import React, { useMemo, useRef } from 'react';
import { format, parseISO, startOfMinute, subMinutes, isBefore } from 'date-fns';
import PageviewsChart from './PageviewsChart';
import { getDateArray } from 'lib/date';
import { DEFAULT_ANIMATION_DURATION } from 'lib/constants';

function mapData(data) {
  let last = 0;
  const arr = [];

  data.reduce((obj, val) => {
    const { created_at } = val;
    const t = startOfMinute(parseISO(created_at));
    if (t.getTime() > last) {
      obj = { t: format(t, 'yyyy-LL-dd HH:mm:00'), y: 1 };
      arr.push(obj);
      last = t;
    } else {
      obj.y += 1;
    }
    return obj;
  }, {});

  return arr;
}

export default function RealtimeChart({ data, unit, ...props }) {
  const endDate = startOfMinute(new Date());
  const startDate = subMinutes(endDate, 30);
  const prevEndDate = useRef(endDate);

  const chartData = useMemo(() => {
    if (data) {
      return {
        pageviews: getDateArray(mapData(data.pageviews), startDate, endDate, unit),
        sessions: getDateArray(mapData(data.sessions), startDate, endDate, unit),
      };
    }
    return { pageviews: [], sessions: [] };
  }, [data]);

  // Don't animate the bars shifting over because it looks weird
  const animationDuration = useMemo(() => {
    if (isBefore(prevEndDate.current, endDate)) {
      prevEndDate.current = endDate;
      return 0;
    }
    return DEFAULT_ANIMATION_DURATION;
  }, [data]);

  return (
    <PageviewsChart
      {...props}
      height={300}
      unit={unit}
      data={chartData}
      animationDuration={animationDuration}
    />
  );
}