62 lines
1.7 KiB
Haskell
62 lines
1.7 KiB
Haskell
module PostgREST.RangeQuery (
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rangeParse
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, rangeRequested
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, rangeLimit
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, rangeOffset
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, NonnegRange
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) where
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import Control.Applicative
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import Network.HTTP.Types.Header
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import PostgREST.Types ()
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import qualified Data.ByteString.Char8 as BS
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import Data.Ranged.Boundaries
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import Data.Ranged.Ranges
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import Data.String.Conversions (cs)
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import Text.Read (readMaybe)
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import Text.Regex.TDFA ((=~))
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import Data.Maybe (fromMaybe, listToMaybe)
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import Prelude
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type NonnegRange = Range Int
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rangeParse :: BS.ByteString -> Maybe NonnegRange
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rangeParse range = do
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let rangeRegex = "^([0-9]+)-([0-9]*)$" :: BS.ByteString
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parsedRange <- listToMaybe (range =~ rangeRegex :: [[BS.ByteString]])
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let [_, from, to] = readMaybe . cs <$> parsedRange
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let lower = fromMaybe emptyRange (rangeGeq <$> from)
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let upper = fromMaybe (rangeGeq 0) (rangeLeq <$> to)
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return $ rangeIntersection lower upper
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rangeRequested :: RequestHeaders -> Maybe NonnegRange
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rangeRequested = (rangeParse =<<) . lookup hRange
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rangeLimit :: NonnegRange -> Maybe Int
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rangeLimit range =
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case [rangeLower range, rangeUpper range] of
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[BoundaryBelow from, BoundaryAbove to] -> Just (1 + to - from)
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_ -> Nothing
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rangeOffset :: NonnegRange -> Int
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rangeOffset range =
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case rangeLower range of
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BoundaryBelow from -> from
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_ -> error "range without lower bound" -- should never happen
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rangeGeq :: Int -> NonnegRange
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rangeGeq n =
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Range (BoundaryBelow n) BoundaryAboveAll
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rangeLeq :: Int -> NonnegRange
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rangeLeq n =
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Range BoundaryBelowAll (BoundaryAbove n)
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