{-# LANGUAGE FlexibleContexts #-}

-- |
-- Module     : Simulation.Aivika.Trans.Resource.Base
-- Copyright  : Copyright (c) 2009-2017, David Sorokin <david.sorokin@gmail.com>
-- License    : BSD3
-- Maintainer : David Sorokin <david.sorokin@gmail.com>
-- Stability  : experimental
-- Tested with: GHC 8.0.1
--
-- This module defines an optimised version of the resource 
-- which can be acquired and then released by the discontinuous 
-- process 'Process'. The resource can be either limited by 
-- the upper bound (run-time check), or it can have no upper bound. 
-- The latter is useful for modeling the infinite queue, for example.
--
-- The module is optimised in the sense that this kind of the resource
-- has neither additional signals, nor counters that would may slow
-- down the simulation.
--
module Simulation.Aivika.Trans.Resource.Base
       (-- * Resource Types
        FCFSResource,
        LCFSResource,
        SIROResource,
        PriorityResource,
        Resource,
        -- * Creating Resource
        newFCFSResource,
        newFCFSResourceWithMaxCount,
        newLCFSResource,
        newLCFSResourceWithMaxCount,
        newSIROResource,
        newSIROResourceWithMaxCount,
        newPriorityResource,
        newPriorityResourceWithMaxCount,
        newResource,
        newResourceWithMaxCount,
        -- * Resource Properties
        resourceStrategy,
        resourceMaxCount,
        resourceCount,
        -- * Requesting for and Releasing Resource
        requestResource,
        requestResourceWithPriority,
        tryRequestResourceWithinEvent,
        releaseResource,
        releaseResourceWithinEvent,
        usingResource,
        usingResourceWithPriority,
        -- * Altering Resource
        incResourceCount,
        decResourceCount) where

import Control.Monad
import Control.Monad.Trans
import Control.Exception

import Simulation.Aivika.Trans.Exception
import Simulation.Aivika.Trans.Ref.Base
import Simulation.Aivika.Trans.DES
import Simulation.Aivika.Trans.Internal.Specs
import Simulation.Aivika.Trans.Internal.Simulation
import Simulation.Aivika.Trans.Internal.Event
import Simulation.Aivika.Trans.Internal.Cont
import Simulation.Aivika.Trans.Internal.Process
import Simulation.Aivika.Trans.QueueStrategy

-- | The ordinary FCFS (First Come - First Serviced) resource.
type FCFSResource m = Resource m FCFS

-- | The ordinary LCFS (Last Come - First Serviced) resource.
type LCFSResource m = Resource m LCFS

-- | The SIRO (Serviced in Random Order) resource.
type SIROResource m = Resource m SIRO

-- | The resource with static priorities.
type PriorityResource m = Resource m StaticPriorities

-- | Represents the resource with strategy @s@ applied for queuing the requests.
data Resource m s = 
  Resource { resourceStrategy :: s,
             -- ^ Return the strategy applied for queuing the requests.
             resourceMaxCount :: Maybe Int,
             -- ^ Return the maximum count of the resource, where 'Nothing'
             -- means that the resource has no upper bound.
             resourceCountRef :: Ref m Int, 
             resourceWaitList :: StrategyQueue m s (FrozenCont m ()) }

-- | Create a new FCFS resource with the specified initial count which value becomes
-- the upper bound as well.
newFCFSResource :: MonadDES m
                   => Int
                   -- ^ the initial count (and maximal count too) of the resource
                   -> Simulation m (FCFSResource m)
{-# INLINABLE newFCFSResource #-}
newFCFSResource = newResource FCFS

-- | Create a new FCFS resource with the specified initial and maximum counts,
-- where 'Nothing' means that the resource has no upper bound.
newFCFSResourceWithMaxCount :: MonadDES m
                               => Int
                               -- ^ the initial count of the resource
                               -> Maybe Int
                               -- ^ the maximum count of the resource, which can be indefinite
                               -> Simulation m (FCFSResource m)
{-# INLINABLE newFCFSResourceWithMaxCount #-}
newFCFSResourceWithMaxCount = newResourceWithMaxCount FCFS

