    {-# LANGUAGE ScopedTypeVariables #-}
    {-# LANGUAGE TypeFamilies #-}
    -- | See <https://github.com/ezyang/ghc-proposals/blob/backpack/proposals/0000-backpack.rst>
    module Distribution.Backpack.LinkedComponent (
        LinkedComponent(..),
        lc_insts,
        lc_uid,
        lc_cid,
        lc_pkgid,
        toLinkedComponent,
        toLinkedComponents,
        dispLinkedComponent,
        LinkedComponentMap,
        extendLinkedComponentMap,
    ) where

    import Prelude ()
    import Distribution.Compat.Prelude hiding ((<>))

    import Distribution.Backpack
    import Distribution.Backpack.FullUnitId
    import Distribution.Backpack.ConfiguredComponent
    import Distribution.Backpack.ModuleShape
    import Distribution.Backpack.PreModuleShape
    import Distribution.Backpack.ModuleScope
    import Distribution.Backpack.UnifyM
    import Distribution.Backpack.MixLink
    import Distribution.Utils.MapAccum

    import Distribution.Types.AnnotatedId
    import Distribution.Types.ComponentName
    import Distribution.Types.ModuleRenaming
    import Distribution.Types.IncludeRenaming
    import Distribution.Types.ComponentInclude
    import Distribution.Types.ComponentId
    import Distribution.Types.PackageId
    import Distribution.Package
    import Distribution.PackageDescription as PD hiding (Flag)
    import Distribution.ModuleName
    import Distribution.Simple.LocalBuildInfo
    import Distribution.Verbosity
    import Distribution.Utils.LogProgress

    import qualified Data.Set as Set
    import qualified Data.Map as Map
    import Data.Traversable
        ( mapM )
    import Distribution.Text
        ( Text(disp) )
    import Text.PrettyPrint
    import Data.Either

    -- | A linked component is a component that has been mix-in linked, at
    -- which point we have determined how all the dependencies of the
    -- component are explicitly instantiated (in the form of an OpenUnitId).
    -- 'ConfiguredComponent' is mix-in linked into 'LinkedComponent', which
    -- is then instantiated into 'ReadyComponent'.
    data LinkedComponent
        = LinkedComponent {
            -- | Uniquely identifies linked component
            lc_ann_id :: AnnotatedId ComponentId,
            -- | Corresponds to 'cc_component'.
            lc_component :: Component,
            -- | @build-tools@ and @build-tool-depends@ dependencies.
            -- Corresponds to 'cc_exe_deps'.
            lc_exe_deps :: [AnnotatedId OpenUnitId],
            -- | Is this the public library of a package?  Corresponds to
            -- 'cc_public'.
            lc_public :: Bool,
            -- | Corresponds to 'cc_includes', but (1) this does not contain
            -- includes of signature packages (packages with no exports),
            -- and (2) the 'ModuleRenaming' for requirements (stored in
            -- 'IncludeRenaming') has been removed, as it is reflected in
            -- 'OpenUnitId'.)
            lc_includes :: [ComponentInclude OpenUnitId ModuleRenaming],
            -- | Like 'lc_includes', but this specifies includes on
            -- signature packages which have no exports.
            lc_sig_includes :: [ComponentInclude OpenUnitId ModuleRenaming],
            -- | The module shape computed by mix-in linking.  This is
            -- newly computed from 'ConfiguredComponent'
            lc_shape :: ModuleShape
          }

    -- | Uniquely identifies a 'LinkedComponent'.  Corresponds to
    -- 'cc_cid'.
    lc_cid :: LinkedComponent -> ComponentId
    lc_cid = ann_id . lc_ann_id

    -- | Corresponds to 'cc_pkgid'.
    lc_pkgid :: LinkedComponent -> PackageId
    lc_pkgid = ann_pid . lc_ann_id

    -- | The 'OpenUnitId' of this component in the "default" instantiation.
    -- See also 'lc_insts'.  'LinkedComponent's cannot be instantiated
    -- (e.g., there is no 'ModSubst' instance for them).
    lc_uid :: LinkedComponent -> OpenUnitId
    lc_uid lc = IndefFullUnitId (lc_cid lc) . Map.fromList $ lc_insts lc

