/************************************************************************************************************************
*System module.
*/
module ecs.system;

import ecs.entity;
import ecs.manager;

/************************************************************************************************************************
*System contain data required to proper glue EntityManager with Systems.
*System callbacks:
*<br/>-void onUpdate(EntitesData);
*<br/>-void onEnable()
*<br/>-void onDisable();
*<br/>-bool onBegin();
*<br/>-void onEnd();
*<br/>-void onCreate()
*<br/>-void onDestroy();
*<br/>-void onAddEntity(EntitesData);
*<br/>-void onRemoveEntity(EntitiesData);
*/
struct System
{

    /************************************************************************************************************************
    *Check if system is enabled.
    */
    export bool enabled() nothrow @nogc
    {
        return m_enabled;
    }

    /************************************************************************************************************************
    *Enable system. If actually it is enabled function do nothing.
    */
    export void enable() nothrow @nogc
    {
        if (!m_enabled && m_enable)
            (cast(void function(void*) nothrow @nogc) m_enable)(m_system_pointer);
        m_enabled = true;
    }

    /************************************************************************************************************************
    *Disable system. If actually it is disabled function do nothing.
    */
    export void disable() nothrow @nogc
    {
        if (m_enabled && m_disable)
            (cast(void function(void*) nothrow @nogc) m_disable)(m_system_pointer);
        m_enabled = false;
    }

    /************************************************************************************************************************
    *Get system priority.
    */
    export int priority() nothrow @nogc
    {
        return m_priority;
    }

    /************************************************************************************************************************
    *Get system priority.
    */
    export bool execute() nothrow @nogc
    {
        return m_execute;
    }

    /************************************************************************************************************************
    *Get system priority.
    */
    export ushort id() nothrow @nogc
    {
        return m_id;
    }

    struct EventCaller
    {
        ushort id;
        void* callback;
    }

package:

    ///should system be executed in current update?
    bool m_execute = true;
    ///system id
    ushort m_id;

    ///should system update and catch events?
    bool m_enabled = false;
    ///system priority
    int m_priority;
    ///pointer to system implementation
    void* m_system_pointer;
    ///system pass index
    int m_pass;

    ///system name
    const(char)[] name;

    ///required components
    ushort[] m_components;
    ///excluded components
    ushort[] m_excluded_components;
    ///optional components
    ushort[] m_optional_components;

    EntityManager.Job[] jobs;

    //System*[] m_dependencies;
    ushort[] m_read_only_components;
    ushort[] m_modified_components;

    EventCaller[] m_event_callers;

    //void function(ref EntityManager.CallData data) m_update;
    void* m_update; ///workaroud for DMD bug with upper line

    /*void function(void* system_pointer) m_enable;
    void function(void* system_pointer) m_disable;

    void function(void* system_pointer) m_create;
    void function(void* system_pointer) m_destroy;

    void function(void* system_pointer) m_begin;
    void function(void* system_pointer) m_end;*/

    void* m_enable;
    void* m_disable;

    void* m_create;
    void* m_destroy;

    void* m_begin;
    void* m_end;

    void* m_add_entity;
    void* m_remove_entity;

    //void function(ref EntityManager.CallData data) m_initialize;
    //void function(ref EntityManager.CallData data) m_deinitilize;
    void* m_initialize;
    void* m_deinitilize;
}