-- | Create a new LCFS resource with the specified initial count which value becomes
-- the upper bound as well.
newLCFSResource :: MonadDES m
                   => Int
                   -- ^ the initial count (and maximal count too) of the resource
                   -> Simulation m (LCFSResource m)
{-# INLINABLE newLCFSResource #-}
newLCFSResource = newResource LCFS

-- | Create a new LCFS resource with the specified initial and maximum counts,
-- where 'Nothing' means that the resource has no upper bound.
newLCFSResourceWithMaxCount :: MonadDES m
                               => Int
                               -- ^ the initial count of the resource
                               -> Maybe Int
                               -- ^ the maximum count of the resource, which can be indefinite
                               -> Simulation m (LCFSResource m)
{-# INLINABLE newLCFSResourceWithMaxCount #-}
newLCFSResourceWithMaxCount = newResourceWithMaxCount LCFS

-- | Create a new SIRO resource with the specified initial count which value becomes
-- the upper bound as well.
newSIROResource :: (MonadDES m, QueueStrategy m SIRO)
                   => Int
                   -- ^ the initial count (and maximal count too) of the resource
                   -> Simulation m (SIROResource m)
{-# INLINABLE newSIROResource #-}
newSIROResource = newResource SIRO

-- | Create a new SIRO resource with the specified initial and maximum counts,
-- where 'Nothing' means that the resource has no upper bound.
newSIROResourceWithMaxCount :: (MonadDES m, QueueStrategy m SIRO)
                               => Int
                               -- ^ the initial count of the resource
                               -> Maybe Int
                               -- ^ the maximum count of the resource, which can be indefinite
                               -> Simulation m (SIROResource m)
{-# INLINABLE newSIROResourceWithMaxCount #-}
newSIROResourceWithMaxCount = newResourceWithMaxCount SIRO

-- | Create a new priority resource with the specified initial count which value becomes
-- the upper bound as well.
newPriorityResource :: (MonadDES m, QueueStrategy m StaticPriorities)
                       => Int
                       -- ^ the initial count (and maximal count too) of the resource
                       -> Simulation m (PriorityResource m)
{-# INLINABLE newPriorityResource #-}
newPriorityResource = newResource StaticPriorities

-- | Create a new priority resource with the specified initial and maximum counts,
-- where 'Nothing' means that the resource has no upper bound.
newPriorityResourceWithMaxCount :: (MonadDES m, QueueStrategy m StaticPriorities)
                                   => Int
                                   -- ^ the initial count of the resource
                                   -> Maybe Int
                                   -- ^ the maximum count of the resource, which can be indefinite
                                   -> Simulation m (PriorityResource m)
{-# INLINABLE newPriorityResourceWithMaxCount #-}
newPriorityResourceWithMaxCount = newResourceWithMaxCount StaticPriorities

-- | Create a new resource with the specified queue strategy and initial count.
-- The last value becomes the upper bound as well.
newResource :: (MonadDES m, QueueStrategy m s)
               => s
               -- ^ the strategy for managing the queuing requests
               -> Int
               -- ^ the initial count (and maximal count too) of the resource
               -> Simulation m (Resource m s)
{-# INLINABLE newResource #-}
newResource s count =
  Simulation $ \r ->
  do when (count < 0) $
       throwComp $
       SimulationRetry $
       "The resource count cannot be negative: " ++
       "newResource."
     countRef <- invokeSimulation r $ newRef count
     waitList <- invokeSimulation r $ newStrategyQueue s
     return Resource { resourceStrategy = s,
                       resourceMaxCount = Just count,
                       resourceCountRef = countRef,
                       resourceWaitList = waitList }

