Start work on primer scanning

src/Main.hs

@@ -4,24 +4,12 @@ import Control.Applicative ((<$>), (<*>), pure)
 import Options.Applicative ((<>), optional)
 import Options.Applicative (Parser, command, info,
                             execParser, strOption, help, switch, help, helper,
-                            fullDesc, progDesc, long, header,
-                            subparser, flag)
+                            fullDesc, progDesc, long, header, str,
+                            subparser, flag, value, argument, metavar)
 
-data IseqOptions = IseqOptions {
-      optVerbose :: Bool
-    , optOutput  :: Maybe String
-    , optCommand :: Command
-    } deriving (Show)
+import Options
+import Scan (scan)
 
-data Command =
-    CmdAlign { optAlignment :: Alignment }
-  | CmdMerge
-  deriving (Show)
-
-data Alignment =
-    GlobalAlignment
-  | LocalAlignment
-  deriving (Show, Eq)
 
 
 main :: IO ()
@@ -30,6 +18,11 @@ main = do
       (fullDesc <> header "Tools for processing Illumina ?iSeq data"))
   print o
 
+  case optCommand o of
+    CmdScan input primer -> scan o input primer
+    _                    -> return ()
+
+
 parser :: Parser IseqOptions
 parser = IseqOptions
   <$> switch (long "verbose" <> help "Be verbose")
@@ -38,6 +31,7 @@ parser = IseqOptions
         command "align" (info alignOptParser $
             progDesc "Align against database")
     <>  command "merge" (info mergeOptParser $ progDesc "Merge paired reads")
+    <>  command "scan" (info scanOptParser $ progDesc "Scan for primer")
     )
 
 alignOptParser :: Parser Command
@@ -47,3 +41,9 @@ alignOptParser = CmdAlign
 
 mergeOptParser :: Parser Command
 mergeOptParser = pure CmdMerge
+
+scanOptParser :: Parser Command
+scanOptParser = CmdScan
+  <$> strOption (long "input" <> value "/dev/stdin"
+      <> help "Fasta file to scan")
+  <*> argument str (metavar "PRIMER" <> help "Primer sequence to scan for")

src/Options.hs

@@ -0,0 +1,27 @@
+module Options (
+    IseqOptions(..)
+  , Command(..)
+  , Alignment(..)
+  ) where
+
+
+data IseqOptions = IseqOptions {
+      optVerbose :: Bool
+    , optOutput  :: Maybe FilePath
+    , optCommand :: Command
+    } deriving (Show)
+
+data Command =
+    CmdAlign { optAlignment :: Alignment }
+  | CmdMerge
+  | CmdScan {
+        optInput  :: FilePath
+      , optPrimer :: String
+      }
+  deriving (Show)
+
+data Alignment =
+    GlobalAlignment
+  | LocalAlignment
+  deriving (Show, Eq)
+

src/Scan.hs

@@ -0,0 +1,32 @@
+{-# LANGUAGE BangPatterns #-}
+
+module Scan (bestMatchWithin, editDist, scan) where
+
+import Data.List (tails, minimumBy)
+import Data.Ord (comparing)
+
+import Options
+
+
+-- Find position within n characters from start of y that minimizes edit
+-- distance to x.
+bestMatchWithin :: Eq a => Int -> [a] -> [a] -> (Int, Int)
+bestMatchWithin n x y = minimumBy (comparing snd) $ zip [1..] distances
+  where
+    distances = map (editDist x) (take (max 1 $ n+1) $ tails y)
+
+
+-- Edit distance between two lists
+editDist :: Eq a => [a] -> [a] -> Int
+editDist = go 0
+  where
+    go !n []        _         = n
+    go !n xs        []        = n + length xs
+    go !n xa@(x:xs) ya@(y:ys)
+        | x == y    = go n xs ys
+        | otherwise = minimum [ go (n+1) xa ys   -- deletion
+                              , go (n+1) xs ya   -- insertion
+                              , go (n+1) xs ys ] -- substitution
+
+
+scan = undefined