Packer.js

// @flow
import XDate from 'xdate';

const offset = 100;

function buildEvent(column, left, width, dayStart) {
  const startTime = XDate(column.start);
  const endTime = column.end ? XDate(column.end) : XDate(startTime).addHours(1);

  const dayStartTime = XDate(dayStart).clearTime();

  column.top = startTime.diffHours(dayStartTime) * offset;
  column.height = endTime.diffHours(startTime) * offset;
  column.width = width;
  column.left = left;
  return column;
}

function collision(a, b) {
  return a.end > b.start && a.start < b.end;
}

function expand(ev, column, columns) {
  let colSpan = 1;

  for (let i = column + 1; i < columns.length; i++) {
    let col = columns[i];
    for (let j = 0; j < col.length; j++) {
      let ev1 = col[j];
      if (collision(ev, ev1)) {
        return colSpan;
      }
    }
    colSpan++;
  }

  return colSpan;
}

function pack(columns, width, calculatedEvents, dayStart) {
  let colLength = columns.length;

  for (let i = 0; i < colLength; i++) {
    let col = columns[i];
    for (let j = 0; j < col.length; j++) {
      const colSpan = expand(col[j], i, columns);
      const L = (i / colLength) * width;
      const W = (width * colSpan) / colLength - 10;

      calculatedEvents.push(buildEvent(col[j], L, W, dayStart));
    }
  }
}

function populateEvents(events, screenWidth, dayStart) {
  let lastEnd;
  let columns;
  let calculatedEvents = [];

  events = events
    .map((ev, index) => ({...ev, index: index}))
    .sort(function (a, b) {
      if (a.start < b.start) return -1;
      if (a.start > b.start) return 1;
      if (a.end < b.end) return -1;
      if (a.end > b.end) return 1;
      return 0;
    });

  columns = [];
  lastEnd = null;

  events.forEach(function (ev) {
    if (lastEnd !== null && ev.start >= lastEnd) {
      pack(columns, screenWidth, calculatedEvents, dayStart);
      columns = [];
      lastEnd = null;
    }

    let placed = false;
    for (let i = 0; i < columns.length; i++) {
      let col = columns[i];
      if (!collision(col[col.length - 1], ev)) {
        col.push(ev);
        placed = true;
        break;
      }
    }

    if (!placed) {
      columns.push([ev]);
    }

    if (lastEnd === null || ev.end > lastEnd) {
      lastEnd = ev.end;
    }
  });

  if (columns.length > 0) {
    pack(columns, screenWidth, calculatedEvents, dayStart);
  }
  return calculatedEvents;
}

export default populateEvents;