module FillInTheGaps where

import Prelude
import Data.Array (foldMap, intercalate)
import Data.Array as A
import Data.Either (Either(..))
import Data.Foldable (foldl, for_)
import Data.Maybe (Maybe(..), fromMaybe, fromMaybe')
import Data.Monoid (guard)
import Data.String (Pattern(..), split)
import Data.String as S
import Data.String.Regex (Regex)
import Data.String.Regex as Regex
import Data.String.Regex.Flags as RegexFlags
import Data.String.Regex.Unsafe (unsafeRegex)
import Data.Tuple.Nested ((/\))
import Effect (Effect)
import Effect.Aff (launchAff_)
import Effect.Class (liftEffect)
import Justifill (justifill)
import Milkis as M
import Milkis.Impl (FetchImpl)
import Milkis.Impl.Window (windowFetch)
import Partial.Unsafe (unsafeCrashWith)
import React.Basic (JSX, ReactComponent, element, fragment)
import React.Basic.DOM (form_)
import React.Basic.DOM as R
import React.Basic.Events (handler_)
import React.Basic.Helpers (jsx)
import React.Basic.Hooks (component, useEffect, useState)
import React.Basic.Hooks as React
import React.Basic.Hooks.Aff (useAff)
import Yoga.Button.Component (ButtonType(..), mkButton)
import Yoga.CompileEditor.Component (compileAndRun)
import Yoga.Helpers ((?||))
import Yoga.InlineCode.Component as InlineCode
import Yoga.Modal.Component as Modal

data Segment
  = ExpectedResult String
  | Start
  | End
  | Filler String
  | Hole Int String

derive instance eqSegment ∷ Eq Segment
getResult ∷ Segment -> Maybe String
getResult = case _ of
  ExpectedResult r -> Just r
  _ -> Nothing

findResult ∷ Array Segment -> String
findResult = fromMaybe' (\_ -> unsafeCrashWith "Even teachers make mistakes") <<< A.findMap getResult

toCode ∷ (Array (Array Segment)) -> String
toCode lines = intercalate "\n" mapped
  where
  mapped = lines <#> (intercalate "" <<< map segmentToCode)
  segmentToCode = case _ of
    Filler s -> s
    Hole _ s -> s
    _ -> ""

complete ∷ (Array (Array Segment)) -> Boolean
complete arr = foldl f true (join arr)
  where
  f acc seg =
    acc
      && case seg of
          Hole _ s -> s /= ""
          _ -> true

renderSegments ∷ ReactComponent InlineCode.Props -> ((Array (Array Segment) -> Array (Array Segment)) -> Effect Unit) -> Array (Array Segment) -> JSX
renderSegments ic update arrs = R.div_ (A.mapWithIndex renderLine (onlyVisible arrs))
  where
  onlyVisible arr = A.slice start end arr
    where
    start = A.findIndex (_ == [ Start ]) arr ?|| 0
    end = A.findIndex (_ == [ End ]) arr ?|| A.length arr
  renderLine i l = R.div_ (A.mapWithIndex (renderSegment i) l)
  renderSegment i j = case _ of
    Filler s -> R.code_ [ R.text s ]
    Hole width _ -> element ic $ justifill { width, onSubmit: \v -> update (updateSegments i j (S.trim v)) }
    _ -> mempty

updateSegments ∷ Int -> Int -> String -> Array (Array Segment) -> Array (Array Segment)
updateSegments i j v arrs = fromMaybe [] (A.modifyAt i (updateLine j v) arrs)

updateLine ∷ Int -> String -> Array Segment -> Array Segment
updateLine idx v arr = fromMaybe [] (A.modifyAt idx f arr)
  where
  f = case _ of
    Hole h _ -> Hole h v
    _ -> unsafeCrashWith "Updated a non-hole"

holeRegex ∷ Regex
holeRegex = unsafeRegex "({-.*?-})" RegexFlags.global

resultRegex ∷ Regex
resultRegex = unsafeRegex "--result" RegexFlags.global

startRegex ∷ Regex
startRegex = unsafeRegex "--start here" RegexFlags.global

endRegex ∷ Regex
endRegex = unsafeRegex "--end here" RegexFlags.global

rawSegments ∷ String -> Array String
rawSegments = Regex.split holeRegex

toSegment ∷ String -> Segment
toSegment = case _ of
  x
    | Regex.test holeRegex x -> Hole (S.length x - 4) ""
  x
    | S.indexOf (Pattern "--result ") x == Just 0 -> ExpectedResult ((S.stripPrefix (Pattern "--result ") x) ?|| "")
  x
    | Regex.test startRegex x -> Start
  x
    | Regex.test endRegex x -> End
  other -> Filler other

mkFillInTheGaps ∷ FetchImpl -> Effect (ReactComponent { code ∷ String })
mkFillInTheGaps fetch = do
  ic <- InlineCode.makeComponent
  modal <- Modal.makeComponent
  button <- mkButton
  component "FillInTheGaps" \{ code } -> React.do
    let
      lines = split (Pattern "\n") code

      initialSegments = lines <#> \line -> rawSegments line <#> toSegment
    segments /\ modifySegments <- useState initialSegments
    result /\ modifyResult <- useState Nothing
    let
      expectedResult = findResult (join segments)

      onClick =
        launchAff_ do
          do
            res <- compileAndRun (M.fetch fetch) { code: toCode segments }
            modifyResult (const (Just $ res)) # liftEffect
    pure
      $ fragment
          [ renderSegments ic (modifySegments) segments
          , jsx button
              { onClick: handler_ onClick
              , buttonType:
                -- if complete segments 
                -- then 
                HighlightedButton 
                -- else DisabledButton
              }
              [ R.text "Try it" ]
          , result
              # foldMap \r ->
                  jsx modal
                    { title:
                      case r of
                        Right { stdout }
                          | stdout == expectedResult -> "Hooray!"
                        Left l -> "Does not compile"
                        Right _ -> "Not " <> (findResult (join segments))
                    }
                    [ R.text $ compileResultToString result ]
          ]

compileResultToString = case _ of
  Nothing -> ""
  Just (Left cr) -> cr.result <#> _.message # intercalate "/n"
  Just (Right r) -> r.stdout