Add reading time to blog posts

Author: szarnyasg

_layouts/post.html

@@ -89,6 +89,9 @@ <h1>{{ page.title }}</h1>
 													<span>Published on</span>
 													<span class="date">{{ page.date | date: "%Y-%m-%d" }}</span>
 												</div>
+												<div class="publishedinfo">
+													<span>Reading time: {{ content | reading_time }}</span>
+												</div>
 											{% endif %}
 										</div>
 									</div>

_plugins/reading_time_filter.rb

@@ -0,0 +1,47 @@
+module ReadingTimeFilter
+  include Liquid::StandardFilters
+
+  def reading_time(input)
+    # Get words count.
+    total_words = get_plain_text(input).split.size
+
+    # Load configuration.
+    config = @context.registers[:site].config["reading_time"]
+
+    # Setup default value.
+    if ! config
+      second_plural = "seconds"
+      minute_singular = "minute"
+      minute_plural = "minutes"
+    else
+      second_plural = config["second_plural"] ? config["second_plural"] : "seconds"
+      minute_singular = config["minute_singular"] ? config["minute_singular"] : "minute"
+      minute_plural = config["minute_plural"] ? config["minute_plural"] : "minutes"
+    end
+
+    # Average reading words per minute.
+    words_per_minute = 150
+
+    # Calculate reading time.
+    case total_words
+    when 0 .. 74
+      return "30 #{second_plural}"
+    when 75 .. 149
+      return "1 #{minute_singular}"
+    else
+      minutes = ( total_words / words_per_minute ).floor
+      return "#{minutes} #{minute_plural}";
+    end
+  end
+
+  def get_plain_text(input)
+    strip_html(strip_pre_tags(input))
+  end
+
+  def strip_pre_tags(input)
+    empty = ''.freeze
+    input.to_s.gsub(/<pre(?:(?!<\/pre).|\s)*<\/pre>/mi, empty)
+  end
+end
+
+Liquid::Template.register_filter(ReadingTimeFilter)