    -- | The instantiation of 'lc_uid'; this always has the invariant
    -- that it is a mapping from a module name @A@ to @<A>@ (the hole A).
    lc_insts :: LinkedComponent -> [(ModuleName, OpenModule)]
    lc_insts lc = [ (req, OpenModuleVar req)
                  | req <- Set.toList (modShapeRequires (lc_shape lc)) ]

    dispLinkedComponent :: LinkedComponent -> Doc
    dispLinkedComponent lc =
        hang (text "unit" <+> disp (lc_uid lc)) 4 $
             vcat [ text "include" <+> disp (ci_id incl) <+> disp (ci_renaming incl)
                  | incl <- lc_includes lc ]
                $+$
             vcat [ text "signature include" <+> disp (ci_id incl)
                  | incl <- lc_sig_includes lc ]
                $+$ dispOpenModuleSubst (modShapeProvides (lc_shape lc))

    instance Package LinkedComponent where
        packageId = lc_pkgid

    toLinkedComponent
        :: Verbosity
        -> FullDb
        -> PackageId
        -> LinkedComponentMap
        -> ConfiguredComponent
        -> LogProgress LinkedComponent
    toLinkedComponent verbosity db this_pid pkg_map ConfiguredComponent {
        cc_ann_id = aid@AnnotatedId { ann_id = this_cid },
        cc_component = component,
        cc_exe_deps = exe_deps,
        cc_public = is_public,
        cc_includes = cid_includes
       } = do
        let
            -- The explicitly specified requirements, provisions and
            -- reexports from the Cabal file.  These are only non-empty for
            -- libraries; everything else is trivial.
            (src_reqs      :: [ModuleName],
             src_provs     :: [ModuleName],
             src_reexports :: [ModuleReexport]) =
                case component of
                    CLib lib -> (signatures lib,
                                 exposedModules lib,
                                 reexportedModules lib)
                    _ -> ([], [], [])
            src_hidden = otherModules (componentBuildInfo component)

            -- Take each included ComponentId and resolve it into an
            -- *unlinked* unit identity.  We will use unification (relying
            -- on the ModuleShape) to resolve these into linked identities.
            unlinked_includes :: [ComponentInclude (OpenUnitId, ModuleShape) IncludeRenaming]
            unlinked_includes = [ ComponentInclude (fmap lookupUid dep_aid) rns i
                                | ComponentInclude dep_aid rns i <- cid_includes ]

            lookupUid :: ComponentId -> (OpenUnitId, ModuleShape)
            lookupUid cid = fromMaybe (error "linkComponent: lookupUid")
                                        (Map.lookup cid pkg_map)

        let orErr (Right x) = return x
            orErr (Left [err]) = dieProgress err
            orErr (Left errs) = do
                dieProgress (vcat (intersperse (text "") -- double newline!
                                    [ hang (text "-") 2 err | err <- errs]))

        -- Pre-shaping
        let pre_shape = mixLinkPreModuleShape $
                PreModuleShape {
                    preModShapeProvides = Set.fromList (src_provs ++ src_hidden),
                    preModShapeRequires = Set.fromList src_reqs
                } : [ renamePreModuleShape (toPreModuleShape sh) rns
                    | ComponentInclude (AnnotatedId { ann_id = (_, sh) }) rns _ <- unlinked_includes ]
            reqs  = preModShapeRequires pre_shape
            insts = [ (req, OpenModuleVar req)
                    | req <- Set.toList reqs ]
            this_uid = IndefFullUnitId this_cid . Map.fromList $ insts

        -- OK, actually do unification
        -- TODO: the unification monad might return errors, in which
        -- case we have to deal.  Use monadic bind for now.
        (linked_shape0  :: ModuleScope,
         linked_includes0 :: [ComponentInclude OpenUnitId ModuleRenaming],
         linked_sig_includes0 :: [ComponentInclude OpenUnitId ModuleRenaming])
          <- orErr $ runUnifyM verbosity this_cid db $ do
            -- The unification monad is implemented using mutable
            -- references.  Thus, we must convert our *pure* data
            -- structures into mutable ones to perform unification.

            let convertMod :: (ModuleName -> ModuleSource) -> ModuleName -> UnifyM s (ModuleScopeU s)
                convertMod from m = do
                    m_u <- convertModule (OpenModule this_uid m)
                    return (Map.singleton m [WithSource (from m) m_u], Map.empty)
            -- Handle 'exposed-modules'
            exposed_mod_shapes_u <- mapM (convertMod FromExposedModules) src_provs
            -- Handle 'other-modules'
            other_mod_shapes_u <- mapM (convertMod FromOtherModules) src_hidden

            -- Handle 'signatures'
            let convertReq :: ModuleName -> UnifyM s (ModuleScopeU s)
                convertReq req = do
                    req_u <- convertModule (OpenModuleVar req)
                    return (Map.empty, Map.singleton req [WithSource (FromSignatures req) req_u])
            req_shapes_u <- mapM convertReq src_reqs

