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{-# LANGUAGE Rank2Types #-}

{-| Implementation of the Ganeti Query2 filterning.

The filtering of results should be done in two phases.

In the first phase, before contacting any remote nodes for runtime

data, the filtering should be executed with 'Nothing' for the runtime

context. This will make all non-runtime filters filter correctly,

whereas all runtime filters will respond successfully. As described in

the Python version too, this makes for example /Or/ filters very

inefficient if they contain runtime fields.

Once this first filtering phase has been done, we hopefully eliminated

some remote nodes out of the list of candidates, we run the remote

data gathering, and we evaluate the filter again, this time with a

'Just' runtime context. This will make all filters work correctly.

Note that the second run will re-evaluate the config/simple fields,

without caching; this is not perfect, but we consider config accesses

very cheap (and the configuration snapshot we have won't change

between the two runs, hence we will not get inconsistent results).

-}

{-

Copyright (C) 2012 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.Query.Filter

  ( compileFilter

  , evaluateFilter

  ) where

import Control.Applicative

import qualified Data.Map as Map

import Data.Traversable (traverse)

import Text.JSON (JSValue(..), fromJSString)

import Text.JSON.Pretty (pp_value)

import qualified Text.Regex.PCRE as PCRE

import Ganeti.BasicTypes

import Ganeti.Objects

import Ganeti.Query.Language

import Ganeti.Query.Types

import Ganeti.JSON

-- | Compiles a filter based on field names to one based on getters.

compileFilter :: FieldMap a b

              -> Filter FilterField

              -> Result (Filter (FieldGetter a b))

compileFilter fm =

  traverse (\field -> maybe (Bad $ "Can't find field named '" ++ field ++ "'")

                      (Ok . snd) (field `Map.lookup` fm))

-- | Wraps a getter, filter pair. If the getter is 'FieldRuntime' but

-- we don't have a runtime context, we skip the filtering, returning

-- \"pass\". Otherwise, we pass the actual value to the filter.

wrapGetter :: ConfigData

           -> Maybe b

           -> a

           -> FieldGetter a b

           -> (JSValue -> Result Bool)

           -> Result Bool

wrapGetter cfg b a getter faction =

  case tryGetter cfg b a getter of

    Nothing -> Ok True -- runtime missing, accepting the value

    Just v ->

      case v of

        ResultEntry RSNormal (Just fval) -> faction fval

        ResultEntry RSNormal Nothing ->

          Bad "Internal error: Getter returned RSNormal/Nothing"

        _ -> Ok True -- filter has no data to work, accepting it

-- | Helper to evaluate a filter getter (and the value it generates) in

-- a boolean context.

trueFilter :: JSValue -> Result Bool

trueFilter (JSBool x) = Ok x

trueFilter v = Bad $ "Unexpected value '" ++ show (pp_value v) ++

               "' in boolean context"

-- | A type synonim for a rank-2 comparator function. This is used so

-- that we can pass the usual '<=', '>', '==' functions to 'binOpFilter'

-- and for them to be used in multiple contexts.

type Comparator = (Eq a, Ord a) => a -> a -> Bool

-- | Helper to evaluate a filder getter (and the value it generates)

-- in a boolean context. Note the order of arguments is reversed from

-- the filter definitions (due to the call chain), make sure to

-- compare in the reverse order too!.

binOpFilter :: Comparator -> FilterValue -> JSValue -> Result Bool

binOpFilter comp (QuotedString y) (JSString x) =

  Ok $ fromJSString x `comp` y

binOpFilter comp (NumericValue y) (JSRational _ x) =

  Ok $ x `comp` fromIntegral y

binOpFilter _ expr actual =

  Bad $ "Invalid types in comparison, trying to compare " ++

      show (pp_value actual) ++ " with '" ++ show expr ++ "'"

-- | Implements the 'RegexpFilter' matching.

regexpFilter :: FilterRegex -> JSValue -> Result Bool

regexpFilter re (JSString val) =

  Ok $ PCRE.match (compiledRegex re) (fromJSString val)

regexpFilter _ x =

  Bad $ "Invalid field value used in regexp matching,\

        \ expecting string but got '" ++ show (pp_value x) ++ "'"

-- | Implements the 'ContainsFilter' matching.

containsFilter :: FilterValue -> JSValue -> Result Bool

-- note: the next two implementations are the same, but we have to

-- repeat them due to the encapsulation done by FilterValue

containsFilter (QuotedString val) lst = do

  lst' <- fromJVal lst

  return $ val `elem` lst'

containsFilter (NumericValue val) lst = do

  lst' <- fromJVal lst

  return $ val `elem` lst'

-- | Verifies if a given item passes a filter. The runtime context

-- might be missing, in which case most of the filters will consider

-- this as passing the filter.

evaluateFilter :: ConfigData -> Maybe b -> a

               -> Filter (FieldGetter a b)

               -> Result Bool

evaluateFilter _ _  _ EmptyFilter = Ok True

evaluateFilter c mb a (AndFilter flts) =

  all id <$> mapM (evaluateFilter c mb a) flts

evaluateFilter c mb a (OrFilter flts)  =

  any id <$> mapM (evaluateFilter c mb a) flts

evaluateFilter c mb a (NotFilter flt)  =

  not <$> evaluateFilter c mb a flt

evaluateFilter c mb a (TrueFilter getter)  =

  wrapGetter c mb a getter trueFilter

evaluateFilter c mb a (EQFilter getter val) =

  wrapGetter c mb a getter (binOpFilter (==) val)

evaluateFilter c mb a (LTFilter getter val) =

  wrapGetter c mb a getter (binOpFilter (<) val)

evaluateFilter c mb a (LEFilter getter val) =

  wrapGetter c mb a getter (binOpFilter (<=) val)

evaluateFilter c mb a (GTFilter getter val) =

  wrapGetter c mb a getter (binOpFilter (>) val)

evaluateFilter c mb a (GEFilter getter val) =

  wrapGetter c mb a getter (binOpFilter (>=) val)

evaluateFilter c mb a (RegexpFilter getter re) =

  wrapGetter c mb a getter (regexpFilter re)

evaluateFilter c mb a (ContainsFilter getter val) =

  wrapGetter c mb a getter (containsFilter val)

-- | Runs a getter with potentially missing runtime context.

tryGetter :: ConfigData -> Maybe b -> a -> FieldGetter a b -> Maybe ResultEntry

tryGetter _   _ item (FieldSimple getter)  = Just $ getter item

tryGetter cfg _ item (FieldConfig getter)  = Just $ getter cfg item

tryGetter _  rt item (FieldRuntime getter) =

  maybe Nothing (\rt' -> Just $ getter rt' item) rt

tryGetter _   _ _    FieldUnknown          = Just $

                                             ResultEntry RSUnknown Nothing