{-| Module abstracting the peer map implementation.

This is abstracted separately since the speed of peermap updates can
be a significant part of the total runtime, and as such changing the
implementation should be easy in case it's needed.

-}

{-

Copyright (C) 2009, 2011 Google Inc.
All rights reserved.

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modification, are permitted provided that the following conditions are
met:

1. Redistributions of source code must retain the above copyright notice,
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2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

-}

module Ganeti.HTools.PeerMap
  ( PeerMap
  , Key
  , Elem
  , empty
  , accumArray
  , Ganeti.HTools.PeerMap.find
  , add
  , remove
  , maxElem
  , sumElems
  ) where

import Data.Maybe (fromMaybe)
import Data.List
import Data.Ord (comparing)

import Ganeti.HTools.Types

-- * Type definitions

-- | Our key type.
type Key = Ndx

-- | Our element type.

type Elem = Int

-- | The definition of a peer map.
type PeerMap = [(Key, Elem)]

-- * Initialization functions

-- | Create a new empty map.
empty :: PeerMap
empty = []

-- | Our reverse-compare function.
pmCompare :: (Key, Elem) -> (Key, Elem) -> Ordering
pmCompare a b = comparing snd b a

-- | Add or update (via a custom function) an element.
addWith :: (Elem -> Elem -> Elem) -> Key -> Elem -> PeerMap -> PeerMap
addWith fn k v lst =
  case lookup k lst of
    Nothing -> insertBy pmCompare (k, v) lst
    Just o -> insertBy pmCompare (k, fn o v) (remove k lst)

-- | Create a PeerMap from an association list, with possible duplicates.
accumArray :: (Elem -> Elem -> Elem) -- ^ function used to merge the elements
              -> [(Key, Elem)]       -- ^ source data
              -> PeerMap             -- ^ results
accumArray _  [] = empty
accumArray fn ((k, v):xs) = addWith fn k v $ accumArray fn xs

-- * Basic operations

-- | Returns either the value for a key or zero if not found.
find :: Key -> PeerMap -> Elem
find k = fromMaybe 0 . lookup k

-- | Add an element to a peermap, overwriting the previous value.
add :: Key -> Elem -> PeerMap -> PeerMap
add = addWith (flip const)

-- | Remove an element from a peermap.
remove :: Key -> PeerMap -> PeerMap
remove _ [] = []
remove k ((x@(x', _)):xs) = if k == x'
                            then xs
                            else x:remove k xs

-- | Find the maximum element.
--
-- Since this is a sorted list, we just get the value at the head of
-- the list, or zero for a null list
maxElem :: PeerMap -> Elem
maxElem (x:_) = snd x
maxElem _ = 0

-- | Sum of all peers.
sumElems :: PeerMap -> Elem
sumElems = sum . map snd