Parse Heroku's DATABASE_URL into a PostgresConf for use in a Yesod application

HerokuConf.hs

{-# LANGUAGE OverloadedStrings #-}
--------------------------------------------------------------------------------
-- |
-- Module      :  Yesod.HerokuConf
-- Copyright   :  (c) Patrick Brisbin 2013
-- License     :  as-is
-- Maintainer  :  pbrisbin@gmail.com
-- Stability   :  unstable
-- Portability :  unportable
--
-- Parses DATABASE_URL into a valid PostgresConf. Useful when running
-- a Yesod app with Postgresql on Heroku.
--
-- > makeFoundation conf = do
-- >     manager <- newManager def
-- >     s <- staticSite
-- >     dbconf <- herokuConf
-- >     p <- Database.Persist.Store.createPoolConfig dbconf
-- >     Database.Persist.Store.runPool dbconf (runMigration migrateAll) p
-- >     return $ App conf s p manager dbconf
--
--------------------------------------------------------------------------------
module Yesod.HerokuConf where

import Data.ByteString (ByteString)
import Data.Text (Text)
import Data.Text.Encoding (encodeUtf8)
import Database.Persist.Postgresql (PostgresConf(..))
import Web.Heroku (dbConnParams)

import qualified Data.Text as T

herokuConf :: IO PostgresConf
herokuConf = do
    params <- dbConnParams

    return PostgresConf
        { pgConnStr  = formatParams params
        , pgPoolSize = 100 -- TODO: how to set this?
        }

    where
        formatParams :: [(Text, Text)] -> ByteString
        formatParams = encodeUtf8 . T.unwords . map toKeyValue

        toKeyValue :: (Text, Text) -> Text
        toKeyValue (k, v) = k `T.append` "=" `T.append` v