const today = moment();
const thisYear = today.year();
const shortYear = (thisYear +'').slice('-2');
const thisWeek = today.isoWeek();
const thisDay = today.format('YYYY[W]WWE');

let current = thisYear;

function leadingZeroPlusOne (n) {
  return ('0'+ (n + 1)).slice(-2);
}

function getWeeksArr (year) {
  const numWeeks = moment([year]).isoWeeksInYear();

  let weeks = [];

  _.range(numWeeks).forEach(function (w) {
    let days = {};

    _.range(7).forEach(function (d) {
      const day = year +'W'+ leadingZeroPlusOne(w) + (d + 1);
      days[day] = {
        unix: moment(day).format('X'),
      };
    });

    weeks.push(days);
  });

  return weeks;
}

function render (year) {
  // cache two-digit year and clear everything
  var yr = (year +'').slice('-2');
  document.body.innerHTML = '';

  // add week rows
  const weeks = getWeeksArr(year);
  weeks.forEach(function (week, i) {
    const wk = leadingZeroPlusOne(i);
    const yrwk = yr + wk;
    const row = document.createElement('div');
    row.className = 'week';
    if (yrwk == shortYear + thisWeek) {
      row.className += ' current';
    }

    const title = document.createElement('h2');
    title.className = 'week-title';
    title.innerText = yrwk;
    row.appendChild(title);

    const days = document.createElement('div');
    days.className = 'days';
    for (day in week) {
      let d = document.createElement('div');
      d.className = 'day';
      if (day == thisDay) {
        d.className += ' current';
      }
      d.innerText = moment(day).format('ddd D MMM');
      days.appendChild(d);
    }
    row.appendChild(days);

    document.body.appendChild(row);
  });

  // scroll to current week
  $('body').animate({
    scrollTop: $('.week.current').offset().top +'px',
  }, 150);
}

render(current);

document.onkeydown = function (e) {
  // left
  if (e.which === 37) {
    current--;
    render(current);
  }
  // right
  if (e.which === 39) {
    current++;
    render(current);
  }
};