module PostgREST.RangeQuery (
rangeParse
, rangeRequested
, rangeLimit
, rangeOffset
, NonnegRange
) where
import Control.Applicative
import Network.HTTP.Types.Header
import qualified Data.ByteString.Char8 as BS
import Data.Ranged.Boundaries
import Data.Ranged.Ranges
import Data.String.Conversions (cs)
import Text.Regex.TDFA ((=~))
import Text.Read (readMaybe)
import Data.Maybe (fromMaybe, listToMaybe)
import Prelude
type NonnegRange = Range Int
rangeParse :: BS.ByteString -> Maybe NonnegRange
rangeParse range = do
let rangeRegex = "^([0-9]+)-([0-9]*)$" :: BS.ByteString
parsedRange <- listToMaybe (range =~ rangeRegex :: [[BS.ByteString]])
let [_, from, to] = readMaybe . cs <$> parsedRange
let lower = fromMaybe emptyRange (rangeGeq <$> from)
let upper = fromMaybe (rangeGeq 0) (rangeLeq <$> to)
return $ rangeIntersection lower upper
rangeRequested :: RequestHeaders -> Maybe NonnegRange
rangeRequested = (rangeParse =<<) . lookup hRange
rangeLimit :: NonnegRange -> Maybe Int
rangeLimit range =
case [rangeLower range, rangeUpper range]
of [BoundaryBelow from, BoundaryAbove to] -> Just (1 + to from)
_ -> Nothing
rangeOffset :: NonnegRange -> Int
rangeOffset range =
case rangeLower range
of BoundaryBelow from -> from
_ -> error "range without lower bound"
rangeGeq :: Int -> NonnegRange
rangeGeq n =
Range (BoundaryBelow n) BoundaryAboveAll
rangeLeq :: Int -> NonnegRange
rangeLeq n =
Range BoundaryBelowAll (BoundaryAbove n)