fix 'go to post' links

lib/philomena_web/controllers/topic_controller.ex

@@ -7,7 +7,7 @@ defmodule PhilomenaWeb.TopicController do
 
   plug :load_and_authorize_resource, model: Forum, id_name: "forum_id", id_field: "short_name", persisted: true
 
-  def show(conn, %{"id" => slug}) do
+  def show(conn, %{"id" => slug} = params) do
     forum = conn.assigns.forum
     topic =
       Topic
@@ -18,6 +18,16 @@ defmodule PhilomenaWeb.TopicController do
     conn = conn |> assign(:topic, topic)
     %{page_number: page} = conn.assigns.pagination
 
+    page =
+      with {post_id, _extra} <- Integer.parse(params["post_id"] || ""),
+           [post] <- Post |> where(id: ^post_id) |> Repo.all()
+      do
+        div(post.topic_position, 25) + 1
+      else
+        _ ->
+          page
+      end
+
     posts =
       Post
       |> where(topic_id: ^conn.assigns.topic.id)

lib/philomena_web/templates/forum/index.html.slime

@@ -26,7 +26,7 @@ h1 Discussion Forums
                 strong
                   => link(forum.last_post.topic.title, to: Routes.forum_topic_path(@conn, :show, forum, forum.last_post.topic))
                 br
-                => link("Go to post", to: Routes.forum_topic_path(@conn, :show, forum, forum.last_post.topic, post_id: forum.last_post.id))
+                => link("Go to post", to: Routes.forum_topic_path(@conn, :show, forum, forum.last_post.topic, post_id: forum.last_post.id) <> "#post_#{forum.last_post.id}")
                 ' by
                 => render PhilomenaWeb.UserAttributionView, "_anon_user.html", object: forum.last_post
                 br

lib/philomena_web/templates/forum/show.html.slime

@@ -46,7 +46,7 @@ h1 = @forum.name
             td.table--communication-list__stats.hide-mobile = topic.post_count
             td.table--communication-list__last-post
               = if topic.last_post do
-                => link("Go to post", to: Routes.forum_topic_path(@conn, :show, @forum, topic, post_id: topic.last_post) <> "post_#{topic.last_post.id}")
+                => link("Go to post", to: Routes.forum_topic_path(@conn, :show, @forum, topic, post_id: topic.last_post) <> "#post_#{topic.last_post.id}")
                 ' by
                 = render PhilomenaWeb.UserAttributionView, "_anon_user.html", object: topic.last_post
                 br

lib/philomena_web/templates/post/_post_options.html.slime

@@ -13,7 +13,7 @@ div
   /      | because:
   /      =<> post.edit_reason
 div
-  - link_path = Routes.forum_topic_path(@conn, :show, @post.topic.forum, @post.topic, post_id: @post.id) <> "post_#{@post.id}"
+  - link_path = Routes.forum_topic_path(@conn, :show, @post.topic.forum, @post.topic, post_id: @post.id) <> "#post_#{@post.id}"
   a.communication__interaction title="Link to post" href=link_path
     i.fa.fa-link>
     ' Link