CSV.hs

{-# LANGUAGE BangPatterns #-}
{-# LANGUAGE ExplicitNamespaces #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE NumericUnderscores #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeApplications #-}

module DataFrame.IO.CSV where

import qualified Data.ByteString as BS
import qualified Data.ByteString.Char8 as C
import qualified Data.ByteString.Lazy as BL
import qualified Data.List as L
import qualified Data.Map.Strict as M
import qualified Data.Proxy as P
import qualified Data.Text as T
import qualified Data.Text.Encoding as TE
import qualified Data.Text.IO as TIO
import qualified Data.Vector as V
import qualified Data.Vector.Mutable as VM
import qualified Data.Vector.Unboxed as VU
import qualified Data.Vector.Unboxed.Mutable as VUM

import Data.Csv.Streaming (Records (..))
import qualified Data.Csv.Streaming as CsvStream

import Control.DeepSeq
import Control.Monad
import Data.Char
import qualified Data.Csv as Csv
import Data.Either
import Data.Function (on)
import Data.Functor
import Data.IORef
import Data.Maybe
import Data.Type.Equality (TestEquality (testEquality))
import Data.Word (Word8)
import DataFrame.Internal.Column
import DataFrame.Internal.DataFrame (DataFrame (..))
import DataFrame.Internal.Parsing
import DataFrame.Internal.Schema
import DataFrame.Operations.Typing
import System.IO
import Type.Reflection
import Prelude hiding (concat, takeWhile)

chunkSize :: Int
chunkSize = 16_384

data PagedVector a = PagedVector
    { pvChunks :: !(IORef [V.Vector a])
    -- ^ Finished chunks (reverse order)
    , pvActive :: !(IORef (VM.IOVector a))
    -- ^ Current mutable chunk
    , pvCount :: !(IORef Int)
    -- ^ Items written in current chunk
    }

data PagedUnboxedVector a = PagedUnboxedVector
    { puvChunks :: !(IORef [VU.Vector a])
    , puvActive :: !(IORef (VUM.IOVector a))
    , puvCount :: !(IORef Int)
    }

data BuilderColumn
    = BuilderInt !(PagedUnboxedVector Int) !(PagedUnboxedVector Word8)
    | BuilderDouble !(PagedUnboxedVector Double) !(PagedUnboxedVector Word8)
    | BuilderText !(PagedVector T.Text) !(PagedUnboxedVector Word8)
    | BuilderBS !(PagedVector BS.ByteString) !(PagedUnboxedVector Word8)

newPagedVector :: IO (PagedVector a)
newPagedVector = do
    active <- VM.unsafeNew chunkSize
    PagedVector <$> newIORef [] <*> newIORef active <*> newIORef 0

newPagedUnboxedVector :: (VUM.Unbox a) => IO (PagedUnboxedVector a)
newPagedUnboxedVector = do
    active <- VUM.unsafeNew chunkSize
    PagedUnboxedVector <$> newIORef [] <*> newIORef active <*> newIORef 0

appendPagedVector :: PagedVector a -> a -> IO ()
appendPagedVector (PagedVector chunksRef activeRef countRef) !val = do
    count <- readIORef countRef
    active <- readIORef activeRef

    if count < chunkSize
        then do
            VM.unsafeWrite active count val
            writeIORef countRef $! count + 1
        else do
            frozen <- V.unsafeFreeze active
            modifyIORef' chunksRef (frozen :)

            newActive <- VM.unsafeNew chunkSize
            VM.unsafeWrite newActive 0 val

            writeIORef activeRef newActive
            writeIORef countRef 1
{-# INLINE appendPagedVector #-}

appendPagedUnboxedVector :: (VUM.Unbox a) => PagedUnboxedVector a -> a -> IO ()
appendPagedUnboxedVector (PagedUnboxedVector chunksRef activeRef countRef) !val = do
    count <- readIORef countRef
    active <- readIORef activeRef

    if count < chunkSize
        then do
            VUM.unsafeWrite active count val
            writeIORef countRef $! count + 1
        else do
            frozen <- VU.unsafeFreeze active
            modifyIORef' chunksRef (frozen :)

            newActive <- VUM.unsafeNew chunkSize
            VUM.unsafeWrite newActive 0 val

            writeIORef activeRef newActive
            writeIORef countRef 1
{-# INLINE appendPagedUnboxedVector #-}

freezePagedVector :: PagedVector a -> IO (V.Vector a)
freezePagedVector (PagedVector chunksRef activeRef countRef) = do
    count <- readIORef countRef
    active <- readIORef activeRef
    chunks <- readIORef chunksRef

    writeIORef chunksRef [] -- release chunk references
    let frozenChunks = reverse chunks
        totalLen = count + sum (map V.length frozenChunks)

    mv <- VM.unsafeNew totalLen

    let copyChunk !offset chunk = do
            V.copy (VM.slice offset (V.length chunk) mv) chunk
            pure (offset + V.length chunk)

    offset <- foldM copyChunk 0 frozenChunks
    VM.copy (VM.slice offset count mv) (VM.slice 0 count active)

