{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE CPP #-}
#ifdef DEBUG_CONFLICT_SETS
{-# LANGUAGE ImplicitParams #-}
#endif
module Distribution.Solver.Modular.Validate (validateTree) where

-- Validation of the tree.
--
-- The task here is to make sure all constraints hold. After validation, any
-- assignment returned by exploration of the tree should be a complete valid
-- assignment, i.e., actually constitute a solution.

import Control.Applicative
import Control.Monad.Reader hiding (sequence)
import Data.Function (on)
import Data.List as L
import Data.Set as S
import Data.Traversable
import Prelude hiding (sequence)

import Language.Haskell.Extension (Extension, Language)

import Distribution.Compat.Map.Strict as M
import Distribution.Compiler (CompilerInfo(..))

import Distribution.Solver.Modular.Assignment
import qualified Distribution.Solver.Modular.ConflictSet as CS
import Distribution.Solver.Modular.Dependency
import Distribution.Solver.Modular.Flag
import Distribution.Solver.Modular.Index
import Distribution.Solver.Modular.Package
import Distribution.Solver.Modular.Tree
import Distribution.Solver.Modular.Version
import qualified Distribution.Solver.Modular.WeightedPSQ as W

import Distribution.Solver.Types.PackagePath
import Distribution.Solver.Types.PkgConfigDb (PkgConfigDb, pkgConfigPkgIsPresent)
import Distribution.Types.UnqualComponentName

#ifdef DEBUG_CONFLICT_SETS
import GHC.Stack (CallStack)
#endif

-- In practice, most constraints are implication constraints (IF we have made
-- a number of choices, THEN we also have to ensure that). We call constraints
-- that for which the preconditions are fulfilled ACTIVE. We maintain a set
-- of currently active constraints that we pass down the node.
--
-- We aim at detecting inconsistent states as early as possible.
--
-- Whenever we make a choice, there are two things that need to happen:
--
--   (1) We must check that the choice is consistent with the currently
--       active constraints.
--
--   (2) The choice increases the set of active constraints. For the new
--       active constraints, we must check that they are consistent with
--       the current state.
--
-- We can actually merge (1) and (2) by saying the the current choice is
-- a new active constraint, fixing the choice.
--
-- If a test fails, we have detected an inconsistent state. We can
-- disable the current subtree and do not have to traverse it any further.
--
-- We need a good way to represent the current state, i.e., the current
-- set of active constraints. Since the main situation where we have to
-- search in it is (1), it seems best to store the state by package: for
-- every package, we store which versions are still allowed. If for any
-- package, we have inconsistent active constraints, we can also stop.
-- This is a particular way to read task (2):
--
--   (2, weak) We only check if the new constraints are consistent with
--       the choices we've already made, and add them to the active set.
--
--   (2, strong) We check if the new constraints are consistent with the
--       choices we've already made, and the constraints we already have.
--
-- It currently seems as if we're implementing the weak variant. However,
-- when used together with 'preferEasyGoalChoices', we will find an
-- inconsistent state in the very next step.
--
-- What do we do about flags?
--
-- Like for packages, we store the flag choices we have already made.
-- Now, regarding (1), we only have to test whether we've decided the
-- current flag before. Regarding (2), the interesting bit is in discovering
-- the new active constraints. To this end, we look up the constraints for
-- the package the flag belongs to, and traverse its flagged dependencies.
-- Wherever we find the flag in question, we start recording dependencies
-- underneath as new active dependencies. If we encounter other flags, we
-- check if we've chosen them already and either proceed or stop.