            -- Handle 'mixins'
            (incl_shapes_u, all_includes_u) <- fmap unzip (mapM convertInclude unlinked_includes)

            failIfErrs -- Prevent error cascade
            -- Mix-in link everything!  mixLink is the real workhorse.
            shape_u <- mixLink $ exposed_mod_shapes_u
                              ++ other_mod_shapes_u
                              ++ req_shapes_u
                              ++ incl_shapes_u

            -- src_reqs_u <- mapM convertReq src_reqs
            -- Read out all the final results by converting back
            -- into a pure representation.
            let convertIncludeU (ComponentInclude dep_aid rns i) = do
                    uid <- convertUnitIdU (ann_id dep_aid)
                    return (ComponentInclude {
                                ci_ann_id = dep_aid { ann_id = uid },
                                ci_renaming = rns,
                                ci_implicit = i
                            })
            shape <- convertModuleScopeU shape_u
            let (includes_u, sig_includes_u) = partitionEithers all_includes_u
            incls <- mapM convertIncludeU includes_u
            sig_incls <- mapM convertIncludeU sig_includes_u
            return (shape, incls, sig_incls)

        let isNotLib (CLib _) = False
            isNotLib _        = True
        when (not (Set.null reqs) && isNotLib component) $
            dieProgress $
                hang (text "Non-library component has unfilled requirements:")
                    4 (vcat [disp req | req <- Set.toList reqs])

        -- NB: do NOT include hidden modules here: GHC 7.10's ghc-pkg
        -- won't allow it (since someone could directly synthesize
        -- an 'InstalledPackageInfo' that violates abstraction.)
        -- Though, maybe it should be relaxed?
        let src_hidden_set = Set.fromList src_hidden
            linked_shape = linked_shape0 {
                modScopeProvides =
                    -- Would rather use withoutKeys but need BC
                    Map.filterWithKey
                        (\k _ -> not (k `Set.member` src_hidden_set))
                        (modScopeProvides linked_shape0)
                }

        -- OK, compute the reexports
        -- TODO: This code reports the errors for reexports one reexport at
        -- a time.  Better to collect them all up and report them all at
        -- once.
        let hdl :: [Either Doc a] -> LogProgress [a]
            hdl es =
                case partitionEithers es of
                    ([], rs) -> return rs
                    (ls, _) ->
                        dieProgress $
                         hang (text "Problem with module re-exports:") 2
                            (vcat [hang (text "-") 2 l | l <- ls])
        reexports_list <- hdl . (flip map) src_reexports $ \reex@(ModuleReexport mb_pn from to) -> do
          case Map.lookup from (modScopeProvides linked_shape) of
            Just cands@(x0:xs0) -> do
              -- Make sure there is at least one candidate
              (x, xs) <-
                case mb_pn of
                  Just pn ->
                    let matches_pn (FromMixins pn' _ _)     = pn == pn'
                        matches_pn (FromBuildDepends pn' _) = pn == pn'
                        matches_pn (FromExposedModules _) = pn == packageName this_pid
                        matches_pn (FromOtherModules _)   = pn == packageName this_pid
                        matches_pn (FromSignatures _)     = pn == packageName this_pid
                    in case filter (matches_pn . getSource) cands of
                        (x1:xs1) -> return (x1, xs1)
                        _ -> Left (brokenReexportMsg reex)
                  Nothing -> return (x0, xs0)
              -- Test that all the candidates are consistent
              case filter (\x' -> unWithSource x /= unWithSource x') xs of
                [] -> return ()
                _ -> Left $ ambiguousReexportMsg reex x xs
              return (to, unWithSource x)
            _ ->
              Left (brokenReexportMsg reex)

        -- TODO: maybe check this earlier; it's syntactically obvious.
        let build_reexports m (k, v)
                | Map.member k m =
                    dieProgress $ hsep
                        [ text "Module name ", disp k, text " is exported multiple times." ]
                | otherwise = return (Map.insert k v m)
        provs <- foldM build_reexports Map.empty $
                    -- TODO: doublecheck we have checked for
                    -- src_provs duplicates already!
                    [ (mod_name, OpenModule this_uid mod_name) | mod_name <- src_provs ] ++
                    reexports_list

        let final_linked_shape = ModuleShape provs (Map.keysSet (modScopeRequires linked_shape))

