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diff --git a/components/bindings/content/timekeeper.js b/components/bindings/content/timekeeper.js
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+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+/**
+ * TimeKeeper keeps track of the time states. Given min, max, step, and
+ * format (12/24hr), TimeKeeper will determine the ranges of possible
+ * selections, and whether or not the current time state is out of range
+ * or off step.
+ *
+ * @param {Object} props
+ *        {
+ *          {Date} min
+ *          {Date} max
+ *          {Number} step
+ *          {String} format: Either "12" or "24"
+ *        }
+ */
+function TimeKeeper(props) {
+  this.props = props;
+  this.state = { time: new Date(0), ranges: {} };
+}
+
+{
+  const debug = 0 ? console.log.bind(console, '[timekeeper]') : function() {};
+
+  const DAY_PERIOD_IN_HOURS = 12,
+        SECOND_IN_MS = 1000,
+        MINUTE_IN_MS = 60000,
+        HOUR_IN_MS = 3600000,
+        DAY_PERIOD_IN_MS = 43200000,
+        DAY_IN_MS = 86400000,
+        TIME_FORMAT_24 = "24";
+
+  TimeKeeper.prototype = {
+    /**
+     * Getters for different time units.
+     * @return {Number}
+     */
+    get hour() {
+      return this.state.time.getUTCHours();
+    },
+    get minute() {
+      return this.state.time.getUTCMinutes();
+    },
+    get second() {
+      return this.state.time.getUTCSeconds();
+    },
+    get millisecond() {
+      return this.state.time.getUTCMilliseconds();
+    },
+    get dayPeriod() {
+      // 0 stands for AM and 12 for PM
+      return this.state.time.getUTCHours() < DAY_PERIOD_IN_HOURS ? 0 : DAY_PERIOD_IN_HOURS;
+    },
+
+    /**
+     * Get the ranges of different time units.
+     * @return {Object}
+     *         {
+     *           {Array<Number>} dayPeriod
+     *           {Array<Number>} hours
+     *           {Array<Number>} minutes
+     *           {Array<Number>} seconds
+     *           {Array<Number>} milliseconds
+     *         }
+     */
+    get ranges() {
+      return this.state.ranges;
+    },
+
+    /**
+     * Set new time, check if the current state is valid, and set ranges.
+     *
+     * @param {Object} timeState: The new time
+     *        {
+     *          {Number} hour [optional]
+     *          {Number} minute [optional]
+     *          {Number} second [optional]
+     *          {Number} millisecond [optional]
+     *        }
+     */
+    setState(timeState) {
+      const { min, max } = this.props;
+      const { hour, minute, second, millisecond } = timeState;
+
+      if (hour != undefined) {
+        this.state.time.setUTCHours(hour);
+      }
+      if (minute != undefined) {
+        this.state.time.setUTCMinutes(minute);
+      }
+      if (second != undefined) {
+        this.state.time.setUTCSeconds(second);
+      }
+      if (millisecond != undefined) {
+        this.state.time.setUTCMilliseconds(millisecond);
+      }
+
+      this.state.isOffStep = this._isOffStep(this.state.time);
+      this.state.isOutOfRange = (this.state.time < min || this.state.time > max);
+      this.state.isInvalid = this.state.isOutOfRange || this.state.isOffStep;
+
+      this._setRanges(this.dayPeriod, this.hour, this.minute, this.second);
+    },
+
+    /**
+     * Set day-period (AM/PM)
+     * @param {Number} dayPeriod: 0 as AM, 12 as PM
+     */
+    setDayPeriod(dayPeriod) {
+      if (dayPeriod == this.dayPeriod) {
+        return;
+      }
+
+      if (dayPeriod == 0) {
+        this.setState({ hour: this.hour - DAY_PERIOD_IN_HOURS });
+      } else {
+        this.setState({ hour: this.hour + DAY_PERIOD_IN_HOURS });
+      }
+    },
+
+    /**
+     * Set hour in 24hr format (0 ~ 23)
+     * @param {Number} hour
+     */
+    setHour(hour) {
+      this.setState({ hour });
+    },
+
+    /**
+     * Set minute (0 ~ 59)
+     * @param {Number} minute
+     */
+    setMinute(minute) {
+      this.setState({ minute });
+    },
+
+    /**
+     * Set second (0 ~ 59)
+     * @param {Number} second
+     */
+    setSecond(second) {
+      this.setState({ second });
+    },
+
+    /**
+     * Set millisecond (0 ~ 999)
+     * @param {Number} millisecond
+     */
+    setMillisecond(millisecond) {
+      this.setState({ millisecond });
+    },
+
+    /**
+     * Calculate the range of possible choices for each time unit.
