From 223b1d8fbcc708a08cef347e750b2fa3ceb10bee Mon Sep 17 00:00:00 2001
From: Benjamin Barenblat <bbaren@google.com>
Date: Wed, 30 Sep 2020 12:42:32 -0400
Subject: xscreensaver-dbus, a bridge between D-Bus and xscreensaver

---
 src/Pool.hs | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)
 create mode 100644 src/Pool.hs

(limited to 'src/Pool.hs')

diff --git a/src/Pool.hs b/src/Pool.hs
new file mode 100644
index 0000000..8bb40eb
--- /dev/null
+++ b/src/Pool.hs
@@ -0,0 +1,55 @@
+-- Copyright 2020 Google LLC
+--
+-- Licensed under the Apache License, Version 2.0 (the "License"); you may not
+-- use this file except in compliance with the License. You may obtain a copy of
+-- the License at
+--
+--     https://www.apache.org/licenses/LICENSE-2.0
+--
+-- Unless required by applicable law or agreed to in writing, software
+-- distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+-- WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+-- License for the specific language governing permissions and limitations under
+-- the License.
+
+{-# OPTIONS_GHC -Wno-missing-import-lists #-}
+module Pool                                                                                                           
+  ( Pool                                                                                                              
+  , empty, withReserved                                                                                               
+  , null                                                                                                              
+  , take, put                                                                                                         
+  ) where                                                                                                             
+                                                                                                                      
+import Prelude hiding (null, take)                                                                                    
+                                                                                                                      
+import Control.Monad (guard)                                                                                          
+import qualified Data.List as List                                                                                    
+import Data.Set (Set)                                                                                                 
+import qualified Data.Set as Set                                                                                      
+                                                                                                                      
+data Pool a = Pool { reserved :: Set a, taken :: Set a } deriving (Eq, Show)                                          
+                                                                                                                      
+empty :: Pool a                                                                                                       
+empty = withReserved Set.empty                                                                                        
+                                                                                                                      
+withReserved :: Set a -> Pool a                                                                                       
+withReserved xs = Pool { reserved = xs, taken = Set.empty }                                                           
+                                                                                                                      
+null :: Pool a -> Bool                                                                                                
+null p = Set.null (taken p)                                                                                           
+                                                                                                                      
+take :: (Bounded a, Enum a, Ord a) => Pool a -> Maybe (a, Pool a)                                                     
+take p = do                                                                                                           
+  x <- nextAvailable p                                                                                                
+  return (x, p { taken = Set.insert x (taken p) })                                                                    
+                                                                                                                      
+nextAvailable :: (Bounded a, Enum a, Ord a) => Pool a -> Maybe a                                                      
+nextAvailable p = List.find (`Set.notMember` unavailable p) (enumFrom minBound)                                       
+                                                                                                                      
+unavailable :: (Ord a) => Pool a -> Set a                                                                             
+unavailable p = reserved p `Set.union` taken p                                                                        
+                                                                                                                      
+put :: Ord a => a -> Pool a -> Maybe (Pool a)                                                                         
+put x p = do                                                                                                          
+  guard $ x `Set.member` taken p                                                                                      
+  return $ p { taken = Set.delete x (taken p) }                                                                       
-- 
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