A reading time filter for Jekyll templates

reading_time.rb

# A reading time filter for Jekyll templates
#
# Author: Daan Sprenkels <hello@dsprenkels.com>
#
# This module implements a filter for post content which calculates a range of
# time to display to the user. The filter is made for English text (and will
# display an English message). However, you can modify this script for your
# personal needs.


module ReadingTimeFilter
  def reading_time(input)
    # Define your personal parameters here
    text_words_per_minute_lo = 400
    text_words_per_minute_hi = 200
    code_lines_per_minute = 20

    # Split the post into text and code
    text = input.gsub(/<code>.*?<\/code>/im, "")
    text_words = text.split.size
    code_lines = input.lines.size - text.lines.size

    # Calculate the time that a user needs for reading your post
    code_minutes = code_lines / code_lines_per_minute
    lo_minutes = text_words / text_words_per_minute_lo + code_minutes
    hi_minutes = text_words / text_words_per_minute_hi + code_minutes
    avg_minutes = (lo_minutes + hi_minutes) / 2

    # Either show the average, or a duration range
    if avg_minutes >= 10
      "#{lo_minutes.round} – #{hi_minutes.round} minute read"
    else
      "#{avg_minutes.round} minute read"
    end
  end
end

Liquid::Template.register_filter(ReadingTimeFilter)