--- MAIN FUNCTION >>>
-- Returns the length of a longest chain of a specified element in a list.

longestElemChainLength :: (Eq a, Integral b) => a -> [a] -> b
longestElemChainLength _ [] = 0
longestElemChainLength elem list = maximum (chainsLengths elem list)

--- <<< MAIN FUNCTION

chainsLengths :: (Eq a, Integral b) => a -> [a] -> [b]
chainsLengths _ [] = []
chainsLengths elem list@(x : xs)
  | x /= elem = chainsLengths elem xs
  | otherwise = n : chainsLengths elem listWithoutFirstZeroes
  where
    n = numberOfFirstElems elem list
    listWithoutFirstZeroes = removeNFirstElems n list

numberOfFirstElems :: (Eq a, Num b) => a -> [a] -> b
numberOfFirstElems _ [] = 0
numberOfFirstElems elem list@(x : xs)
  | x /= elem = 0
  | otherwise = 1 + numberOfFirstElems elem xs

removeNFirstElems :: (Integral a) => a -> [b] -> [b]
removeNFirstElems _ [] = []
removeNFirstElems n list@(x : xs)
  | n == 0 = list
  | otherwise = removeNFirstElems (n -1) xs