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|
-- |
-- Copyright : (c) Sam Truzjan 2013
-- License : BSD3
-- Maintainer : pxqr.sta@gmail.com
-- Stability : experimental
-- Portability : portable
--
-- Piece selection algorithms.
--
module Network.BitTorrent.Exchange.Selection
( -- * Selection
Selector
, selector
, strategyClass
, strictFirst
, strictLast
, rarestFirst
, randomFirst
, endGame
) where
import Data.Ratio
import Data.Torrent.Bitfield
type Selector = Bitfield -- ^ Indices of client /have/ pieces.
-> Bitfield -- ^ Indices of peer /have/ pieces.
-> [Bitfield] -- ^ Indices of other peers /have/ pieces.
-> Maybe PieceIx -- ^ Zero-based index of piece to request
-- to, if any.
selector :: Selector -- ^ Selector to use at the start.
-> Ratio PieceCount
-> Selector -- ^ Selector to use after the client have
-- the C pieces.
-> Selector -- ^ Selector that changes behaviour based
-- on completeness.
selector start pt ready h a xs =
case strategyClass pt h of
SCBeginning -> start h a xs
SCReady -> ready h a xs
SCEnd -> endGame h a xs
data StartegyClass
= SCBeginning
| SCReady
| SCEnd
deriving (Show, Eq, Ord, Enum, Bounded)
strategyClass :: Ratio PieceCount -> Bitfield -> StartegyClass
strategyClass threshold = classify . completeness
where
classify c
| c < threshold = SCBeginning
| c + 1 % numerator c < 1 = SCReady
-- FIXME numerator have is not total count
| otherwise = SCEnd
-- | Select the first available piece.
strictFirst :: Selector
strictFirst h a _ = Just $ findMin (difference a h)
-- | Select the last available piece.
strictLast :: Selector
strictLast h a _ = Just $ findMax (difference a h)
-- |
rarestFirst :: Selector
rarestFirst h a xs = rarest (map (intersection want) xs)
where
want = difference h a
-- | In average random first is faster than rarest first strategy but
-- only if all pieces are available.
randomFirst :: Selector
randomFirst = do
-- randomIO
error "randomFirst"
endGame :: Selector
endGame = strictLast
|