-- | The state needed during validation.
data ValidateState = VS {
  supportedExt  :: Extension -> Bool,
  supportedLang :: Language  -> Bool,
  presentPkgs   :: PkgconfigName -> VR  -> Bool,
  index :: Index,

  -- Saved, scoped, dependencies. Every time 'validate' makes a package choice,
  -- it qualifies the package's dependencies and saves them in this map. Then
  -- the qualified dependencies are available for subsequent flag and stanza
  -- choices for the same package.
  saved :: Map QPN (FlaggedDeps QPN),

  pa    :: PreAssignment,

  -- Map from package name to the executables that are provided by the chosen
  -- instance of that package.
  availableExes  :: Map QPN [UnqualComponentName],

  -- Map from package name to the executables that are required from that
  -- package.
  requiredExes   :: Map QPN ExeDeps,

  qualifyOptions :: QualifyOptions
}

newtype Validate a = Validate (Reader ValidateState a)
  deriving (Functor, Applicative, Monad, MonadReader ValidateState)

runValidate :: Validate a -> ValidateState -> a
runValidate (Validate r) = runReader r

-- | A preassignment comprises knowledge about variables, but not
-- necessarily fixed values.
data PreAssignment = PA PPreAssignment FAssignment SAssignment

-- | A (partial) package preassignment. Qualified package names
-- are associated with MergedPkgDeps.
type PPreAssignment = Map QPN MergedPkgDep

-- | A dependency on a package, including its DependencyReason.
data PkgDep = PkgDep (DependencyReason QPN) (Maybe UnqualComponentName) QPN CI

-- | Map from executable name to one of the reasons that the executable is
-- required.
type ExeDeps = Map UnqualComponentName (DependencyReason QPN)

-- | MergedPkgDep records constraints about the instances that can still be
-- chosen, and in the extreme case fixes a concrete instance. Otherwise, it is a
-- list of version ranges paired with the goals / variables that introduced
-- them. It also records whether a package is a build-tool dependency, for each
-- reason that it was introduced.
--
-- It is important to store the executable name with the version constraint, for
-- error messages, because whether something is a build-tool dependency affects
-- its qualifier, which affects which constraint is applied.
data MergedPkgDep =
    MergedDepFixed (Maybe UnqualComponentName) (DependencyReason QPN) I
  | MergedDepConstrained [VROrigin]

-- | Version ranges paired with origins.
type VROrigin = (VR, Maybe UnqualComponentName, DependencyReason QPN)

-- | The information needed to create a 'Fail' node.
type Conflict = (ConflictSet, FailReason)

validate :: Tree d c -> Validate (Tree d c)
validate = cata go
  where
    go :: TreeF d c (Validate (Tree d c)) -> Validate (Tree d c)

    go (PChoiceF qpn rdm gr       ts) = PChoice qpn rdm gr <$> sequence (W.mapWithKey (goP qpn) ts)
    go (FChoiceF qfn rdm gr b m d ts) =
      do
        -- Flag choices may occur repeatedly (because they can introduce new constraints
        -- in various places). However, subsequent choices must be consistent. We thereby
        -- collapse repeated flag choice nodes.
        PA _ pfa _ <- asks pa -- obtain current flag-preassignment
        case M.lookup qfn pfa of
          Just rb -> -- flag has already been assigned; collapse choice to the correct branch
                     case W.lookup rb ts of
                       Just t  -> goF qfn rb t
                       Nothing -> return $ Fail (varToConflictSet (F qfn)) (MalformedFlagChoice qfn)
          Nothing -> -- flag choice is new, follow both branches
                     FChoice qfn rdm gr b m d <$> sequence (W.mapWithKey (goF qfn) ts)
    go (SChoiceF qsn rdm gr b   ts) =
      do
        -- Optional stanza choices are very similar to flag choices.
        PA _ _ psa <- asks pa -- obtain current stanza-preassignment
        case M.lookup qsn psa of
          Just rb -> -- stanza choice has already been made; collapse choice to the correct branch
                     case W.lookup rb ts of
                       Just t  -> goS qsn rb t
                       Nothing -> return $ Fail (varToConflictSet (S qsn)) (MalformedStanzaChoice qsn)
          Nothing -> -- stanza choice is new, follow both branches
                     SChoice qsn rdm gr b <$> sequence (W.mapWithKey (goS qsn) ts)

    -- We don't need to do anything for goal choices or failure nodes.
    go (GoalChoiceF rdm           ts) = GoalChoice rdm <$> sequence ts
    go (DoneF       rdm s           ) = pure (Done rdm s)
    go (FailF    c fr               ) = pure (Fail c fr)

