summaryrefslogtreecommitdiffstats
path: root/StackSet.hs
blob: 1cf205d43fd40639f2628675b8dc5e07ea59ce09 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
-----------------------------------------------------------------------------
-- |
-- Module      :  StackSet
-- Copyright   :  (c) Don Stewart 2007
-- License     :  BSD3-style (see LICENSE)
-- 
-- Maintainer  :  dons@cse.unsw.edu.au
-- Stability   :  stable
-- Portability :  portable, needs GHC 6.6
--
-----------------------------------------------------------------------------
--
-- The 'StackSet' data type encodes a set of stacks. A given stack in the
-- set is always current. Elements may appear only once in the entire
-- stack set.
--
-- A StackSet provides a nice data structure for multiscreen
-- window managers, where each screen has a stack of windows, and a window
-- may be on only 1 screen at any given time.
--

module StackSet {- everything -} where

import Data.Maybe
import qualified Data.List     as L (nub,delete)
import qualified Data.Map      as M
import qualified Data.IntMap   as I

------------------------------------------------------------------------

-- | The StackSet data structure. A table of stacks, with a current pointer
data StackSet a =
    StackSet
        { current:: {-# UNPACK #-} !Int             -- ^ the currently visible stack
        , stacks :: {-# UNPACK #-} !(I.IntMap [a])  -- ^ the separate stacks
        , cache  :: {-# UNPACK #-} !(M.Map a Int)   -- ^ a cache of windows back to their stacks
        } deriving Eq

instance Show a => Show (StackSet a) where
    showsPrec p s r = showsPrec p (show . toList $ s) r

-- Ord a constraint on 'a' as we use it as a key.
--
-- The cache is used to check on insertion that we don't already have
-- this window managed on another stack

------------------------------------------------------------------------

-- | /O(n)/. Create a new empty stacks of size 'n', indexed from 0. The
-- 0-indexed stack will be current.
empty :: Int -> StackSet a
empty n = StackSet { current = 0
                   , stacks  = I.fromList (zip [0..n-1] (repeat []))
                   , cache   = M.empty }

-- | /O(log w)/. True if x is somewhere in the StackSet
member :: Ord a => a -> StackSet a -> Bool
member a w = M.member a (cache w)

-- | /O(n)/. Number of stacks
size :: StackSet a -> Int
size = I.size . stacks

------------------------------------------------------------------------

-- | fromList. Build a new StackSet from a list of list of elements
-- If there are duplicates in the list, the last occurence wins.
fromList :: Ord a => (Int,[[a]]) -> StackSet a
fromList (_,[]) = error "Cannot build a StackSet from an empty list"

fromList (n,xs) | n < 0 || n >= length xs
                = error $ "Cursor index is out of range: " ++ show (n, length xs)

fromList (o,xs) = view o $ foldr (\(i,ys) s ->
                                foldr (\a t -> insert a i t) s ys)
                                    (empty (length xs)) (zip [0..] xs)

-- | toList. Flatten a stackset to a list of lists
toList  :: StackSet a -> (Int,[[a]])
toList x = (current x, map snd $ I.toList (stacks x))

-- | Push. Insert an element onto the top of the current stack. 
-- If the element is already in the current stack, it is moved to the top.
-- If the element is managed on another stack, it is removed from that
-- stack first.
push :: Ord a => a -> StackSet a -> StackSet a
push k w = insert k (current w) w

-- | /O(log s)/. Extract the element on the top of the current stack. If no such
-- element exists, Nothing is returned.
peek :: StackSet a -> Maybe a
peek w = listToMaybe $ index (current w) w

-- | /O(log s)/. Index. Extract the stack at index 'n'.
-- If the index is invalid, an exception is thrown.
index :: Int -> StackSet a -> [a]
index k w = fromJust (I.lookup k (stacks w))

-- | /O(1)/. view. Set the stack specified by the Int argument as being the
-- current StackSet. If the index is out of range an exception is thrown.
view :: Int -> StackSet a -> StackSet a
view n w | n >= 0 && n < I.size (stacks w) = w { current = n }
         | otherwise                       = error $ "view: index out of bounds: " ++ show n

-- | /O(log n)/. rotate. cycle the current window list up or down.
--
--  rotate EQ   -->  [5,6,7,8,1,2,3,4]
--  rotate GT   -->  [6,7,8,1,2,3,4,5]
--  rotate LT   -->  [4,5,6,7,8,1,2,3]
--
--  where xs = [5..8] ++ [1..4]
--
rotate :: Ordering -> StackSet a -> StackSet a
rotate o w = w { stacks = I.adjust rot (current w) (stacks w) }
    where rot s = take l . drop offset . cycle $ s
           where n      = fromEnum o - 1
                 l      = length s
                 offset = if n < 0 then l + n else n

-- | /O(log n)/. shift. move the client on top of the current stack to
-- the top of stack 'n'. If the stack to move to is not valid, and
-- exception is thrown.
--
shift :: Ord a => Int -> StackSet a -> StackSet a
shift n w = maybe w (\k -> insert k n (delete k w)) (peek w)

-- | /O(log n)/. Insert an element onto the top of stack 'n'.
-- If the element is already in the stack 'n', it is moved to the top.
-- If the element exists on another stack, it is removed from that stack.
-- If the index is wrong an exception is thrown.
--
insert :: Ord a => a -> Int -> StackSet a -> StackSet a
insert k n old = new { cache  = M.insert k n (cache new)
                     , stacks = I.adjust (L.nub . (k:)) n (stacks new) }
    where new = delete k old

-- | /O(log n)/. Delete an element entirely from from the StackSet.
-- This can be used to ensure that a given element is not managed elsewhere.
-- If the element doesn't exist, the original StackSet is returned unmodified.
delete :: Ord a => a -> StackSet a -> StackSet a
delete k w = maybe w tweak (M.lookup k (cache w))
  where tweak i = w { cache  = M.delete k (cache w)
                    , stacks = I.adjust (L.delete k) i (stacks w) }