propellor/Propellor/Property.hs

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module Propellor.Property where
import System.Directory
import Control.Monad
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import Propellor.Types
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import Propellor.Engine
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import Utility.Monad
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makeChange :: IO () -> IO Result
makeChange a = a >> return MadeChange
noChange :: IO Result
noChange = return NoChange
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{- | Combines a list of properties, resulting in a single property
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- that when run will run each property in the list in turn,
- and print out the description of each as it's run. Does not stop
- on failure; does propigate overall success/failure.
-}
propertyList :: Desc -> [Property] -> Property
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propertyList desc ps = Property desc $ ensureProperties' ps
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{- | Combines a list of properties, resulting in one property that
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- ensures each in turn, stopping on failure. -}
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combineProperties :: [Property] -> Property
combineProperties ps = Property desc $ go ps NoChange
where
go [] rs = return rs
go (l:ls) rs = do
r <- ensureProperty l
case r of
FailedChange -> return FailedChange
_ -> go ls (combineResult r rs)
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desc = case ps of
(p:_) -> propertyDesc p
_ -> "(empty)"
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{- | Makes a perhaps non-idempotent Property be idempotent by using a flag
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- file to indicate whether it has run before.
- Use with caution. -}
flagFile :: Property -> FilePath -> Property
flagFile property flagfile = Property (propertyDesc property) $
go =<< doesFileExist flagfile
where
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go True = return NoChange
go False = do
r <- ensureProperty property
when (r == MadeChange) $
writeFile flagfile ""
return r
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{- | Whenever a change has to be made for a Property, causes a hook
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- Property to also be run, but not otherwise. -}
onChange :: Property -> Property -> Property
property `onChange` hook = Property (propertyDesc property) $ do
r <- ensureProperty property
case r of
MadeChange -> do
r' <- ensureProperty hook
return $ combineResult r r'
_ -> return r
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{- | Indicates that the first property can only be satisfied once
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- the second is. -}
requires :: Property -> Property -> Property
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x `requires` y = combineProperties [y, x] `describe` propertyDesc x
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describe :: Property -> Desc -> Property
describe p d = p { propertyDesc = d }
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(==>) :: Desc -> Property -> Property
(==>) = flip describe
infixl 1 ==>
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{- | Makes a Property only be performed when a test succeeds. -}
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check :: IO Bool -> Property -> Property
check c property = Property (propertyDesc property) $ ifM c
( ensureProperty property
, return NoChange
)