git-annex/Git/AutoCorrect.hs

{- git autocorrection using Damerau-Levenshtein edit distance
 -
 - Copyright 2012 Joey Hess <joey@kitenet.net>
 -
 - Licensed under the GNU GPL version 3 or higher.
 -}

module Git.AutoCorrect where

import Common
import Git.Types
import qualified Git.Config

import Text.EditDistance
import Control.Concurrent

{- These are the same cost values as used in git. -}
gitEditCosts :: EditCosts
gitEditCosts = EditCosts
	{ deletionCosts = ConstantCost 4
	, insertionCosts = ConstantCost 1
	, substitutionCosts = ConstantCost 2
	, transpositionCosts = ConstantCost 0
	}
		
{- Git's source calls this "an empirically derived magic number" -}
similarityFloor :: Int
similarityFloor = 7

{- Finds inexact matches for the input among the choices.
 - Returns an ordered list of good enough matches, or an empty list if
 - nothing matches well. -}
fuzzymatches :: String -> (c -> String) -> [c] -> [c]
fuzzymatches input showchoice choices = fst $ unzip $
	sortBy comparecost $ filter similarEnough $ zip choices costs
  where
	distance = restrictedDamerauLevenshteinDistance gitEditCosts input
	costs = map (distance . showchoice) choices
	comparecost a b = compare (snd a) (snd b)
	similarEnough (_, cst) = cst < similarityFloor

{- Takes action based on git's autocorrect configuration, in preparation for
 - an autocorrected command being run. -}
prepare :: String -> (c -> String) -> [c] -> Maybe Repo -> IO ()
prepare input showmatch matches r =
	case readish . Git.Config.get "help.autocorrect" "0" =<< r of
		Just n
			| n == 0 -> list
			| n < 0 -> warn
			| otherwise -> sleep n
		Nothing -> list
  where
	list = error $ unlines $
		[ "Unknown command '" ++ input ++ "'"
		, ""
		, "Did you mean one of these?"
		] ++ map (\m -> "\t" ++ showmatch m) matches
	warn = 
		hPutStr stderr $ unlines
			[ "WARNING: You called a command named '" ++
			  input ++ "', which does not exist."
			, "Continuing under the assumption that you meant '" ++
			  showmatch (Prelude.head matches) ++ "'"
			]
	sleep n = do
		warn
		hPutStrLn stderr $ unwords
			[ "in"
			, show (fromIntegral n / 10 :: Float)
			, "seconds automatically..."]
		threadDelay (n * 100000) -- deciseconds to microseconds