/*
  SCHEDULER.hpp  -  coordination of render activities under timing and dependency constraints

  Copyright (C)         Lumiera.org
    2023,               Hermann Vosseler <Ichthyostega@web.de>

  This program is free software; you can redistribute it and/or
  modify it under the terms of the GNU General Public License as
  published by the Free Software Foundation; either version 2 of
  the License, or (at your option) any later version.

  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with this program; if not, write to the Free Software
  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

*/


/** @file scheduler.hpp
 ** Service for coordination and dispatch of render activities.
 ** The implementation of scheduling services is provided by an integration
 ** of two layers of functionality:
 ** - Layer-1 allows to enqueue and prioritise render activity records
 ** - Layer-2 connects and coordinates activities to conduct complex calculations 
 ** 
 ** @see SchedulerUsage_test Component integration test
 ** @see scheduler.cpp implementation details
 ** @see SchedulerInvocation Layer-1
 ** @see SchedulerCommutator Layer-2
 ** 
 ** @todo WIP-WIP-WIP 6/2023 »Playback Vertical Slice«
 ** 
 */


#ifndef SRC_VAULT_GEAR_SCHEDULER_H_
#define SRC_VAULT_GEAR_SCHEDULER_H_


#include "lib/error.hpp"
#include "vault/gear/block-flow.hpp"
#include "vault/gear/work-force.hpp"
#include "vault/gear/activity-lang.hpp"
#include "vault/gear/scheduler-commutator.hpp"
#include "vault/gear/scheduler-invocation.hpp"
#include "vault/gear/load-controller.hpp"
#include "vault/gear/engine-observer.hpp"
//#include "lib/symbol.hpp"
#include  "lib/nocopy.hpp"
//#include "lib/util.hpp"

//#include <string>


namespace vault{
namespace gear {
  
//  using util::isnil;
//  using std::string;
  
    namespace { // Scheduler default config
      
      const auto   IDLE_WAIT = 20ms;           ///< sleep-recheck cycle for workers deemed _idle_
      const size_t DISMISS_CYCLES = 100;       ///< number of wait cycles before an idle worker terminates completely
      Offset POLL_WAIT_DELAY{FSecs(1,1000)};   ///< delay until re-evaluating a condition previously found unsatisfied
    }
  
  
  
  
  /******************************************************//**
   * »Scheduler-Service« : coordinate render activities.
   * @todo WIP-WIP 6/2023
   * @see BlockFlow
   * @see SchedulerUsage_test
   */
  class Scheduler
    : util::NonCopyable
    {
      /** Binding of worker callbacks to the scheduler implementation */
      struct Setup : work::Config
        {
          Scheduler& scheduler;
          activity::Proc doWork() { return scheduler.getWork();          }
          void finalHook (bool _) { scheduler.handleWorkerTermination(_);}
        };
      
      
      SchedulerInvocation layer1_;
      SchedulerCommutator layer2_;
      WorkForce<Setup> workForce_;
      
      ActivityLang activityLang_;
      LoadController loadControl_;
      EngineObserver& engineObserver_;
      
      
    public:
      Scheduler (BlockFlowAlloc& activityAllocator
                ,EngineObserver& engineObserver)
        : layer1_{}
        , layer2_{}
        , workForce_{Setup{IDLE_WAIT, DISMISS_CYCLES, *this}}
        , activityLang_{activityAllocator}
        , loadControl_{activityAllocator}
        , engineObserver_{engineObserver}
        { }
      
      
      /**
       * 
       */
      void
      terminateProcessing()
        {
          UNIMPLEMENTED("suicide");
        }
      
      
      /**
       * 
       */
      double
      getLoadIndicator()
        {
          UNIMPLEMENTED("load indicator");
        }
      
      
      /**
       * 
       */
      void
      seedCalcStream()
        {
          UNIMPLEMENTED("get it going");
        }
      
      
      /**
       * 
       */
      void
      buildJob()
        {
          UNIMPLEMENTED("wrap the ActivityTerm");
        }
      
      
      /**
       * 
       */
      activity::Proc
      getWork()
        {
          UNIMPLEMENTED("the Worker-Funkction");
        }
      
    private:
      void
      handleWorkerTermination (bool isFailure)
        {
          UNIMPLEMENTED("die harder");
        }
      
      
      /** @internal expose a binding for Activity execution */
      class ExecutionCtx;
    };
  
  
  /**
   * @remark when due, the scheduled Activities are performed within the
   *  [Activity-Language execution environment](\ref ActivityLang::dispatchChain());
   *  some aspects of Activity _activation_ however require external functionality,
   *  which — for the purpose of language definition — was abstracted as _Execution-context._
   *  The implementation of these binding functions fills in relevant external effects and
   *  is in fact supplied by the implementation internals of the scheduler itself.   
   */
  class Scheduler::ExecutionCtx
    : private Scheduler
    {
    public:
      static ExecutionCtx&
      from (Scheduler& self)
      {
        return static_cast<ExecutionCtx&> (self);
      }
      
      /* ==== Implementation of the Concept ExecutionCtx ==== */
      
      /** λ-post: */
      activity::Proc
      post (Time when, Activity& chain, ExecutionCtx& ctx)
        {
          return layer2_.postDispatch (&chain, when, ctx, layer1_);
        }
      
      void
      work (Time, size_t)
        {
          UNIMPLEMENTED ("λ-work");
        }
      
      void
      done (Time, size_t)
        {
          UNIMPLEMENTED ("λ-done");
        }
      
      activity::Proc
      tick (Time)
        {
          UNIMPLEMENTED ("λ-tick");
        }
      
      Offset
      getWaitDelay()
        {
          return POLL_WAIT_DELAY;
        }
      
      Time
      getSchedTime()
        {
          UNIMPLEMENTED ("access scheduler Time");
        }
    };
  
  
  
  
}} // namespace vault::gear
#endif /*SRC_VAULT_GEAR_SCHEDULER_H_*/