Add alternate comparison types to versions

- The types are:
-- Previous: The default and the previously used type
-- Subsequent: Compares against the next version
-- Current: Compares against the current version
- Allow switching between comparison types in index and diff views
-- Have links vary depending upon current comparison type

app/controllers/application_controller.rb

@@ -39,6 +39,10 @@ class ApplicationController < ActionController::Base
     super
   end
 
+  def set_version_comparison
+    params[:type] = %w[previous subsequent current].include?(params[:type]) ? params[:type] : "previous"
+  end
+
   def model_name
     controller_name.classify
   end

app/controllers/artist_commentary_versions_controller.rb

@@ -2,6 +2,7 @@ class ArtistCommentaryVersionsController < ApplicationController
   respond_to :html, :xml, :json
 
   def index
+    set_version_comparison
     @commentary_versions = ArtistCommentaryVersion.paginated_search(params)
     @commentary_versions = @commentary_versions.includes(:updater, post: :uploader) if request.format.html?
 

app/controllers/artist_versions_controller.rb

@@ -2,6 +2,7 @@ class ArtistVersionsController < ApplicationController
   respond_to :html, :xml, :json
 
   def index
+    set_version_comparison
     @artist_versions = ArtistVersion.paginated_search(params)
     @artist_versions = @artist_versions.includes(:updater, artist: :urls) if request.format.html?
 

app/controllers/note_versions_controller.rb

@@ -2,6 +2,7 @@ class NoteVersionsController < ApplicationController
   respond_to :html, :xml, :json
 
   def index
+    set_version_comparison
     @note_versions = NoteVersion.paginated_search(params)
     @note_versions = @note_versions.includes(:updater) if request.format.html?
 

app/controllers/pool_versions_controller.rb

@@ -4,6 +4,7 @@ class PoolVersionsController < ApplicationController
   around_action :set_timeout
 
   def index
+    set_version_comparison
     @pool_versions = PoolVersion.paginated_search(params)
     @pool_versions = @pool_versions.includes(:updater, :pool) if request.format.html?
 
@@ -19,7 +20,8 @@ class PoolVersionsController < ApplicationController
     if params[:other_id]
       @other_version = PoolVersion.find(params[:other_id])
     else
-      @other_version = @pool_version.previous
+      set_version_comparison
+      @other_version = @pool_version.send(params[:type])
     end
   end
 

app/controllers/post_versions_controller.rb

@@ -6,6 +6,7 @@ class PostVersionsController < ApplicationController
   respond_to :js, only: [:undo]
 
   def index
+    set_version_comparison
     @post_versions = PostVersion.paginated_search(params)
 
     if request.format.html?

app/controllers/wiki_page_versions_controller.rb

@@ -3,6 +3,7 @@ class WikiPageVersionsController < ApplicationController
   layout "sidebar"
 
   def index
+    set_version_comparison
     @wiki_page_versions = WikiPageVersion.paginated_search(params)
     @wiki_page_versions = @wiki_page_versions.includes(:updater) if request.format.html?
 
@@ -16,15 +17,20 @@ class WikiPageVersionsController < ApplicationController
 
   def diff
     if params[:thispage].blank? || params[:otherpage].blank?
-      redirect_back fallback_location: wiki_pages_path, notice: "You must select two versions to diff"
-      return
-    end
-
-    @thispage = WikiPageVersion.find(params[:thispage])
-    @otherpage = WikiPageVersion.find(params[:otherpage])
-
-    if @thispage.id < @otherpage.id
-      @thispage, @otherpage = @otherpage, @thispage
+      page_id = params[:thispage] || params[:otherpage]
+      if page_id.blank?
+        redirect_back fallback_location: wiki_pages_path, notice: "You must select at least one version to diff"
+        return
+      end
+      set_version_comparison
+      @thispage = WikiPageVersion.find(page_id)
+      @otherpage = @thispage.send(params[:type])
+    else
+      @thispage = WikiPageVersion.find(params[:thispage])
+      @otherpage = WikiPageVersion.find(params[:otherpage])
+      if @thispage.id < @otherpage.id
+        @thispage, @otherpage = @otherpage, @thispage
+      end
     end
 
     respond_with([@thispage, @otherpage])

app/helpers/application_helper.rb

@@ -5,37 +5,45 @@ module ApplicationHelper
     (fields.reduce(false) { |acc, field| acc || params.dig(:search, field).present? } && (!member_check || CurrentUser.is_member?) ? types[0] : types[1])
   end
 
