module Block6.Task4
  ( listlistParser
  ) where

import Block6.Task1
import Block6.Task2 (element, satisfy)
import Block6.Task3 (parseNumber)
import Control.Applicative (many, (<|>))
import Prelude hiding (cycle)
import Text.Read (readMaybe)

listlistParser :: Parser Char [[Int]]
listlistParser =
  Parser $ \s -> do
    (len, rest) <- runParser cycleOrNumber s
    runParser (add (exactly len) (listlistParser <|> eof)) rest

spaces :: Parser Char [Char]
spaces = many $ element ' '

comma :: Parser Char Char
comma = element ','

exactly :: Int -> Parser Char [Int]
exactly n =
  Parser $ \s ->
    if n == 0
      then Just ([], s)
      else runParser (add cycleOrNumber (exactly $ n - 1)) s

cycle :: Parser Char Int
cycle = spaces *> comma *> spaces *> parseNumber

cycleOrNumber :: Parser Char Int
cycleOrNumber = cycle <|> parseNumber

add :: Parser s a -> Parser s [a] -> Parser s [a]
add p res =
  Parser $ \s -> do
    (first, rest) <- runParser p s
    (other, t) <- runParser res rest
    return ([first] ++ other, t)

eof :: Parser s [[Int]]
eof =
  Parser $ \s ->
    case s of
      [] -> Just ([[]], [])
      _  -> Nothing