// Copyright 2023 Dolphin Emulator Project
// SPDX-License-Identifier: GPL-2.0-or-later

#pragma once

#include "Common/Logging/Log.h"
#include "Common/StringLiteral.h"

#include <functional>
#include <memory>
#include <string>
#include <string_view>
#include <vector>

// A hookable event system.

// Define Events in a header as:
//
//     using MyLoveyEvent = Event<"My lovely event", std::string>;
//
// Register listeners anywhere you need them as:
//    EventHook myHook = MyLoveyEvent::Register([](std::string foo) {
//       // Do something
//   }, "Name of the hook");
//
// The hook will be automatically unregistered when the EventHook object goes out of scope.
// Trigger events by doing:
//
//   MyLoveyEvent::Trigger("Hello world");
//

struct HookBase
{
  virtual ~HookBase() = default;
};

using EventHook = std::unique_ptr<HookBase>;

template<StringLiteral EventName, typename... CallbackArgs>
class Event
{
public:
  using CallbackType = std::function<void(CallbackArgs...)>;

private:
  struct HookImpl : public HookBase
  {
    ~HookImpl() override { Event::Remove(this); }
    HookImpl(CallbackType callback, std::string name) : m_fn(callback), m_name(name){ }
    CallbackType m_fn;
    std::string m_name;
  };
public:

  // Returns a handle that will unregister the listener when destroyed.
  static EventHook Register(CallbackType callback, std::string name)
  {
    DEBUG_LOG_FMT(COMMON, "Registering {} handler at {} event hook", name, EventName.value);
    auto handle = std::make_unique<HookImpl>(callback, name);
    m_listeners.push_back(handle.get());
    return handle;
  }

  static void Trigger(CallbackArgs... args)
  {
    for (auto& handle : m_listeners)
      handle->m_fn(args...);
  }

private:
  static void Remove(HookImpl* handle)
  {
    auto it = std::find(m_listeners.begin(), m_listeners.end(), handle);
    if (it != m_listeners.end())
      m_listeners.erase(it);
  }

  inline static std::vector<HookImpl*> m_listeners = {};
};