Add estimated reading time

This adds the helper for calculating the reading time
of each document and shows it at the bottom of the page.

1 files changed, 34 insertions, 0 deletions

diff --git a/lib/helpers/reading_time.rb b/lib/helpers/reading_time.rb
new file mode 100644
index 00000000..1f96dcf5
--- /dev/null
+++ b/lib/helpers/reading_time.rb
@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+
+#
+# https://www.perpetual-beta.org/weblog/estimated-reading-time-in-nanoc.html
+#
+# Count the number of words in the document and, assuming the average
+# reading speed by words-per-minute, calculate the time taken in
+# minutes to read the given number of words. If there are any seconds
+# in the estimated reading time, then increment the minutes by one.
+#
+module Nanoc::Helpers
+  module ReadingTimeHelper
+    #
+    # Words per minute
+    # http://en.wikipedia.org/wiki/Words_per_minute#Reading_and_comprehension
+    #
+    # This is a rough estimate and given that the algorithm to find the words
+    # is very simple, it's best to overcalculate and increase the WPM.
+    # Otherwise, we end up with big reading time numbers.
+    #
+    WPM = 230
+
+    def reading_time(words)
+      minutes = (words / WPM).ceil
+      seconds = (words % WPM / (WPM / 60)).floor
+
+      if seconds > 0
+        minutes += 1
+      end
+
+      (minutes <= 1 ? 'about a minute' : '~' + minutes.to_s + ' minutes')
+    end
+  end
+end