    -----------------------------------------------------------------------------
    -- |
    -- Module      :  Distribution.Simple.PackageIndex
    -- Copyright   :  (c) David Himmelstrup 2005,
    --                    Bjorn Bringert 2007,
    --                    Duncan Coutts 2008-2009
    --
    -- Maintainer  :  cabal-devel@haskell.org
    -- Portability :  portable
    --
    -- An index of packages.
    --
    module Distribution.Simple.PackageIndex (
      -- * Package index data type
      PackageIndex,

      -- * Creating an index
      fromList,

      -- * Updates
      merge,

      insert,

      deleteInstalledPackageId,
      deleteSourcePackageId,
      deletePackageName,
    --  deleteDependency,

      -- * Queries

      -- ** Precise lookups
      lookupInstalledPackageId,
      lookupSourcePackageId,
      lookupPackageName,
      lookupDependency,

      -- ** Case-insensitive searches
      searchByName,
      SearchResult(..),
      searchByNameSubstring,

      -- ** Bulk queries
      allPackages,
      allPackagesByName,

      -- ** Special queries
      brokenPackages,
      dependencyClosure,
      reverseDependencyClosure,
      topologicalOrder,
      reverseTopologicalOrder,
      dependencyInconsistencies,
      dependencyCycles,
      dependencyGraph,
      moduleNameIndex,
      ) where

    import Prelude hiding (lookup)
    import Control.Exception (assert)
    import qualified Data.Map as Map
    import Data.Map (Map)
    import qualified Data.Tree  as Tree
    import qualified Data.Graph as Graph
    import qualified Data.Array as Array
    import Data.Array ((!))
    import Data.List as List
             ( null, foldl', sort
             , groupBy, sortBy, find, isInfixOf, nubBy, deleteBy, deleteFirstsBy )
    import Data.Monoid (Monoid(..))
    import Data.Maybe (isNothing, fromMaybe)

    import Distribution.Package
             ( PackageName(..), PackageId
             , Package(..), packageName, packageVersion
             , Dependency(Dependency)--, --PackageFixedDeps(..)
             , InstalledPackageId(..) )
    import Distribution.ModuleName
             ( ModuleName )
    import Distribution.InstalledPackageInfo
             ( InstalledPackageInfo, installedPackageId )
    import qualified Distribution.InstalledPackageInfo as IPI
    import Distribution.Version
             ( Version, withinRange )
    import Distribution.Simple.Utils (lowercase, comparing, equating)

    -- | The collection of information about packages from one or more 'PackageDB's.
    --
    -- Packages are uniquely identified in by their 'InstalledPackageId', they can
    -- also be effeciently looked up by package name or by name and version.
    --
    data PackageIndex = PackageIndex
      -- The primary index. Each InstalledPackageInfo record is uniquely identified
      -- by its InstalledPackageId.
      --
      !(Map InstalledPackageId InstalledPackageInfo)

      -- This auxillary index maps package names (case-sensitively) to all the
      -- versions and instances of that package. This allows us to find all
      -- versions satisfying a dependency.
      --
      -- It is a three-level index. The first level is the package name,
      -- the second is the package version and the final level is instances
      -- of the same package version. These are unique by InstalledPackageId
      -- and are kept in preference order.
      --
      !(Map PackageName (Map Version [InstalledPackageInfo]))

      deriving (Show, Read)

    instance Monoid PackageIndex where
      mempty  = PackageIndex Map.empty Map.empty
      mappend = merge
      --save one mappend with empty in the common case:
      mconcat [] = mempty
      mconcat xs = foldr1 mappend xs

    invariant :: PackageIndex -> Bool
    invariant (PackageIndex pids pnames) =
         map installedPackageId (Map.elems pids)
      == sort
         [ assert pinstOk (installedPackageId pinst)
         | (pname, pvers)  <- Map.toList pnames
         , let pversOk = not (Map.null pvers)
         , (pver,  pinsts) <- assert pversOk $ Map.toList pvers
         , let pinsts'  = sortBy (comparing installedPackageId) pinsts
               pinstsOk = all (\g -> length g == 1)
                              (groupBy (equating installedPackageId) pinsts')
         , pinst           <- assert pinstsOk $ pinsts'
         , let pinstOk = packageName    pinst == pname
                      && packageVersion pinst == pver
         ]

