{-# LANGUAGE ExplicitNamespaces #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeApplications #-}
module DataFrame.Operations.Core where

import qualified Data.List as L
import qualified Data.Map as M
import qualified Data.Map.Strict as MS
import qualified Data.Set as S
import qualified Data.Text as T
import qualified Data.Vector.Generic as VG
import qualified Data.Vector as V
import qualified Data.Vector.Unboxed as VU

import Control.Exception ( throw )
import DataFrame.Errors
import DataFrame.Internal.Column ( Column(..), fromVector, fromList, columnLength, columnTypeString, expandColumn, Columnable)
import DataFrame.Internal.DataFrame (DataFrame(..), getColumn, null, empty)
import DataFrame.Internal.Parsing (isNullish)
import Data.Either
import Data.Function (on, (&))
import Data.Maybe
import Data.Type.Equality (type (:~:)(Refl), TestEquality(..))
import Type.Reflection
import Prelude hiding (null)

-- | O(1) Get DataFrame dimensions i.e. (rows, columns)
dimensions :: DataFrame -> (Int, Int)
dimensions = dataframeDimensions
{-# INLINE dimensions #-}

-- | O(k) Get column names of the DataFrame in order of insertion.
columnNames :: DataFrame -> [T.Text]
columnNames = map fst . L.sortBy (compare `on` snd). M.toList . columnIndices
{-# INLINE columnNames #-}

-- | /O(n)/ Adds a vector to the dataframe.
insertVector ::
  forall a.
  Columnable a =>
  -- | Column Name
  T.Text ->
  -- | Vector to add to column
  V.Vector a ->
  -- | DataFrame to add column to
  DataFrame ->
  DataFrame
insertVector name xs = insertColumn name (fromVector xs)
{-# INLINE insertVector #-}

cloneColumn :: T.Text -> T.Text -> DataFrame -> DataFrame
cloneColumn original new df = fromMaybe (throw $ ColumnNotFoundException original "cloneColumn" (map fst $ M.toList $ columnIndices df)) $ do
  column <- getColumn original df
  return $ insertColumn new column df

-- | /O(n)/ Adds an unboxed vector to the dataframe.
insertUnboxedVector ::
  forall a.
  (Columnable a, VU.Unbox a) =>
  -- | Column Name
  T.Text ->
  -- | Unboxed vector to add to column
  VU.Vector a ->
  -- | DataFrame to add to column
  DataFrame ->
  DataFrame
insertUnboxedVector name xs = insertColumn name (UnboxedColumn xs)

-- -- | /O(n)/ Add a column to the dataframe. Not meant for external use.
insertColumn ::
  -- | Column Name
  T.Text ->
  -- | Column to add
  Column ->
  -- | DataFrame to add to column
  DataFrame ->
  DataFrame
insertColumn name column d = let
    (r, c) = dataframeDimensions d
    n = max (columnLength column) r
  in case M.lookup name (columnIndices d) of
    Just i  -> DataFrame (V.map (expandColumn n) (columns d V.// [(i, column)])) (columnIndices d) (n, c)
    Nothing -> DataFrame (V.map (expandColumn n) (columns d `V.snoc` column)) (M.insert name c (columnIndices d)) (n, c + 1)

-- | /O(k)/ Add a column to the dataframe providing a default.
-- This constructs a new vector and also may convert it
-- to an unboxed vector if necessary. Since columns are usually
-- large the runtime is dominated by the length of the list, k.
insertVectorWithDefault ::
  forall a.
  (Columnable a) =>
  -- | Default Value
  a ->
  -- | Column name
  T.Text ->
  -- | Data to add to column
  V.Vector a ->
  -- | DataFrame to add to column
  DataFrame ->
  DataFrame
insertVectorWithDefault defaultValue name xs d =
  let (rows, _) = dataframeDimensions d
      values = xs V.++ V.replicate (rows - V.length xs) defaultValue
   in insertColumn name (fromVector values) d

rename :: T.Text -> T.Text -> DataFrame -> DataFrame
rename orig new df = either throw id (renameSafe orig new df)

renameMany :: [(T.Text, T.Text)] -> DataFrame -> DataFrame
renameMany replacements df = fold (uncurry rename) replacements df

renameSafe :: T.Text -> T.Text -> DataFrame -> Either DataFrameException DataFrame
renameSafe orig new df = fromMaybe (Left $ ColumnNotFoundException orig "rename" (map fst $ M.toList $ columnIndices df)) $ do
  columnIndex <- M.lookup orig (columnIndices df)
  let origRemoved = M.delete orig (columnIndices df)
  let newAdded = M.insert new columnIndex origRemoved
  return (Right df { columnIndices = newAdded })

-- | O(1) Get the number of elements in a given column.
columnSize :: T.Text -> DataFrame -> Maybe Int
columnSize name df = columnLength <$> getColumn name df

data ColumnInfo = ColumnInfo {
    nameOfColumn :: !T.Text,
    nonNullValues :: !Int,
    nullValues :: !Int,
    partiallyParsedValues :: !Int,
    uniqueValues :: !Int,
    typeOfColumn :: !T.Text
  }

