import {useReducer} from "react";
import calculateDiff from "../helpers/diff";

const DEFAULT = {
  milestones: [],
  prevDiff: 0,
  prevLongDiff: 0,
};

function reducer(state, {type, payload}) {
  switch (type) {
    case "measure":
      let {prevDiff, prevLongDiff, milestones} = state;
      const {minutes, seconds, calories, program} = payload;

      if (minutes === 0 || seconds !== 0) {
        return state;
      }

      const isFive = minutes % 5 === 0;
      const diff = calculateDiff(program, minutes, seconds, calories);
      let newMilestones = milestones.filter(m => m.minutes !== minutes);
      newMilestones.push({
        minutes, seconds, calories, diff,
        prevDiff: isFive ? prevLongDiff : prevDiff
      });

      if (isFive) {
        newMilestones = newMilestones.filter(m => m.minutes % 5 === 0);
        prevLongDiff = diff;
      }
      prevDiff = diff;

      return {prevLongDiff, prevDiff, milestones: newMilestones};
    case "clear":
      return {...DEFAULT};
    default:
      throw new Error(`Unknown type: ${type}`)
  }
}

export default function useMilestones() {
  const [state, msDispatch] = useReducer(reducer, {...DEFAULT});
  const {prevLongDiff, prevDiff, milestones} = state || {...DEFAULT};

  return {milestones, prevDiff, prevLongDiff, msDispatch};
}