{- metadata based branch views
 -
 - Copyright 2014 Joey Hess <joey@kitenet.net>
 -
 - Licensed under the GNU GPL version 3 or higher.
 -}

{-# LANGUAGE CPP #-}

module Annex.View where

import Common.Annex
import Types.View
import Types.MetaData
import qualified Git.Types as Git
import qualified Git.Ref
import qualified Git.DiffTree
import qualified Git.Branch
import Git.Sha (nullSha)

import qualified Data.Set as S
import Data.Char
import System.Path.WildMatch
import "mtl" Control.Monad.Writer

#ifdef WITH_TDFA
import Text.Regex.TDFA
import Text.Regex.TDFA.String
#else
#endif

matchGlob :: Glob -> String -> Bool
#ifdef WITH_TDFA
matchGlob (Glob _ r) s = case execute r s of
	Right (Just _) -> True
	_ -> False
#else
matchGlob (Glob g) = wildCheckCase g
#endif

data ViewChange = Unchanged | Narrowing | Widening
	deriving (Ord, Eq, Show)

{- Updates a view, adding a new field to filter on (Narrowing), 
 - or allowing a new value in an existing field (Widening).
 -}
refineView :: View -> MetaField -> String -> (View, ViewChange)
refineView view field wanted
	| field `elem` (map viewField view) = 
		let (view', viewchanges) = runWriter $ mapM updatefield view
		in (view', maximum viewchanges)
	| otherwise = (ViewComponent field viewfilter : view, Narrowing)
  where
	viewfilter
		| any (`elem` wanted) "*?" = 
#ifdef WITH_TDFA
			case compile defaultCompOpt defaultExecOpt ('^':wildToRegex wanted) of
				Right r -> FilterGlob (Glob wanted r)
				Left _ -> FilterValues $ S.singleton $ toMetaValue wanted
#else
			FilterGlob (Glob wanted)
#endif
		| otherwise = FilterValues $ S.singleton $ toMetaValue wanted
	updatefield :: ViewComponent -> Writer [ViewChange] ViewComponent
	updatefield v
		| viewField v == field = do
			let (newvf, viewchange) = combineViewFilter (viewFilter v) viewfilter
			tell [viewchange]
			return $ v { viewFilter = newvf }
		| otherwise = return v

{- Combine old and new ViewFilters, yielding a results that matches
 - either old+new, or only new.
 -
 - If we have FilterValues and change to a FilterGlob,
 - it's always a widening change, because the glob could match other
 - values. OTOH, going the other way, it's a Narrowing change if the old
 - glob matches all the new FilterValues.
 -
 - With two globs, the old one is discarded, and the new one is used.
 - We can tell if that's a narrowing change by checking if the old
 - glob matches the new glob. For example, "*" matches "foo*",
 - so that's narrowing. While "f?o" does not match "f??", so that's
 - widening.
 -}
combineViewFilter :: ViewFilter -> ViewFilter -> (ViewFilter, ViewChange)
combineViewFilter old@(FilterValues olds) (FilterValues news)
	| combined == old = (combined, Unchanged)
	| otherwise = (combined, Widening)
  where
	combined = FilterValues (S.union olds news)
combineViewFilter (FilterValues _) newglob@(FilterGlob _) =
	(newglob, Widening)
combineViewFilter (FilterGlob oldglob) new@(FilterValues s)
	| all (matchGlob oldglob . fromMetaValue) (S.toList s) = (new, Narrowing)
	| otherwise = (new, Widening)
combineViewFilter (FilterGlob old) newglob@(FilterGlob new)
	| old == new = (newglob, Unchanged)
	| matchGlob old (getGlob new) = (newglob, Narrowing)
	| otherwise = (newglob, Widening)

{- Can a ViewFilter match multiple different MetaValues? -}
multiValue :: ViewFilter -> Bool
multiValue (FilterValues s) = S.size s > 1
multiValue (FilterGlob _) = True

{- Each multivalued ViewFilter in a view results in another level of
 - subdirectory nesting. When a file matches multiple ways, it will appear
 - in multiple subdirectories. This means there is a bit of an exponential
 - blowup with a single file appearing in a crazy number of places!
 -
 - Capping the view size to 5 is reasonable; why wants to dig
 - through 5+ levels of subdirectories to find anything?
 -}
viewTooLarge :: View -> Bool
viewTooLarge view = length (filter (multiValue . viewFilter) view) > 5