    -- What to do for package nodes ...
    goP :: QPN -> POption -> Validate (Tree d c) -> Validate (Tree d c)
    goP qpn@(Q _pp pn) (POption i _) r = do
      PA ppa pfa psa <- asks pa    -- obtain current preassignment
      extSupported   <- asks supportedExt  -- obtain the supported extensions
      langSupported  <- asks supportedLang -- obtain the supported languages
      pkgPresent     <- asks presentPkgs -- obtain the present pkg-config pkgs
      idx            <- asks index -- obtain the index
      svd            <- asks saved -- obtain saved dependencies
      aExes          <- asks availableExes
      rExes          <- asks requiredExes
      qo             <- asks qualifyOptions
      -- obtain dependencies and index-dictated exclusions introduced by the choice
      let (PInfo deps exes _ mfr) = idx ! pn ! i
      -- qualify the deps in the current scope
      let qdeps = qualifyDeps qo qpn deps
      -- the new active constraints are given by the instance we have chosen,
      -- plus the dependency information we have for that instance
      let newactives = extractAllDeps pfa psa qdeps
      -- We now try to extend the partial assignment with the new active constraints.
      let mnppa = extend extSupported langSupported pkgPresent newactives
                   =<< extendWithPackageChoice (PI qpn i) ppa
      -- In case we continue, we save the scoped dependencies
      let nsvd = M.insert qpn qdeps svd
      case mfr of
        Just fr -> -- The index marks this as an invalid choice. We can stop.
                   return (Fail (varToConflictSet (P qpn)) fr)
        Nothing ->
          let newDeps :: Either Conflict (PPreAssignment, Map QPN ExeDeps)
              newDeps = do
                nppa <- mnppa
                rExes' <- extendRequiredExes aExes rExes newactives
                checkExesInNewPackage rExes qpn exes
                return (nppa, rExes')
          in case newDeps of
               Left (c, fr)         -> -- We have an inconsistency. We can stop.
                                       return (Fail c fr)
               Right (nppa, rExes') -> -- We have an updated partial assignment for the recursive validation.
                                       local (\ s -> s { pa = PA nppa pfa psa
                                                       , saved = nsvd
                                                       , availableExes = M.insert qpn exes aExes
                                                       , requiredExes = rExes'
                                                       }) r

    -- What to do for flag nodes ...
    goF :: QFN -> Bool -> Validate (Tree d c) -> Validate (Tree d c)
    goF qfn@(FN qpn _f) b r = do
      PA ppa pfa psa <- asks pa -- obtain current preassignment
      extSupported   <- asks supportedExt  -- obtain the supported extensions
      langSupported  <- asks supportedLang -- obtain the supported languages
      pkgPresent     <- asks presentPkgs   -- obtain the present pkg-config pkgs
      svd            <- asks saved         -- obtain saved dependencies
      aExes          <- asks availableExes
      rExes          <- asks requiredExes
      -- Note that there should be saved dependencies for the package in question,
      -- because while building, we do not choose flags before we see the packages
      -- that define them.
      let qdeps = svd ! qpn
      -- We take the *saved* dependencies, because these have been qualified in the
      -- correct scope.
      --
      -- Extend the flag assignment
      let npfa = M.insert qfn b pfa
      -- We now try to get the new active dependencies we might learn about because
      -- we have chosen a new flag.
      let newactives = extractNewDeps (F qfn) b npfa psa qdeps
          mNewRequiredExes = extendRequiredExes aExes rExes newactives
      -- As in the package case, we try to extend the partial assignment.
      let mnppa = extend extSupported langSupported pkgPresent newactives ppa
      case liftM2 (,) mnppa mNewRequiredExes of
        Left (c, fr)         -> return (Fail c fr) -- inconsistency found
        Right (nppa, rExes') ->
            local (\ s -> s { pa = PA nppa npfa psa, requiredExes = rExes' }) r