+     * Reuse the old result if the input has not changed.
+     *
+     * @param {Number} dayPeriod
+     * @param {Number} hour
+     * @param {Number} minute
+     * @param {Number} second
+     */
+    _setRanges(dayPeriod, hour, minute, second) {
+      this.state.ranges.dayPeriod =
+        this.state.ranges.dayPeriod || this._getDayPeriodRange();
+
+      if (this.state.dayPeriod != dayPeriod) {
+        this.state.ranges.hours = this._getHoursRange(dayPeriod);
+      }
+
+      if (this.state.hour != hour) {
+        this.state.ranges.minutes = this._getMinutesRange(hour);
+      }
+
+      if (this.state.hour != hour || this.state.minute != minute) {
+        this.state.ranges.seconds = this._getSecondsRange(hour, minute);
+      }
+
+      if (this.state.hour != hour || this.state.minute != minute || this.state.second != second) {
+        this.state.ranges.milliseconds = this._getMillisecondsRange(hour, minute, second);
+      }
+
+      // Save the time states for comparison.
+      this.state.dayPeriod = dayPeriod;
+      this.state.hour = hour;
+      this.state.minute = minute;
+      this.state.second = second;
+    },
+
+    /**
+     * Get the AM/PM range. Return an empty array if in 24hr mode.
+     *
+     * @return {Array<Number>}
+     */
+    _getDayPeriodRange() {
+      if (this.props.format == TIME_FORMAT_24) {
+        return [];
+      }
+
+      const start = 0;
+      const end = DAY_IN_MS - 1;
+      const minStep = DAY_PERIOD_IN_MS;
+      const formatter = (time) =>
+        new Date(time).getUTCHours() < DAY_PERIOD_IN_HOURS ? 0 : DAY_PERIOD_IN_HOURS;
+
+      return this._getSteps(start, end, minStep, formatter);
+    },
+
+    /**
+     * Get the hours range.
+     *
+     * @param  {Number} dayPeriod
+     * @return {Array<Number>}
+     */
+    _getHoursRange(dayPeriod) {
+      const { format } = this.props;
+      const start = format == "24" ? 0 : dayPeriod * HOUR_IN_MS;
+      const end = format == "24" ? DAY_IN_MS - 1 : start + DAY_PERIOD_IN_MS - 1;
+      const minStep = HOUR_IN_MS;
+      const formatter = (time) => new Date(time).getUTCHours();
+
+      return this._getSteps(start, end, minStep, formatter);
+    },
+
+    /**
+     * Get the minutes range
+     *
+     * @param  {Number} hour
+     * @return {Array<Number>}
+     */
+    _getMinutesRange(hour) {
+      const start = hour * HOUR_IN_MS;
+      const end = start + HOUR_IN_MS - 1;
+      const minStep = MINUTE_IN_MS;
+      const formatter = (time) => new Date(time).getUTCMinutes();
+
+      return this._getSteps(start, end, minStep, formatter);
+    },
+
+    /**
+     * Get the seconds range
+     *
+     * @param  {Number} hour
+     * @param  {Number} minute
+     * @return {Array<Number>}
+     */
+    _getSecondsRange(hour, minute) {
+      const start = hour * HOUR_IN_MS + minute * MINUTE_IN_MS;
+      const end = start + MINUTE_IN_MS - 1;
+      const minStep = SECOND_IN_MS;
+      const formatter = (time) => new Date(time).getUTCSeconds();
+
+      return this._getSteps(start, end, minStep, formatter);
+    },
+
+    /**
+     * Get the milliseconds range
+     * @param  {Number} hour
+     * @param  {Number} minute
+     * @param  {Number} second
+     * @return {Array<Number>}
+     */
+    _getMillisecondsRange(hour, minute, second) {
+      const start = hour * HOUR_IN_MS + minute * MINUTE_IN_MS + second * SECOND_IN_MS;
+      const end = start + SECOND_IN_MS - 1;
+      const minStep = 1;
+      const formatter = (time) => new Date(time).getUTCMilliseconds();
+
+      return this._getSteps(start, end, minStep, formatter);
+    },
+
+    /**
+     * Calculate the range of possible steps.
