make the prettyDate implementation generic

there is a `RelativeUnit` type now, which is pattern-matched on and then
the result of that is used in the generic formatting.

elm/PrettyDate.elm

@@ -10,39 +10,39 @@ prettyDate reference date =
        diffSeconds = referenceSeconds - dateSeconds
    in format << toRelativeTime <| diffSeconds
type RelativeTime = JustNow
                  | Minute Int
                  | Hour Int
                  | Day Int
                  | Week Int
                  | Month Int
                  | Year Int
                  | Future RelativeTime
type RelativeUnit = JustNow
                  | Minute
                  | Hour
                  | Day
                  | Week
                  | Month
                  | Year
type RelativeTime = Past RelativeUnit Int
                  | Future RelativeUnit Int
stringForm relativeUnit =
    case relativeUnit of
      Minute  -> ("a minute", "minutes")
      Hour    -> ("an hour", "hours")
      Day     -> ("a day", "days")
      Week    -> ("a week", "weeks")
      Month   -> ("a month", "months")
      Year    -> ("a year", "years")
format : RelativeTime -> String
format relativeTime =
    case relativeTime of
      JustNow -> "moments ago"
      Minute 1 -> "a minute ago"
      Minute n -> toString n ++ " minutes ago"
      Hour 1 -> "hour ago"
      Hour n -> toString n ++ " hours ago"
      Day 1 -> "a day ago"
      Day n -> toString n ++ " years ago"
      Week 1 -> "a week ago"
      Week n -> toString n ++ " weeks ago"
      Month 1 -> "a month ago"
      Month n -> toString n ++ " months ago"
      Year 1 -> "a year ago"
      Year n -> toString n ++ "years ago"
      Future (JustNow) -> "in a moment"
      Future (Minute n) -> "in " ++ toString n ++ " hours"
      Future (Hour n) -> "in " ++ toString n ++ " hours"
      Future (Day n) -> "in " ++ toString n ++ " days"
      Future (Week n) -> "in " ++ toString n ++ " weeks"
      Future (Month n) -> "in " ++ toString n ++ " months"
      Future (Year n) -> "in " ++ toString n ++ " years"
      _ -> "???"
      Past   JustNow _ -> "moments ago"
      Future JustNow _ -> "in a moment"
      Past   unit n    -> format' ""    " ago" unit n
      Future unit n    -> format' "in " ""     unit n
format' prefix suffix unit n =
    let (singular, plural) = stringForm unit
    in if n == 1
       then prefix ++ singular
       else prefix ++ toString n ++ " " ++ plural ++ suffix
toRelativeTime : Float -> RelativeTime
toRelativeTime origDiff =
@@ -55,14 +55,14 @@ toRelativeTime origDiff =
        roundToString = toString << ceiling
        inThePast = origDiff > 0
        diff = abs origDiff
        relativeTime =
            if | diff < minute -> JustNow
               | diff < hour   -> Minute <| round (diff / minute)
               | diff < day    -> Hour <| round (diff / hour)
               | diff < week   -> Day <| round (diff / day)
               | diff < month  -> Week <| round (diff / week)
               | diff < year   -> Month <| round (diff / month)
               | otherwise     -> Year <| round (diff / year)
        (relativeUnit, n) =
            if | diff < minute -> (JustNow, 0)
               | diff < hour   -> (Minute, round (diff / minute))
               | diff < day    -> (Hour, round (diff / hour))
               | diff < week   -> (Day, round (diff / day))
               | diff < month  -> (Week, round (diff / week))
               | diff < year   -> (Month, round (diff / month))
               | otherwise     -> (Year, round (diff / year))
    in if inThePast
       then relativeTime
       else Future relativeTime
       then Past relativeUnit n
       else Future relativeUnit n