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app/javascript/gabsocial/components/relative_timestamp.js

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+import { injectIntl, defineMessages } from 'react-intl'
+
+const messages = defineMessages({
+  just_now: { id: 'relative_time.just_now', defaultMessage: 'now' },
+  seconds: { id: 'relative_time.seconds', defaultMessage: '{number}s' },
+  minutes: { id: 'relative_time.minutes', defaultMessage: '{number}m' },
+  hours: { id: 'relative_time.hours', defaultMessage: '{number}h' },
+  days: { id: 'relative_time.days', defaultMessage: '{number}d' },
+  moments_remaining: { id: 'time_remaining.moments', defaultMessage: 'Moments remaining' },
+  seconds_remaining: { id: 'time_remaining.seconds', defaultMessage: '{number, plural, one {# second} other {# seconds}} left' },
+  minutes_remaining: { id: 'time_remaining.minutes', defaultMessage: '{number, plural, one {# minute} other {# minutes}} left' },
+  hours_remaining: { id: 'time_remaining.hours', defaultMessage: '{number, plural, one {# hour} other {# hours}} left' },
+  days_remaining: { id: 'time_remaining.days', defaultMessage: '{number, plural, one {# day} other {# days}} left' },
+})
+
+const dateFormatOptions = {
+  hour12: false,
+  year: 'numeric',
+  month: 'short',
+  day: '2-digit',
+  hour: '2-digit',
+  minute: '2-digit',
+}
+
+const shortDateFormatOptions = {
+  month: 'short',
+  day: 'numeric',
+}
+
+const SECOND = 1000
+const MINUTE = 1000 * 60
+const HOUR = 1000 * 60 * 60
+const DAY = 1000 * 60 * 60 * 24
+
+const MAX_DELAY = 2147483647
+
+const selectUnits = delta => {
+  const absDelta = Math.abs(delta)
+
+  if (absDelta < MINUTE) {
+    return 'second'
+  } else if (absDelta < HOUR) {
+    return 'minute'
+  } else if (absDelta < DAY) {
+    return 'hour'
+  }
+
+  return 'day'
+}
+
+const getUnitDelay = units => {
+  switch (units) {
+    case 'second':
+      return SECOND
+    case 'minute':
+      return MINUTE
+    case 'hour':
+      return HOUR
+    case 'day':
+      return DAY
+    default:
+      return MAX_DELAY
+  }
+}
+
+export const timeAgoString = (intl, date, now, year) => {
+  const delta = now - date.getTime()
+
+  let relativeTime
+
+  if (delta < 10 * SECOND) {
+    relativeTime = intl.formatMessage(messages.just_now)
+  } else if (delta < 7 * DAY) {
+    if (delta < MINUTE) {
+      relativeTime = intl.formatMessage(messages.seconds, { number: Math.floor(delta / SECOND) })
+    } else if (delta < HOUR) {
+      relativeTime = intl.formatMessage(messages.minutes, { number: Math.floor(delta / MINUTE) })
+    } else if (delta < DAY) {
+      relativeTime = intl.formatMessage(messages.hours, { number: Math.floor(delta / HOUR) })
+    } else {
+      relativeTime = intl.formatMessage(messages.days, { number: Math.floor(delta / DAY) })
+    }
+  } else if (date.getFullYear() === year) {
+    relativeTime = intl.formatDate(date, shortDateFormatOptions)
+  } else {
+    relativeTime = intl.formatDate(date, { ...shortDateFormatOptions, year: 'numeric' })
+  }
+
+  return relativeTime
+}
+
+const timeRemainingString = (intl, date, now) => {
+  const delta = date.getTime() - now
+
+  let relativeTime
+
+  if (delta < 10 * SECOND) {
+    relativeTime = intl.formatMessage(messages.moments_remaining)
+  } else if (delta < MINUTE) {
+    relativeTime = intl.formatMessage(messages.seconds_remaining, { number: Math.floor(delta / SECOND) })
+  } else if (delta < HOUR) {
+    relativeTime = intl.formatMessage(messages.minutes_remaining, { number: Math.floor(delta / MINUTE) })
+  } else if (delta < DAY) {
+    relativeTime = intl.formatMessage(messages.hours_remaining, { number: Math.floor(delta / HOUR) })
+  } else {
+    relativeTime = intl.formatMessage(messages.days_remaining, { number: Math.floor(delta / DAY) })
+  }
+
+  return relativeTime
+}
+
+export default @injectIntl
+class RelativeTimestamp extends Component {
+
+  static propTypes = {
+    intl: PropTypes.object.isRequired,
+    timestamp: PropTypes.string.isRequired,
+    year: PropTypes.number.isRequired,
+    futureDate: PropTypes.bool,
+  }
+
+  state = {
+    now: this.props.intl.now(),
+  }
+
+  static defaultProps = {
+    year: (new Date()).getFullYear(),
+  }
+
+  shouldComponentUpdate(nextProps, nextState) {
+    // As of right now the locale doesn't change without a new page load,
+    // but we might as well check in case that ever changes.
+    return this.props.timestamp !== nextProps.timestamp ||
+      this.props.intl.locale !== nextProps.intl.locale ||
+      this.state.now !== nextState.now
+  }
+
+  componentWillReceiveProps(nextProps) {
+    if (this.props.timestamp !== nextProps.timestamp) {
+      this.setState({ now: this.props.intl.now() })
+    }
+  }
+
+  componentDidMount() {
+    this._scheduleNextUpdate(this.props, this.state)
+  }
+
+  componentWillUpdate(nextProps, nextState) {
+    this._scheduleNextUpdate(nextProps, nextState)
+  }
+
+  componentWillUnmount() {
+    clearTimeout(this._timer)
+  }
+
+  _scheduleNextUpdate(props, state) {
+    clearTimeout(this._timer)
+
+    const { timestamp } = props
+    const delta = (new Date(timestamp)).getTime() - state.now
+    const unitDelay = getUnitDelay(selectUnits(delta))
+    const unitRemainder = Math.abs(delta % unitDelay)
+    const updateInterval = 1000 * 10
+    const delay = delta < 0 ? Math.max(updateInterval, unitDelay - unitRemainder) : Math.max(updateInterval, unitRemainder)
+
+    this._timer = setTimeout(() => {
+      this.setState({ now: this.props.intl.now() })
+    }, delay)
+  }
+
+  render() {
+    const { timestamp, intl, year, futureDate } = this.props
+
+    const date = new Date(timestamp)
+    const relativeTime = futureDate ? timeRemainingString(intl, date, this.state.now) : timeAgoString(intl, date, this.state.now, year)
+
+    return (
+      <time dateTime={timestamp} title={intl.formatDate(date, dateFormatOptions)}>
+        {relativeTime}
+      </time>
+    )
+  }
+
+}