-  def diff_list_html(new, old, latest, ul_class: ["diff-list"], li_class: [])
-    diff = SetDiff.new(new, old, latest)
+  def diff_list_html(this_list, other_list, ul_class: ["diff-list"], li_class: [])
+    diff = SetDiff.new(this_list, other_list)
     render "diff_list", diff: diff, ul_class: ul_class, li_class: li_class
   end
 
-  def diff_name_html(this_name, prev_name)
+  def diff_name_html(this_name, other_name)
     pattern = Regexp.new('.')
-    DiffBuilder.new(this_name, prev_name, pattern).build
+    DiffBuilder.new(this_name, other_name, pattern).build
   end
 
-  def diff_body_html(record, previous, field)
-    return h(record[field]).gsub(/\r?\n/, '<span class="paragraph-mark">¶</span><br>').html_safe if previous.blank?
+  def diff_body_html(record, other, field)
+    if record.blank? || other.blank?
+      diff_record = other.presence || record
+      return h(diff_record[field]).gsub(/\r?\n/, '<span class="paragraph-mark">¶</span><br>').html_safe
+    end
 
     pattern = Regexp.new('(?:<.+?>)|(?:\w+)|(?:[ \t]+)|(?:\r?\n)|(?:.+?)')
-    DiffBuilder.new(record[field], previous[field], pattern).build
+    DiffBuilder.new(record[field], other[field], pattern).build
   end
 
-  def status_diff_html(record)
-    previous = record.previous
+  def status_diff_html(record, type)
+    other = record.send(type)
 
-    return "New" if previous.blank?
+    if other.blank?
+      return type == "previous" ? "New" : ""
+    end
 
     statuses = []
     record.class.status_fields.each do |field, status|
       if record.has_attribute?(field)
-        statuses += [status] if record[field] != previous[field]
+        statuses += [status] if record[field] != other[field]
       else
-        statuses += [status] if record.send(field)
+        statuses += [status] if record.send(field, type)
       end
     end
-    statuses.join("<br>").html_safe
+
+    altered = record.updater_id != other.updater_id
+
+    %(<div class="version-statuses" data-altered="#{altered}">#{statuses.join("<br>")}</div>).html_safe
   end
 
   def wordbreakify(string)
@@ -44,6 +52,18 @@ module ApplicationHelper
     raw(wordbreaked_string)
   end
 
+  def version_type_links(params)
+    html = []
+    %w[previous subsequent current].each do |type|
+      if type == params[:type]
+        html << %(<span>#{type}</span>)
+      else
+        html << tag.li(link_to(type, params.except(:controller, :action).merge(type: type).permit!))
+      end
+    end
+    html.join(" | ").html_safe
+  end
+
   def nav_link_to(text, url, **options)
     klass = options.delete(:class)
 

app/helpers/artist_commentary_versions_helper.rb

@@ -0,0 +1,10 @@
+module ArtistCommentaryVersionsHelper
+  def commentary_version_field_diff(commentary_version, type, field)
+    other = commentary_version.send(params[:type])
+    if type == "previous"
+      diff_body_html(commentary_version, other, field)
+    else
+      diff_body_html(other, commentary_version, field)
+    end
+  end
+end

app/helpers/artist_versions_helper.rb

@@ -1,34 +1,63 @@
 module ArtistVersionsHelper
-  def artist_version_other_names_diff(artist_version)
-    new_names = artist_version.other_names
-    old_names = artist_version.previous.try(:other_names)
-    latest_names = artist_version.artist.other_names
+  def artist_version_other_names_diff(artist_version, type)
+    other = artist_version.send(type)
+    this_names = artist_version.other_names
+    if other.present?
+      other_names = other.other_names
+    elsif type == "subsequent"
+      other_names = this_names
+    else
+      other_names = []
+    end
 
