src/talks.sh: Handle display of future dates

Display future dates as "Will be presented on" rather than "Presented
on".

src/talks.sh

@@ -49,6 +49,23 @@ talk-field()
 }
 
 
+# Produce string to handle past or future dates.
+present-relative()
+{
+  local -r date=${1?Missing date}
+
+  local -i now udate
+  now=$(date +%s)
+  udate=$( date --date="$date" +%s )
+
+  if [ "$now" -lt "$udate" ]; then
+    echo 'Will be presented'
+  else
+    echo Presented
+  fi
+}
+
+
 # Generate abstract for talk.
 abstract()
 {
@@ -72,6 +89,8 @@ abstract()
     watch_title="Watch $location Talk"
   fi
 
+  present=$( present-relative "$date" )
+
   cat <<EOF
 <article class="abstract talk">
   <h2 class="title" id="$id">$title</h2>
@@ -87,7 +106,7 @@ abstract()
 
   $abstract_html
 
-  <p class="date">Presented on $date at
+  <p class="date">$present on $date at
     <a href="$event_link">$location</a>.</p>
 </article>
 EOF