{-# LANGUAGE MultiParamTypeClasses #-}

module DataLib where

class Record a where
  getId :: a -> Int

insert :: Record a => a -> [a] -> [a]
insert r rs = r : rs

update :: Record a => a -> [a] -> [a]
update r rs = map (\r' -> if getId r == getId r' then r else r') rs

delete :: Record a => Int -> [a] -> [a]
delete i rs = filter (\r' -> getId r' /= i) rs


data Person = Person { personId :: Int, name :: String }
instance Record Person where
  getId = personId

data Book = Book { bookId :: Int, title :: String }
instance Record Book where
  getId = bookId

data Database = Database { employees :: [Person], books :: [Book], customers :: [Person] }

class (Record r) => Table r t where
  getRecords :: t -> Database -> [r]
  setRecords :: t -> [r] -> Database -> Database

insertRecord :: (Table r t) => t -> r -> Database -> Database
insertRecord t r db =
  let records = getRecords t db
      newRecords = insert r records
  in setRecords t newRecords db

updateRecord :: (Table r t) => t -> r -> Database -> Database
updateRecord t r db =
  let records = getRecords t db
      newRecords = update r records
  in setRecords t newRecords db

deleteRecord :: (Table r t) => t -> Int -> Database -> Database
deleteRecord t i db =
  let records = getRecords t db
      newRecords = delete i records
  in setRecords t newRecords db

data ET = EmployeeTable
instance (Table Person) ET where
  getRecords t db = employees db
  setRecords t records db = Database records (books db) (customers db)

data BT = BookTable
instance (Table Book) BT where
  getRecords t db = books db
  setRecords t records db = Database (employees db) records (customers db)

data CT = CustomerTable
instance (Table Person) CT where
  getRecords t db = customers db
  setRecords t records db = Database (employees db) (books db) records