-    diff_list_html(new_names, old_names, latest_names)
+    if type == "previous"
+      diff_list_html(this_names, other_names)
+    else
+      diff_list_html(other_names, this_names)
+    end
   end
 
-  def artist_version_urls_diff(artist_version)
-    new_urls = artist_version.urls
-    old_urls = artist_version.previous.try(:urls)
-    latest_urls = artist_version.artist.urls.map(&:to_s)
+  def artist_version_urls_diff(artist_version, type)
+    other = artist_version.send(type)
+    this_urls = artist_version.urls
+    if other.present?
+      other_urls = other.urls
+    elsif type == "subsequent"
+      other_urls = this_urls
+    else
+      other_urls = []
+    end
 
-    diff_list_html(new_urls, old_urls, latest_urls)
+    if type == "previous"
+      diff_list_html(this_urls, other_urls)
+    else
+      diff_list_html(other_urls, this_urls)
+    end
   end
 
-  def artist_version_name_diff(artist_version)
-    previous = artist_version.previous
-    if previous.present? && (artist_version.name != previous.name)
-      name_diff = diff_name_html(artist_version.name, previous.name)
+  def artist_version_name_diff(artist_version, type)
+    other = artist_version.send(type)
+    if other.present? && (artist_version.name != other.name)
+      if type == "previous"
+        name_diff = diff_name_html(artist_version.name, other.name)
+      else
+        name_diff = diff_name_html(other.name, artist_version.name)
+      end
       %(<br><br><b>Rename:</b><br>&ensp;#{name_diff}</p>).html_safe
     else
       ""
     end
   end
 
-  def artist_version_group_name_diff(artist_version)
-    previous = artist_version.previous
-    if artist_version.group_name.present? || (previous.present? && previous.group_name.present?)
-      group_name_diff = diff_name_html(artist_version.group_name, previous.group_name)
+  def artist_version_group_name_diff(artist_version, type)
+    other = artist_version.send(type)
+    if artist_version.group_name.present? || (other.present? && other.group_name.present?)
+      other_group_name = (other.present? ? other.group_name : artist_version.group_name)
+      if type == "previous"
+        group_name_diff = diff_name_html(artist_version.group_name, other_group_name)
+      else
+        group_name_diff = diff_name_html(other_group_name, artist_version.group_name)
+      end
       %(<b>Group:</b><br>&ensp;#{group_name_diff}<br><br>).html_safe
     else
       ""

app/helpers/note_versions_helper.rb

@@ -1,23 +1,36 @@
 module NoteVersionsHelper
-  def note_version_position_diff(note_version)
-    previous = note_version.previous
+  def note_version_position_diff(note_version, type)
+    other = note_version.send(type)
 
     html = "#{note_version.x},#{note_version.y}"
-    if previous.nil? || (note_version.x == previous.x && note_version.y == previous.y)
+    if other.nil? || (note_version.x == other.x && note_version.y == other.y)
       html
+    elsif type == "previous"
+      "#{other.x},#{other.y} -> " + html
     else
-      "#{previous.x},#{previous.y} -> " + html
+      html + " -> #{other.x},#{other.y}"
     end
   end
 