        -- See Note Note [Signature package special case]
        let (linked_includes, linked_sig_includes)
                | Set.null reqs = (linked_includes0 ++ linked_sig_includes0, [])
                | otherwise     = (linked_includes0, linked_sig_includes0)

        return $ LinkedComponent {
                    lc_ann_id = aid,
                    lc_component = component,
                    lc_public = is_public,
                    -- These must be executables
                    lc_exe_deps = map (fmap (\cid -> IndefFullUnitId cid Map.empty)) exe_deps,
                    lc_shape = final_linked_shape,
                    lc_includes = linked_includes,
                    lc_sig_includes = linked_sig_includes
               }

    -- Note [Signature package special case]
    -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    -- Suppose we have p-indef, which depends on str-sig and inherits
    -- the hole from that signature package.  When we instantiate p-indef,
    -- it's a bit pointless to also go ahead and build str-sig, because
    -- str-sig cannot possibly have contributed any code to the package
    -- in question.  Furthermore, because the signature was inherited to
    -- p-indef, if we test matching against p-indef, we also have tested
    -- matching against p-sig.  In fact, skipping p-sig is *mandatory*,
    -- because p-indef may have thinned it (so that an implementation may
    -- match p-indef but not p-sig.)
    --
    -- However, suppose that we have a package which mixes together str-sig
    -- and str-bytestring, with the intent of *checking* that str-sig is
    -- implemented by str-bytestring.  Here, it's quite important to
    -- build an instantiated str-sig, since that is the only way we will
    -- actually end up testing if the matching works.  Note that this
    -- admonition only applies if the package has NO requirements; if it
    -- has any requirements, we will typecheck it as an indefinite
    -- package, at which point the signature includes will be passed to
    -- GHC who will in turn actually do the checking to make sure they
    -- are instantiated correctly.

    -- Handle mix-in linking for components.  In the absence of Backpack,
    -- every ComponentId gets converted into a UnitId by way of SimpleUnitId.
    toLinkedComponents
        :: Verbosity
        -> FullDb
        -> PackageId
        -> LinkedComponentMap
        -> [ConfiguredComponent]
        -> LogProgress [LinkedComponent]
    toLinkedComponents verbosity db this_pid lc_map0 comps
       = fmap snd (mapAccumM go lc_map0 comps)
     where
      go :: Map ComponentId (OpenUnitId, ModuleShape)
         -> ConfiguredComponent
         -> LogProgress (Map ComponentId (OpenUnitId, ModuleShape), LinkedComponent)
      go lc_map cc = do
        lc <- addProgressCtx (text "In the stanza" <+> text (componentNameStanza (cc_name cc))) $
                toLinkedComponent verbosity db this_pid lc_map cc
        return (extendLinkedComponentMap lc lc_map, lc)

    type LinkedComponentMap = Map ComponentId (OpenUnitId, ModuleShape)

    extendLinkedComponentMap :: LinkedComponent
                             -> LinkedComponentMap
                             -> LinkedComponentMap
    extendLinkedComponentMap lc m =
        Map.insert (lc_cid lc) (lc_uid lc, lc_shape lc) m

    brokenReexportMsg :: ModuleReexport -> Doc
    brokenReexportMsg (ModuleReexport (Just pn) from _to) =
      vcat [ text "The package" <+> quotes (disp pn)
           , text "does not export a module" <+> quotes (disp from) ]
    brokenReexportMsg (ModuleReexport Nothing from _to) =
      vcat [ text "The module" <+> quotes (disp from)
           , text "is not exported by any suitable package."
           , text "It occurs in neither the 'exposed-modules' of this package,"
           , text "nor any of its 'build-depends' dependencies." ]

    ambiguousReexportMsg :: ModuleReexport -> ModuleWithSource -> [ModuleWithSource] -> Doc
    ambiguousReexportMsg (ModuleReexport mb_pn from _to) y1 ys =
      vcat [ text "Ambiguous reexport" <+> quotes (disp from)
           , hang (text "It could refer to either:") 2
                (vcat (msg : msgs))
           , help_msg mb_pn ]
      where
        msg  = text "  " <+> displayModuleWithSource y1
        msgs = [text "or" <+> displayModuleWithSource y | y <- ys]
        help_msg Nothing =
          -- TODO: This advice doesn't help if the ambiguous exports
          -- come from a package named the same thing
          vcat [ text "The ambiguity can be resolved by qualifying the"
               , text "re-export with a package name."
               , text "The syntax is 'packagename:ModuleName [as NewName]'." ]
        -- Qualifying won't help that much.
        help_msg (Just _) =
          vcat [ text "The ambiguity can be resolved by using the"
               , text "mixins field to rename one of the module"
               , text "names differently." ]
        displayModuleWithSource y
          = vcat [ quotes (disp (unWithSource y))
                 , text "brought into scope by" <+>
                    dispModuleSource (getSource y)
                 ]