    --
    -- * Internal helpers
    --

    mkPackageIndex :: Map InstalledPackageId InstalledPackageInfo
                   -> Map PackageName (Map Version [InstalledPackageInfo])
                   -> PackageIndex
    mkPackageIndex pids pnames = assert (invariant index) index
      where index = PackageIndex pids pnames

    --
    -- * Construction
    --

    -- | Build an index out of a bunch of packages.
    --
    -- If there are duplicates by 'InstalledPackageId' then later ones mask earlier
    -- ones.
    --
    fromList :: [InstalledPackageInfo] -> PackageIndex
    fromList pkgs = mkPackageIndex pids pnames
      where
        pids      = Map.fromList [ (installedPackageId pkg, pkg) | pkg <- pkgs ]
        pnames    =
          Map.fromList
            [ (packageName (head pkgsN), pvers)
            | pkgsN <- groupBy (equating  packageName)
                     . sortBy  (comparing packageId)
                     $ pkgs
            , let pvers =
                    Map.fromList
                    [ (packageVersion (head pkgsNV),
                       nubBy (equating installedPackageId) (reverse pkgsNV))
                    | pkgsNV <- groupBy (equating packageVersion) pkgsN
                    ]
            ]

    --
    -- * Updates
    --

    -- | Merge two indexes.
    --
    -- Packages from the second mask packages from the first if they have the exact
    -- same 'InstalledPackageId'.
    --
    -- For packages with the same source 'PackageId', packages from the second are
    -- \"preferred\" over those from the first. Being preferred means they are top
    -- result when we do a lookup by source 'PackageId'. This is the mechanism we
    -- use to prefer user packages over global packages.
    --
    merge :: PackageIndex -> PackageIndex -> PackageIndex
    merge (PackageIndex pids1 pnames1) (PackageIndex pids2 pnames2) =
      mkPackageIndex (Map.union pids1 pids2)
                     (Map.unionWith (Map.unionWith mergeBuckets) pnames1 pnames2)
      where
        -- Packages in the second list mask those in the first, however preferred
        -- packages go first in the list.
        mergeBuckets xs ys = ys ++ (xs \\ ys)
        (\\) = deleteFirstsBy (equating installedPackageId)

    -- | Inserts a single package into the index.
    --
    -- This is equivalent to (but slightly quicker than) using 'mappend' or
    -- 'merge' with a singleton index.
    --
    insert :: InstalledPackageInfo -> PackageIndex -> PackageIndex
    insert pkg (PackageIndex pids pnames) =
        mkPackageIndex pids' pnames'

      where
        pids'   = Map.insert (installedPackageId pkg) pkg pids
        pnames' = insertPackageName pnames
        insertPackageName =
          Map.insertWith' (\_ -> insertPackageVersion)
                         (packageName pkg)
                         (Map.singleton (packageVersion pkg) [pkg])

        insertPackageVersion =
          Map.insertWith' (\_ -> insertPackageInstance)
                         (packageVersion pkg) [pkg]

        insertPackageInstance pkgs =
          pkg : deleteBy (equating installedPackageId) pkg pkgs

    -- | Removes a single installed package from the index.
    --
    deleteInstalledPackageId :: InstalledPackageId -> PackageIndex -> PackageIndex
    deleteInstalledPackageId ipkgid original@(PackageIndex pids pnames) =
      case Map.updateLookupWithKey (\_ _ -> Nothing) ipkgid pids of
        (Nothing,     _)     -> original
        (Just spkgid, pids') -> mkPackageIndex pids'
                                              (deletePkgName spkgid pnames)

      where
        deletePkgName spkgid =
          Map.update (deletePkgVersion spkgid) (packageName spkgid)

        deletePkgVersion spkgid =
            (\m -> if Map.null m then Nothing else Just m)
          . Map.update deletePkgInstance (packageVersion spkgid)

        deletePkgInstance =
            (\xs -> if List.null xs then Nothing else Just xs)
          . List.deleteBy (\_ pkg -> installedPackageId pkg == ipkgid) undefined

