# 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
  # Render the OG image meta HTML tag for the currently rendered page.
  class RenderOGImageTag < Liquid::Tag
    # The path to be used when the current page does not have a specific image.
    DEFAULT_PATH = "/images/default.png"

    def render(context)
      img  = normalize(context["raw_title"]) + ".png"
      path = image_exists?(img) ? "/images/posts/#{img}" : DEFAULT_PATH
      render_meta("og:image", "http://jo.mssola.com#{path}")
    end

    protected

    # Returns true if the given image exists inside of /images/posts.
    def image_exists?(image)
      return false if image == ".png"

      path = File.expand_path(File.join(File.dirname(__FILE__), "..", "images", "posts", image))
      File.file?(path)
    end

    # Downcases the given string and replaces space characters with "-"
    def normalize(str)
      str.gsub(/\s/, "-").downcase
    end

    # Render an HTML meta tag with the given property and content attributes.
    def render_meta(property, content)
      "<meta property=\"#{property}\" content=\"#{content}\" />"
    end
  end
end

Liquid::Template.register_tag("render_og_image", Jekyll::RenderOGImageTag)