seo: increase sitemap coverage.

Rework sitemaps to provide more coverage of the site. We want every
important page on the site - including every post, tag, and wiki page -
to be indexed by Google. We do this by generating sitemaps and sitemap
indexes that contain links to every important page on the site.

app/controllers/static_controller.rb

@@ -22,10 +22,34 @@ class StaticController < ApplicationController
   def site_map
   end
 
-  def sitemap
-    @reportbooru_service = ReportbooruService.new
-    @posts = Post.where("created_at > ?", 1.week.ago).order(score: :desc).limit(200)
-    @posts = @posts.select(&:visible?)
-    render layout: false
+  def sitemap_index
+    @sitemap = params[:sitemap]
+    @limit = params.fetch(:limit, 10000).to_i
+
+    case @sitemap
+    when "artists"
+      @relation = Artist.undeleted
+      @search = { is_deleted: "false" }
+    when "forum_topics"
+      @relation = ForumTopic.undeleted
+      @search = { is_deleted: "false" }
+    when "pools"
+      @relation = Pool.undeleted
+      @search = { is_deleted: "false" }
+    when "posts"
+      @relation = Post.order(id: :asc)
+      @serach = {}
+    when "tags"
+      @relation = Tag.nonempty
+      @search = {}
+    when "users"
+      @relation = User.all
+      @search = {}
+    when "wiki_pages"
+      @relation = WikiPage.undeleted
+      @search = { is_deleted: "false" }
+    else
+      raise NotImplementedError
+    end
   end
 end