add tags to post file urls

app/models/post.rb

@@ -99,17 +99,31 @@ class Post < ActiveRecord::Base
     end
 
     def file_url
-      "/data/#{file_path_prefix}#{md5}.#{file_ext}"
+      if Danbooru.config.enable_seo_post_urls
+        # the seo tags should be stripped out by nginx
+        "/data/--#{seo_tags}--#{file_path_prefix}#{md5}.#{file_ext}"
+      else
+        "/data/#{file_path_prefix}#{md5}.#{file_ext}"
+      end
     end
 
     def large_file_url
       if has_large?
-        "/data/sample/#{file_path_prefix}#{Danbooru.config.large_image_prefix}#{md5}.#{large_file_ext}"
+        if Danbooru.config.enable_seo_post_urls
+          # the seo tags should be stripped out by nginx
+          "/data/sample/--#{seo_tags}--#{file_path_prefix}#{Danbooru.config.large_image_prefix}#{md5}.#{large_file_ext}"
+        else
+          "/data/sample/#{file_path_prefix}#{Danbooru.config.large_image_prefix}#{md5}.#{large_file_ext}"
+        end 
       else
         file_url
       end
     end
 
+    def seo_tags
+      @seo_tags ||= humanized_essential_tag_string.gsub(/[^a-z0-9]+/, "-").gsub(/(^-+)|(-+$)/, "")
+    end
+
     def preview_file_url
       if !has_preview?
         return "/images/download-preview.png"
@@ -778,26 +792,37 @@ class Post < ActiveRecord::Base
       end
     end
 
-    def essential_tag_string
-      tag_array.each do |tag|
-        if tag_categories[tag] == Danbooru.config.tag_category_mapping["copyright"]
-          return tag
-        end
-      end
+    def humanized_essential_tag_string
+      @humanized_essential_tag_string ||= begin
+        string = []
 
-      tag_array.each do |tag|
-        if tag_categories[tag] == Danbooru.config.tag_category_mapping["character"]
-          return tag
+        if character_tags.any?
+          chartags = character_tags.slice(0, 5)
+          if character_tags.length > 5
+            chartags << "others"
+          end
+          chartags = chartags.map do |tag|
+            tag.match(/^(.+?)(?:_\(.+\))?$/)[1]
+          end
+          string << chartags.to_sentence
         end
-      end
 
-      tag_array.each do |tag|
-        if tag_categories[tag] == Danbooru.config.tag_category_mapping["artist"]
-          return tag
+        if copyright_tags.any?
+          copytags = copyright_tags.slice(0, 5)
+          if copyright_tags.length > 5
+            copytags << "others"
+          end
+          copytags = copytags.to_sentence
+          string << (character_tags.any? ? "(#{copytags})" : copytags)
         end
-      end
 
-      return tag_array.first
+        if artist_tags_excluding_hidden.any?
+          string << "drawn by"
+          string << artist_tags_excluding_hidden.to_sentence
+        end
+
+        string.empty? ? "##{id}" : string.join(" ").tr("_", " ")
+      end
     end
 
     def tag_string_copyright

app/presenters/post_presenter.rb

@@ -104,34 +104,7 @@ class PostPresenter < Presenter
   end
 
   def humanized_essential_tag_string
-    string = []
-
-    if @post.character_tags.any?
-      chartags = @post.character_tags.slice(0, 5)
-      if @post.character_tags.length > 5
-        chartags << "others"
-      end
-      chartags = chartags.map do |tag|
-        tag.match(/^(.+?)(?:_\(.+\))?$/)[1]
-      end
-      string << chartags.to_sentence
-    end
-
-    if @post.copyright_tags.any?
-      copytags = @post.copyright_tags.slice(0, 5)
-      if @post.copyright_tags.length > 5
-        copytags << "others"
-      end
-      copytags = copytags.to_sentence
-      string << (@post.character_tags.any? ? "(#{copytags})" : copytags)
-    end
-
-    if @post.artist_tags_excluding_hidden.any?
-      string << "drawn by"
-      string << @post.artist_tags_excluding_hidden.to_sentence
-    end
-
-    string.empty? ? "##{@post.id}" : string.join(" ").tr("_", " ")
+    @post.humanized_essential_tag_string
   end
 
   def categorized_tag_string

config/danbooru_default_config.rb

@@ -396,6 +396,10 @@ module Danbooru
     def addthis_key
     end
 
+    def enable_seo_post_urls
+      false
+    end
+
     # enable some (donmai-specific) optimizations for post counts
     def estimate_post_counts
       true