-- | O(n) Returns the number of non-null columns in the dataframe and the type associated
-- with each column.
describeColumns :: DataFrame -> DataFrame
describeColumns df = empty & insertColumn "Column Name" (fromList (map nameOfColumn infos))
                      & insertColumn "# Non-null Values" (fromList (map nonNullValues infos))
                      & insertColumn "# Null Values" (fromList (map nullValues infos))
                      & insertColumn "# Partially parsed" (fromList (map partiallyParsedValues infos))
                      & insertColumn "# Unique Values" (fromList (map uniqueValues infos))
                      & insertColumn "Type" (fromList (map typeOfColumn infos))
  where
    infos = L.sortBy (compare `on` nonNullValues) (V.ifoldl' go [] (columns df)) :: [ColumnInfo]
    indexMap = M.fromList (map (\(a, b) -> (b, a)) $ M.toList (columnIndices df))
    columnName i = M.lookup i indexMap
    go acc i col@(OptionalColumn (c :: V.Vector a)) = let
        cname = columnName i
        countNulls = nulls col
        countPartial = partiallyParsed col
        columnType = T.pack $ show $ typeRep @a
        unique = S.size $ VG.foldr S.insert S.empty c
      in if isNothing cname then acc else ColumnInfo (fromMaybe "" cname) (columnLength col - countNulls) countNulls countPartial unique columnType : acc
    go acc i col@(BoxedColumn (c :: V.Vector a)) = let
        cname = columnName i
        countPartial = partiallyParsed col
        columnType = T.pack $ show $ typeRep @a
        unique = S.size $ VG.foldr S.insert S.empty c
      in if isNothing cname then acc else ColumnInfo (fromMaybe "" cname) (columnLength col) 0 countPartial unique columnType : acc
    go acc i col@(UnboxedColumn c) = let
        cname = columnName i
        columnType = T.pack $ columnTypeString col
        unique = S.size $ VG.foldr S.insert S.empty c
        -- Unboxed columns cannot have nulls since Maybe
        -- is not an instance of Unbox a
      in if isNothing cname then acc else ColumnInfo (fromMaybe "" cname) (columnLength col) 0 0 unique columnType : acc

nulls :: Column -> Int
nulls (OptionalColumn xs) = VG.length $ VG.filter isNothing xs
nulls (BoxedColumn (xs :: V.Vector a)) = case testEquality (typeRep @a) (typeRep @T.Text) of
  Just Refl -> VG.length $ VG.filter isNullish xs
  Nothing -> case testEquality (typeRep @a) (typeRep @String) of
    Just Refl -> VG.length $ VG.filter (isNullish . T.pack) xs
    Nothing -> case typeRep @a of
      App t1 t2 -> case eqTypeRep t1 (typeRep @Maybe) of
          Just HRefl -> VG.length $ VG.filter isNothing xs
          Nothing -> 0
      _ -> 0
nulls _ = 0

partiallyParsed :: Column -> Int
partiallyParsed (BoxedColumn (xs :: V.Vector a)) =
  case typeRep @a of
    App (App tycon t1) t2 -> case eqTypeRep tycon (typeRep @Either) of
      Just HRefl -> VG.length $ VG.filter isLeft xs
      Nothing -> 0
    _ -> 0
partiallyParsed _ = 0

fromNamedColumns :: [(T.Text, Column)] -> DataFrame
fromNamedColumns = L.foldl' (\df (name, column) -> insertColumn name column df) empty

fromUnnamedColumns :: [Column] -> DataFrame
fromUnnamedColumns = fromNamedColumns . zip (map (T.pack . show) [0..])

-- | O (k * n) Counts the occurences of each value in a given column.
valueCounts :: forall a. (Columnable a) => T.Text -> DataFrame -> [(a, Int)]
valueCounts columnName df = case getColumn columnName df of
      Nothing -> throw $ ColumnNotFoundException columnName "valueCounts" (map fst $ M.toList $ columnIndices df)
      Just (BoxedColumn (column' :: V.Vector c)) ->
        let
          column = V.foldl' (\m v -> MS.insertWith (+) v (1 :: Int) m) M.empty column'
        in case (typeRep @a) `testEquality` (typeRep @c) of
              Nothing -> throw $ TypeMismatchException (MkTypeErrorContext
                                                          { userType = Right $ typeRep @a
                                                          , expectedType = Right $ typeRep @c
                                                          , errorColumnName = Just (T.unpack columnName)
                                                          , callingFunctionName = Just "valueCounts"
                                                          })
              Just Refl -> M.toAscList column
      Just (OptionalColumn (column' :: V.Vector c)) ->
        let
          column = V.foldl' (\m v -> MS.insertWith (+) v (1 :: Int) m) M.empty column'
        in case (typeRep @a) `testEquality` (typeRep @c) of
              Nothing -> throw $ TypeMismatchException (MkTypeErrorContext
                                                          { userType = Right $ typeRep @a
                                                          , expectedType = Right $ typeRep @c
                                                          , errorColumnName = Just (T.unpack columnName)
                                                          , callingFunctionName = Just "valueCounts"
                                                          })
              Just Refl -> M.toAscList column
      Just (UnboxedColumn (column' :: VU.Vector c)) -> let
          column = V.foldl' (\m v -> MS.insertWith (+) v (1 :: Int) m) M.empty (V.convert column')
        in case (typeRep @a) `testEquality` (typeRep @c) of
          Nothing -> throw $ TypeMismatchException (MkTypeErrorContext
                                                          { userType = Right $ typeRep @a
                                                          , expectedType = Right $ typeRep @c
                                                          , errorColumnName = Just (T.unpack columnName)
                                                          , callingFunctionName = Just "valueCounts"
                                                          })
          Just Refl -> M.toAscList column

fold :: (a -> DataFrame -> DataFrame) -> [a] -> DataFrame -> DataFrame
fold f xs acc = L.foldl' (flip f) acc xs