Synnefo » snf-ganeti » ganeti-local

{-| Utility functions. -}

{-

Copyright (C) 2009, 2010, 2011 Google Inc.

This program is free software; you can redistribute it and/or modify

it under the terms of the GNU General Public License as published by

the Free Software Foundation; either version 2 of the License, or

(at your option) any later version.

This program is distributed in the hope that it will be useful, but

WITHOUT ANY WARRANTY; without even the implied warranty of

MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

General Public License for more details.

You should have received a copy of the GNU General Public License

along with this program; if not, write to the Free Software

Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA

02110-1301, USA.

-}

module Ganeti.HTools.Utils

  ( debug

  , debugFn

  , debugXy

  , sepSplit

  , stdDev

  , if'

  , select

  , applyIf

  , commaJoin

  , tryRead

  , formatTable

  , parseUnit

  ) where

import Data.Char (toUpper)

import Data.List

import Debug.Trace

-- * Debug functions

-- | To be used only for debugging, breaks referential integrity.

debug :: Show a => a -> a

debug x = trace (show x) x

-- | Displays a modified form of the second parameter before returning

-- it.

debugFn :: Show b => (a -> b) -> a -> a

debugFn fn x = debug (fn x) `seq` x

-- | Show the first parameter before returning the second one.

debugXy :: Show a => a -> b -> b

debugXy = seq . debug

-- * Miscellaneous

-- | Apply the function if condition holds, otherwise use default value.

applyIf :: Bool -> (a -> a) -> a -> a

applyIf b f x = if b then f x else x

-- | Comma-join a string list.

commaJoin :: [String] -> String

commaJoin = intercalate ","

-- | Split a list on a separator and return an array.

sepSplit :: Eq a => a -> [a] -> [[a]]

sepSplit sep s

  | null s    = []

  | null xs   = [x]

  | null ys   = [x,[]]

  | otherwise = x:sepSplit sep ys

  where (x, xs) = break (== sep) s

        ys = drop 1 xs

-- * Mathematical functions

-- Simple and slow statistical functions, please replace with better

-- versions

-- | Standard deviation function.

stdDev :: [Double] -> Double

stdDev lst =

  -- first, calculate the list length and sum lst in a single step,

  -- for performance reasons

  let (ll', sx) = foldl' (\(rl, rs) e ->

                           let rl' = rl + 1

                               rs' = rs + e

                           in rl' `seq` rs' `seq` (rl', rs')) (0::Int, 0) lst

      ll = fromIntegral ll'::Double

      mv = sx / ll

      av = foldl' (\accu em -> let d = em - mv in accu + d * d) 0.0 lst

  in sqrt (av / ll) -- stddev

-- *  Logical functions

-- Avoid syntactic sugar and enhance readability. These functions are proposed

-- by some for inclusion in the Prelude, and at the moment they are present

-- (with various definitions) in the utility-ht package. Some rationale and

-- discussion is available at <http://www.haskell.org/haskellwiki/If-then-else>

-- | \"if\" as a function, rather than as syntactic sugar.

if' :: Bool -- ^ condition

    -> a    -- ^ \"then\" result

    -> a    -- ^ \"else\" result

    -> a    -- ^ \"then\" or "else" result depending on the condition

if' True x _ = x

if' _    _ y = y

-- | Return the first result with a True condition, or the default otherwise.

select :: a            -- ^ default result

       -> [(Bool, a)]  -- ^ list of \"condition, result\"

       -> a            -- ^ first result which has a True condition, or default

select def = maybe def snd . find fst

-- * Parsing utility functions

-- | Parse results from readsPrec.

parseChoices :: (Monad m, Read a) => String -> String -> [(a, String)] -> m a

parseChoices _ _ ((v, ""):[]) = return v

parseChoices name s ((_, e):[]) =

    fail $ name ++ ": leftover characters when parsing '"

           ++ s ++ "': '" ++ e ++ "'"

parseChoices name s _ = fail $ name ++ ": cannot parse string '" ++ s ++ "'"

-- | Safe 'read' function returning data encapsulated in a Result.

tryRead :: (Monad m, Read a) => String -> String -> m a

tryRead name s = parseChoices name s $ reads s

-- | Format a table of strings to maintain consistent length.

formatTable :: [[String]] -> [Bool] -> [[String]]

formatTable vals numpos =

    let vtrans = transpose vals  -- transpose, so that we work on rows

                                 -- rather than columns

        mlens = map (maximum . map length) vtrans

        expnd = map (\(flds, isnum, ml) ->

                         map (\val ->

                                  let delta = ml - length val

                                      filler = replicate delta ' '

                                  in if delta > 0

                                     then if isnum

                                          then filler ++ val

                                          else val ++ filler

                                     else val

                             ) flds

                    ) (zip3 vtrans numpos mlens)

   in transpose expnd

-- | Tries to extract number and scale from the given string.

--

-- Input must be in the format NUMBER+ SPACE* [UNIT]. If no unit is

-- specified, it defaults to MiB. Return value is always an integral

-- value in MiB.

parseUnit :: (Monad m, Integral a, Read a) => String -> m a

parseUnit str =

  -- TODO: enhance this by splitting the unit parsing code out and

  -- accepting floating-point numbers

  case reads str of

    [(v, suffix)] ->

      let unit = dropWhile (== ' ') suffix

          upper = map toUpper unit

          siConvert x = x * 1000000 `div` 1048576

      in case () of

           _ | null unit -> return v

             | unit == "m" || upper == "MIB" -> return v

             | unit == "M" || upper == "MB"  -> return $ siConvert v

             | unit == "g" || upper == "GIB" -> return $ v * 1024

             | unit == "G" || upper == "GB"  -> return $ siConvert

                                                (v * 1000)

             | unit == "t" || upper == "TIB" -> return $ v * 1048576

             | unit == "T" || upper == "TB"  -> return $

                                                siConvert (v * 1000000)

             | otherwise -> fail $ "Unknown unit '" ++ unit ++ "'"

    _ -> fail $ "Can't parse string '" ++ str ++ "'"