    -- | Removes all packages with this source 'PackageId' from the index.
    --
    deleteSourcePackageId :: PackageId -> PackageIndex -> PackageIndex
    deleteSourcePackageId pkgid original@(PackageIndex pids pnames) =
      case Map.lookup (packageName pkgid) pnames of
        Nothing     -> original
        Just pvers  -> case Map.lookup (packageVersion pkgid) pvers of
          Nothing   -> original
          Just pkgs -> mkPackageIndex
                         (foldl' (flip (Map.delete . installedPackageId)) pids pkgs)
                         (deletePkgName pnames)
      where
        deletePkgName =
          Map.update deletePkgVersion (packageName pkgid)

        deletePkgVersion =
            (\m -> if Map.null m then Nothing else Just m)
          . Map.delete (packageVersion pkgid)

    -- | Removes all packages with this (case-sensitive) name from the index.
    --
    deletePackageName :: PackageName -> PackageIndex -> PackageIndex
    deletePackageName name original@(PackageIndex pids pnames) =
      case Map.lookup name pnames of
        Nothing     -> original
        Just pvers  -> mkPackageIndex
                         (foldl' (flip (Map.delete . installedPackageId)) pids
                                 (concat (Map.elems pvers)))
                         (Map.delete name pnames)

    {-
    -- | Removes all packages satisfying this dependency from the index.
    --
    deleteDependency :: Dependency -> PackageIndex -> PackageIndex
    deleteDependency (Dependency name verstionRange) =
      delete' name (\pkg -> packageVersion pkg `withinRange` verstionRange)
    -}

    --
    -- * Bulk queries
    --

    -- | Get all the packages from the index.
    --
    allPackages :: PackageIndex -> [InstalledPackageInfo]
    allPackages (PackageIndex pids _) = Map.elems pids

    -- | Get all the packages from the index.
    --
    -- They are grouped by package name, case-sensitively.
    --
    allPackagesByName :: PackageIndex -> [[InstalledPackageInfo]]
    allPackagesByName (PackageIndex _ pnames) =
      concatMap Map.elems (Map.elems pnames)

    --
    -- * Lookups
    --

    -- | Does a lookup by source package id (name & version).
    --
    -- Since multiple package DBs mask each other by 'InstalledPackageId',
    -- then we get back at most one package.
    --
    lookupInstalledPackageId :: PackageIndex -> InstalledPackageId
                             -> Maybe InstalledPackageInfo
    lookupInstalledPackageId (PackageIndex pids _) pid = Map.lookup pid pids

    -- | Does a lookup by source package id (name & version).
    --
    -- There can be multiple installed packages with the same source 'PackageId'
    -- but different 'InstalledPackageId'. They are returned in order of
    -- preference, with the most preferred first.
    --
    lookupSourcePackageId :: PackageIndex -> PackageId -> [InstalledPackageInfo]
    lookupSourcePackageId (PackageIndex _ pnames) pkgid =
      case Map.lookup (packageName pkgid) pnames of
        Nothing     -> []
        Just pvers  -> case Map.lookup (packageVersion pkgid) pvers of
          Nothing   -> []
          Just pkgs -> pkgs -- in preference order

    -- | Does a lookup by source package name.
    --
    lookupPackageName :: PackageIndex -> PackageName
                      -> [(Version, [InstalledPackageInfo])]
    lookupPackageName (PackageIndex _ pnames) name =
      case Map.lookup name pnames of
        Nothing     -> []
        Just pvers  -> Map.toList pvers

    -- | Does a lookup by source package name and a range of versions.
    --
    -- We get back any number of versions of the specified package name, all
    -- satisfying the version range constraint.
    --
    lookupDependency :: PackageIndex -> Dependency
                     -> [(Version, [InstalledPackageInfo])]
    lookupDependency (PackageIndex _ pnames) (Dependency name versionRange) =
      case Map.lookup name pnames of
        Nothing    -> []
        Just pvers -> [ entry
                      | entry@(ver, _) <- Map.toList pvers
                      , ver `withinRange` versionRange ]

