main :: IO()
main = do
  print $ "Task 2"
  print $ Animal "Lion" 1 Carnivore 3 -- Lion(1,Carnivore,3)
  print $ updateDiet zoo 3 Herbivore -- [Lion(1,Carnivore,3),Elephant(2,Herbivore,3),Bear(3,Herbivore,6),Turtle(4,Herbivore,2)]
  print $ feedAnimal zoo 3 1 -- [Lion(1,Carnivore,6),Elephant(2,Herbivore,3),Bear(3,Omnivore,6),Turtle(4,Herbivore,2)]
  print $ feedIfHungry zoo 3 [1,2,3,4] -- [Lion(1,Carnivore,6),Elephant(2,Herbivore,6),Bear(3,Omnivore,6),Turtle(4,Herbivore,5)]
  print $ feedIfHungry zoo 3 [3] -- [Lion(1,Carnivore,3),Elephant(2,Herbivore,3),Bear(3,Omnivore,6),Turtle(4,Herbivore,2)]
  print $ findAnimalById zoo 10 -- Nothing
  print $ findAnimalById zoo 2 -- Just Elephant(2,Herbivore,3)
  where zoo = [ Animal "Lion" 1 Carnivore 3
              , Animal "Elephant" 2 Herbivore 3
              , Animal "Bear" 3 Omnivore 6
              , Animal "Turtle" 4 Herbivore 2]

type Species = String
type AnimalId = Int
data Diet = Herbivore | Carnivore | Omnivore deriving (Show, Eq)
data Animal = Animal { species :: Species, animalId :: AnimalId,
  diet :: Diet, hungerLevel :: Int } deriving Eq

instance Show Animal where
  show (Animal s id d hunger) =
    s ++ "(" ++ show id ++ "," ++ show d ++ "," ++ show hunger ++ ")"

updateDiet :: [Animal] -> AnimalId -> Diet -> [Animal]
updateDiet zoo id d =
  [if animalId a == id then a { diet = d } else a | a <- zoo]

feedAnimal :: [Animal] -> Int -> AnimalId -> [Animal]
feedAnimal zoo k id =
  map (\ a -> if animalId a == id
              then a { hungerLevel = hungerLevel a + k }
              else a)
      zoo

feedIfHungry :: [Animal] -> Int -> [AnimalId] -> [Animal]
feedIfHungry zoo k =
  foldr (\ id zoo -> if elem id hungryAnimals
                        then feedAnimal zoo k id
                        else zoo)
        zoo
  where
    hungryAnimals =
      [animalId a | a <- zoo, hungerLevel a < 5]

findAnimalById :: [Animal] -> AnimalId -> Maybe Animal
findAnimalById []     _  = Nothing
findAnimalById (a:as) id =
  if animalId a == id then Just a
  else findAnimalById as id