import { identity } from "../Function";

/*
 * -------------------------------------------
 * Monad Iterable
 * -------------------------------------------
 */

function* genChain<A, B>(ia: Iterator<A>, f: (a: A) => Iterable<B>) {
   while (true) {
      const result = ia.next();
      if (result.done) {
         break;
      }
      const ib = f(result.value)[Symbol.iterator]();
      while (true) {
         const result = ib.next();
         if (result.done) {
            break;
         }
         yield result.value;
      }
   }
}

export const chain = <A, B>(f: (a: A) => Iterable<B>) => (ma: Iterable<A>): Iterable<B> => ({
   [Symbol.iterator]: () => genChain(ma[Symbol.iterator](), f)
});

export const chain_ = <A, B>(ma: Iterable<A>, f: (a: A) => Iterable<B>): Iterable<B> => ({
   [Symbol.iterator]: () => genChain(ma[Symbol.iterator](), f)
});

export const flatten = <A>(mma: Iterable<Iterable<A>>) => chain_(mma, identity);