    --
    -- * Case insensitive name lookups
    --

    -- | Does a case-insensitive search by package name.
    --
    -- If there is only one package that compares case-insentiviely to this name
    -- then the search is unambiguous and we get back all versions of that package.
    -- If several match case-insentiviely but one matches exactly then it is also
    -- unambiguous.
    --
    -- If however several match case-insentiviely and none match exactly then we
    -- have an ambiguous result, and we get back all the versions of all the
    -- packages. The list of ambiguous results is split by exact package name. So
    -- it is a non-empty list of non-empty lists.
    --
    searchByName :: PackageIndex -> String -> SearchResult [InstalledPackageInfo]
    searchByName (PackageIndex _ pnames) name =
      case [ pkgs | pkgs@(PackageName name',_) <- Map.toList pnames
                  , lowercase name' == lname ] of
        []               -> None
        [(_,pvers)]      -> Unambiguous (concat (Map.elems pvers))
        pkgss            -> case find ((PackageName name==) . fst) pkgss of
          Just (_,pvers) -> Unambiguous (concat (Map.elems pvers))
          Nothing        -> Ambiguous (map (concat . Map.elems . snd) pkgss)
      where lname = lowercase name

    data SearchResult a = None | Unambiguous a | Ambiguous [a]

    -- | Does a case-insensitive substring search by package name.
    --
    -- That is, all packages that contain the given string in their name.
    --
    searchByNameSubstring :: PackageIndex -> String -> [InstalledPackageInfo]
    searchByNameSubstring (PackageIndex _ pnames) searchterm =
      [ pkg
      | (PackageName name, pvers) <- Map.toList pnames
      , lsearchterm `isInfixOf` lowercase name
      , pkgs <- Map.elems pvers
      , pkg <- pkgs ]
      where lsearchterm = lowercase searchterm

    --
    -- * Special queries
    --

    -- None of the stuff below depends on the internal representation of the index.
    --

    -- | Find if there are any cycles in the dependency graph. If there are no
    -- cycles the result is @[]@.
    --
    -- This actually computes the strongly connected components. So it gives us a
    -- list of groups of packages where within each group they all depend on each
    -- other, directly or indirectly.
    --
    dependencyCycles :: PackageIndex -> [[InstalledPackageInfo]]
    dependencyCycles index =
      [ vs | Graph.CyclicSCC vs <- Graph.stronglyConnComp adjacencyList ]
      where
        adjacencyList = [ (pkg, installedPackageId pkg, IPI.depends pkg)
                        | pkg <- allPackages index ]

    -- | All packages that have immediate dependencies that are not in the index.
    --
    -- Returns such packages along with the dependencies that they're missing.
    --
    brokenPackages :: PackageIndex -> [(InstalledPackageInfo, [InstalledPackageId])]
    brokenPackages index =
      [ (pkg, missing)
      | pkg  <- allPackages index
      , let missing = [ pkg' | pkg' <- IPI.depends pkg
                             , isNothing (lookupInstalledPackageId index pkg') ]
      , not (null missing) ]

    -- | Tries to take the transitive closure of the package dependencies.
    --
    -- If the transitive closure is complete then it returns that subset of the
    -- index. Otherwise it returns the broken packages as in 'brokenPackages'.
    --
    -- * Note that if the result is @Right []@ it is because at least one of
    -- the original given 'PackageId's do not occur in the index.
    --
    dependencyClosure :: PackageIndex
                      -> [InstalledPackageId]
                      -> Either PackageIndex
                                [(InstalledPackageInfo, [InstalledPackageId])]
    dependencyClosure index pkgids0 = case closure mempty [] pkgids0 of
      (completed, []) -> Left completed
      (completed, _)  -> Right (brokenPackages completed)
     where
        closure completed failed []             = (completed, failed)
        closure completed failed (pkgid:pkgids) = case lookupInstalledPackageId index pkgid of
          Nothing   -> closure completed (pkgid:failed) pkgids
          Just pkg  -> case lookupInstalledPackageId completed (installedPackageId pkg) of
            Just _  -> closure completed  failed pkgids
            Nothing -> closure completed' failed pkgids'
              where completed' = insert pkg completed
                    pkgids'    = IPI.depends pkg ++ pkgids