    -- What to do for stanza nodes (similar to flag nodes) ...
    goS :: QSN -> Bool -> Validate (Tree d c) -> Validate (Tree d c)
    goS qsn@(SN qpn _f) b r = do
      PA ppa pfa psa <- asks pa -- obtain current preassignment
      extSupported   <- asks supportedExt  -- obtain the supported extensions
      langSupported  <- asks supportedLang -- obtain the supported languages
      pkgPresent     <- asks presentPkgs -- obtain the present pkg-config pkgs
      svd            <- asks saved         -- obtain saved dependencies
      aExes          <- asks availableExes
      rExes          <- asks requiredExes
      -- Note that there should be saved dependencies for the package in question,
      -- because while building, we do not choose flags before we see the packages
      -- that define them.
      let qdeps = svd ! qpn
      -- We take the *saved* dependencies, because these have been qualified in the
      -- correct scope.
      --
      -- Extend the flag assignment
      let npsa = M.insert qsn b psa
      -- We now try to get the new active dependencies we might learn about because
      -- we have chosen a new flag.
      let newactives = extractNewDeps (S qsn) b pfa npsa qdeps
          mNewRequiredExes = extendRequiredExes aExes rExes newactives
      -- As in the package case, we try to extend the partial assignment.
      let mnppa = extend extSupported langSupported pkgPresent newactives ppa
      case liftM2 (,) mnppa mNewRequiredExes of
        Left (c, fr)         -> return (Fail c fr) -- inconsistency found
        Right (nppa, rExes') ->
            local (\ s -> s { pa = PA nppa pfa npsa, requiredExes = rExes' }) r

-- | Check that a newly chosen package instance contains all executables that
-- are required from that package so far.
checkExesInNewPackage :: Map QPN ExeDeps
                      -> QPN
                      -> [UnqualComponentName]
                      -> Either Conflict ()
checkExesInNewPackage required qpn providedExes =
    case M.toList $ deleteKeys providedExes (M.findWithDefault M.empty qpn required) of
      (missingExe, dr) : _ -> let cs = CS.insert (P qpn) $ dependencyReasonToCS dr
                              in Left (cs, NewPackageIsMissingRequiredExe missingExe dr)
      []                   -> Right ()
  where
    deleteKeys :: Ord k => [k] -> Map k v -> Map k v
    deleteKeys ks m = L.foldr M.delete m ks

-- | We try to extract as many concrete dependencies from the given flagged
-- dependencies as possible. We make use of all the flag knowledge we have
-- already acquired.
extractAllDeps :: FAssignment -> SAssignment -> FlaggedDeps QPN -> [LDep QPN]
extractAllDeps fa sa deps = do
  d <- deps
  case d of
    Simple sd _         -> return sd
    Flagged qfn _ td fd -> case M.lookup qfn fa of
                             Nothing    -> mzero
                             Just True  -> extractAllDeps fa sa td
                             Just False -> extractAllDeps fa sa fd
    Stanza qsn td       -> case M.lookup qsn sa of
                             Nothing    -> mzero
                             Just True  -> extractAllDeps fa sa td
                             Just False -> []

-- | We try to find new dependencies that become available due to the given
-- flag or stanza choice. We therefore look for the choice in question, and then call
-- 'extractAllDeps' for everything underneath.
extractNewDeps :: Var QPN -> Bool -> FAssignment -> SAssignment -> FlaggedDeps QPN -> [LDep QPN]
extractNewDeps v b fa sa = go
  where
    go :: FlaggedDeps QPN -> [LDep QPN]
    go deps = do
      d <- deps
      case d of
        Simple _ _           -> mzero
        Flagged qfn' _ td fd
          | v == F qfn'      -> if b then extractAllDeps fa sa td else extractAllDeps fa sa fd
          | otherwise        -> case M.lookup qfn' fa of
                                  Nothing    -> mzero
                                  Just True  -> go td
                                  Just False -> go fd
        Stanza qsn' td
          | v == S qsn'      -> if b then extractAllDeps fa sa td else []
          | otherwise        -> case M.lookup qsn' sa of
                                  Nothing    -> mzero
                                  Just True  -> go td
                                  Just False -> []

