add VerifiedCopy data type

There should be no behavior changes in this commit, it just adds a more
expressive data type and adjusts code that had been passing around a [UUID]
or sometimes a Maybe Remote to instead use [VerifiedCopy].

Although, since some functions were taking two different [UUID] lists,
there's some potential for me to have gotten it horribly wrong.

Types/NumCopies.hs

@@ -1,4 +1,4 @@
-{- git-annex numcopies type
+{- git-annex numcopies types
  -
  - Copyright 2014 Joey Hess <id@joeyh.name>
  -
@@ -7,8 +7,48 @@
 
 module Types.NumCopies where
 
+import Types.UUID
+
+import qualified Data.Map as M
+
 newtype NumCopies = NumCopies Int
 	deriving (Ord, Eq)
 
 fromNumCopies :: NumCopies -> Int
 fromNumCopies (NumCopies n) = n
+
+data VerifiedCopy
+	{- Use when a repository cannot be accessed, but it's
+	 - a trusted repository, which is presumably not going to
+	 - lose a copy. This is the weakest level of verification. -}
+	= TrustedCopy UUID
+	{- Represents a recent verification that a copy of an
+	 - object exists in a repository with the given UUID. -}
+	| VerifiedCopy UUID
+ 	{- The strongest proof of the existence of a copy.
+	 - Until its associated action is called to unlock it,
+	 - the copy is locked in the repository and is guaranteed
+	 - not to be dropped by any git-annex process. -}
+	| VerifiedCopyLock UUID (IO ())
+
+instance ToUUID VerifiedCopy where
+	toUUID (VerifiedCopy u) = u
+	toUUID (VerifiedCopyLock u _) = u
+	toUUID (TrustedCopy u) = u
+
+instance Show VerifiedCopy where
+	show (TrustedCopy u) = "TrustedCopy " ++ show u
+	show (VerifiedCopy u) = "VerifiedCopy " ++ show u
+	show (VerifiedCopyLock u _) = "VerifiedCopyLock " ++ show u
+
+strongestVerifiedCopy :: VerifiedCopy -> VerifiedCopy -> VerifiedCopy
+strongestVerifiedCopy a@(VerifiedCopyLock _ _) _ = a
+strongestVerifiedCopy _ b@(VerifiedCopyLock _ _) = b
+strongestVerifiedCopy a@(VerifiedCopy _) _ = a
+strongestVerifiedCopy _ b@(VerifiedCopy _) = b
+strongestVerifiedCopy a@(TrustedCopy _) _  = a
+
+-- Retains stronger verifications over weaker for the same uuid.
+deDupVerifiedCopies :: [VerifiedCopy] -> [VerifiedCopy]
+deDupVerifiedCopies l = M.elems $
+	M.fromListWith strongestVerifiedCopy (zip (map toUUID l) l)