import { Eq } from 'fp-ts/lib/Eq'
import { pipe } from 'fp-ts/lib/function'
import * as M from 'fp-ts/lib/Map'
import * as O from 'fp-ts/lib/Option'

export * from 'fp-ts/lib/Map'

/**
 * Allows removal, modification, or insertion of values into a map.
 *
 * The `alter` function is passed an `Option<A>` and returns an `Option<A>`,
 * so the cases are:
 *  in: `some`, out: `some` -> update
 *  in: `some`, out: `none` -> remove
 *  in: `none`, out: `some` -> insert
 *  in: `none`, out: `none` -> noop
 */
export const alterAt = <K>(eq: Eq<K>) => <A>(
  k: K,
  alter: (a: O.Option<A>) => O.Option<A>,
) => (map: Map<K, A>): Map<K, A> =>
  pipe(
    map,
    M.lookup(eq)(k),
    alter,
    O.fold(
      () => M.deleteAt(eq)(k)(map),
      a => M.insertAt(eq)(k, a)(map),
    ),
  )