CloudConfigYaml.hs

{-# LANGUAGE OverloadedStrings #-}

{-| This contains a 'YamlObject' for Canonicals @cloud-init@.

For some reason, cloud-config yaml documents __MUST__
contain @#cloud-config@ in the first line.

This is documented in the <https://cloudinit.readthedocs.io/en/latest/topics/format.html#cloud-config-data cloud config documentation>.

Otherwise, this is just a wrapper around 'YamlObject'.

@Since 0.5.62
-}
module B9.Artifact.Content.CloudConfigYaml
  ( CloudConfigYaml(..)
  , cloudConfigFileHeader
  )
where

import           B9.Artifact.Content.AST
import           B9.Artifact.Content.YamlObject
import           B9.Text
import           Control.Parallel.Strategies    ( NFData )
import           Data.Data                      ( Data
                                                , Typeable
                                                )
import           Data.Text                     as Text
import           Data.Hashable                  ( Hashable )
import           GHC.Generics                   ( Generic )
import           Test.QuickCheck                ( Arbitrary )

-- | Cloud-init @meta-data@ configuration Yaml.
--
-- @cloud-config@ yaml documents contain:
 -- @#cloud-config@ as first line.
--
-- @Since 0.5.62
newtype CloudConfigYaml = MkCloudConfigYaml
  { fromCloudConfigYaml :: YamlObject
  } deriving (Hashable, NFData, Eq, Data, Typeable, Generic, Arbitrary, Read, Show, Semigroup)

-- | The header line, which must be the first line in the
-- text file containing the cloud-config Yaml document.
--
-- @Since 0.5.62
cloudConfigFileHeader :: Text
cloudConfigFileHeader = "#cloud-config\n"

instance FromAST CloudConfigYaml where
  fromAST ast = MkCloudConfigYaml <$> fromAST (fromCloudConfigYaml <$> ast)

instance Textual CloudConfigYaml where
  parseFromText txt = do
-- skip the optional header line
    let header = Text.take (Text.length cloudConfigFileHeader) txt
        txt'   = if header == cloudConfigFileHeader
          then Text.drop (Text.length cloudConfigFileHeader) txt
          else txt
    y <- parseFromText txt'
    return (MkCloudConfigYaml y)

  renderToText (MkCloudConfigYaml y) = do
    txt <- renderToText y
    return (Text.unlines [cloudConfigFileHeader, txt])