    -- | Takes the transitive closure of the packages reverse dependencies.
    --
    -- * The given 'PackageId's must be in the index.
    --
    reverseDependencyClosure :: PackageIndex
                             -> [InstalledPackageId]
                             -> [InstalledPackageInfo]
    reverseDependencyClosure index =
        map vertexToPkg
      . concatMap Tree.flatten
      . Graph.dfs reverseDepGraph
      . map (fromMaybe noSuchPkgId . pkgIdToVertex)

      where
        (depGraph, vertexToPkg, pkgIdToVertex) = dependencyGraph index
        reverseDepGraph = Graph.transposeG depGraph
        noSuchPkgId = error "reverseDependencyClosure: package is not in the graph"

    topologicalOrder :: PackageIndex -> [InstalledPackageInfo]
    topologicalOrder index = map toPkgId
                           . Graph.topSort
                           $ graph
      where (graph, toPkgId, _) = dependencyGraph index

    reverseTopologicalOrder :: PackageIndex -> [InstalledPackageInfo]
    reverseTopologicalOrder index = map toPkgId
                                  . Graph.topSort
                                  . Graph.transposeG
                                  $ graph
      where (graph, toPkgId, _) = dependencyGraph index

    -- | Builds a graph of the package dependencies.
    --
    -- Dependencies on other packages that are not in the index are discarded.
    -- You can check if there are any such dependencies with 'brokenPackages'.
    --
    dependencyGraph :: PackageIndex
                    -> (Graph.Graph,
                        Graph.Vertex -> InstalledPackageInfo,
                        InstalledPackageId -> Maybe Graph.Vertex)
    dependencyGraph index = (graph, vertex_to_pkg, id_to_vertex)
      where
        graph = Array.listArray bounds
                  [ [ v | Just v <- map id_to_vertex (IPI.depends pkg) ]
                  | pkg <- pkgs ]

        pkgs             = sortBy (comparing packageId) (allPackages index)
        vertices         = zip (map installedPackageId pkgs) [0..]
        vertex_map       = Map.fromList vertices
        id_to_vertex pid = Map.lookup pid vertex_map

        vertex_to_pkg vertex = pkgTable ! vertex

        pkgTable   = Array.listArray bounds pkgs
        topBound = length pkgs - 1
        bounds = (0, topBound)

    -- | Given a package index where we assume we want to use all the packages
    -- (use 'dependencyClosure' if you need to get such a index subset) find out
    -- if the dependencies within it use consistent versions of each package.
    -- Return all cases where multiple packages depend on different versions of
    -- some other package.
    --
    -- Each element in the result is a package name along with the packages that
    -- depend on it and the versions they require. These are guaranteed to be
    -- distinct.
    --
    dependencyInconsistencies :: PackageIndex
                              -> [(PackageName, [(PackageId, Version)])]
    dependencyInconsistencies index =
      [ (name, [ (pid,packageVersion dep) | (dep,pids) <- uses, pid <- pids])
      | (name, ipid_map) <- Map.toList inverseIndex
      , let uses = Map.elems ipid_map
      , reallyIsInconsistent (map fst uses) ]

      where -- for each PackageName,
            --   for each package with that name,
            --     the InstalledPackageInfo and the package Ids of packages
            --     that depend on it.
            inverseIndex :: Map PackageName
                                (Map InstalledPackageId
                                     (InstalledPackageInfo, [PackageId]))
            inverseIndex = Map.fromListWith (Map.unionWith (\(a,b) (_,b') -> (a,b++b')))
              [ (packageName dep,
                 Map.fromList [(ipid,(dep,[packageId pkg]))])
              | pkg <- allPackages index
              , ipid <- IPI.depends pkg
              , Just dep <- [lookupInstalledPackageId index ipid]
              ]

            reallyIsInconsistent :: [InstalledPackageInfo] -> Bool
            reallyIsInconsistent []       = False
            reallyIsInconsistent [_p]     = False
            reallyIsInconsistent [p1, p2] =
                 installedPackageId p1 `notElem` IPI.depends p2
              && installedPackageId p2 `notElem` IPI.depends p1
            reallyIsInconsistent _ = True

    moduleNameIndex :: PackageIndex -> Map ModuleName [InstalledPackageInfo]
    moduleNameIndex index =
      Map.fromListWith (++)
        [ (moduleName, [pkg])
        | pkg        <- allPackages index
        , moduleName <- IPI.exposedModules pkg ]