-- | Create a new resource with the specified queue strategy, initial and maximum counts,
-- where 'Nothing' means that the resource has no upper bound.
newResourceWithMaxCount :: (MonadDES m, QueueStrategy m s)
                           => s
                           -- ^ the strategy for managing the queuing requests
                           -> Int
                           -- ^ the initial count of the resource
                           -> Maybe Int
                           -- ^ the maximum count of the resource, which can be indefinite
                           -> Simulation m (Resource m s)
{-# INLINABLE newResourceWithMaxCount #-}
newResourceWithMaxCount s count maxCount =
  Simulation $ \r ->
  do when (count < 0) $
       throwComp $
       SimulationRetry $
       "The resource count cannot be negative: " ++
       "newResourceWithMaxCount."
     case maxCount of
       Just maxCount | count > maxCount ->
         throwComp $
         SimulationRetry $
         "The resource count cannot be greater than " ++
         "its maximum value: newResourceWithMaxCount."
       _ ->
         return ()
     countRef <- invokeSimulation r $ newRef count
     waitList <- invokeSimulation r $ newStrategyQueue s
     return Resource { resourceStrategy = s,
                       resourceMaxCount = maxCount,
                       resourceCountRef = countRef,
                       resourceWaitList = waitList }

-- | Return the current count of the resource.
resourceCount :: MonadDES m => Resource m s -> Event m Int
{-# INLINABLE resourceCount #-}
resourceCount r =
  Event $ \p -> invokeEvent p $ readRef (resourceCountRef r)

-- | Request for the resource decreasing its count in case of success,
-- otherwise suspending the discontinuous process until some other 
-- process releases the resource.
requestResource :: (MonadDES m, EnqueueStrategy m s)
                   => Resource m s 
                   -- ^ the requested resource
                   -> Process m ()
{-# INLINABLE requestResource #-}
requestResource r =
  Process $ \pid ->
  Cont $ \c ->
  Event $ \p ->
  do a <- invokeEvent p $ readRef (resourceCountRef r)
     if a == 0 
       then do c <- invokeEvent p $
                    freezeContReentering c () $
                    invokeCont c $
                    invokeProcess pid $
                    requestResource r
               invokeEvent p $
                 strategyEnqueue (resourceWaitList r) c
       else do let a' = a - 1
               a' `seq` invokeEvent p $ writeRef (resourceCountRef r) a'
               invokeEvent p $ resumeCont c ()

-- | Request with the priority for the resource decreasing its count
-- in case of success, otherwise suspending the discontinuous process
-- until some other process releases the resource.
requestResourceWithPriority :: (MonadDES m, PriorityQueueStrategy m s p)
                               => Resource m s
                               -- ^ the requested resource
                               -> p
                               -- ^ the priority
                               -> Process m ()
{-# INLINABLE requestResourceWithPriority #-}
requestResourceWithPriority r priority =
  Process $ \pid ->
  Cont $ \c ->
  Event $ \p ->
  do a <- invokeEvent p $ readRef (resourceCountRef r)
     if a == 0 
       then do c <- invokeEvent p $
                    freezeContReentering c () $
                    invokeCont c $
                    invokeProcess pid $
                    requestResourceWithPriority r priority
               invokeEvent p $
                 strategyEnqueueWithPriority (resourceWaitList r) priority c
       else do let a' = a - 1
               a' `seq` invokeEvent p $ writeRef (resourceCountRef r) a'
               invokeEvent p $ resumeCont c ()

-- | Release the resource increasing its count and resuming one of the
-- previously suspended processes as possible.
releaseResource :: (MonadDES m, DequeueStrategy m s)
                   => Resource m s
                   -- ^ the resource to release
                   -> Process m ()
{-# INLINABLE releaseResource #-}
releaseResource r = 
  Process $ \_ ->
  Cont $ \c ->
  Event $ \p ->
  do invokeEvent p $ releaseResourceWithinEvent r
     invokeEvent p $ resumeCont c ()

