{-# LANGUAGE OverloadedRecordDot #-}
{-# LANGUAGE OverloadedStrings #-}

module Dojang.Types.FileRoute
  ( FileRoute (..)
  , RouteWarning (..)
  , fileRoute
  , fileRoute'
  , dispatch
  , routePath
  ) where

import Data.List (sortOn)
import Data.Ord (Down (Down))
import Prelude hiding (lookup)

import Data.HashMap.Strict (lookup)
import Data.HashSet (HashSet, singleton, union, unions)
import Data.Text (unpack)
import System.OsPath (OsPath)
import System.OsString (OsString)

import Dojang.MonadFileSystem (FileType, MonadFileSystem (..))
import Dojang.Types.Environment (Environment)
import Dojang.Types.EnvironmentPredicate (EnvironmentPredicate (..))
import Dojang.Types.EnvironmentPredicate.Evaluate (EvaluationWarning, evaluate')
import Dojang.Types.EnvironmentPredicate.Specificity (Specificity, specificity)
import Dojang.Types.FilePathExpression (EnvironmentVariable, FilePathExpression)
import Dojang.Types.FilePathExpression.Expansion
  ( ExpansionWarning
  , expandFilePath
  )
import Dojang.Types.MonikerMap (MonikerMap, MonikerResolver)
import Dojang.Types.MonikerName (MonikerName)


-- | A route that maps 'EnvironmentPredicate's to 'FilePathExpression's.
--
-- Each 'EnvironmentPredicate' represents a condition that must be met for the
-- 'FilePathExpression' to be dispatched.  The 'FilePathExpression' is
-- the path to the directory that should be dispatched to.  If it is 'Nothing',
-- then it is considered a "null route" and will be ignored.
--
-- Note that a null route will still be considered a match, and will be
-- dispatched as 'Nothing'.
data FileRoute = FileRoute
  { monikerResolver :: MonikerResolver
  -- ^ The 'MonikerResolver' used to resolve 'MonikerName's.
  , predicates :: [(EnvironmentPredicate, Maybe FilePathExpression)]
  -- ^ The pairs of 'EnvironmentPredicate's and 'FilePathExpression's that make
  -- up the 'FileRoute'.  If the file path expression is 'Nothing', then it is
  -- considered a "null route" and will be ignored.
  , fileType :: FileType
  -- ^ Whether the 'FileRoute' represents a file or a directory.
  }


instance Eq FileRoute where
  a == b =
    (a.fileType == b.fileType)
      && (a.predicates == b.predicates)
      && all (\m -> a.monikerResolver m == b.monikerResolver m) allMonikerRefs
   where
    monikerRefs :: EnvironmentPredicate -> HashSet MonikerName
    monikerRefs predicates' =
      case predicates' of
        Moniker monikerName -> singleton monikerName
        Or ps -> foldMap monikerRefs ps
        And ps -> foldMap monikerRefs ps
        Not p -> monikerRefs p
        OperatingSystem _ -> mempty
        Architecture _ -> mempty
        Always -> mempty
        KernelName _ -> mempty
        KernelRelease _ -> mempty
        KernelReleasePrefix _ -> mempty
        KernelReleaseSuffix _ -> mempty
    allMonikerRefs :: HashSet MonikerName
    allMonikerRefs =
      unions (monikerRefs . fst <$> a.predicates)
        `union` unions (monikerRefs . fst <$> b.predicates)


-- | Creates a 'FileRoute' from a 'MonikerMap' and pairs of
-- 'MonikerName's and 'FilePathExpression's.
fileRoute
  :: MonikerMap
  -- ^ The 'MonikerMap' to resolve 'MonikerName's against.
  -> [(MonikerName, Maybe FilePathExpression)]
  -- ^ The pairs of 'MonikerName's and 'FilePathExpression's that make up the
  -- 'FileRoute'.  If the file path expression is 'Nothing', then it is
  -- considered a "null route" and will be ignored.
  -> FileType
  -- ^ Whether the 'FileRoute' represents a file or a directory.
  -> FileRoute
  -- ^ The resulting 'FileRoute'.
fileRoute monikerMap predicates' =
  fileRoute'
    (`lookup` monikerMap)
    [(Moniker name, pathExpr) | (name, pathExpr) <- predicates']


