Split into another module

PgQuery.hs

@@ -0,0 +1,74 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+module PgQuery where
+
+import Data.Functor ( (<$>) )
+import Data.Maybe (fromMaybe)
+import Data.List (intercalate)
+import Data.Monoid ((<>))
+
+import qualified Data.Text as T
+import qualified Data.ByteString.Lazy as BL
+import qualified Data.ByteString.Char8 as BS
+
+import Database.HDBC hiding (colType, colNullable)
+import Database.HDBC.PostgreSQL
+
+import Network.HTTP.Types.URI
+
+selectWhere :: T.Text -> Query -> Connection -> IO BL.ByteString
+selectWhere table qq conn = do
+  s <- selectSql
+  w <- whereClause conn qq
+  r <- quickQuery conn (BS.unpack $ s <> w) []
+  return $ case r of
+                [[json]] -> fromSql json
+                _        -> "" :: BL.ByteString
+
+  where
+    selectSql = pgFormat conn
+          "select array_to_json(array_agg(row_to_json(t)))\
+          \  from (select * from %I.%I) t"
+        [toSql (T.pack "base"), toSql table]
+
+
+whereClause :: Connection -> Query -> IO BS.ByteString
+whereClause _    [] = return ""
+whereClause conn qs =
+  (" where " <>) <$> clause
+
+  where
+    clause :: IO BS.ByteString
+    clause = BS.intercalate " and " <$> preds
+
+    preds :: IO [BS.ByteString]
+    preds = sequence $ map (wherePred conn) qs
+
+
+wherePred :: Connection -> QueryItem -> IO BS.ByteString
+wherePred conn (column, predicate) =
+  pgFormat conn ("t.%I " <> op <> "%L") $ map toSql [column, value]
+
+  where
+    opCode:rest = BS.split ':' $ fromMaybe "" predicate
+    value = BS.intercalate ":" rest
+    op = case opCode of
+              "eq"  -> "="
+              "gt"  -> ">"
+              "lt"  -> "<"
+              "gte" -> ">="
+              "lte" -> "<="
+              "neq" -> "<>"
+              _     -> "="
+
+
+pgFormat :: Connection -> String -> [SqlValue] -> IO BS.ByteString
+pgFormat conn sql args = do
+  [[escaped]] <- quickQuery conn q args
+  return $ fromSql escaped
+
+  where
+    q = concat [ "select format('", sql, "', ", placeholders args, ")" ]
+
+    placeholders :: [a] -> String
+    placeholders = intercalate ", " . map (const "?::varchar")