OptionalConfiguration.hs

   1 {-# LANGUAGE DeriveDataTypeable #-}
   2 {-# LANGUAGE FlexibleInstances #-}
   3 {-# LANGUAGE OverloadedStrings #-}
   4 {-# LANGUAGE StandaloneDeriving #-}
   5
   6 -- | An OptionalConfiguration is just like a 'Configuration', except
   7 --   all of its fields are optional. The user can set options in two
   8 --   places: the command-line, and a configuration file. Obviously if
   9 --   a parameter is set in one place, it doesn't need to be set in the
  10 --   other. Thus, the latter needs to be optional.
  11 --
  12 module OptionalConfiguration (
  13   OptionalConfiguration(..),
  14   from_rc,
  15   merge_maybes )
  16 where
  17
  18 import qualified Data.Configurator as DC (
  19   Worth(Optional),
  20   load,
  21   lookup )
  22 import qualified Data.Configurator.Types as DCT (
  23   Configured,
  24   Value( String ),
  25   convert )
  26 import Data.Data ( Data )
  27 import Data.Monoid ( Monoid(..) )
  28 import Data.Typeable ( Typeable )
  29 import Paths_htsn_import ( getSysconfDir )
  30 import System.Directory ( getHomeDirectory )
  31 import System.FilePath ( (</>) )
  32 import System.IO.Error ( catchIOError )
  33 import System.Log ( Priority(..) )
  34 import Text.Read ( readMaybe )
  35
  36 import Backend ( Backend(..) )
  37 import Network.Services.TSN.Report ( report_error )
  38
  39
  40 -- Derive standalone instances of Data and Typeable for Priority. This
  41 -- is necessary for OptionalConfiguration (which contains a Maybe
  42 -- Priority) to derive Data and Typeable.
  43 deriving instance Data Priority
  44 deriving instance Typeable Priority
  45
  46 -- | The same as Configuration, except everything is optional. It's easy to
  47 --   merge two of these by simply dropping the Nothings in favor of
  48 --   the Justs. The 'feed_hosts' are left un-maybed so that cmdargs
  49 --   can parse more than one of them.
  50 --
  51 data OptionalConfiguration =
  52   OptionalConfiguration {
  53     backend           :: Maybe Backend,
  54     connection_string :: Maybe String,
  55     log_file          :: Maybe FilePath,
  56     log_level         :: Maybe Priority,
  57     syslog            :: Maybe Bool,
  58     xml_files         :: [FilePath] }
  59     deriving (Show, Data, Typeable)
  60
  61
  62 -- | Combine two Maybes into one, essentially mashing them
  63 --   together. We give precedence to the second argument when both are
  64 --   Justs.
  65 merge_maybes :: (Maybe a) -> (Maybe a) -> (Maybe a)
  66 merge_maybes Nothing Nothing   = Nothing
  67 merge_maybes (Just x) Nothing  = Just x
  68 merge_maybes Nothing (Just x)  = Just x
  69 merge_maybes (Just _) (Just y) = Just y
  70
  71
  72 -- | The Monoid instance for these lets us "combine" two
  73 --   OptionalConfigurations. The "combine" operation that we'd like to
  74 --   perform is, essentially, to mash them together. So if we have two
  75 --   OptionalConfigurations, each half full, we could combine them
  76 --   into one big one.
  77 --
  78 --   This is used to merge command-line and config-file settings.
  79 --
  80 instance Monoid OptionalConfiguration where
  81   -- | An empty OptionalConfiguration.
  82   mempty = OptionalConfiguration Nothing Nothing Nothing Nothing Nothing []
  83
  84
  85   -- | Combine @cfg1@ and @cfg2@, giving precedence to @cfg2@.
  86   --   XML files can only be specified on the command-line, so we
  87   --   just join them together here.
  88   cfg1 `mappend` cfg2 =
  89     OptionalConfiguration
  90      (merge_maybes (backend cfg1) (backend cfg2))
  91       (merge_maybes (connection_string cfg1) (connection_string cfg2))
  92       (merge_maybes (log_file cfg1) (log_file cfg2))
  93       (merge_maybes (log_level cfg1) (log_level cfg2))
  94       (merge_maybes (syslog cfg1) (syslog cfg2))
  95       ((xml_files cfg1) ++ (xml_files cfg2))
  96
  97 instance DCT.Configured Priority where
  98   -- | This allows us to read a Priority level out of a Configurator
  99   --   config file. By default Configurator wouldn't know what to do,
 100   --   so we have to tell it that we expect one of the valid Priority
 101   --   constructors.
 102   convert (DCT.String "INFO") = Just INFO
 103   convert (DCT.String "WARNING") = Just WARNING
 104   convert (DCT.String "ERROR") = Just ERROR
 105   convert _ = Nothing
 106
 107
 108 -- | Obtain an OptionalConfiguration from htsn-importrc in either the global
 109 --   configuration directory or the user's home directory. The one in
 110 --   $HOME is prefixed by a dot so that it is hidden.
 111 --
 112 --   We make an attempt at cross-platform compatibility; we will try
 113 --   to find the correct directory even on Windows. But if the calls
 114 --   to getHomeDirectory/getSysconfDir fail for whatever reason, we
 115 --   fall back to using the Unix-specific /etc and $HOME.
 116 --
 117 from_rc :: IO OptionalConfiguration
 118 from_rc = do
 119   etc  <- catchIOError getSysconfDir (\e -> do
 120                                         report_error (show e)
 121                                         return "/etc")
 122   home <- catchIOError getHomeDirectory (\e -> do
 123                                            report_error (show e)
 124                                            return "$(HOME)")
 125   let global_config_path = etc </> "htsn-importrc"
 126   let user_config_path = home </> ".htsn-importrc"
 127   cfg <- DC.load [ DC.Optional global_config_path,
 128                    DC.Optional user_config_path ]
 129   cfg_backend <- DC.lookup cfg "backend"
 130   cfg_connection_string <- DC.lookup cfg "connection_string"
 131   cfg_log_file <- DC.lookup cfg "log_file"
 132   cfg_log_level <- DC.lookup cfg "log_level"
 133   cfg_syslog <- DC.lookup cfg "syslog"
 134   let cfg_xml_files = [] -- This won't be in the config file.
 135   return $ OptionalConfiguration
 136              (case cfg_backend of -- Try to convert a String to a Backend.
 137                 Nothing -> Nothing
 138                 Just s -> readMaybe s)
 139              cfg_connection_string
 140              cfg_log_file
 141              cfg_log_level
 142              cfg_syslog
 143              cfg_xml_files