Synnefo » snf-ganeti » ganeti-local

{-| Utility functions -}

{-

Copyright (C) 2009 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

    , sepSplit

    , fst3

    , varianceCoeff

    , commaJoin

    , readEitherString

    , loadJSArray

    , fromObj

    , tryFromObj

    , fromJVal

    , asJSObject

    , asObjectList

    , fromJResult

    , tryRead

    , formatTable

    , annotateResult

    ) where

import Data.List

import Control.Monad

import qualified Text.JSON as J

import Text.Printf (printf)

import Debug.Trace

import Ganeti.HTools.Types

-- * Debug functions

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

debug :: Show a => a -> a

debug x = trace (show x) x

-- * Miscelaneous

-- | Comma-join a string list.

commaJoin :: [String] -> String

commaJoin = intercalate ","

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

sepSplit :: Char -> String -> [String]

sepSplit sep s

    | x == "" && xs == [] = []

    | xs == []            = [x]

    | ys == []            = [x,""]

    | otherwise           = x:sepSplit sep ys

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

          ys = drop 1 xs

-- | Simple version of 'fst' for a triple

fst3 :: (a, b, c) -> a

fst3 (a, _, _) = a

-- * Mathematical functions

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

-- | Mean value of a list.

meanValue :: [Double] -> Double

meanValue lst = sum lst / fromIntegral (length lst)

-- | Standard deviation.

stdDev :: [Double] -> Double

stdDev lst =

    let mv = meanValue lst

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

        bv = sqrt (av / fromIntegral (length lst))

    in bv

-- | Coefficient of variation.

varianceCoeff :: [Double] -> Double

varianceCoeff lst = stdDev lst / fromIntegral (length lst)

-- * JSON-related functions

-- | Converts a JSON Result into a monadic value.

fromJResult :: Monad m => J.Result a -> m a

fromJResult (J.Error x) = fail x

fromJResult (J.Ok x) = return x

-- | Tries to read a string from a JSON value.

--

-- In case the value was not a string, we fail the read (in the

-- context of the current monad.

readEitherString :: (Monad m) => J.JSValue -> m String

readEitherString v =

    case v of

      J.JSString s -> return $ J.fromJSString s

      _ -> fail "Wrong JSON type"

-- | Converts a JSON message into an array of JSON objects.

loadJSArray :: (Monad m) => String -> m [J.JSObject J.JSValue]

loadJSArray = fromJResult . J.decodeStrict

-- | Reads a the value of a key in a JSON object.

fromObj :: (J.JSON a, Monad m) => String -> [(String, J.JSValue)] -> m a

fromObj k o =

    case lookup k o of

      Nothing -> fail $ printf "key '%s' not found in %s" k (show o)

      Just val -> fromJResult $ J.readJSON val

-- | Annotate a Result with an ownership information

annotateResult :: String -> Result a -> Result a

annotateResult owner (Bad s) = Bad $ owner ++ ": " ++ s

annotateResult _ v = v

-- | Try to extract a key from a object with better error reporting

-- than fromObj

tryFromObj :: (J.JSON a) =>

              String -> [(String, J.JSValue)] -> String -> Result a

tryFromObj t o k = annotateResult (t ++ " key '" ++ k ++ "'") (fromObj k o)

-- | Small wrapper over readJSON.

fromJVal :: (Monad m, J.JSON a) => J.JSValue -> m a

fromJVal v =

    case J.readJSON v of

      J.Error s -> fail ("Cannot convert value " ++ show v ++ ", error: " ++ s)

      J.Ok x -> return x

-- | Converts a JSON value into a JSON object.

asJSObject :: (Monad m) => J.JSValue -> m (J.JSObject J.JSValue)

asJSObject (J.JSObject a) = return a

asJSObject _ = fail "not an object"

-- | Coneverts a list of JSON values into a list of JSON objects.

asObjectList :: (Monad m) => [J.JSValue] -> m [J.JSObject J.JSValue]

asObjectList = mapM asJSObject

-- * 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