Add modified_at info at the post layout

At the bottom of every blog post, there will now be a small text containing:

1. The localized date of the last modified time the blog post was
   modified (taking Git as a reference).
2. A link to the log at git.mssola.com for the given file.

This way readers have a better understanding of the versioning of a given page.

Signed-off-by: Miquel Sabaté Solà <msabate@suse.com>

3 files changed, 131 insertions, 14 deletions

diff --git a/_plugins/log.rb b/_plugins/log.rb
new file mode 100644
index 0000000..2331f10
--- /dev/null
+++ b/_plugins/log.rb
@@ -0,0 +1,94 @@
+# frozen_string_literal: true
+
+# Copyright (C) 2019 Miquel Sabaté Solà <mikisabate@gmail.com>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+require "date"
+require_relative "modified_time_helper"
+
+module Jekyll
+  # Render the last modification time of the given page.
+  class RenderModifiedAt < Liquid::Tag
+    include ::Jekyll::ModifiedTimeHelper
+
+    def render(context)
+      time = Time.iso8601(modified_time(context["page"]))
+
+      if context["page"]["lang"] == "en"
+        time.strftime("%B %-d, %Y, at %H:%m")
+      else
+        time.strftime("%-d de #{catalan_month(time.month)} de %Y, a les %H:%m")
+      end
+    end
+
+    protected
+
+    # Given a month number, return its catalan translation.
+    # rubocop:disable Metrics/MethodLength, Metrics/CyclomaticComplexity
+    def catalan_month(month)
+      case month
+      when 1
+        "gener"
+      when 2
+        "febrer"
+      when 3
+        "març"
+      when 4
+        "abril"
+      when 5
+        "maig"
+      when 6
+        "juny"
+      when 7
+        "juliol"
+      when 8
+        "agost"
+      when 9
+        "setembre"
+      when 10
+        "octubre"
+      when 11
+        "novembre"
+      when 12
+        "desembre"
+      else
+        ""
+      end
+    end
+    # rubocop:enable Metrics/MethodLength, Metrics/CyclomaticComplexity
+  end
+
+  # Render the link to git.mssola.com of the given page.
+  class RenderLogLink < Liquid::Tag
+    include ::Jekyll::ModifiedTimeHelper
+
+    WEBSITE_BASE = "http://git.mssola.com"
+    WEBSITE_REPO = "jo.git"
+
+    def render(context)
+      page = context["page"]
+      url  = "#{WEBSITE_BASE}/#{WEBSITE_REPO}/log/#{page["relative_path"]}"
+
+      if page["lang"] == "en"
+        "<a href=\"#{url}\" title=\"Log for this page\">here</a>"
+      else
+        "<a href=\"#{url}\" title=\"Historial d'aquesta pàgina (anglès)\">aquí</a>"
+      end
+    end
+  end
+end
+
+Liquid::Template.register_tag("render_modified_at", Jekyll::RenderModifiedAt)
+Liquid::Template.register_tag("render_log_link", Jekyll::RenderLogLink)
diff --git a/_plugins/modified_time_helper.rb b/_plugins/modified_time_helper.rb
new file mode 100644
index 0000000..9c6b880
--- /dev/null
+++ b/_plugins/modified_time_helper.rb
@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+# Copyright (C) 2019 Miquel Sabaté Solà <mikisabate@gmail.com>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+module Jekyll
+  # ModifiedTimeHelper offers methods to fetch the modified time of a given page.
+  module ModifiedTimeHelper
+    # Returns the modified time of the given page.
+    def modified_time(page)
+      path = File.expand_path(File.join(File.dirname(__FILE__), "..", page["path"]))
+      out  = `git log -n 1 --pretty='format:%cd' --date=iso8601-strict -- #{path}`
+
+      begin
+        Time.iso8601(out)
+        out
+      rescue ArgumentError => e
+        puts "[WARNING] Could not parse the given modified time from Git: #{e}"
+        nil
+      end
+    end
+  end
+end
diff --git a/_plugins/type.rb b/_plugins/type.rb
index 3107b4a..211e7e0 100644
--- a/_plugins/type.rb
+++ b/_plugins/type.rb
@@ -17,11 +17,13 @@
 
 require "time"
 require_relative "render_helper"
+require_relative "modified_time_helper"
 
 module Jekyll
   # Render og:type related tags.
   class RenderTypeTags < Liquid::Tag
     include ::Jekyll::RenderHelper
+    include ::Jekyll::ModifiedTimeHelper
 
     def render(context)
       if ["posts"].include?(context["page"]["collection"])
@@ -55,20 +57,6 @@ module Jekyll
       # Jekyll completely disregards the hour, minutes, etc., so why bother.
       page["date"].to_s.split.first
     end
-
-    # Returns the modified time of the given page.
-    def modified_time(page)
-      path = File.expand_path(File.join(File.dirname(__FILE__), "..", page["path"]))
-      out  = `git log -n 1 --pretty='format:%cd' --date=iso8601-strict -- #{path}`
-
-      begin
-        Time.iso8601(out)
-        out
-      rescue ArgumentError => e
-        puts "[WARNING] Could not parse the given modified time from Git: #{e}"
-        nil
-      end
-    end
   end
 end