    {-# LANGUAGE OverloadedStrings #-}
    -- Copyright 2020 United States Government as represented by the Administrator
    -- of the National Aeronautics and Space Administration. All Rights Reserved.
    --
    -- Disclaimers
    --
    -- Licensed under the Apache License, Version 2.0 (the "License"); you may
    -- not use this file except in compliance with the License. You may obtain a
    -- copy of the License at
    --
    --      https://www.apache.org/licenses/LICENSE-2.0
    --
    -- Unless required by applicable law or agreed to in writing, software
    -- distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
    -- WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
    -- License for the specific language governing permissions and limitations
    -- under the License.
    --
    -- | Auxiliary functions for working with directories.
    module System.Directory.Extra
        ( copyTemplate
        )
      where

    -- External imports
    import           Control.Monad             ( filterM, forM_ )
    import           Data.Aeson                ( Value (..) )
    import qualified Data.ByteString.Lazy      as B
    import           Data.Text.Lazy            ( pack, unpack )
    import           Data.Text.Lazy.Encoding   ( encodeUtf8 )
    import           Distribution.Simple.Utils ( getDirectoryContentsRecursive )
    import           System.Directory          ( createDirectoryIfMissing,
                                                 doesFileExist )
    import           System.FilePath           ( makeRelative, splitFileName,
                                                 takeDirectory, (</>) )
    import           Text.Microstache          ( compileMustacheFile,
                                                 compileMustacheText,
                                                 renderMustache )

    -- | Copy a template directory into a target location, expanding variables
    -- provided in a map in a JSON value, both in the file contents and in the
    -- filepaths themselves.
    copyTemplate :: FilePath -> Value -> FilePath -> IO ()
    copyTemplate :: FilePath -> Value -> FilePath -> IO ()
    copyTemplate FilePath
    templateDir Value
    subst FilePath
    targetDir = do

      -- Get all files (not directories) in the template dir. To keep a directory,
      -- create an empty file in it (e.g., .keep).
      [FilePath]
    tmplContents <- (FilePath -> FilePath) -> [FilePath] -> [FilePath]
    forall a b. (a -> b) -> [a] -> [b]
    map (FilePath
    templateDir FilePath -> FilePath -> FilePath
    </>) ([FilePath] -> [FilePath])
    -> ([FilePath] -> [FilePath]) -> [FilePath] -> [FilePath]
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . (FilePath -> Bool) -> [FilePath] -> [FilePath]
    forall a. (a -> Bool) -> [a] -> [a]
    filter (FilePath -> [FilePath] -> Bool
    forall (t :: * -> *) a. (Foldable t, Eq a) => a -> t a -> Bool
    `notElem` [FilePath
    "..", FilePath
    "."])
                        ([FilePath] -> [FilePath]) -> IO [FilePath] -> IO [FilePath]
    forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
    <$> FilePath -> IO [FilePath]
    getDirectoryContentsRecursive FilePath
    templateDir
      [FilePath]
    tmplFiles <- (FilePath -> IO Bool) -> [FilePath] -> IO [FilePath]
    forall (m :: * -> *) a.
    Applicative m =>
    (a -> m Bool) -> [a] -> m [a]
    filterM FilePath -> IO Bool
    doesFileExist [FilePath]
    tmplContents

      -- Copy files to new locations, expanding their name and contents as
      -- mustache templates.
      [FilePath] -> (FilePath -> IO ()) -> IO ()
    forall (t :: * -> *) (m :: * -> *) a b.
    (Foldable t, Monad m) =>
    t a -> (a -> m b) -> m ()
    forM_ [FilePath]
    tmplFiles ((FilePath -> IO ()) -> IO ()) -> (FilePath -> IO ()) -> IO ()
    forall a b. (a -> b) -> a -> b
    $ \FilePath
    fp -> do

        -- New file name in target directory, treating file
        -- name as mustache template.
        let fullPath :: FilePath
    fullPath = FilePath
    targetDir FilePath -> FilePath -> FilePath
    </> FilePath
    newFP
              where
                -- If file name has mustache markers, expand, otherwise use
                -- relative file path
                newFP :: FilePath
    newFP = (ParseError -> FilePath)
    -> (Template -> FilePath) -> Either ParseError Template -> FilePath
    forall a c b. (a -> c) -> (b -> c) -> Either a b -> c
    either (FilePath -> ParseError -> FilePath
    forall a b. a -> b -> a
    const FilePath
    relFP)
                               (Text -> FilePath
    unpack (Text -> FilePath) -> (Template -> Text) -> Template -> FilePath
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . (Template -> Value -> Text
    `renderMustache` Value
    subst))
                               Either ParseError Template
    fpAsTemplateE

                -- Local file name within template dir
                relFP :: FilePath
    relFP = FilePath -> FilePath -> FilePath
    makeRelative FilePath
    templateDir FilePath
    fp

                -- Apply mustache substitutions to file name
                fpAsTemplateE :: Either ParseError Template
    fpAsTemplateE = PName -> Text -> Either ParseError Template
    compileMustacheText PName
    "fp" (FilePath -> Text
    pack FilePath
    relFP)

        -- File contents, treated as a mustache template.
        ByteString
    contents <- Text -> ByteString
    encodeUtf8 (Text -> ByteString)
    -> (Template -> Text) -> Template -> ByteString
    forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
    <$> (Template -> Value -> Text
    `renderMustache` Value
    subst)
                               (Template -> ByteString) -> IO Template -> IO ByteString
    forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
    <$> FilePath -> IO Template
    compileMustacheFile FilePath
    fp

        -- Create target directory if necessary
        let dirName :: FilePath
    dirName = (FilePath, FilePath) -> FilePath
    forall a b. (a, b) -> a
    fst ((FilePath, FilePath) -> FilePath)
    -> (FilePath, FilePath) -> FilePath
    forall a b. (a -> b) -> a -> b
    $ FilePath -> (FilePath, FilePath)
    splitFileName FilePath
    fullPath
        Bool -> FilePath -> IO ()
    createDirectoryIfMissing Bool
    True FilePath
    dirName

        -- Write expanded contents to expanded file path
        FilePath -> ByteString -> IO ()
    B.writeFile FilePath
    fullPath ByteString
    contents