    -----------------------------------------------------------------------------
    -- |
    -- Module      :  Distribution.Simple.Build.Macros
    -- Copyright   :  Isaac Jones 2003-2005,
    --                Ross Paterson 2006,
    --                Duncan Coutts 2007-2008
    --
    -- Maintainer  :  cabal-devel@haskell.org
    -- Portability :  portable
    --
    -- Generating the Paths_pkgname module.
    --
    -- This is a module that Cabal generates for the benefit of packages. It
    -- enables them to find their version number and find any installed data files
    -- at runtime. This code should probably be split off into another module.
    --
    module Distribution.Simple.Build.PathsModule (
        generate, pkgPathEnvVar
      ) where

    import Distribution.System
             ( OS(Windows), buildOS, Arch(..), buildArch )
    import Distribution.Simple.Compiler
             ( CompilerFlavor(..), compilerFlavor, compilerVersion )
    import Distribution.Package
             ( packageId, packageName, packageVersion )
    import Distribution.PackageDescription
             ( PackageDescription(..), hasLibs )
    import Distribution.Simple.LocalBuildInfo
             ( LocalBuildInfo(..), InstallDirs(..)
             , absoluteInstallDirs, prefixRelativeInstallDirs )
    import Distribution.Simple.Setup ( CopyDest(NoCopyDest) )
    import Distribution.Simple.BuildPaths
             ( autogenModuleName )
    import Distribution.Simple.Utils
             ( shortRelativePath )
    import Distribution.Text
             ( display )
    import Distribution.Version
             ( Version(..), orLaterVersion, withinRange )

    import System.FilePath
             ( pathSeparator )
    import Data.Maybe
             ( fromJust, isNothing )

    -- ------------------------------------------------------------
    -- * Building Paths_<pkg>.hs
    -- ------------------------------------------------------------

    generate :: PackageDescription -> LocalBuildInfo -> String
    generate pkg_descr lbi =
       let pragmas
            | absolute = ""
            | supports_language_pragma =
              "{-# LANGUAGE ForeignFunctionInterface #-}\n"
            | otherwise =
              "{-# OPTIONS_GHC -fffi #-}\n"++
              "{-# OPTIONS_JHC -fffi #-}\n"

           foreign_imports
            | absolute = ""
            | otherwise =
              "import Foreign\n"++
              "import Foreign.C\n"

           reloc_imports
            | reloc =
              "import System.Environment (getExecutablePath)\n"
            | otherwise = ""

           header =
            pragmas++
            "module " ++ display paths_modulename ++ " (\n"++
            "    version,\n"++
            "    getBinDir, getLibDir, getDataDir, getLibexecDir,\n"++
            "    getDataFileName, getSysconfDir\n"++
            "  ) where\n"++
            "\n"++
            foreign_imports++
            "import qualified Control.Exception as Exception\n"++
            "import Data.Version (Version(..))\n"++
            "import System.Environment (getEnv)\n"++
            reloc_imports ++
            "import Prelude\n"++
            "\n"++
            "catchIO :: IO a -> (Exception.IOException -> IO a) -> IO a\n"++
            "catchIO = Exception.catch\n" ++
            "\n"++
            "version :: Version"++
            "\nversion = Version " ++ show branch ++ " " ++ show tags
              where Version branch tags = packageVersion pkg_descr