-  def note_version_size_diff(note_version)
-    previous = note_version.previous
+  def note_version_size_diff(note_version, type)
+    other = note_version.send(type)
 
     html = "#{note_version.width}x#{note_version.height}"
-    if previous.nil? || (note_version.width == previous.width && note_version.height == previous.height)
+    if other.nil? || (note_version.width == other.width && note_version.height == other.height)
       html
+    elsif type == "previous"
+      "#{other.width}x#{other.height} -> " + html
     else
-      "#{previous.width}x#{previous.height}  -> " + html
+      html + " -> #{other.width}x#{other.height}"
+    end
+  end
+
+  def note_version_body_diff(note_version, type)
+    other = note_version.send(params[:type])
+    if type == "previous"
+      diff_body_html(note_version, other, :body)
+    else
+      diff_body_html(other, note_version, :body)
     end
   end
 end

app/helpers/pool_versions_helper.rb

@@ -1,29 +1,38 @@
 module PoolVersionsHelper
-  def pool_version_show_diff(pool_version)
-    previous = pool_version.previous
-    previous.present? && pool_version.description != previous.description
+  def pool_version_show_diff(pool_version, type)
+    other = pool_version.send(type)
+    other.present? && pool_version.description != other.description
   end
 
-  def pool_version_name_diff(pool_version)
-    previous = pool_version.previous
-    if previous.present? && (pool_version.name != previous.name)
-      name_diff = diff_name_html(pool_version.pretty_name, previous.pretty_name)
+  def pool_version_name_diff(pool_version, type)
+    other = pool_version.send(type)
+    if other.present? && (pool_version.name != other.name)
+      if type == "previous"
+        name_diff = diff_name_html(pool_version.name, other.name)
+      else
+        name_diff = diff_name_html(other.name, pool_version.name)
+      end
       %(<br><br><b>Rename:</b><br>&ensp;#{name_diff}</p>).html_safe
     else
       ""
     end
   end
 
-  def pool_version_post_diff(pool_version)
-    previous = pool_version.previous
+  def pool_version_post_diff(pool_version, type)
+    other = pool_version.send(type)
     diff = {}
 
-    if previous.present?
-      diff[:added_post_ids] = pool_version.post_ids - previous.post_ids
-      diff[:removed_post_ids] = previous.post_ids - pool_version.post_ids
-    else
+    if other.present? && type == "previous"
+      diff[:added_post_ids] = pool_version.post_ids - other.post_ids
+      diff[:removed_post_ids] = other.post_ids - pool_version.post_ids
+    elsif other.present?
+      diff[:added_post_ids] = other.post_ids - pool_version.post_ids
+      diff[:removed_post_ids] = pool_version.post_ids - other.post_ids
+    elsif type == "previous"
       diff[:added_post_ids] = pool_version.added_post_ids
       diff[:removed_post_ids] = pool_version.removed_post_ids
+    else
+      return ""
     end
 
     render "pool_versions/diff", diff: diff

app/helpers/post_versions_helper.rb

@@ -1,45 +1,38 @@
 module PostVersionsHelper
-  def post_version_diff(post_version)
-    previous = post_version.previous
-    post = post_version.post
+  def post_version_diff(post_version, type)
+    other = post_version.send(type)
 
-    if post.nil?
-      latest_tags = post_version.tag_array
+    this_tags = post_version.tag_array
+    this_tags << "rating:#{post_version.rating}" if post_version.rating.present?
+    this_tags << "parent:#{post_version.parent_id}" if post_version.parent_id.present?
+    this_tags << "source:#{post_version.source}" if post_version.source.present?
+
+    other_tags = other.present? ? other.tag_array : []
+    if other.present?
+      other_tags << "rating:#{other.rating}" if other.rating.present?
+      other_tags << "parent:#{other.parent_id}" if other.parent_id.present?
+      other_tags << "source:#{other.source}" if other.source.present?
+    elsif type == "subsequent"
+      other_tags = this_tags
+    end
+
+    if type == "previous"
+      added_tags = this_tags - other_tags
+      removed_tags = other_tags - this_tags
     else
-      latest_tags = post.tag_array
-      latest_tags << "rating:#{post.rating}" if post.rating.present?
-      latest_tags << "parent:#{post.parent_id}" if post.parent_id.present?
-      latest_tags << "source:#{post.source}" if post.source.present?
+      added_tags = other_tags - this_tags
+      removed_tags = this_tags - other_tags
     end
-
-    new_tags = post_version.tag_array
-    new_tags << "rating:#{post_version.rating}" if post_version.rating.present?
-    new_tags << "parent:#{post_version.parent_id}" if post_version.parent_id.present?
-    new_tags << "source:#{post_version.source}" if post_version.source.present?
-
-    old_tags = previous.present? ? previous.tag_array : []
-    if previous.present?
-      old_tags << "rating:#{previous.rating}" if previous.rating.present?
-      old_tags << "parent:#{previous.parent_id}" if previous.parent_id.present?
-      old_tags << "source:#{previous.source}" if previous.source.present?
-    end
-
-    added_tags = new_tags - old_tags
-    removed_tags = old_tags - new_tags
-    obsolete_added_tags = added_tags - latest_tags,
-    obsolete_removed_tags = removed_tags & latest_tags,
-    unchanged_tags = new_tags & old_tags
+    unchanged_tags = this_tags & other_tags
 
