src/Main.hs

   1 {-# LANGUAGE DoAndIfThenElse #-}
   2 {-# LANGUAGE NoMonomorphismRestriction #-}
   3 module Main
   4 where
   5
   6 import Data.Maybe ( fromMaybe )
   7 import Data.Monoid ( (<>) )
   8 import Data.String.Utils ( join )
   9 import Database.HDBC.PostgreSQL ( connectPostgreSQL )
  10 import Database.HDBC.Sqlite3 ( connectSqlite3 )
  11 import System.Console.CmdArgs ( def )
  12 import System.Directory ( doesFileExist )
  13
  14 import CommandLine ( get_args )
  15 import Configuration ( Configuration(..), merge_optional )
  16 import qualified OptionalConfiguration as OC ( from_rc )
  17 import Report ( report )
  18
  19
  20 -- | Construct a connection string (postgres-only, for now) from a
  21 --   'Configuration'. All of these are optional, at least for
  22 --   Postgres, and so we want to avoid appending e.g. \"host=\" to the
  23 --   connection string if @(host cfg)@ is 'Nothing'.
  24 --
  25 --   Examples:
  26 --
  27 --   >>> let default_cfg = def :: Configuration
  28 --   >>> let cfg = default_cfg { host = Just "localhost" }
  29 --   >>> connection_string cfg
  30 --   "host=localhost"
  31 --   >>> let cfg2 = cfg { username = Just "postgres" }
  32 --   >>> connection_string cfg2
  33 --   "host=localhost user=postgres"
  34 --
  35 connection_string :: Configuration -> String
  36 connection_string cfg =
  37   trim $ join " " [host_part, port_part, user_part, pw_part, db_part]
  38   where
  39     -- | Strip leading/trailing whitespace, and collapse multiple
  40     --   consecutive spaces into one.
  41     trim :: String -> String
  42     trim = unwords . words
  43
  44     host_part = let h = fmap ("host=" ++) (host cfg) in  fromMaybe "" h
  45     port_part = let p = fmap (("port=" ++) . show) (port cfg) in fromMaybe "" p
  46     user_part = let u = fmap ("user=" ++) (username cfg) in fromMaybe "" u
  47     pw_part = let pw = fmap ("password=" ++) (password cfg) in fromMaybe "" pw
  48     db_part = let db = fmap ("dbname=" ++) (database cfg) in fromMaybe "" db
  49
  50
  51 main :: IO ()
  52 main = do
  53   rc_cfg <- OC.from_rc
  54   cmd_cfg <- get_args
  55
  56     -- Merge the config file options with the command-line ones,
  57   -- prefering the command-line ones.
  58   let opt_config = rc_cfg <> cmd_cfg
  59
  60   -- Update a default config with any options that have been set in
  61   -- either the config file or on the command-line.  We initialize
  62   -- logging before the missing parameter checks below so that we can
  63   -- log the errors.
  64   let cfg = (def :: Configuration) `merge_optional` opt_config
  65
  66   -- If a database name was specified, and that name exists as a file
  67   -- on the system, assume that the user wanted to use SQLite.
  68   r <- case (database cfg) of
  69       Nothing -> connectPostgreSQL (connection_string cfg) >>= report cfg
  70
  71       Just dbname -> do
  72         exists <- doesFileExist dbname
  73         if exists
  74         then connectSqlite3 dbname >>= report cfg
  75         else connectPostgreSQL (connection_string cfg) >>= report cfg
  76
  77   -- The DB connection is implicitly closed when it gets garbage collected.
  78   putStrLn r