74 lines
2.0 KiB
Haskell
74 lines
2.0 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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, restrictRange
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, rangeGeq
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, allRange
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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 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 Integer
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rangeParse :: BS.ByteString -> NonnegRange
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rangeParse range = do
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let rangeRegex = "^([0-9]+)-([0-9]*)$" :: BS.ByteString
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case listToMaybe (range =~ rangeRegex :: [[BS.ByteString]]) of
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Just parsedRange ->
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let [_, from, to] = readMaybe . cs <$> parsedRange
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lower = fromMaybe emptyRange (rangeGeq <$> from)
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upper = fromMaybe allRange (rangeLeq <$> to) in
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rangeIntersection lower upper
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Nothing -> allRange
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rangeRequested :: RequestHeaders -> NonnegRange
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rangeRequested headers = fromMaybe allRange $
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rangeParse <$> lookup hRange headers
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restrictRange :: Maybe Integer -> NonnegRange -> NonnegRange
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restrictRange Nothing r = r
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restrictRange (Just limit) r =
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rangeIntersection r $
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Range BoundaryBelowAll (BoundaryAbove $ rangeOffset r + limit - 1)
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rangeLimit :: NonnegRange -> Maybe Integer
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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 -> Integer
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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 :: Integer -> NonnegRange
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rangeGeq n =
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Range (BoundaryBelow n) BoundaryAboveAll
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allRange :: NonnegRange
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allRange = rangeGeq 0
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rangeLeq :: Integer -> NonnegRange
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rangeLeq n =
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Range BoundaryBelowAll (BoundaryAbove n)
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