           body
            | reloc =
              "\n\nbindirrel :: FilePath\n" ++
              "bindirrel = " ++ show flat_bindirreloc ++
              "\n"++
              "\ngetBinDir, getLibDir, getDataDir, getLibexecDir, getSysconfDir :: IO FilePath\n"++
              "getBinDir = "++mkGetEnvOrReloc "bindir" flat_bindirreloc++"\n"++
              "getLibDir = "++mkGetEnvOrReloc "libdir" flat_libdirreloc++"\n"++
              "getDataDir = "++mkGetEnvOrReloc "datadir" flat_datadirreloc++"\n"++
              "getLibexecDir = "++mkGetEnvOrReloc "libexecdir" flat_libexecdirreloc++"\n"++
              "getSysconfDir = "++mkGetEnvOrReloc "sysconfdir" flat_sysconfdirreloc++"\n"++
              "\n"++
              "getDataFileName :: FilePath -> IO FilePath\n"++
              "getDataFileName name = do\n"++
              "  dir <- getDataDir\n"++
              "  return (dir `joinFileName` name)\n"++
              "\n"++
              get_prefix_reloc_stuff++
              "\n"++
              filename_stuff
            | absolute =
              "\nbindir, libdir, datadir, libexecdir, sysconfdir :: FilePath\n"++
              "\nbindir     = " ++ show flat_bindir ++
              "\nlibdir     = " ++ show flat_libdir ++
              "\ndatadir    = " ++ show flat_datadir ++
              "\nlibexecdir = " ++ show flat_libexecdir ++
              "\nsysconfdir = " ++ show flat_sysconfdir ++
              "\n"++
              "\ngetBinDir, getLibDir, getDataDir, getLibexecDir, getSysconfDir :: IO FilePath\n"++
              "getBinDir = "++mkGetEnvOr "bindir" "return bindir"++"\n"++
              "getLibDir = "++mkGetEnvOr "libdir" "return libdir"++"\n"++
              "getDataDir = "++mkGetEnvOr "datadir" "return datadir"++"\n"++
              "getLibexecDir = "++mkGetEnvOr "libexecdir" "return libexecdir"++"\n"++
              "getSysconfDir = "++mkGetEnvOr "sysconfdir" "return sysconfdir"++"\n"++
              "\n"++
              "getDataFileName :: FilePath -> IO FilePath\n"++
              "getDataFileName name = do\n"++
              "  dir <- getDataDir\n"++
              "  return (dir ++ "++path_sep++" ++ name)\n"
            | otherwise =
              "\nprefix, bindirrel :: FilePath" ++
              "\nprefix        = " ++ show flat_prefix ++
              "\nbindirrel     = " ++ show (fromJust flat_bindirrel) ++
              "\n\n"++
              "getBinDir :: IO FilePath\n"++
              "getBinDir = getPrefixDirRel bindirrel\n\n"++
              "getLibDir :: IO FilePath\n"++
              "getLibDir = "++mkGetDir flat_libdir flat_libdirrel++"\n\n"++
              "getDataDir :: IO FilePath\n"++
              "getDataDir =  "++ mkGetEnvOr "datadir"
                                  (mkGetDir flat_datadir flat_datadirrel)++"\n\n"++
              "getLibexecDir :: IO FilePath\n"++
              "getLibexecDir = "++mkGetDir flat_libexecdir flat_libexecdirrel++"\n\n"++
              "getSysconfDir :: IO FilePath\n"++
              "getSysconfDir = "++mkGetDir flat_sysconfdir flat_sysconfdirrel++"\n\n"++
              "getDataFileName :: FilePath -> IO FilePath\n"++
              "getDataFileName name = do\n"++
              "  dir <- getDataDir\n"++
              "  return (dir `joinFileName` name)\n"++
              "\n"++
              get_prefix_stuff++
              "\n"++
              filename_stuff
       in header++body

     where
            InstallDirs {
              prefix     = flat_prefix,
              bindir     = flat_bindir,
              libdir     = flat_libdir,
              datadir    = flat_datadir,
              libexecdir = flat_libexecdir,
              sysconfdir = flat_sysconfdir
            } = absoluteInstallDirs pkg_descr lbi NoCopyDest
            InstallDirs {
              bindir     = flat_bindirrel,
              libdir     = flat_libdirrel,
              datadir    = flat_datadirrel,
              libexecdir = flat_libexecdirrel,
              sysconfdir = flat_sysconfdirrel
            } = prefixRelativeInstallDirs (packageId pkg_descr) lbi

            flat_bindirreloc = shortRelativePath flat_prefix flat_bindir
            flat_libdirreloc = shortRelativePath flat_prefix flat_libdir
            flat_datadirreloc = shortRelativePath flat_prefix flat_datadir
            flat_libexecdirreloc = shortRelativePath flat_prefix flat_libexecdir
            flat_sysconfdirreloc = shortRelativePath flat_prefix flat_sysconfdir

            mkGetDir _   (Just dirrel) = "getPrefixDirRel " ++ show dirrel
            mkGetDir dir Nothing       = "return " ++ show dir

            mkGetEnvOrReloc var dirrel = "catchIO (getEnv \""++var'++"\")" ++
                                         " (\\_ -> getPrefixDirReloc \"" ++ dirrel ++
                                         "\")"
              where var' = pkgPathEnvVar pkg_descr var

            mkGetEnvOr var expr = "catchIO (getEnv \""++var'++"\")"++
                                  " (\\_ -> "++expr++")"
              where var' = pkgPathEnvVar pkg_descr var

            -- In several cases we cannot make relocatable installations
            absolute =
                 hasLibs pkg_descr        -- we can only make progs relocatable
              || isNothing flat_bindirrel -- if the bin dir is an absolute path
              || not (supportsRelocatableProgs (compilerFlavor (compiler lbi)))

            reloc = relocatable lbi

            supportsRelocatableProgs GHC  = case buildOS of
                               Windows   -> True
                               _         -> False
            supportsRelocatableProgs GHCJS = case buildOS of
                               Windows   -> True
                               _         -> False
            supportsRelocatableProgs _    = False

            paths_modulename = autogenModuleName pkg_descr

            get_prefix_stuff = get_prefix_win32 buildArch

            path_sep = show [pathSeparator]

            supports_language_pragma =
              (compilerFlavor (compiler lbi) == GHC &&
                (compilerVersion (compiler lbi)
                  `withinRange` orLaterVersion (Version [6,6,1] []))) ||
               compilerFlavor (compiler lbi) == GHCJS

