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{-| 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

    , asJSObject

    , asObjectList

    , fromJResult

    ) where

import Data.List

import Control.Monad

import qualified Text.JSON as J

import Text.Printf (printf)

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

-- * 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 :: Floating a => [a] -> a

meanValue lst = sum lst / fromIntegral (length lst)

-- | Standard deviation.

stdDev :: Floating a => [a] -> a

stdDev lst =

    let mv = meanValue lst

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

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

    in bv

-- | Coefficient of variation.

varianceCoeff :: Floating a => [a] -> a

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 -> J.JSObject J.JSValue -> m a

fromObj k o =

    case lookup k (J.fromJSObject o) of

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

      Just val -> fromJResult $ J.readJSON val

-- | 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