    V.unsafeFreeze mv

freezePagedUnboxedVector ::
    (VUM.Unbox a) => PagedUnboxedVector a -> IO (VU.Vector a)
freezePagedUnboxedVector (PagedUnboxedVector chunksRef activeRef countRef) = do
    count <- readIORef countRef
    active <- readIORef activeRef
    chunks <- readIORef chunksRef

    writeIORef chunksRef [] -- release chunk references
    let frozenChunks = reverse chunks
        totalLen = count + sum (map VU.length frozenChunks)

    mv <- VUM.unsafeNew totalLen

    let copyChunk !offset chunk = do
            VU.copy (VUM.slice offset (VU.length chunk) mv) chunk
            pure (offset + VU.length chunk)

    offset <- foldM copyChunk 0 frozenChunks
    VUM.copy (VUM.slice offset count mv) (VUM.slice 0 count active)

    VU.unsafeFreeze mv

-- | STANDARD CONFIG TYPES
data HeaderSpec = NoHeader | UseFirstRow | ProvideNames [T.Text]
    deriving (Eq, Show)

data TypeSpec
    = InferFromSample Int
    | SpecifyTypes [(T.Text, SchemaType)] TypeSpec
    | NoInference

-- | CSV read parameters.
data ReadOptions = ReadOptions
    { headerSpec :: HeaderSpec
    -- ^ Where to get the headers from. (default: UseFirstRow)
    , typeSpec :: TypeSpec
    -- ^ Whether/how to infer types. (default: InferFromSample 100)
    , safeRead :: Bool
    -- ^ Whether to partially parse values into `Maybe`/`Either`. (default: True)
    , dateFormat :: String
    {- ^ Format of date fields as recognized by the Data.Time.Format module.

    __Examples:__

    @
    > parseTimeM True defaultTimeLocale "%Y/%-m/%-d" "2010/3/04" :: Maybe Day
    Just 2010-03-04
    > parseTimeM True defaultTimeLocale "%d/%-m/%-Y" "04/3/2010" :: Maybe Day
    Just 2010-03-04
    @
    -}
    , columnSeparator :: Char
    -- ^ Character that separates column values.
    , numColumns :: Maybe Int
    -- ^ Number of columns to read.
    , missingIndicators :: [T.Text]
    -- ^ Values that should be read as `Nothing`.
    }

shouldInferFromSample :: TypeSpec -> Bool
shouldInferFromSample (InferFromSample _) = True
shouldInferFromSample (SpecifyTypes _ fallback) = shouldInferFromSample fallback
shouldInferFromSample _ = False

schemaTypeMap :: TypeSpec -> M.Map T.Text SchemaType
schemaTypeMap (SpecifyTypes xs _) = M.fromList xs
schemaTypeMap _ = M.empty

typeInferenceSampleSize :: TypeSpec -> Int
typeInferenceSampleSize (InferFromSample n) = n
typeInferenceSampleSize (SpecifyTypes _ fallback) = typeInferenceSampleSize fallback
typeInferenceSampleSize _ = 0

defaultReadOptions :: ReadOptions
defaultReadOptions =
    ReadOptions
        { headerSpec = UseFirstRow
        , typeSpec = InferFromSample 100
        , safeRead = True
        , dateFormat = "%Y-%m-%d"
        , columnSeparator = ','
        , numColumns = Nothing
        , missingIndicators =
            ["Nothing", "NULL", "", " ", "nan", "null", "N/A", "NaN", "NAN", "NA"]
        }

{- | Read CSV file from path and load it into a dataframe.

==== __Example__
@
ghci> D.readCsv ".\/data\/taxi.csv"

@
-}
readCsv :: FilePath -> IO DataFrame
readCsv = readSeparated defaultReadOptions

{- | Read CSV file from path and load it into a dataframe.

