#pragma once

#include <chrono>
#include <cstdint>
#include <functional>
#include <map>
#include <memory>
#include <string>
#include <utility>
#include <variant>
#include <vector>

#include "secsgem/gem/substrate_state.hpp"

namespace secsgem::gem {

// One entry in a substrate's per-axis transition log.  Holds the
// post-transition state on one axis (the other stays at NoState),
// the triggering event encoded back into the SubstrateEvent or
// SubstrateProcessingEvent enum (held discriminated by `is_processing`),
// the location string at the moment, and a steady_clock timestamp.
struct SubstrateHistoryEntry {
  std::chrono::steady_clock::time_point at;
  SubstrateState           location_to{SubstrateState::NoState};
  SubstrateProcessingState processing_to{SubstrateProcessingState::NoState};
  std::variant<SubstrateEvent, SubstrateProcessingEvent> event;
  std::string location_label;  // free-form location at the time of the event
};

struct Substrate {
  std::string substid;        // SUBSTID — E90 wafer identifier
  std::string carrierid;      // CARRIERID where this wafer originated
  uint8_t     slot = 0;       // 1-based slot in the source carrier
  std::string location;       // free-form: equipment-defined module name
  std::vector<SubstrateHistoryEntry> history;
  std::unique_ptr<SubstrateStateMachine> fsm;
};

class SubstrateStore {
 public:
  using LocationChangeHandler =
      std::function<void(const std::string& substid, SubstrateState from,
                         SubstrateState to, SubstrateEvent)>;
  using ProcessingChangeHandler =
      std::function<void(const std::string& substid,
                         SubstrateProcessingState from,
                         SubstrateProcessingState to,
                         SubstrateProcessingEvent)>;

  SubstrateStore() = default;
  SubstrateStore(const SubstrateStore&) = delete;
  SubstrateStore& operator=(const SubstrateStore&) = delete;
  SubstrateStore(SubstrateStore&&) = delete;
  SubstrateStore& operator=(SubstrateStore&&) = delete;

  void set_location_handler(LocationChangeHandler h)     { on_loc_ = std::move(h); }
  void set_processing_handler(ProcessingChangeHandler h) { on_proc_ = std::move(h); }

  enum class CreateResult { Created, Denied_AlreadyExists };

  // Cap per-substrate history retention to keep memory bounded.  0 ==
  // unlimited.  Default cap is 256 entries which comfortably covers a
  // typical wafer's lifecycle.
  void set_history_limit(std::size_t n) { history_limit_ = n; }
  std::size_t history_limit() const { return history_limit_; }

  CreateResult create(std::string substid, std::string carrierid = "",
                      uint8_t slot = 0) {
    if (subs_.count(substid)) return CreateResult::Denied_AlreadyExists;
    auto fsm = std::make_unique<SubstrateStateMachine>();
    const std::string id = substid;
    fsm->set_location_handler(
        [this, id](SubstrateState f, SubstrateState t, SubstrateEvent e) {
          record_history(id, t, SubstrateProcessingState::NoState, e);
          if (on_loc_) on_loc_(id, f, t, e);
        });
    fsm->set_processing_handler(
        [this, id](SubstrateProcessingState f, SubstrateProcessingState t,
                   SubstrateProcessingEvent e) {
          record_history(id, SubstrateState::NoState, t, e);
          if (on_proc_) on_proc_(id, f, t, e);
        });
    subs_.emplace(substid,
                  Substrate{substid, std::move(carrierid), slot, "",
                            {}, std::move(fsm)});
    return CreateResult::Created;
  }

  bool has(const std::string& id) const { return subs_.count(id) > 0; }
  const Substrate* get(const std::string& id) const {
    auto it = subs_.find(id);
    return it == subs_.end() ? nullptr : &it->second;
  }
  Substrate* get(const std::string& id) {
    auto it = subs_.find(id);
    return it == subs_.end() ? nullptr : &it->second;
  }

  bool fire_location_event(const std::string& id, SubstrateEvent e,
                           std::string new_location = "") {
    auto* s = get(id);
    if (!s) return false;
    if (!new_location.empty()) s->location = std::move(new_location);
    return s->fsm->on_location_event(e);
  }
  bool fire_processing_event(const std::string& id, SubstrateProcessingEvent e) {
    auto* s = get(id);
    return s && s->fsm->on_processing_event(e);
  }

  bool remove(const std::string& id) { return subs_.erase(id) > 0; }
  std::size_t size() const { return subs_.size(); }
  std::vector<std::string> ids() const {
    std::vector<std::string> out;
    out.reserve(subs_.size());
    for (const auto& kv : subs_) out.push_back(kv.first);
    return out;
  }

  const std::vector<SubstrateHistoryEntry>* history(const std::string& id) const {
    const auto* s = get(id);
    return s ? &s->history : nullptr;
  }

 private:
  template <typename Event>
  void record_history(const std::string& id, SubstrateState loc_to,
                      SubstrateProcessingState proc_to, Event ev) {
    auto* s = get(id);
    if (!s) return;
    SubstrateHistoryEntry entry;
    entry.at             = std::chrono::steady_clock::now();
    entry.location_to    = loc_to;
    entry.processing_to  = proc_to;
    entry.event          = ev;
    entry.location_label = s->location;
    s->history.push_back(std::move(entry));
    if (history_limit_ != 0 && s->history.size() > history_limit_) {
      // Drop the oldest entry; vector shift is fine for the small caps
      // we expect (default 256, typically a few dozen per substrate).
      s->history.erase(s->history.begin());
    }
  }

  std::map<std::string, Substrate> subs_;
  LocationChangeHandler   on_loc_;
  ProcessingChangeHandler on_proc_;
  std::size_t history_limit_ = 256;
};

}  // namespace secsgem::gem