-- | Similar to 'FileRoute', but it takes more raw arguments: a 'MonikerResolver'
-- (instead of a 'MonikerMap'), and a pairs of 'EnvironmentPredicate' (instead
-- of 'MonikerName') and 'FilePathExpression'.
fileRoute'
  :: MonikerResolver
  -- ^ A function that resolves a 'MonikerName' to an 'EnvironmentPredicate'.
  -> [(EnvironmentPredicate, Maybe FilePathExpression)]
  -- ^ The pairs of 'EnvironmentPredicate's and 'FilePathExpression's that make
  -- up the 'FileRoute'.  If the file path expression is 'Nothing', then it is
  -- considered a "null route" and will be ignored.
  -> FileType
  -- ^ Whether the 'FileRoute' represents a file or a directory.
  -> FileRoute
  -- ^ The resulting 'FileRoute'.
fileRoute' resolver predicates' =
  FileRoute resolver $ sortOn sortKey predicates'
 where
  sortKey
    :: (EnvironmentPredicate, Maybe FilePathExpression)
    -> Down (Specificity, String)
  sortKey (pred', _) = Down (specificity resolver pred', show pred')


-- | Dispatches the given 'FileRoute' against the given 'Environment'.
dispatch
  :: Environment
  -- ^ The 'Environment' to dispatch against.
  -> FileRoute
  -- ^ The 'FileRoute' to dispatch.
  -> ([Maybe FilePathExpression], [EvaluationWarning])
  -- ^ The list of 'Maybe' 'FilePathExpression's that matched
  -- the given 'Environment' and 'MonikerMap'.  Even if matches are made,
  -- their values may be 'Nothing' if the 'FilePathExpression' was
  -- a "null route".
  -- The 'snd' of the result is a list of warnings that occurred
  -- during evaluation  whether or not any 'FilePathExpression' matched.
dispatch environment (FileRoute resolver route _) =
  (matched, warnings)
 where
  eval :: EnvironmentPredicate -> (Bool, [EvaluationWarning])
  eval = evaluate' environment resolver
  evaluated :: [((Bool, [EvaluationWarning]), Maybe FilePathExpression)]
  evaluated = [(eval predicate, expr) | (predicate, expr) <- route]
  warnings :: [EvaluationWarning]
  warnings = concatMap (snd . fst) evaluated
  matched :: [Maybe FilePathExpression]
  matched = [expr | ((True, _), expr) <- evaluated]


-- | A warning that can occur during path routing.
data RouteWarning
  = -- | A warning that can occur during environment predicate evaluation.
    EnvironmentPredicateWarning EvaluationWarning
  | -- | A warning that can occur during file path expression expansion.
    FilePathExpressionWarning ExpansionWarning
  deriving (Eq, Show)


-- | Routes the given 'FileRoute' against the given 'Environment', and expands
-- the resulting 'FilePathExpression' into an 'OsPath', if any.  For null
-- routes, returns 'Nothing'.
routePath
  :: (MonadFileSystem m)
  => FileRoute
  -- ^ The 'FileRoute' to route and expand.
  -> Environment
  -- ^ The environment to use when evaluating environment predicates.
  -> (EnvironmentVariable -> m (Maybe OsString))
  -- ^ A function that can look up an environment variable.
  -> m (Maybe OsPath, [RouteWarning])
  -- ^ The resulting 'OsPath', if any, and a list of warnings that occurred
  -- during evaluation and expansion.  For null routes, returns 'Nothing',
  -- but still returns any warnings that occurred (if any).
routePath route env lookupEnvVar = do
  let (matched, warnings) = dispatch env route
  let predWarnings = map EnvironmentPredicateWarning warnings
  case matched of
    [] -> return (Nothing, predWarnings)
    (Nothing : _) -> return (Nothing, predWarnings)
    (Just pathExpr : _) -> do
      (path, exprWarnings) <-
        expandFilePath pathExpr lookupEnvVar (encodePath . unpack)
      return (Just path, predWarnings ++ map FilePathExpressionWarning exprWarnings)


instance Show FileRoute where
  show (FileRoute _ route fileType') =
    "FileRoute " ++ show route ++ " " ++ show fileType'