+ Add Selection module skeleton.

1 files changed, 64 insertions, 0 deletions

diff --git a/src/Network/BitTorrent/PeerWire/Selection.hs b/src/Network/BitTorrent/PeerWire/Selection.hs
new file mode 100644
index 00000000..04049812
--- /dev/null
+++ b/src/Network/BitTorrent/PeerWire/Selection.hs
@@ -0,0 +1,64 @@
+-- TODO tests
+-- |
+--   Copyright   :  (c) Sam T. 2013
+--   License     :  MIT
+--   Maintainer  :  pxqr.sta@gmail.com
+--   Stability   :  experimental
+--   Portability :  portable
+--
+--   This module provides commonly used piece seletion algorithms
+--   which used to find out which one next piece to download.
+--   Selectors considered to be used in the following order:
+--
+--     * Random first or rarest first selection - at the start.
+--
+--     * Rarest first selection - performed to avoid situation when
+--     rarest piece is unaccessible.
+--
+--     * _End game_ seletion - performed after a peer has requested all
+--     the subpieces of the content.
+--
+--   Note that BitTorrent applies the strict priority policy for
+--   _subpiece_ or _blocks_ selection.
+--
+module Network.BitTorrent.PeerWire.Selection
+       ( Selector
+       , strictFirst, rarestFirst, randomFirst, endGame, autoSelector
+       ) where
+
+import Network.BitTorrent.PeerWire.Block
+import Network.BitTorrent.PeerWire.Message
+import Network.BitTorrent.PeerWire.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.
+
+-- | Select the first available piece.
+strictFirst :: Selector
+strictFirst h a _ = findMin (difference a h)
+
+
+-- |
+rarestFirst :: Selector
+rarestFirst h a xs = error "rarestFirst"
+    -- rarest (frequencies (map (intersection want) xs))
+  where
+    want = difference h a
+    rarest = undefined
+
+-- | In general random first is faster than rarest first strategy but
+--    only if all pieces are available.
+randomFirst :: IO Selector
+randomFirst = do
+--  randomIO
+  error "randomFirst"
+
+endGame :: Selector
+endGame = undefined
+
+autoSelector :: Selector
+autoSelector = undefined