     html = '<span class="diff-list">'
 
     added_tags.each do |tag|
-      prefix = obsolete_added_tags.include?(tag) ? '+<ins class="obsolete">' : '<ins>+'
-      html << prefix + link_to(wordbreakify(tag), posts_path(:tags => tag)) + '</ins>'
+      html << '<ins>+' + link_to(wordbreakify(tag), posts_path(:tags => tag)) + '</ins>'
       html << " "
     end
     removed_tags.each do |tag|
-      prefix = obsolete_removed_tags.include?(tag) ? '-<del class="obsolete">' : '<del>-'
-      html << prefix + link_to(wordbreakify(tag), posts_path(:tags => tag)) + '</del>'
+      html << '<del>-' + link_to(wordbreakify(tag), posts_path(:tags => tag)) + '</del>'
       html << " "
     end
     unchanged_tags.each do |tag|

app/helpers/wiki_page_versions_helper.rb

@@ -1,25 +1,28 @@
 module WikiPageVersionsHelper
-  def wiki_version_show_diff(wiki_page_version)
-    previous = wiki_page_version.previous
-    previous.present? && ((wiki_page_version.body != previous.body) || wiki_page_version.other_names_changed)
+  def wiki_version_show_diff(wiki_page_version, type)
+    other = wiki_page_version.send(type)
+    other.present? && ((wiki_page_version.body != other.body) || wiki_page_version.other_names_changed(type))
   end
 
-  def wiki_version_show_other_names(new_version, old_version)
-    ((new_version.other_names - old_version.other_names) | (old_version.other_names - new_version.other_names)).length > 0
+  def wiki_version_show_other_names(this_version, other_version)
+    ((this_version.other_names - other_version.other_names) | (other_version.other_names - this_version.other_names)).length.positive?
   end
 
-  def wiki_version_other_names_diff(new_version, old_version)
-    new_names = new_version.other_names
-    old_names = old_version.other_names
-    latest_names = new_version.wiki_page.other_names
+  def wiki_version_other_names_diff(this_version, other_version)
+    this_names = this_version.other_names
+    other_names = other_version.other_names
 
-    diff_list_html(new_names, old_names, latest_names, ul_class: ["wiki-other-names-diff-list list-inline"], li_class: ["wiki-other-name"])
+    diff_list_html(this_names, other_names, ul_class: ["wiki-other-names-diff-list list-inline"], li_class: ["wiki-other-name"])
   end
 
-  def wiki_version_title_diff(wiki_page_version)
-    previous = wiki_page_version.previous
-    if previous.present? && (wiki_page_version.title != previous.title)
-      name_diff = diff_name_html(wiki_page_version.title, previous.title)
+  def wiki_version_title_diff(wiki_page_version, type)
+    other = wiki_page_version.send(type)
+    if other.present? && (wiki_page_version.title != other.title)
+      if type == "previous"
+        name_diff = diff_name_html(wiki_page_version.title, other.title)
+      else
+        name_diff = diff_name_html(other.title, wiki_page_version.title)
+      end
       %((<b>Rename:</b>&ensp;#{name_diff})).html_safe
     else
       ""

app/javascript/src/styles/base/040_colors.css

@@ -88,8 +88,6 @@
 
   --diff-list-added-color: green;
   --diff-list-removed-color: red;
-  --diff-list-obsolete-added-color: darkGreen;
-  --diff-list-obsolete-removed-color: darkRed;
 
