module Brick.Widgets.TabularList.Internal.Common (
  visibleRows
, visibleRowHdrs
, visibleRowsAndRowHdrs
) where

import Brick.Widgets.TabularList.Types
-- base
import Data.Maybe (fromMaybe, catMaybes)
import Data.Foldable (toList)
-- Third party libraries
import Lens.Micro
import Data.Sequence (Seq)
-- Brick
import Brick.Widgets.List

type Start = Int
type AvailHeight = Int
visibleRowsWithStart :: GenericList n Seq row -> AvailHeight -> ([row], Start)
visibleRowsWithStart l aH = let
  idx = fromMaybe 0 (l^.listSelectedL)
  numPerHeight = case aH `divMod` (l^.listItemHeightL) of
    (nph, 0) -> nph
    (nph, _) -> nph + 1
  start = max 0 $ idx - numPerHeight + 1
  length = numPerHeight * 2
  rows = toList $ slice start length $ l^.listElementsL
  in (rows, start)

-- | Return visible rows, given 'GenericList' and height available for list elements
visibleRows :: GenericList n Seq row -> AvailHeight -> [row]
visibleRows l aH = visibleRowsWithStart l aH ^. _1

-- | Return visible row headers, given 'GenericList' and height available for list elements
visibleRowHdrs :: GenericList n Seq row -> AvailHeight -> (row -> RowIndex -> Maybe rowH) -> [rowH]
visibleRowHdrs l aH rowH = visibleRowsAndRowHdrs l aH rowH ^. _2

-- | Return visible rows and visible row headers, given 'GenericList', available height, and row header function.
visibleRowsAndRowHdrs :: GenericList n Seq row -> AvailHeight -> (row -> RowIndex -> Maybe rowH) -> ([row], [rowH])
visibleRowsAndRowHdrs l aH rowH = let
  (rows, start) = visibleRowsWithStart l aH
  in (rows, catMaybes $ zipWith rowH rows [start..])