content: {-# LANGUAGE DeriveGeneric, StandaloneDeriving, BangPatterns, CPP #-}
  module GenericsBenchCache (readPackageDescriptionCache) where
  
  import qualified Data.ByteString.Lazy                          as L
  import qualified Data.ByteString.Lazy.Char8                    as LC8
  import qualified Codec.Compression.GZip                        as GZip
  
  import           Cabal24 (PackageDescription)
  
  import           System.Directory
  import           System.Exit
  
  import           GenericsBenchTypes                            ()
  
  #if ! MIN_VERSION_base(4,8,0)
  import           Control.Applicative                           ((<$>))
  #endif
  
  readPackageDescriptionCache :: Int -> IO [PackageDescription]
  readPackageDescriptionCache amount = do
    cacheExists <- doesFileExist cacheFilePath
    bs <-
      if cacheExists
        then do
          putStrLn "reading the cache file, might take a moment..."
          L.readFile cacheFilePath
        else do
          -- In older versions of this benchmark, there was machinery to
          -- regenerate the cache using the data in @~/.cabal@. Now the cache is
          -- simply stored in the repo to avoid a dependency on Cabal the library.
          putStrLn (cacheFilePath ++ " missing, aborting")
          exitFailure
    let str = LC8.unpack (GZip.decompress bs)
        pds = take amount (read str)
    -- PackageDescription doesn't implement NFData, let's force with the following line
    (length (show pds)) `seq` putStrLn "done reading the cache file"
    return pds
  
  cacheFilePath :: String
  cacheFilePath = "generics-bench.cache.gz"
  