codeSequenceEpic.js

const codeSequenceEpic = (
  action$,
) => (
  action$
  .pipe(
    ofType('START_CODE_SEQUENCE_LISTENER'),
    mergeMap(({
      codeSequence,
    }) => (
      action$
      .pipe(
        takeUntil(
          action$
          .pipe(
            ofType('STOP_CODE_SEQUENCE_LISTENER'),
            filter(({
              codeSequence: stopSequence,
            }) => (
              stopSequence === codeSequence
            )),
          )
        ),
        ofType('ON_KEYPRESS'),
        mergeMap(({
          pressedKey: firstPressedKey,
        }) => (
          action$
          .pipe(
            takeUntil(
              action$
              .pipe(
                ofType('STOP_CODE_SEQUENCE_LISTENER'),
                filter(({
                  codeSequence: stopSequence,
                }) => (
                  stopSequence === codeSequence
                )),
              )
            ),
            ofType('ON_KEYPRESS'),
            pluck('pressedKey'),
            startWith(firstPressedKey),
            scan(
              (
                { codeSequenceIndex },
                pressedKey,
              ) => ({
                codeSequenceIndex: codeSequenceIndex + 1,
                done: codeSequenceIndex === codeSequence.length - 1,
                isMatching: pressedKey === codeSequence[codeSequenceIndex],
              }),
              {
                codeSequenceIndex: 0,
              }
            ),
            takeWhile(({
              isMatching,
            }) => (
              isMatching
            )),
            filter(({
              done,
            }) => (
              done
            )),
            mapTo([
              {
                codeSequence,
                type: 'STOP_CODE_SEQUENCE_LISTENER',
              },
              {
                codeSequence,
                type: 'ACTIVATED_CODE_SEQUENCE',
              },
            ]),
            mergeAll(),
          )
        )),
      )
    )),
  )
)