Generated by XState Viz: https://xstate.js.org/viz

machine.js

const START_CHAR = '-';
const END_CHAR = '-';

const CONTROL_SEQUENCE_COUNT = 3;

const CONTROL_SEQUENCE_TIMEOUT = 500;
const DATA_TIMEOUT = 2000;

const scannerMachine = Machine(
  {
    id: 'scannerMachine',
    initial: 'waitingForChars',
    context: {
      code: '',
      startCharCount: CONTROL_SEQUENCE_COUNT,
      endCharCount: CONTROL_SEQUENCE_COUNT,
    },
    states: {
      waitingForChars: {
        entry: assign({
          code: '',
          startCharCount: CONTROL_SEQUENCE_COUNT,
          endCharCount: CONTROL_SEQUENCE_COUNT,
        }),
        on: {
          KEYPRESS: { target: 'startSeq', cond: 'isStartChar' },
        },
      },
      startSeq: {
        entry: assign({
          startCharCount: ({ startCharCount }) => startCharCount - 1,
        }),
        on: {
          KEYPRESS: [
            {
              target: 'startSeq',
              cond: 'isStartChar',
            },
            { target: 'waitingForChars' },
          ],
          '': { target: 'receiving', cond: 'isStarted' },
        },
        after: {
          [CONTROL_SEQUENCE_TIMEOUT]: 'waitingForChars',
        },
      },
      receiving: {
        entry: assign({
          startCharCount: 3,
          endCharCount: 3,
        }),
        on: {
          KEYPRESS: [
            {
              target: 'endSeq',
              cond: 'isEndChar',
            },
            {
              target: 'receiving',
              actions: assign({
                code: ({ code }, { key }) => code + key,
              }),
            },
          ],
        },
        after: {
          [DATA_TIMEOUT]: 'waitingForChars',
        },
      },
      endSeq: {
        entry: assign({
          endCharCount: ({ endCharCount }) => endCharCount - 1,
        }),
        on: {
          KEYPRESS: [
            {
              target: 'endSeq',
              cond: 'isEndChar',
            },
            {
              target: 'receiving',
              actions: assign({
                code: ({ code, endCharCount }, { key }) => code + '\\'.repeat(CONTROL_SEQUENCE_COUNT - endCharCount) + key,
              }),
            },
          ],
          '': {
            target: 'received',
            cond: 'isEnded',
          },
        },
        after: {
          [CONTROL_SEQUENCE_TIMEOUT]: 'waitingForChars',
        },
      },
      received: {
        entry: 'codeReceived',
        on: {
          '': 'waitingForChars',
        },
      },
    },
  },
  {
    guards: {
      isStartChar: (_, { key }) => key === START_CHAR,
      isEndChar: (_, { key }) => key === END_CHAR,

      isStarted: ({ startCharCount }) => startCharCount === 0,
      isEnded: ({ endCharCount }) => endCharCount === 0,
    },
    actions: {
      codeReceived: console.log.bind(console, 'codeReceived'),
    },
  }
);