document-lastModified-utils.js

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const DOCUMENT_LASTMODIFIED_REGEX = /^([0-9]{2})\/([0-9]{2})\/([0-9]{4}) ([0-9]{2}):([0-9]{2}):([0-9]{2})$/;

function assert_document_lastmodified_string_approximately_now(str) {

  // We want to test that |str| was a time in the user's local

  // timezone generated within a few seconds prior to the present.

  // This requires some care, since it is possible that:

  //  - the few second difference may have crossed a

  //    year/month/day/hour/minute boundary

  //  - the few second difference may have crossed a change in the

  //    local timezone's UTC offset

  //  - the local time might be one that has multiple valid UTC

  //    representations (for example, because it's in the hour

  //    following a shift from summer time to winter time)

  // We will make some assumptions to do this:

  //  - local time's UTC offset doesn't change more than once per

  //    minute

  //  - local time's UTC offset only changes by integral numbers of

  //    minutes

  // The date must be equal to or earlier than the present time.

  var dmax = new Date();

  // The date must be equal to or later than 2.5 seconds ago.

  var TOLERANCE_MILLISECONDS = 2500;

  var dmin = new Date();

  dmin.setTime(dmax.getTime() - TOLERANCE_MILLISECONDS);

  // Extract the year/month/date/hours/minutes/seconds from str.  It

  // is important that we do *not* try to construct a Date object from

  // these, since the core of the date object is a timestamp in UTC,

  // and there are cases (such as the hour on each side of a change

  // from summer time to winter time) where there are multiple

  // possible UTC timestamps for a given YYYY-MM-DD HH:MM:SS, and

  // constructing a Date object would pick one of them, which might be

  // the wrong one.  However, we already have the right one in dmin

  // and dmax, so we should instead extract local time from those

  // rather than converting these values to UTC.

  var m = DOCUMENT_LASTMODIFIED_REGEX.exec(str);

  var syear = Number(m[3]);

  var smonth = Number(m[1]) - 1; // match Javascript 0-based months

  var sdate = Number(m[2]);

  var shours = Number(m[4]);

  var sminutes = Number(m[5]);

  var sseconds = Number(m[6]);

  if (dmin.getFullYear() == dmax.getFullYear() &&

      dmin.getMonth() == dmax.getMonth() &&

      dmin.getDate() == dmax.getDate() &&

      dmin.getHours() == dmax.getHours() &&

      dmin.getMinutes() == dmax.getMinutes()) {

    // min and max have the same minute

    assert_equals(smonth, dmin.getMonth(), "month");

    assert_equals(sdate, dmin.getDate(), "date");

    assert_equals(syear, dmin.getFullYear(), "year");

    assert_equals(shours, dmin.getHours(), "hours");

    assert_equals(sminutes, dmin.getMinutes(), "minutes");

    assert_true(dmin.getSeconds() <= sseconds &&

                sseconds <= dmax.getSeconds(), "seconds");

  } else if (dmin.getFullYear() == syear &&

             dmin.getMonth() == smonth &&

             dmin.getDate() == sdate &&

             dmin.getHours() == shours &&

             dmin.getMinutes() == sminutes) {

    // actual value has the same minute as min

    assert_true(dmin.getSeconds() <= sseconds, "dmin.getSeconds() <= sseconds");

    assert_true(57 <= dmin.getSeconds(), "unexpected local time rules (dmin match)");

  } else if (dmax.getFullYear() == syear &&

             dmax.getMonth() == smonth &&

             dmax.getDate() == sdate &&

             dmax.getHours() == shours &&

             dmax.getMinutes() == sminutes) {

    // actual value has the same minute as max

    assert_true(sseconds <= dmax.getSeconds(), "sseconds <= dmax.getSeconds()");

    assert_true(dmax.getSeconds() <= 2, "unexpected local time rules (dmax match)");

  } else {

    assert_unreached("unexpected local time rules (no match)");