{- Checks if metadata matches a filter, and if so returns the value,
 - or values that match. -}
matchFilter :: MetaData -> ViewComponent -> Maybe [MetaValue]
matchFilter metadata (ViewComponent metafield (FilterValues s)) = nonEmptyList $
	S.intersection s (currentMetaDataValues metafield metadata)
matchFilter metadata (ViewComponent metafield (FilterGlob glob)) = nonEmptyList $
	S.filter (matchGlob glob . fromMetaValue) (currentMetaDataValues metafield metadata)

nonEmptyList :: S.Set a -> Maybe [a]
nonEmptyList s
	| S.null s = Nothing
	| otherwise = Just $ S.toList s

{- Converts a filepath used in a reference branch to the
 - filename that will be used in the view.
 -
 - No two filepaths from the same branch should yeild the same result,
 - so all directory structure needs to be included in the output file
 - in some way. However, the branch's directory structure is not relevant
 - in the view.
 -
 - So, from dir/subdir/file.foo, generate file{dir}{subdir}.foo
 -
 - (To avoid collisions with a filename that already contains {foo},
 - that is doubled to {{foo}}.)
 -}
fileViewFromReference :: MkFileView
fileViewFromReference f = concat
	[ double base
	, concatMap (\d -> "{" ++ double d ++ "}") dirs
	, double $ concat extensions
	]
  where
	(path, basefile) = splitFileName f
	dirs = filter (/= ".") $ map dropTrailingPathSeparator (splitPath path)
	(base, extensions) = splitShortExtensions basefile

	double = replace "{" "{{" . replace "}" "}}"

{- Generates views for a file from a branch, based on its metadata
 - and the filename used in the branch.
 -
 - Note that a file may appear multiple times in a view, when it
 - has multiple matching values for a MetaField used in the View.
 -
 - Of course if its MetaData does not match the View, it won't appear at
 - all.
 -}
fileViews :: View -> MkFileView -> FilePath -> MetaData -> [FileView]
fileViews view mkfileview file metadata
	| any isNothing matches = []
	| otherwise = map (</> mkfileview file) $ pathProduct $ 
		map (map toViewPath) (visible matches)
  where
  	matches :: [Maybe [MetaValue]]
	matches = map (matchFilter metadata) view
	visible :: [Maybe [MetaValue]] -> [[MetaValue]]
	visible = map (fromJust . snd) .
		filter (multiValue . fst) .
		zip (map viewFilter view)

toViewPath :: MetaValue -> FilePath
toViewPath = concatMap escapeslash . fromMetaValue
  where
	escapeslash c
		| c == '/' = [pseudoSlash]
		| c == '\\' = [pseudoBackslash]
		| c == pseudoSlash = [pseudoSlash, pseudoSlash]
		| c == pseudoBackslash = [pseudoBackslash, pseudoBackslash]
		| otherwise = [c]

fromViewPath :: FilePath -> MetaValue
fromViewPath = toMetaValue . deescapeslash []
  where
  	deescapeslash s [] = reverse s
  	deescapeslash s (c:cs)
		| c == pseudoSlash = case cs of
			(c':cs')
				| c' == pseudoSlash -> deescapeslash (pseudoSlash:s) cs'
			_ -> deescapeslash ('/':s) cs
		| c == pseudoBackslash = case cs of
			(c':cs')
				| c' == pseudoBackslash -> deescapeslash (pseudoBackslash:s) cs'
			_ -> deescapeslash ('/':s) cs
		| otherwise = deescapeslash (c:s) cs

pseudoSlash :: Char
pseudoSlash = '\8725' -- '∕' /= '/'

pseudoBackslash :: Char
pseudoBackslash = '\9586' -- '╲' /= '\'

pathProduct :: [[FilePath]] -> [FilePath]
pathProduct [] = []
pathProduct (l:ls) = foldl combinel l ls
  where
	combinel xs ys = [combine x y | x <- xs, y <- ys]