   --wiki-page-versions-diff-del-background: #FCC;
   --wiki-page-versions-diff-ins-background: #CFC;
@@ -301,8 +299,6 @@ body[data-current-user-theme="dark"] {
 
   --diff-list-added-color: var(--green-1);
   --diff-list-removed-color: var(--red-1);
-  --diff-list-obsolete-added-color: var(--green-3);
-  --diff-list-obsolete-removed-color: var(--red-3);
 
   --dtext-blockquote-background: var(--grey-3);
   --dtext-blockquote-border: 1px solid var(--grey-4);

app/javascript/src/styles/common/diffs.scss

@@ -5,20 +5,12 @@
     margin-right: 0.5em;
   }
 
-  .added.obsolete, .added.obsolete a {
-    color: var(--diff-list-obsolete-added-color);
-  }
-
   .removed, .removed a {
     color: var(--diff-list-removed-color);
     text-decoration: line-through;
     margin-right: 0.5em;
   }
 
-  .removed.obsolete, .removed.obsolete a {
-    color: var(--diff-list-obsolete-removed-color);
-  }
-
   ins, ins a {
     color: var(--diff-list-added-color);
     text-decoration: none;
@@ -30,14 +22,6 @@
     text-decoration: line-through;
     margin-right: 0.5em;
   }
-
-  ins.obsolete, ins.obsolete a {
-    color: var(--diff-list-obsolete-added-color);
-  }
-
-  del.obsolete, del.obsolete a {
-    color: var(--diff-list-obsolete-removed-color);
-  }
 }
 
 .diff-body {

app/javascript/src/styles/common/versions.scss

@@ -3,7 +3,7 @@ body.a-index {
     display: flex;
 
     table.striped {
-      flex: 1; 
+      flex: 1;
     }
   }
 
@@ -11,3 +11,15 @@ body.a-index {
     margin-top: 2em;
   }
 }
+
+div#version-comparisons {
+  margin-bottom: 1em;
+
+  span {
+    font-weight: bold;
+  }
+
+  ul#version-comparisons-list, ul#version-comparisons-list li {
+    display: inline;
+  }
+}

app/javascript/src/styles/specific/wiki_page_versions.scss

@@ -9,10 +9,6 @@ div#c-wiki-page-versions {
       background: var(--wiki-page-versions-diff-ins-background);
       text-decoration: none;
     }
-
-    ul.wiki-other-names-diff-list li.obsolete {
-      text-decoration: dotted underline;
-    }
   }
 
   #a-index {

app/logical/set_diff.rb

@@ -1,14 +1,12 @@
 class SetDiff
-  attr_reader :additions, :removals, :added, :removed, :obsolete_added, :obsolete_removed, :changed, :unchanged
+  attr_reader :additions, :removals, :added, :removed, :changed, :unchanged
 
-  def initialize(new, old, latest)
-    new, old, latest = new.to_a, old.to_a, latest.to_a
+  def initialize(this_list, other_list)
+    this, other = this_list.to_a, other_list.to_a
 
-    @additions = new - old
-    @removals = old - new
-    @unchanged = new & old
-    @obsolete_added = additions - latest
-    @obsolete_removed = removals & latest
+    @additions = this - other
+    @removals = other - this
+    @unchanged = this & other
     @added, @removed, @changed = changes(additions, removals)
   end
 

app/models/artist_commentary_version.rb

@@ -15,6 +15,20 @@ class ArtistCommentaryVersion < ApplicationRecord
     @previous.first
   end
 