-- | Extend a package preassignment.
--
-- Takes the variable that causes the new constraints, a current preassignment
-- and a set of new dependency constraints.
--
-- We're trying to extend the preassignment with each dependency one by one.
-- Each dependency is for a particular variable. We check if we already have
-- constraints for that variable in the current preassignment. If so, we're
-- trying to merge the constraints.
--
-- Either returns a witness of the conflict that would arise during the merge,
-- or the successfully extended assignment.
extend :: (Extension -> Bool)            -- ^ is a given extension supported
       -> (Language  -> Bool)            -- ^ is a given language supported
       -> (PkgconfigName -> VR  -> Bool) -- ^ is a given pkg-config requirement satisfiable
       -> [LDep QPN]
       -> PPreAssignment
       -> Either Conflict PPreAssignment
extend extSupported langSupported pkgPresent newactives ppa = foldM extendSingle ppa newactives
  where

    extendSingle :: PPreAssignment -> LDep QPN -> Either Conflict PPreAssignment
    extendSingle a (LDep dr (Ext  ext ))  =
      if extSupported  ext  then Right a
                            else Left (dependencyReasonToCS dr, UnsupportedExtension ext)
    extendSingle a (LDep dr (Lang lang))  =
      if langSupported lang then Right a
                            else Left (dependencyReasonToCS dr, UnsupportedLanguage lang)
    extendSingle a (LDep dr (Pkg pn vr))  =
      if pkgPresent pn vr then Right a
                          else Left (dependencyReasonToCS dr, MissingPkgconfigPackage pn vr)
    extendSingle a (LDep dr (Dep mExe qpn ci)) =
      let mergedDep = M.findWithDefault (MergedDepConstrained []) qpn a
      in  case (\ x -> M.insert qpn x a) <$> merge mergedDep (PkgDep dr mExe qpn ci) of
            Left (c, (d, d')) -> Left (c, ConflictingConstraints d d')
            Right x           -> Right x

-- | Extend a package preassignment with a package choice. For example, when
-- the solver chooses foo-2.0, it tries to add the constraint foo==2.0.
extendWithPackageChoice :: PI QPN -> PPreAssignment -> Either Conflict PPreAssignment
extendWithPackageChoice (PI qpn i) ppa =
  let mergedDep = M.findWithDefault (MergedDepConstrained []) qpn ppa
      newChoice = PkgDep (DependencyReason qpn [] []) Nothing qpn (Fixed i)
  in  case (\ x -> M.insert qpn x ppa) <$> merge mergedDep newChoice of
        Left (c, (d, _d')) -> -- Don't include the package choice in the
                              -- FailReason, because it is redundant.
                              Left (c, NewPackageDoesNotMatchExistingConstraint d)
        Right x            -> Right x

-- | Merge constrained instances. We currently adopt a lazy strategy for
-- merging, i.e., we only perform actual checking if one of the two choices
-- is fixed. If the merge fails, we return a conflict set indicating the
-- variables responsible for the failure, as well as the two conflicting
-- fragments.
--
-- Note that while there may be more than one conflicting pair of version
-- ranges, we only return the first we find.
--
-- The ConflictingDeps are returned in order, i.e., the first describes the
-- conflicting part of the MergedPkgDep, and the second describes the PkgDep.
--
-- TODO: Different pairs might have different conflict sets. We're
-- obviously interested to return a conflict that has a "better" conflict
-- set in the sense the it contains variables that allow us to backjump
-- further. We might apply some heuristics here, such as to change the
-- order in which we check the constraints.
merge ::
#ifdef DEBUG_CONFLICT_SETS
  (?loc :: CallStack) =>
#endif
  MergedPkgDep -> PkgDep -> Either (ConflictSet, (ConflictingDep, ConflictingDep)) MergedPkgDep
merge (MergedDepFixed mExe1 vs1 i1) (PkgDep vs2 mExe2 p ci@(Fixed i2))
  | i1 == i2  = Right $ MergedDepFixed mExe1 vs1 i1
  | otherwise =
      Left ( (CS.union `on` dependencyReasonToCS) vs1 vs2
           , ( ConflictingDep vs1 mExe1 p (Fixed i1)
             , ConflictingDep vs2 mExe2 p ci ) )