==== __Example__
@
ghci> D.readCsvWithOpts ".\/data\/taxi.csv" (D.defaultReadOptions { dateFormat = "%d/%-m/%-Y" })

@
-}
readCsvWithOpts :: ReadOptions -> FilePath -> IO DataFrame
readCsvWithOpts = readSeparated

{- | Read TSV (tab separated) file from path and load it into a dataframe.

==== __Example__
@
ghci> D.readTsv ".\/data\/taxi.tsv"

@
-}
readTsv :: FilePath -> IO DataFrame
readTsv = readSeparated (defaultReadOptions{columnSeparator = '\t'})

{- | Read text file with specified delimiter into a dataframe.

==== __Example__
@
ghci> D.readSeparated (D.defaultReadOptions { columnSeparator = ';' }) ".\/data\/taxi.txt"

@
-}
readSeparated :: ReadOptions -> FilePath -> IO DataFrame
readSeparated opts !path = do
    let stripUtf8Bom bs = fromMaybe bs (BL.stripPrefix "\xEF\xBB\xBF" bs)
    csvData <- stripUtf8Bom <$> BL.readFile path
    fmap force (decodeSeparated opts csvData)

decodeSeparated :: ReadOptions -> BL.ByteString -> IO DataFrame
decodeSeparated !opts csvData = do
    let sep = columnSeparator opts
    let decodeOpts = Csv.defaultDecodeOptions{Csv.decDelimiter = fromIntegral (ord sep)}
    let stream = CsvStream.decodeWith decodeOpts Csv.NoHeader csvData

    let peekStream (Cons (Right row) rest) = return (row, rest)
        peekStream (Cons (Left err) _) = error $ "Error parsing CSV header: " ++ err
        peekStream (Nil Nothing _) = error "Empty CSV file"
        peekStream (Nil (Just err) _) = error err

    (firstRowRaw, dataStream) <- peekStream stream

    let (columnNames, rowsToProcess) = case headerSpec opts of
            NoHeader ->
                ( map (T.pack . show) [0 .. V.length firstRowRaw - 1]
                , Cons (Right firstRowRaw) dataStream
                )
            UseFirstRow ->
                ( map (T.strip . TE.decodeUtf8Lenient . BL.toStrict) (V.toList firstRowRaw)
                , dataStream
                )
            ProvideNames ns ->
                ( ns ++ drop (length ns) (map (T.pack . show) [0 .. V.length firstRowRaw - 1])
                , Cons (Right firstRowRaw) dataStream
                )

    (sampleRow, _) <- peekStream rowsToProcess
    builderCols <- initializeColumns columnNames (V.toList sampleRow) opts
    let !builderColsV = V.fromList builderCols
    processStream
        (missingIndicators opts)
        rowsToProcess
        builderColsV
        (numColumns opts)

    frozenCols <- V.mapM (finalizeBuilderColumn opts) builderColsV
    let numRows = maybe 0 columnLength (frozenCols V.!? 0)

    let df =
            DataFrame
                frozenCols
                (M.fromList (zip columnNames [0 ..]))
                (numRows, V.length frozenCols)
                M.empty -- TODO give typed column references
    pure $ parseWithTypes (safeRead opts) (schemaTypeMap (typeSpec opts)) df

initializeColumns ::
    [T.Text] -> [BL.ByteString] -> ReadOptions -> IO [BuilderColumn]
initializeColumns names row opts = zipWithM initColumn names (map lookupType names)
  where
    typeMap = schemaTypeMap (typeSpec opts)
    -- Return Nothing for columns that should be inferred from BS
    shouldInfer = case typeSpec opts of
        InferFromSample _ -> True
        SpecifyTypes _ fallback -> shouldInferFromSample fallback
        NoInference -> False
    lookupType name = M.lookup name typeMap
    initColumn :: T.Text -> Maybe SchemaType -> IO BuilderColumn
    initColumn _ Nothing | shouldInfer = do
        validityRef <- newPagedUnboxedVector
        BuilderBS <$> newPagedVector <*> pure validityRef
    initColumn _ mtype = do
        validityRef <- newPagedUnboxedVector
        let t = fromMaybe (schemaType @T.Text) mtype
        case t of
            SType (_ :: P.Proxy a) -> case testEquality (typeRep @a) (typeRep @Int) of
                Just Refl -> BuilderInt <$> newPagedUnboxedVector <*> pure validityRef
                Nothing -> case testEquality (typeRep @a) (typeRep @Double) of
                    Just Refl -> BuilderDouble <$> newPagedUnboxedVector <*> pure validityRef
                    Nothing -> BuilderText <$> newPagedVector <*> pure validityRef