+  def subsequent
+    @subsequent ||= begin
+      ArtistCommentaryVersion.where("post_id = ? and updated_at > ?", post_id, updated_at).order("updated_at asc").limit(1).to_a
+    end
+    @subsequent.first
+  end
+
+  def current
+    @current ||= begin
+      ArtistCommentaryVersion.where("post_id = ?", post_id).order("updated_at desc").limit(1).to_a
+    end
+    @current.first
+  end
+
   def self.status_fields
     {
       original_title: "OrigTitle",

app/models/artist_version.rb

@@ -30,6 +30,20 @@ class ArtistVersion < ApplicationRecord
     @previous.first
   end
 
+  def subsequent
+    @subsequent ||= begin
+      ArtistVersion.where("artist_id = ? and created_at > ?", artist_id, created_at).order("created_at asc").limit(1).to_a
+    end
+    @subsequent.first
+  end
+
+  def current
+    @previous ||= begin
+      ArtistVersion.where("artist_id = ?", artist_id).order("created_at desc").limit(1).to_a
+    end
+    @previous.first
+  end
+
   def self.status_fields
     {
       name: "Renamed",
@@ -43,28 +57,50 @@ class ArtistVersion < ApplicationRecord
     }
   end
 
-  def other_names_changed
-    ((other_names - previous.other_names) | (previous.other_names - other_names)).length > 0
+  def other_names_changed(type)
+    other = self.send(type)
+    ((other_names - other.other_names) | (other.other_names - other_names)).length.positive?
   end
 
-  def urls_changed
-    ((urls - previous.urls) | (previous.urls - urls)).length > 0
+  def urls_changed(type)
+    other = self.send(type)
+    ((urls - other.urls) | (other.urls - urls)).length.positive?
   end
 
-  def was_deleted
-    is_deleted && !previous.is_deleted
+  def was_deleted(type)
+    other = self.send(type)
+    if type == "previous"
+      is_deleted && !other.is_deleted
+    else
+      !is_deleted && other.is_deleted
+    end
   end
 
-  def was_undeleted
-    !is_deleted && previous.is_deleted
+  def was_undeleted(type)
+    other = self.send(type)
+    if type == "previous"
+      !is_deleted && other.is_deleted
+    else
+      is_deleted && !other.is_deleted
+    end
   end
 
-  def was_banned
-    is_banned && !previous.is_banned
+  def was_banned(type)
+    other = self.send(type)
+    if type == "previous"
+      is_banned && !other.is_banned
+    else
+      !is_banned && other.is_banned
+    end
   end
 
-  def was_unbanned
-    !is_banned && previous.is_banned
+  def was_unbanned(type)
+    other = self.send(type)
+    if type == "previous"
+      !is_banned && other.is_banned
+    else
+      is_banned && !other.is_banned
+    end
   end
 
   def self.available_includes

app/models/note_version.rb

@@ -14,11 +14,25 @@ class NoteVersion < ApplicationRecord
 
   def previous
     @previous ||= begin
-      NoteVersion.where("note_id = ? and updated_at < ?", note_id, updated_at).order("updated_at desc").limit(1).to_a
+      NoteVersion.where("note_id = ? and version < ?", note_id, version).order("updated_at desc").limit(1).to_a
     end
     @previous.first
   end
 
+  def subsequent
+    @subsequent ||= begin
+      NoteVersion.where("note_id = ? and version > ?", note_id, version).order("updated_at asc").limit(1).to_a
+    end
+    @subsequent.first
+  end
+
+  def current
+    @current ||= begin
+      NoteVersion.where("note_id = ?", note_id).order("updated_at desc").limit(1).to_a
+    end
+    @current.first
+  end
+
   def self.status_fields
     {
       body: "Body",
@@ -29,20 +43,32 @@ class NoteVersion < ApplicationRecord
     }
   end
 
-  def was_moved
-    x != previous.x || y != previous.y
+  def was_moved(type)
+    other = self.send(type)
+    x != other.x || y != other.y
   end
 
-  def was_resized
-    width != previous.width || height != previous.height
+  def was_resized(type)
+    other = self.send(type)
+    width != other.width || height != other.height
   end
 
