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

    , commaJoin

    , readEitherString

    , JSRecord

    , loadJSArray

    , fromObj

    , fromObjWithDefault

    , maybeFromObj

    , tryFromObj

    , fromJVal

    , asJSObject

    , asObjectList

    , fromJResult

    , tryRead

    , formatTable

    , annotateResult

    , defaultGroupID

    ) where

import Control.Monad (liftM)

import Data.List

import Data.Maybe (fromMaybe)

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

-- | 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 a b = debug a `seq` b

-- * Miscellaneous

-- | 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

-- * JSON-related functions

-- | A type alias for the list-based representation of J.JSObject.

type JSRecord = [(String, J.JSValue)]

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

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

fromJResult s (J.Error x) = fail (s ++ ": " ++ 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 -- ^ Operation description (for error reporting)

               -> String -- ^ Input message

               -> m [J.JSObject J.JSValue]

loadJSArray s = fromJResult s . J.decodeStrict

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

fromObj :: (J.JSON a, Monad m) => JSRecord -> String -> m a

fromObj o k =

    case lookup k o of

      Nothing -> fail $ printf "key '%s' not found, object contains only %s"

                 k (show (map fst o))

      Just val -> fromKeyValue k val

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

maybeFromObj :: (J.JSON a, Monad m) =>

                JSRecord -> String -> m (Maybe a)

maybeFromObj o k =

    case lookup k o of

      Nothing -> return Nothing

      Just val -> liftM Just (fromKeyValue k val)

-- | Reads the value of a key in a JSON object with a default if missing.

fromObjWithDefault :: (J.JSON a, Monad m) =>

                      JSRecord -> String -> a -> m a

fromObjWithDefault o k d = liftM (fromMaybe d) $ maybeFromObj o k

-- | Reads a JValue, that originated from an object key.

fromKeyValue :: (J.JSON a, Monad m)

              => String     -- ^ The key name

              -> J.JSValue  -- ^ The value to read

              -> m a

fromKeyValue k val =

  fromJResult (printf "key '%s', value '%s'" k (show val)) (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     -- ^ Textual "owner" in error messages

           -> JSRecord   -- ^ The object array

           -> String     -- ^ The desired key from the object

           -> Result a

tryFromObj t o = annotateResult t . fromObj 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

-- | Default group UUID (just a string, not a real UUID).

defaultGroupID :: GroupID

defaultGroupID = "00000000-0000-0000-0000-000000000000"