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>

1 files changed, 35 insertions, 0 deletions

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