src/Main.hs

   1 {-# LANGUAGE DoAndIfThenElse #-}
   2 {-# LANGUAGE NoMonomorphismRestriction #-}
   3 module Main ( main )
   4 where
   5
   6 import Data.Maybe ( fromMaybe )
   7 import Data.String.Utils ( join )
   8 import Database.HDBC ( SqlError( seNativeError, seErrorMsg ), handleSql )
   9 import Database.HDBC.PostgreSQL ( connectPostgreSQL )
  10 import Database.HDBC.Sqlite3 ( connectSqlite3 )
  11 import System.Console.CmdArgs ( def )
  12 import System.Directory ( doesFileExist )
  13 import System.IO ( hPutStrLn, stderr )
  14 import CommandLine ( get_args )
  15 import Configuration (
  16   Configuration( host, port, username, password, database ),
  17   merge_optional )
  18 import qualified OptionalConfiguration as OC ( from_rc )
  19 import Report ( report )
  20
  21
  22 -- | Construct a connection string (postgres-only, for now) from a
  23 --   'Configuration'. All of these are optional, at least for
  24 --   Postgres, and so we want to avoid appending e.g. \"host=\" to the
  25 --   connection string if @(host cfg)@ is 'Nothing'.
  26 --
  27 --   Examples:
  28 --
  29 --   >>> let default_cfg = def :: Configuration
  30 --   >>> let cfg = default_cfg { host = Just "localhost" }
  31 --   >>> connection_string cfg
  32 --   "host=localhost"
  33 --   >>> let cfg2 = cfg { username = Just "postgres" }
  34 --   >>> connection_string cfg2
  35 --   "host=localhost user=postgres"
  36 --
  37 connection_string :: Configuration -> String
  38 connection_string cfg =
  39   trim $ join " " [host_part, port_part, user_part, pw_part, db_part]
  40   where
  41     -- | Strip leading/trailing whitespace, and collapse multiple
  42     --   consecutive spaces into one.
  43     trim :: String -> String
  44     trim = unwords . words
  45
  46     host_part = let h = fmap ("host=" ++) (host cfg) in  fromMaybe "" h
  47     port_part = let p = fmap (("port=" ++) . show) (port cfg) in fromMaybe "" p
  48     user_part = let u = fmap ("user=" ++) (username cfg) in fromMaybe "" u
  49     pw_part = let pw = fmap ("password=" ++) (password cfg) in fromMaybe "" pw
  50     db_part = let db = fmap ("dbname=" ++) (database cfg) in fromMaybe "" db
  51
  52
  53 main :: IO ()
  54 main = do
  55   rc_cfg <- OC.from_rc
  56   cmd_cfg <- get_args
  57
  58     -- Merge the config file options with the command-line ones,
  59   -- prefering the command-line ones.
  60   let opt_config = rc_cfg <> cmd_cfg
  61
  62   -- Update a default config with any options that have been set in
  63   -- either the config file or on the command-line.  We initialize
  64   -- logging before the missing parameter checks below so that we can
  65   -- log the errors.
  66   let cfg = (def :: Configuration) `merge_optional` opt_config
  67
  68   -- If a database name was specified, and that name exists as a file
  69   -- on the system, assume that the user wanted to use SQLite.
  70   handleSql show_sql_error $ do
  71     r <- case (database cfg) of
  72         Nothing -> connectPostgreSQL (connection_string cfg) >>= report cfg
  73
  74         Just dbname -> do
  75           exists <- doesFileExist dbname
  76           if exists
  77           then connectSqlite3 dbname >>= report cfg
  78           else connectPostgreSQL (connection_string cfg) >>= report cfg
  79
  80     -- The DB connection is implicitly closed when it gets garbage collected.
  81     putStrLn r
  82
  83   where
  84     show_sql_error :: SqlError -> IO ()
  85     show_sql_error se = hPutStrLn stderr $
  86       "SQL Error (" ++ (show $ seNativeError se) ++ "): " ++ (seErrorMsg se)