processStream ::
    [T.Text] ->
    CsvStream.Records (V.Vector BL.ByteString) ->
    V.Vector BuilderColumn ->
    Maybe Int ->
    IO ()
processStream _ _ _ (Just 0) = return ()
processStream missing (Cons (Right row) rest) cols n =
    processRow missing row cols
        >> processStream missing rest cols (fmap (flip (-) 1) n)
processStream missing (Cons (Left err) _) _ _ = error ("CSV Parse Error: " ++ err)
processStream missing (Nil _ _) _ _ = return ()

processRow ::
    [T.Text] -> V.Vector BL.ByteString -> V.Vector BuilderColumn -> IO ()
processRow missing !vals !cols = V.zipWithM_ processValue vals cols
  where
    processValue !bs !col = do
        let !bs' = BL.toStrict bs
        case col of
            BuilderInt gv valid -> case readByteStringInt bs' of
                Just !i -> appendPagedUnboxedVector gv i >> appendPagedUnboxedVector valid 1
                Nothing -> appendPagedUnboxedVector gv 0 >> appendPagedUnboxedVector valid 0
            BuilderDouble gv valid -> case readByteStringDouble bs' of
                Just !d -> appendPagedUnboxedVector gv d >> appendPagedUnboxedVector valid 1
                Nothing -> appendPagedUnboxedVector gv 0.0 >> appendPagedUnboxedVector valid 0
            BuilderText gv valid -> do
                let !val = T.strip (TE.decodeUtf8Lenient bs')
                if val `elem` missing
                    then appendPagedVector gv T.empty >> appendPagedUnboxedVector valid 0
                    else appendPagedVector gv val >> appendPagedUnboxedVector valid 1
            BuilderBS gv valid -> do
                let !bs'' = C.strip bs'
                if TE.decodeUtf8Lenient bs'' `elem` missing
                    then appendPagedVector gv BS.empty >> appendPagedUnboxedVector valid 0
                    else appendPagedVector gv bs'' >> appendPagedUnboxedVector valid 1

freezeBuilderColumn :: BuilderColumn -> IO Column
freezeBuilderColumn (BuilderInt gv validRef) = do
    vec <- freezePagedUnboxedVector gv
    valid <- freezePagedUnboxedVector validRef
    if VU.all (== 1) valid
        then return $! UnboxedColumn vec
        else constructOptional vec valid
freezeBuilderColumn (BuilderDouble gv validRef) = do
    vec <- freezePagedUnboxedVector gv
    valid <- freezePagedUnboxedVector validRef
    if VU.all (== 1) valid
        then return $! UnboxedColumn vec
        else constructOptional vec valid
freezeBuilderColumn (BuilderText gv validRef) = do
    vec <- freezePagedVector gv
    valid <- freezePagedUnboxedVector validRef
    if VU.all (== 1) valid
        then return $! BoxedColumn vec
        else constructOptionalBoxed vec valid
freezeBuilderColumn (BuilderBS _ _) =
    error
        "freezeBuilderColumn: BuilderBS must be finalized via finalizeBuilderColumn"

finalizeBuilderColumn :: ReadOptions -> BuilderColumn -> IO Column
finalizeBuilderColumn opts (BuilderBS gv validRef) = do
    vec <- freezePagedVector gv
    valid <- freezePagedUnboxedVector validRef
    return $! inferColumnFromBS opts vec valid
finalizeBuilderColumn _ bc = freezeBuilderColumn bc

inferColumnFromBS ::
    ReadOptions -> V.Vector BS.ByteString -> VU.Vector Word8 -> Column
inferColumnFromBS opts vec valid =
    let sampleN = let n = typeInferenceSampleSize (typeSpec opts) in if n == 0 then 100 else n
        dfmt = dateFormat opts
        asMaybeFull = V.generate (V.length vec) $ \i ->
            if valid VU.! i == 1 then Just (vec V.! i) else Nothing
        samples = V.take sampleN asMaybeFull
        assumption = makeParsingAssumptionBS dfmt samples
     in case assumption of
            IntAssumption -> handleBSInt dfmt asMaybeFull
            DoubleAssumption -> handleBSDouble asMaybeFull
            BoolAssumption -> handleBSBool asMaybeFull
            DateAssumption -> handleBSDate dfmt asMaybeFull
            TextAssumption -> handleBSText asMaybeFull
            NoAssumption -> handleBSNo dfmt asMaybeFull