    -- | Generates the name of the environment variable controlling the path
    -- component of interest.
    pkgPathEnvVar :: PackageDescription
                  -> String     -- ^ path component; one of \"bindir\", \"libdir\",
                                -- \"datadir\", \"libexecdir\", or \"sysconfdir\"
                  -> String     -- ^ environment variable name
    pkgPathEnvVar pkg_descr var =
        showPkgName (packageName pkg_descr) ++ "_" ++ var
        where
            showPkgName = map fixchar . display
            fixchar '-' = '_'
            fixchar c   = c

    get_prefix_reloc_stuff :: String
    get_prefix_reloc_stuff =
      "getPrefixDirReloc :: FilePath -> IO FilePath\n"++
      "getPrefixDirReloc dirRel = do\n"++
      "  exePath <- getExecutablePath\n"++
      "  let (bindir,_) = splitFileName exePath\n"++
      "  return ((bindir `minusFileName` bindirrel) `joinFileName` dirRel)\n"

    get_prefix_win32 :: Arch -> String
    get_prefix_win32 arch =
      "getPrefixDirRel :: FilePath -> IO FilePath\n"++
      "getPrefixDirRel dirRel = try_size 2048 -- plenty, PATH_MAX is 512 under Win32.\n"++
      "  where\n"++
      "    try_size size = allocaArray (fromIntegral size) $ \\buf -> do\n"++
      "        ret <- c_GetModuleFileName nullPtr buf size\n"++
      "        case ret of\n"++
      "          0 -> return (prefix `joinFileName` dirRel)\n"++
      "          _ | ret < size -> do\n"++
      "              exePath <- peekCWString buf\n"++
      "              let (bindir,_) = splitFileName exePath\n"++
      "              return ((bindir `minusFileName` bindirrel) `joinFileName` dirRel)\n"++
      "            | otherwise  -> try_size (size * 2)\n"++
      "\n"++
      "foreign import " ++ cconv ++ " unsafe \"windows.h GetModuleFileNameW\"\n"++
      "  c_GetModuleFileName :: Ptr () -> CWString -> Int32 -> IO Int32\n"
        where cconv = case arch of
                      I386 -> "stdcall"
                      X86_64 -> "ccall"
                      _ -> error "win32 supported only with I386, X86_64"

    filename_stuff :: String
    filename_stuff =
      "minusFileName :: FilePath -> String -> FilePath\n"++
      "minusFileName dir \"\"     = dir\n"++
      "minusFileName dir \".\"    = dir\n"++
      "minusFileName dir suffix =\n"++
      "  minusFileName (fst (splitFileName dir)) (fst (splitFileName suffix))\n"++
      "\n"++
      "joinFileName :: String -> String -> FilePath\n"++
      "joinFileName \"\"  fname = fname\n"++
      "joinFileName \".\" fname = fname\n"++
      "joinFileName dir \"\"    = dir\n"++
      "joinFileName dir fname\n"++
      "  | isPathSeparator (last dir) = dir++fname\n"++
      "  | otherwise                  = dir++pathSeparator:fname\n"++
      "\n"++
      "splitFileName :: FilePath -> (String, String)\n"++
      "splitFileName p = (reverse (path2++drive), reverse fname)\n"++
      "  where\n"++
      "    (path,drive) = case p of\n"++
      "       (c:':':p') -> (reverse p',[':',c])\n"++
      "       _          -> (reverse p ,\"\")\n"++
      "    (fname,path1) = break isPathSeparator path\n"++
      "    path2 = case path1 of\n"++
      "      []                           -> \".\"\n"++
      "      [_]                          -> path1   -- don't remove the trailing slash if \n"++
      "                                              -- there is only one character\n"++
      "      (c:path') | isPathSeparator c -> path'\n"++
      "      _                             -> path1\n"++
      "\n"++
      "pathSeparator :: Char\n"++
      (case buildOS of
           Windows   -> "pathSeparator = '\\\\'\n"
           _         -> "pathSeparator = '/'\n") ++
      "\n"++
      "isPathSeparator :: Char -> Bool\n"++
      (case buildOS of
           Windows   -> "isPathSeparator c = c == '/' || c == '\\\\'\n"
           _         -> "isPathSeparator c = c == '/'\n")