common-reducers/counter.js at master · samuelchvez/common-reducers · GitHub

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// @flow

type CounterConfigurationType = {
  incremented?: Array<string>,
  decremented?: Array<string>,
  reset?: Array<string>,
};

type CounterActionType = {
  type: string,
  payload: {
    step: number,
  },
};

const counter = (configuration: CounterConfigurationType) => (
  state: number = 0,
  action: CounterActionType,
): number => {
  const {
    incremented,
    decremented,
    reset,
  } = configuration;

  const { payload } = action;

  if (incremented != null && incremented.includes(action.type)) {
    if (typeof payload !== 'undefined') {
      return state + (payload.step || 1);
    }
  }

  if (decremented != null && decremented.includes(action.type)) {
    if (typeof payload !== 'undefined') {
      return state - (payload.step || 1);
    }
  }

  if (reset != null && reset.includes(action.type)) {
    return 0;
  }

  return state;
};


export default counter;