+     *
+     * @param  {Number} startValue: Start time in ms
+     * @param  {Number} endValue: End time in ms
+     * @param  {Number} minStep: Smallest step in ms for the time unit
+     * @param  {Function} formatter: Outputs time in a particular format
+     * @return {Array<Object>}
+     *         {
+     *           {Number} value
+     *           {Boolean} enabled
+     *         }
+     */
+    _getSteps(startValue, endValue, minStep, formatter) {
+      const { min, max, step } = this.props;
+      // The timeStep should be big enough so that there won't be
+      // duplications. Ex: minimum step for minute should be 60000ms,
+      // if smaller than that, next step might return the same minute.
+      const timeStep = Math.max(minStep, step);
+
+      // Make sure the starting point and end point is not off step
+      let time = min.valueOf() + Math.ceil((startValue - min.valueOf()) / timeStep) * timeStep;
+      let maxValue = min.valueOf() + Math.floor((max.valueOf() - min.valueOf()) / step) * step;
+      let steps = [];
+
+      // Increment by timeStep until reaching the end of the range.
+      while (time <= endValue) {
+        steps.push({
+          value: formatter(time),
+          // Check if the value is within the min and max. If it's out of range,
+          // also check for the case when minStep is too large, and has stepped out
+          // of range when it should be enabled.
+          enabled: (time >= min.valueOf() && time <= max.valueOf()) ||
+            (time > maxValue && startValue <= maxValue &&
+              endValue >= maxValue && formatter(time) == formatter(maxValue))
+        });
+        time += timeStep;
+      }
+
+      return steps;
+    },
+
+    /**
+     * A generic function for stepping up or down from a value of a range.
+     * It stops at the upper and lower limits.
+     *
+     * @param  {Number} current: The current value
+     * @param  {Number} offset: The offset relative to current value
+     * @param  {Array<Object>} range: List of possible steps
+     * @return {Number} The new value
+     */
+    _step(current, offset, range) {
+      const index = range.findIndex(step => step.value == current);
+      const newIndex = offset > 0 ?
+                     Math.min(index + offset, range.length - 1) :
+                     Math.max(index + offset, 0);
+      return range[newIndex].value;
+    },
+
+    /**
+     * Step up or down AM/PM
+     *
+     * @param  {Number} offset
+     */
+    stepDayPeriodBy(offset) {
+      const current = this.dayPeriod;
+      const dayPeriod = this._step(current, offset, this.state.ranges.dayPeriod);
+
+      if (current != dayPeriod) {
+        this.hour < DAY_PERIOD_IN_HOURS ?
+          this.setState({ hour: this.hour + DAY_PERIOD_IN_HOURS }) :
+          this.setState({ hour: this.hour - DAY_PERIOD_IN_HOURS });
+      }
+    },
+
+    /**
+     * Step up or down hours
+     *
+     * @param  {Number} offset
+     */
+    stepHourBy(offset) {
+      const current = this.hour;
+      const hour = this._step(current, offset, this.state.ranges.hours);
+
+      if (current != hour) {
+        this.setState({ hour });
+      }
+    },
+
+    /**
+     * Step up or down minutes
+     *
+     * @param  {Number} offset
+     */
+    stepMinuteBy(offset) {
+      const current = this.minute;
+      const minute = this._step(current, offset, this.state.ranges.minutes);
+
+      if (current != minute) {
+        this.setState({ minute });
+      }
+    },
+
+    /**
+     * Step up or down seconds
+     *
+     * @param  {Number} offset
+     */
+    stepSecondBy(offset) {
+      const current = this.second;
+      const second = this._step(current, offset, this.state.ranges.seconds);
+
+      if (current != second) {
+        this.setState({ second });
+      }
+    },
+
+    /**
+     * Step up or down milliseconds
+     *
+     * @param  {Number} offset
+     */
+    stepMillisecondBy(offset) {
+      const current = this.milliseconds;
+      const millisecond = this._step(current, offset, this.state.ranges.millisecond);
+
+      if (current != millisecond) {
+        this.setState({ millisecond });
+      }
+    },
+
+    /**
+     * Checks if the time state is off step.
+     *
+     * @param  {Date} time
+     * @return {Boolean}
+     */
+    _isOffStep(time) {
+      const { min, step } = this.props;
+
+      return (time.valueOf() - min.valueOf()) % step != 0;
+    }
+  };
+}