{- Extracts the metadata from a fileview, based on the view that was used
 - to construct it. -}
fromView :: View -> FileView -> MetaData
fromView view f = foldr (uncurry updateMetaData) newMetaData (zip fields values)
  where
	visible = filter (multiValue . viewFilter) view
	fields = map viewField visible
	paths = splitDirectories $ dropFileName f
	values = map fromViewPath paths

{- Constructing a view that will match arbitrary metadata, and applying
 - it to a file yields a set of FileViews which all contain the same
 - MetaFields that were present in the input metadata
 - (excluding fields that are not multivalued). -}
prop_view_roundtrips :: FilePath -> MetaData -> Bool
prop_view_roundtrips f metadata = null f || viewTooLarge view ||
	all hasfields (fileViews view fileViewFromReference f metadata)
  where
	view = map (\(mf, mv) -> ViewComponent mf (FilterValues $ S.filter (not . null . fromMetaValue) mv))
		(fromMetaData metadata)
	visiblefields = sort (map viewField $ filter (multiValue . viewFilter) view)
	hasfields fv = sort (map fst (fromMetaData (fromView view fv))) == visiblefields

{- Generates a git branch name for a View.
 - 
 - There is no guarantee that each view gets a unique branch name,
 - but the branch name is used to express the view as well as possible.
 -}
branchView :: View -> Git.Branch
branchView view
	| null name = Git.Ref "refs/views"
	| otherwise = Git.Ref $ "refs/views/" ++ name
  where
	name = intercalate "/" $ map branchcomp view
	branchcomp c
		| multiValue (viewFilter c) = branchcomp' c
		| otherwise = "(" ++ branchcomp' c ++ ")"
	branchcomp' (ViewComponent metafield viewfilter)
		| metafield == tagMetaField = branchvals viewfilter
		| otherwise = concat
			[ forcelegal (fromMetaField metafield)
			, "="
			, branchvals viewfilter
			]
	branchvals (FilterValues set) = forcelegal $
		intercalate "," $ map fromMetaValue $ S.toList set
	branchvals (FilterGlob glob) = forcelegal $ getGlob glob
	forcelegal s
		| Git.Ref.legal True s = s
		| otherwise = map (\c -> if isAlphaNum c then c else '_') s

prop_branchView_legal :: View -> Bool
prop_branchView_legal = Git.Ref.legal False . show . branchView

{- Applies a view to the currently checked out branch, generating a new
 - branch for the view.
 -}
applyView :: View -> Annex Git.Branch
applyView = applyView' fileViewFromReference

{- Generates a new branch for a View, which must be a more narrow
 - version of the View originally used to generate the currently
 - checked out branch.
 -}
narrowView :: View -> Annex Git.Branch
narrowView = applyView' id

{- Go through each file in the currently checked out branch.
 - If the file is not annexed, skip it, unless it's a dotfile in the top.
 - Look up the metadata of annexed files, and generate any FileViews,
 - and stage them into the (temporary) index.
 -}
applyView' :: MkFileView -> View -> Annex Git.Branch
applyView' mkfileview view = genViewBranch view $ do
	error "TODO"

{- Applies a view to the reference branch, generating a new branch
 - for the View.
 -
 - This needs to work incrementally, to quickly update the view branch
 - when the reference branch is changed. So, it works based on an
 - old version of the reference branch, uses diffTree to find the
 - changes, and applies those changes to the view branch.
 -}
updateView :: View -> Git.Ref -> Git.Ref -> Annex Git.Branch
updateView view ref oldref = genViewBranch view $ do
	(diffs, cleanup) <- inRepo $ Git.DiffTree.diffTree oldref ref
	forM_ diffs go
	void $ liftIO cleanup
  where
	go diff
		| Git.DiffTree.dstsha diff == nullSha = error "TODO delete file"
		| otherwise = error "TODO add file"

{- Generates a branch for a view. This is done by creating a temporary
 - index file, which starts off empty. An action is run to stage the files
 - that will be in the branch. Then a commit is made, to the view branch.
 - The view branch is not checked out, but entering it will display the
 - view. -}
genViewBranch :: View -> Annex () -> Annex Git.Branch
genViewBranch view a = withTempIndex $ do
	a
	let branch = branchView view
	void $ inRepo $ Git.Branch.commit True (show branch) branch []
	return branch

{- -}
withTempIndex :: Annex a -> Annex a
withTempIndex a = error "TODO"