makeParsingAssumptionBS ::
    String -> V.Vector (Maybe BS.ByteString) -> ParsingAssumption
makeParsingAssumptionBS dfmt asMaybe
    | V.all (== Nothing) asMaybe = NoAssumption
    | vecSameConstructor asMaybe asMaybeBool = BoolAssumption
    | vecSameConstructor asMaybe asMaybeInt
        && vecSameConstructor asMaybe asMaybeDouble =
        IntAssumption
    | vecSameConstructor asMaybe asMaybeDouble = DoubleAssumption
    | vecSameConstructor asMaybe asMaybeDate = DateAssumption
    | otherwise = TextAssumption
  where
    asMaybeBool = V.map (>>= readByteStringBool) asMaybe
    asMaybeInt = V.map (>>= readByteStringInt) asMaybe
    asMaybeDouble = V.map (>>= readByteStringDouble) asMaybe
    asMaybeDate = V.map (>>= readByteStringDate dfmt) asMaybe

handleBSBool :: V.Vector (Maybe BS.ByteString) -> Column
handleBSBool asMaybe
    | parsableAsBool =
        maybe (fromVector asMaybeBool) fromVector (sequenceA asMaybeBool)
    | otherwise = handleBSText asMaybe
  where
    asMaybeBool = V.map (>>= readByteStringBool) asMaybe
    parsableAsBool = vecSameConstructor asMaybe asMaybeBool

handleBSInt :: String -> V.Vector (Maybe BS.ByteString) -> Column
handleBSInt dfmt asMaybe
    | parsableAsInt =
        maybe (fromVector asMaybeInt) fromVector (sequenceA asMaybeInt)
    | parsableAsDouble =
        maybe (fromVector asMaybeDouble) fromVector (sequenceA asMaybeDouble)
    | otherwise = handleBSText asMaybe
  where
    asMaybeInt = V.map (>>= readByteStringInt) asMaybe
    asMaybeDouble = V.map (>>= readByteStringDouble) asMaybe
    parsableAsInt =
        vecSameConstructor asMaybe asMaybeInt
            && vecSameConstructor asMaybe asMaybeDouble
    parsableAsDouble = vecSameConstructor asMaybe asMaybeDouble

handleBSDouble :: V.Vector (Maybe BS.ByteString) -> Column
handleBSDouble asMaybe
    | parsableAsDouble =
        maybe (fromVector asMaybeDouble) fromVector (sequenceA asMaybeDouble)
    | otherwise = handleBSText asMaybe
  where
    asMaybeDouble = V.map (>>= readByteStringDouble) asMaybe
    parsableAsDouble = vecSameConstructor asMaybe asMaybeDouble

handleBSDate :: String -> V.Vector (Maybe BS.ByteString) -> Column
handleBSDate dfmt asMaybe
    | parsableAsDate =
        maybe (fromVector asMaybeDate) fromVector (sequenceA asMaybeDate)
    | otherwise = handleBSText asMaybe
  where
    asMaybeDate = V.map (>>= readByteStringDate dfmt) asMaybe
    parsableAsDate = vecSameConstructor asMaybe asMaybeDate

handleBSText :: V.Vector (Maybe BS.ByteString) -> Column
handleBSText asMaybe =
    let asMaybeText = V.map (fmap TE.decodeUtf8Lenient) asMaybe
     in maybe (fromVector asMaybeText) fromVector (sequenceA asMaybeText)

handleBSNo :: String -> V.Vector (Maybe BS.ByteString) -> Column
handleBSNo dfmt asMaybe
    | V.all (== Nothing) asMaybe =
        fromVector (V.map (const (Nothing :: Maybe T.Text)) asMaybe)
    | parsableAsBool =
        maybe (fromVector asMaybeBool) fromVector (sequenceA asMaybeBool)
    | parsableAsInt =
        maybe (fromVector asMaybeInt) fromVector (sequenceA asMaybeInt)
    | parsableAsDouble =
        maybe (fromVector asMaybeDouble) fromVector (sequenceA asMaybeDouble)
    | parsableAsDate =
        maybe (fromVector asMaybeDate) fromVector (sequenceA asMaybeDate)
    | otherwise = handleBSText asMaybe
  where
    asMaybeBool = V.map (>>= readByteStringBool) asMaybe
    asMaybeInt = V.map (>>= readByteStringInt) asMaybe
    asMaybeDouble = V.map (>>= readByteStringDouble) asMaybe
    asMaybeDate = V.map (>>= readByteStringDate dfmt) asMaybe
    parsableAsBool = vecSameConstructor asMaybe asMaybeBool
    parsableAsInt =
        vecSameConstructor asMaybe asMaybeInt
            && vecSameConstructor asMaybe asMaybeDouble
    parsableAsDouble = vecSameConstructor asMaybe asMaybeDouble
    parsableAsDate = vecSameConstructor asMaybe asMaybeDate