merge (MergedDepFixed mExe1 vs1 i@(I v _)) (PkgDep vs2 mExe2 p ci@(Constrained vr))
  | checkVR vr v = Right $ MergedDepFixed mExe1 vs1 i
  | otherwise    =
      Left ( (CS.union `on` dependencyReasonToCS) vs1 vs2
           , ( ConflictingDep vs1 mExe1 p (Fixed i)
             , ConflictingDep vs2 mExe2 p ci ) )

merge (MergedDepConstrained vrOrigins) (PkgDep vs2 mExe2 p ci@(Fixed i@(I v _))) =
    go vrOrigins -- I tried "reverse vrOrigins" here, but it seems to slow things down ...
  where
    go :: [VROrigin] -> Either (ConflictSet, (ConflictingDep, ConflictingDep)) MergedPkgDep
    go [] = Right (MergedDepFixed mExe2 vs2 i)
    go ((vr, mExe1, vs1) : vros)
       | checkVR vr v = go vros
       | otherwise    =
           Left ( (CS.union `on` dependencyReasonToCS) vs1 vs2
                , ( ConflictingDep vs1 mExe1 p (Constrained vr)
                  , ConflictingDep vs2 mExe2 p ci ) )

merge (MergedDepConstrained vrOrigins) (PkgDep vs2 mExe2 _ (Constrained vr)) =
    Right (MergedDepConstrained $

    -- TODO: This line appends the new version range, to preserve the order used
    -- before a refactoring. Consider prepending the version range, if there is
    -- no negative performance impact.
    vrOrigins ++ [(vr, mExe2, vs2)])

-- | Takes a list of new dependencies and uses it to try to update the map of
-- known executable dependencies. It returns a failure when a new dependency
-- requires an executable that is missing from one of the previously chosen
-- packages.
extendRequiredExes :: Map QPN [UnqualComponentName]
                   -> Map QPN ExeDeps
                   -> [LDep QPN]
                   -> Either Conflict (Map QPN ExeDeps)
extendRequiredExes available = foldM extendSingle
  where
    extendSingle :: Map QPN ExeDeps -> LDep QPN -> Either Conflict (Map QPN ExeDeps)
    extendSingle required (LDep dr (Dep (Just exe) qpn _)) =
      let exeDeps = M.findWithDefault M.empty qpn required
      in -- Only check for the existence of the exe if its package has already
         -- been chosen.
         case M.lookup qpn available of
           Just exes
             | L.notElem exe exes -> let cs = CS.insert (P qpn) (dependencyReasonToCS dr)
                                     in Left (cs, PackageRequiresMissingExe qpn exe)
           _                      -> Right $ M.insertWith M.union qpn (M.insert exe dr exeDeps) required
    extendSingle required _                                = Right required

-- | Interface.
validateTree :: CompilerInfo -> Index -> PkgConfigDb -> Tree d c -> Tree d c
validateTree cinfo idx pkgConfigDb t = runValidate (validate t) VS {
    supportedExt   = maybe (const True) -- if compiler has no list of extensions, we assume everything is supported
                           (\ es -> let s = S.fromList es in \ x -> S.member x s)
                           (compilerInfoExtensions cinfo)
  , supportedLang  = maybe (const True)
                           (flip L.elem) -- use list lookup because language list is small and no Ord instance
                           (compilerInfoLanguages  cinfo)
  , presentPkgs    = pkgConfigPkgIsPresent pkgConfigDb
  , index          = idx
  , saved          = M.empty
  , pa             = PA M.empty M.empty M.empty
  , availableExes  = M.empty
  , requiredExes   = M.empty
  , qualifyOptions = defaultQualifyOptions idx
  }
