//========= Copyright Valve Corporation, All rights reserved. ============//
//
// Purpose: An application framework
//
// $Revision: $
// $NoKeywords: $
//=============================================================================//

#ifndef IAPPSYSTEM_H
#define IAPPSYSTEM_H

#ifdef _WIN32
#pragma once
#endif

#include "../tier1/interface.h"

//-----------------------------------------------------------------------------
// Client systems are singleton objects in the client codebase responsible for
// various tasks
// The order in which the client systems appear in this list are the
// order in which they are initialized and updated. They are shut down in
// reverse order from which they are initialized.
//-----------------------------------------------------------------------------

enum InitReturnVal_t {
    INIT_FAILED = 0,
    INIT_OK,

    INIT_LAST_VAL,
};

abstract_class IAppSystem {
   public:
    // Here's where the app systems get to learn about each other
    virtual bool Connect(CreateInterfaceFn factory) = 0;
    virtual void Disconnect() = 0;

    // Here's where systems can access other interfaces implemented by this
    // object Returns NULL if it doesn't implement the requested interface
    virtual void *QueryInterface(const char *pInterfaceName) = 0;

    // Init, shutdown
    virtual InitReturnVal_t Init() = 0;
    virtual void Shutdown() = 0;
};

//-----------------------------------------------------------------------------
// Helper empty implementation of an IAppSystem
//-----------------------------------------------------------------------------
template <class IInterface>
class CBaseAppSystem : public IInterface {
   public:
    // Here's where the app systems get to learn about each other
    virtual bool Connect(CreateInterfaceFn factory) { return true; }
    virtual void Disconnect() {}

    // Here's where systems can access other interfaces implemented by this
    // object Returns NULL if it doesn't implement the requested interface
    virtual void *QueryInterface(const char *pInterfaceName) { return NULL; }

    // Init, shutdown
    virtual InitReturnVal_t Init() { return INIT_OK; }
    virtual void Shutdown() {}
};

//-----------------------------------------------------------------------------
// Helper implementation of an IAppSystem for tier0
//-----------------------------------------------------------------------------
template <class IInterface>
class CTier0AppSystem : public CBaseAppSystem<IInterface> {
   public:
    CTier0AppSystem(bool bIsPrimaryAppSystem = true) {
        m_bIsPrimaryAppSystem = bIsPrimaryAppSystem;
    }

   protected:
    // NOTE: a single DLL may have multiple AppSystems it's trying to
    // expose. If this is true, you must return true from only
    // one of those AppSystems; not doing so will cause all static
    // libraries connected to it to connect/disconnect multiple times

    // NOTE: We don't do this as a virtual function to avoid
    // having to up the version on all interfaces
    bool IsPrimaryAppSystem() { return m_bIsPrimaryAppSystem; }

   private:
    bool m_bIsPrimaryAppSystem;
};

//-----------------------------------------------------------------------------
// This is the version of IAppSystem shipped 10/15/04
// NOTE: Never change this!!!
//-----------------------------------------------------------------------------
abstract_class IAppSystemV0 {
   public:
    // Here's where the app systems get to learn about each other
    virtual bool Connect(CreateInterfaceFn factory) = 0;
    virtual void Disconnect() = 0;

    // Here's where systems can access other interfaces implemented by this
    // object Returns NULL if it doesn't implement the requested interface
    virtual void *QueryInterface(const char *pInterfaceName) = 0;

    // Init, shutdown
    virtual InitReturnVal_t Init() = 0;
    virtual void Shutdown() = 0;
};

#endif  // IAPPSYSTEM_H