constructOptional ::
    (VU.Unbox a, Columnable a) => VU.Vector a -> VU.Vector Word8 -> IO Column
constructOptional vec valid = do
    let size = VU.length vec
    mvec <- VM.new size
    forM_ [0 .. size - 1] $ \i ->
        if (valid VU.! i) == 0
            then VM.write mvec i Nothing
            else VM.write mvec i (Just (vec VU.! i))
    OptionalColumn <$> V.freeze mvec

constructOptionalBoxed :: V.Vector T.Text -> VU.Vector Word8 -> IO Column
constructOptionalBoxed vec valid = do
    let size = V.length vec
    mvec <- VM.new size
    forM_ [0 .. size - 1] $ \i ->
        if (valid VU.! i) == 0
            then VM.write mvec i Nothing
            else VM.write mvec i (Just (vec V.! i))
    OptionalColumn <$> V.freeze mvec

writeCsv :: FilePath -> DataFrame -> IO ()
writeCsv = writeSeparated ','

writeTsv :: FilePath -> DataFrame -> IO ()
writeTsv = writeSeparated '\t'

writeSeparated ::
    -- | Separator
    Char ->
    -- | Path to write to
    FilePath ->
    DataFrame ->
    IO ()
writeSeparated c filepath df = withFile filepath WriteMode $ \handle -> do
    let (rows, _) = dataframeDimensions df
    let headers = map fst (L.sortBy (compare `on` snd) (M.toList (columnIndices df)))
    TIO.hPutStrLn handle (T.intercalate "," headers)
    forM_ [0 .. (rows - 1)] $ \i -> do
        let row = getRowAsText df i
        TIO.hPutStrLn handle (T.intercalate "," row)

getRowAsText :: DataFrame -> Int -> [T.Text]
getRowAsText df i = V.ifoldr go [] (columns df)
  where
    indexMap = M.fromList (map (\(a, b) -> (b, a)) $ M.toList (columnIndices df))
    go k (BoxedColumn (c :: V.Vector a)) acc = case c V.!? i of
        Just e -> textRep : acc
          where
            textRep = case testEquality (typeRep @a) (typeRep @T.Text) of
                Just Refl -> e
                Nothing -> case typeRep @a of
                    App t1 t2 -> case eqTypeRep t1 (typeRep @Maybe) of
                        Just HRefl -> case testEquality t2 (typeRep @T.Text) of
                            Just Refl -> fromMaybe "null" e
                            Nothing -> (fromOptional . T.pack . show) e
                              where
                                fromOptional s
                                    | T.isPrefixOf "Just " s = T.drop (T.length "Just ") s
                                    | otherwise = "null"
                        Nothing -> (T.pack . show) e
                    _ -> (T.pack . show) e
        Nothing ->
            error $
                "Column "
                    ++ T.unpack (indexMap M.! k)
                    ++ " has less items than "
                    ++ "the other columns at index "
                    ++ show i
    go k (UnboxedColumn c) acc = case c VU.!? i of
        Just e -> T.pack (show e) : acc
        Nothing ->
            error $
                "Column "
                    ++ T.unpack (indexMap M.! k)
                    ++ " has less items than "
                    ++ "the other columns at index "
                    ++ show i
    go k (OptionalColumn (c :: V.Vector (Maybe a))) acc = case c V.!? i of
        Just e -> case testEquality (typeRep @a) (typeRep @T.Text) of
            Just Refl -> fromMaybe T.empty e : acc
            Nothing -> maybe T.empty (T.pack . show) e : acc
        Nothing ->
            error $
                "Column "
                    ++ T.unpack (indexMap M.! k)
                    ++ " has less items than "
                    ++ "the other columns at index "
                    ++ show i

stripQuotes :: T.Text -> T.Text
stripQuotes txt =
    case T.uncons txt of
        Just ('"', rest) ->
            case T.unsnoc rest of
                Just (middle, '"') -> middle
                _ -> txt
        _ -> txt