")             return EptState::Standby;
  if (s == "Productive")          return EptState::Productive;
  if (s == "NoState")             return EptState::NoState;
  return std::nullopt;
}

const char* ept_event_name(EptEvent e) {
  switch (e) {
    case EptEvent::EnterNonScheduled:    return "EnterNonScheduled";
    case EptEvent::EnterScheduledDown:   return "EnterScheduledDown";
    case EptEvent::EnterUnscheduledDown: return "EnterUnscheduledDown";
    case EptEvent::EnterEngineering:     return "EnterEngineering";
    case EptEvent::EnterStandby:         return "EnterStandby";
    case EptEvent::EnterProductive:      return "EnterProductive";
  }
  return "?";
}

namespace {
// Each event has exactly one target state regardless of source.
EptState target_of(EptEvent e) {
  switch (e) {
    case EptEvent::EnterNonScheduled:    return EptState::NonScheduledTime;
    case EptEvent::EnterScheduledDown:   return EptState::ScheduledDowntime;
    case EptEvent::EnterUnscheduledDown: return EptState::UnscheduledDowntime;
    case EptEvent::EnterEngineering:     return EptState::Engineering;
    case EptEvent::EnterStandby:         return EptState::Standby;
    case EptEvent::EnterProductive:      return EptState::Productive;
  }
  return EptState::NoState;
}
}  // namespace

EptTable default_ept_table() {
  EptTable t;
  // Cross-product: every source state accepts every event.  The FSM is
  // a classifier, not a strict workflow, so all transitions are legal.
  for (auto src : {EptState::NonScheduledTime, EptState::ScheduledDowntime,
                   EptState::UnscheduledDowntime, EptState::Engineering,
                   EptState::Standby, EptState::Productive}) {
    for (auto ev : {EptEvent::EnterNonScheduled, EptEvent::EnterScheduledDown,
                    EptEvent::EnterUnscheduledDown, EptEvent::EnterEngineering,
                    EptEvent::EnterStandby, EptEvent::EnterProductive}) {
      t.add({src, ev, target_of(ev), std::nullopt});
    }
  }
  return t;
}

EptStateMachine::EptStateMachine()
    : table_(default_ept_table()),
      entered_(std::chrono::steady_clock::now()),
      reset_anchor_(entered_) {}

bool EptStateMachine::on_event(EptEvent e) {
  const auto* row = table_.find(state_, e);
  if (!row) return false;
  if (row->to && *row->to != state_) {
    auto prev = state_;
    auto now = std::chrono::steady_clock::now();
    auto dwell = std::chrono::duration_cast<std::chrono::milliseconds>(
        now - entered_);
    buckets_[static_cast<size_t>(prev)] += dwell;
    state_   = *row->to;
    entered_ = now;
    if (on_change_) on_change_(prev, state_, e, dwell);
  }
  return true;
}

std::chrono::milliseconds EptStateMachine::accumulated(EptState s) const {
  const auto idx = static_cast<size_t>(s);
  if (idx >= buckets_.size()) return std::chrono::milliseconds{0};
  auto base = buckets_[idx];
  if (state_ == s) {
    const auto now = std::chrono::steady_clock::now();
    base += std::chrono::duration_cast<std::chrono::milliseconds>(now - entered_);
  }
  return base;
}

std::chrono::milliseconds EptStateMachine::total_elapsed() const {
  return std::chrono::duration_cast<std::chrono::milliseconds>(
      std::chrono::steady_clock::now() - reset_anchor_);
}

void EptStateMachine::reset_history() {
  buckets_.fill(std::chrono::milliseconds{0});
  const auto now = std::chrono::steady_clock::now();
  entered_      = now;
  reset_anchor_ = now;
}

}  // namespace secsgem::gem