#425

backend/app/services/tag_group_markdown_renderer.rb

@@ -0,0 +1,114 @@
+class TagGroupMarkdownRenderer
+  class UnsupportedStructure < StandardError
+    ;
+  end
+
+  def self.render group
+    new(group).render
+  end
+
+  def initialize group
+    @group = group
+  end
+
+  def render
+    placements = @group.fetch('placements')
+    validate_membership!(placements)
+    blocks = []
+    blocks << clean_text(@group['description']) if @group['description'].present?
+
+    sections = placements.select { _1.key?('section_name') }
+    if sections.any? && sections.size != placements.size
+      raise UnsupportedStructure,
+          '最上位の見出し Section と Placement の混在は Markdown にできません．'
+    end
+
+    if placements.all? { _1.key?('section_name') }
+      blocks.concat(placements.map { render_heading(_1, 1) })
+    else
+      blocks << render_list(placements, 0)
+    end
+
+    blocks.compact.reject(&:empty?).join("\n\n").sub(/\n+\z/, '')
+  end
+
+  private
+
+  def validate_membership! placements
+    placed = placement_members(placements).uniq.sort
+    members = @group.fetch('members').map do |member|
+      if member['tag']
+        ['tag', member.fetch('tag').fetch('id')]
+      else
+        ['tag_group', member.fetch('tag_group').fetch('id')]
+      end
+    end.uniq.sort
+    missing = members - placed
+    raise UnsupportedStructure, '掲載位置のない membership は Markdown にできません．' if missing.any?
+  end
+
+  def placement_members nodes
+    nodes.flat_map do |node|
+      own = if node['tag']
+        [['tag', node.fetch('tag').fetch('id')]]
+      elsif node['tag_group']
+        [['tag_group', node.fetch('tag_group').fetch('id')]]
+      else
+        []
+      end
+      own + placement_members(node.fetch('children'))
+    end
+  end
+
+  def render_heading section, level
+    header = "#{ '#' * level } #{ clean_text(section.fetch('section_name')) }"
+    blocks = [header]
+    blocks << clean_text(section['description']) if section['description'].present?
+    children = section.fetch('children')
+    section_indexes = children.each_index.select { |index| children[index].key?('section_name') }
+    if section_indexes.any?
+      first_section = section_indexes.first
+      if children[first_section..].any? { !_1.key?('section_name') }
+        raise UnsupportedStructure,
+            '見出し Section と兄弟 Placement の交互配置は Markdown にできません．'
+      end
+      list_nodes = children[0...first_section]
+      blocks << render_list(list_nodes, 0) if list_nodes.any?
+      blocks.concat(children[first_section..].map { render_heading(_1, level + 1) })
+    elsif children.any?
+      blocks << render_list(children, 0)
+    end
+    blocks.join("\n\n")
+  end
+
+  def render_list nodes, depth
+    nodes.map do |node|
+      indent = '  ' * depth
+      if node.key?('section_name')
+        raise UnsupportedStructure,
+            'リスト内 Section の説明文は Markdown にできません．' if node['description'].present?
+
+        children = node.fetch('children')
+        head = "#{ indent }- #{ clean_text(node.fetch('section_name')) }:"
+        tail = render_list(children, depth + 1) if children.any?
+        [head, tail].compact.join("\n")
+      else
+        label = if node['tag']
+          node.fetch('tag').fetch('name')
+        else
+          "#{ TagGroupRepr::PREFIX }#{ node.fetch('tag_group').fetch('name') }"
+        end
+        raise UnsupportedStructure, '名称のない Placement は Markdown にできません．' if label.blank?
+
+        head = "#{ indent }- #{ clean_text(label) }"
+        children = node.fetch('children')
+        tail = render_list(children, depth + 1) if children.any?
+        [head, tail].compact.join("\n")
+      end
+    end.join("\n")
+  end
+
+  def clean_text value
+    value.to_s.gsub(/\r\n?/, "\n").lines.map(&:rstrip).join("\n").strip
+  end
+end