{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE CPP #-}

module Main ( main ) where

import Distribution.Nixpkgs.Fetch
import Distribution.Nixpkgs.Haskell.Derivation
import Distribution.Nixpkgs.Haskell.FromCabal
import Distribution.Nixpkgs.Haskell.FromCabal.Flags

import Control.Lens
import Control.Monad
import qualified Data.Set as Set
import Distribution.Compiler
import Distribution.Package
#if MIN_VERSION_Cabal(3,8,1)
import Distribution.Simple.PackageDescription
import Distribution.Types.GenericPackageDescription
#else
import Distribution.PackageDescription
import Distribution.PackageDescription.Parsec
#endif
import Distribution.System
import Distribution.Verbosity
import Distribution.Version
import Language.Nix
import System.Directory
import System.FilePath
import System.Process
import Test.Tasty
import Test.Tasty.Golden
import Text.PrettyPrint.HughesPJClass

main :: IO ()
main = do
  -- TODO: Run this test with all kinds of setLocaleEncoding values to ensure we don't
  --       depend on the system environment: https://github.com/NixOS/cabal2nix/issues/333.
  --
  -- TODO: Run this test without $HOME defined to ensure that we don't need that variable.
  cabal2nix <- findExecutable "cabal2nix" >>= \case
    Nothing -> fail "cannot find 'cabal2nix' in $PATH"
    Just exe -> pure exe
  testCases <- listDirectoryFilesBySuffix ".cabal" "test/golden-test-cases"
  defaultMain $ testGroup "regression-tests"
    [ testGroup "cabal2nix library" (map testLibrary testCases)
    , testGroup "cabal2nix executable" (map (testExecutable cabal2nix) testCases)
    ]

testLibrary :: String -> TestTree
testLibrary cabalFile = do
  let nixFile = cabalFile `replaceExtension` "nix"
      goldenFile = nixFile `addExtension` "golden"

      cabal2nix :: GenericPackageDescription -> Derivation
      cabal2nix gpd = fromGenericPackageDescription
                         (const True)
                         (\i -> Just (binding # (i, path # [ident # "pkgs", i])))
                         (Platform X86_64 Linux)
                         (unknownCompilerInfo (CompilerId GHC (mkVersion [8,2])) NoAbiTag)
                         (configureCabalFlags (packageId gpd))
                         []
                         gpd
                       & src .~ DerivationSource
                                  { derivKind     = Just (DerivKindUrl DontUnpackArchive )
                                  , derivUrl      = "mirror://hackage/foo.tar.gz"
                                  , derivRevision = ""
                                  , derivHash     = "deadbeef"
                                  , derivSubmodule = Nothing
                                  }
                       & extraFunctionArgs %~ Set.union (Set.singleton "inherit lib")
  goldenVsFileDiff
    nixFile
    (\ref new -> ["diff", "-u", ref, new])
    goldenFile
    nixFile
    (readGenericPackageDescription silent cabalFile >>= writeFileLn nixFile . prettyShow . cabal2nix)

-- | TODO:
--
--  * Run cabal2nix in an empty environment. Currently, this fails because the
--    tool uses $HOME to write cache files for SHA256 hashes. To fix this, use
--    of the cache directory ought to be optional. Arguably, the whole notion
--    of caching those hashes is a bit silly in the presence of format 01
--    cabal-install tarballs which contain them already.
--
--  * If we cannot get along without $HOME, then we should at least set it to
--    some temporary location that is empty.
--
--  * Run this test with different kinds of encodings.
--
--  * Run tests with a different target OS, like Darwin. The packages "iconv",
--    "crypt-sha512", "gl" might be worthwhile for testing since their output
--    differs on Darwin.

testExecutable :: FilePath -> FilePath -> TestTree
testExecutable exe cabalFile = do
  let nixFile = cabalFile `replaceExtension` "nix"
      goldenFile = nixFile `addExtension` "golden"
  goldenVsFileDiff
    nixFile
    (\ref new -> ["diff", "-u", ref, new])
    goldenFile
    nixFile
    (callCommand (unwords ["env LANG=C.UTF-8", exe, "--sha256=deadbeef", "--system=x86_64-linux", "--compiler=ghc-8.2", "--", cabalFile, ">"++nixFile]))

-------------------------------------------------------------------------------
-- * Helper functions
-------------------------------------------------------------------------------

-- | Find all *files* in the given directory that end with the given suffix.
-- This function does not recurse, nor does it include the special entries
-- @'.'@ or @'..'@ in the result.
--
-- "Test.Tasty.Golden" offers 'findByExtension', which does something similar
-- (and arguably more general) as those two functions, but unfortunately that
-- function recurses through the directory hierarchy and in the process needs
-- plenty of stack space. There might be a space leak in that code, I am not
-- sure. Anyhow, since our test suite is supposed to run with 1K stack space,
-- we prefer our own simpler code.

listDirectoryFilesBySuffix :: String -> FilePath -> IO [FilePath]
listDirectoryFilesBySuffix suff dirPath = do
  entries <- listDirectory dirPath
  filterM doesFileExist [ dirPath </> e | e <- entries, takeExtension e == suff ]

-- | A variant of 'writeFile' that appends a newline to the end of the buffer
-- before writing.

writeFileLn :: FilePath -> String -> IO ()
writeFileLn p buf = writeFile p (buf ++ "\n")