module CabalApi (
  cabalBuildInfo,
  cabalDependPackages
  ) where

import Control.Applicative

import Data.Maybe (fromJust, maybeToList)
import Data.Set (fromList, toList)

import Distribution.Verbosity (silent)
import Distribution.Package (Dependency(Dependency), PackageName(PackageName))
import Distribution.PackageDescription
  (GenericPackageDescription,
   condLibrary, condExecutables, condTestSuites, condBenchmarks,
   BuildInfo, libBuildInfo, buildInfo,
   CondTree, condTreeConstraints, condTreeData)
import Distribution.PackageDescription.Parse (readPackageDescription)

----------------------------------------------------------------

-- Causes error, catched in the upper function.
cabalBuildInfo :: FilePath -> IO BuildInfo
cabalBuildInfo file = do
    cabal <- readPackageDescription silent file
    return . fromJust $ fromLibrary cabal <|> fromExecutable cabal
  where
    fromLibrary c     = libBuildInfo . condTreeData <$> condLibrary c
    fromExecutable c  = buildInfo . condTreeData . snd <$> toMaybe (condExecutables c)
    toMaybe [] = Nothing
    toMaybe (x:_) = Just x

parseGenericDescription :: FilePath -> IO GenericPackageDescription
parseGenericDescription =  readPackageDescription silent

getDepsOfPairs :: [(a1, CondTree v [b] a)] -> [b]
getDepsOfPairs =  concatMap (condTreeConstraints . snd)

allDependsOfDescription :: GenericPackageDescription -> [Dependency]
allDependsOfDescription pd =
  concat [depLib, depExe, depTests, depBench]
  where
    depLib   = concatMap condTreeConstraints (maybeToList . condLibrary $ pd)
    depExe   = getDepsOfPairs . condExecutables $ pd
    depTests = getDepsOfPairs . condTestSuites  $ pd
    depBench = getDepsOfPairs . condBenchmarks  $ pd

getDependencyPackageName :: Dependency -> String
getDependencyPackageName (Dependency (PackageName n) _) = n

cabalDependPackages :: FilePath -> IO [String]
cabalDependPackages =
  fmap (toList . fromList
        . map getDependencyPackageName
        . allDependsOfDescription)
  . parseGenericDescription