-- | Release the resource increasing its count and resuming one of the
-- previously suspended processes as possible.
releaseResourceWithinEvent :: (MonadDES m, DequeueStrategy m s)
                              => Resource m s
                              -- ^ the resource to release
                              -> Event m ()
{-# INLINABLE releaseResourceWithinEvent #-}
releaseResourceWithinEvent r =
  Event $ \p ->
  do a <- invokeEvent p $ readRef (resourceCountRef r)
     let a' = a + 1
     case resourceMaxCount r of
       Just maxCount | a' > maxCount ->
         throwComp $
         SimulationRetry $
         "The resource count cannot be greater than " ++
         "its maximum value: releaseResourceWithinEvent."
       _ ->
         return ()
     f <- invokeEvent p $
          strategyQueueNull (resourceWaitList r)
     if f 
       then a' `seq` invokeEvent p $ writeRef (resourceCountRef r) a'
       else do c <- invokeEvent p $
                    strategyDequeue (resourceWaitList r)
               c <- invokeEvent p $ unfreezeCont c
               case c of
                 Nothing ->
                   invokeEvent p $ releaseResourceWithinEvent r
                 Just c  ->
                   invokeEvent p $ enqueueEvent (pointTime p) $ resumeCont c ()

-- | Try to request for the resource decreasing its count in case of success
-- and returning 'True' in the 'Event' monad; otherwise, returning 'False'.
tryRequestResourceWithinEvent :: MonadDES m
                                 => Resource m s
                                 -- ^ the resource which we try to request for
                                 -> Event m Bool
{-# INLINABLE tryRequestResourceWithinEvent #-}
tryRequestResourceWithinEvent r =
  Event $ \p ->
  do a <- invokeEvent p $ readRef (resourceCountRef r)
     if a == 0 
       then return False
       else do let a' = a - 1
               a' `seq` invokeEvent p $ writeRef (resourceCountRef r) a'
               return True
               
-- | Acquire the resource, perform some action and safely release the resource               
-- in the end, even if the 'IOException' was raised within the action. 
usingResource :: (MonadDES m, EnqueueStrategy m s)
                 => Resource m s
                 -- ^ the resource we are going to request for and then release in the end
                 -> Process m a
                 -- ^ the action we are going to apply having the resource
                 -> Process m a
                 -- ^ the result of the action
{-# INLINABLE usingResource #-}
usingResource r m =
  do requestResource r
     finallyProcess m $ releaseResource r

-- | Acquire the resource with the specified priority, perform some action and
-- safely release the resource in the end, even if the 'IOException' was raised
-- within the action.
usingResourceWithPriority :: (MonadDES m, PriorityQueueStrategy m s p)
                             => Resource m s
                             -- ^ the resource we are going to request for and then
                             -- release in the end
                             -> p
                             -- ^ the priority
                             -> Process m a
                             -- ^ the action we are going to apply having the resource
                             -> Process m a
                             -- ^ the result of the action
{-# INLINABLE usingResourceWithPriority #-}
usingResourceWithPriority r priority m =
  do requestResourceWithPriority r priority
     finallyProcess m $ releaseResource r

-- | Increase the count of available resource by the specified number,
-- invoking the awaiting processes as needed.
incResourceCount :: (MonadDES m, DequeueStrategy m s)
                    => Resource m s
                    -- ^ the resource
                    -> Int
                    -- ^ the increment for the resource count
                    -> Event m ()
{-# INLINABLE incResourceCount #-}
incResourceCount r n
  | n < 0     = throwEvent $ SimulationRetry "The increment cannot be negative: incResourceCount"
  | n == 0    = return ()
  | otherwise =
    do releaseResourceWithinEvent r
       incResourceCount r (n - 1)

-- | Decrease the count of available resource by the specified number,
-- waiting for the processes capturing the resource as needed.
decResourceCount :: (MonadDES m, EnqueueStrategy m s)
                    => Resource m s
                    -- ^ the resource
                    -> Int
                    -- ^ the decrement for the resource count
                    -> Process m ()
{-# INLINABLE decResourceCount #-}
decResourceCount r n
  | n < 0     = throwProcess $ SimulationRetry "The decrement cannot be negative: decResourceCount"
  | n == 0    = return ()
  | otherwise =
    do requestResource r
       decResourceCount r (n - 1)