-  def was_deleted
-    !is_active && previous.is_active
+  def was_deleted(type)
+    other = self.send(type)
+    if type == "previous"
+      !is_active && other.is_active
+    else
+      is_active && !other.is_active
+    end
   end
 
-  def was_undeleted
-    is_active && !previous.is_active
+  def was_undeleted(type)
+    other = self.send(type)
+    if type == "previous"
+      is_active && !other.is_active
+    else
+      !is_active && other.is_active
+    end
   end
 
   def self.available_includes

app/models/pool_version.rb

@@ -96,6 +96,20 @@ class PoolVersion < ApplicationRecord
     @previous.first
   end
 
+  def subsequent
+    @subsequent ||= begin
+      PoolVersion.where("pool_id = ? and version > ?", pool_id, version).order("version asc").limit(1).to_a
+    end
+    @subsequent.first
+  end
+
+  def current
+    @current ||= begin
+      PoolVersion.where("pool_id = ?", pool_id).order("version desc").limit(1).to_a
+    end
+    @current.first
+  end
+
   def self.status_fields
     {
       posts_changed: "Posts",
@@ -108,24 +122,45 @@ class PoolVersion < ApplicationRecord
     }
   end
 
-  def posts_changed
-    ((post_ids - previous.post_ids) | (previous.post_ids - post_ids)).length > 0
+  def posts_changed(type)
+    other = self.send(type)
+    ((post_ids - other.post_ids) | (other.post_ids - post_ids)).length.positive?
   end
 
-  def was_deleted
-    is_deleted && !previous.is_deleted
+  def was_deleted(type)
+    other = self.send(type)
+    if type == "previous"
+      is_deleted && !other.is_deleted
+    else
+      !is_deleted && other.is_deleted
+    end
   end
 
-  def was_undeleted
-    !is_deleted && previous.is_deleted
+  def was_undeleted(type)
+    other = self.send(type)
+    if type == "previous"
+      !is_deleted && other.is_deleted
+    else
+      is_deleted && !other.is_deleted
+    end
   end
 
-  def was_activated
-    is_active && !previous.is_active
+  def was_activated(type)
+    other = self.send(type)
+    if type == "previous"
+      is_active && !other.is_active
+    else
+      !is_active && other.is_active
+    end
   end
 
-  def was_deactivated
-    !is_active && previous.is_active
+  def was_deactivated(type)
+    other = self.send(type)
+    if type == "previous"
+      !is_active && other.is_active
+    else
+      is_active && !other.is_active
+    end
   end
 
   def pretty_name

app/models/post_version.rb

@@ -99,6 +99,20 @@ class PostVersion < ApplicationRecord
     @previous.first
   end
 
+  def subsequent
+    @subsequent ||= begin
+      PostVersion.where("post_id = ? and version > ?", post_id, version).order("version asc").limit(1).to_a
+    end
+    @subsequent.first
+  end
+
+  def current
+    @current ||= begin
+      PostVersion.where("post_id = ?", post_id).order("version desc").limit(1).to_a
+    end
+    @current.first
+  end
+
   def visible?
     post&.visible?
   end

app/models/wiki_page_version.rb

@@ -30,6 +30,20 @@ class WikiPageVersion < ApplicationRecord
     @previous.first
   end
 
+  def subsequent
+    @subsequent ||= begin
+      WikiPageVersion.where("wiki_page_id = ? and id > ?", wiki_page_id, id).order("id asc").limit(1).to_a
+    end
+    @subsequent.first
+  end
+
+  def current
+    @current ||= begin
+      WikiPageVersion.where("wiki_page_id = ?", wiki_page_id).order("id desc").limit(1).to_a
+    end
+    @current.first
+  end
+
   def self.status_fields
     {
       body: "Body",
@@ -40,16 +54,27 @@ class WikiPageVersion < ApplicationRecord
     }
   end
 
-  def other_names_changed
-    ((other_names - previous.other_names) | (previous.other_names - other_names)).length > 0
+  def other_names_changed(type)
+    other = self.send(type)
+    ((other_names - other.other_names) | (other.other_names - other_names)).length.positive?
   end
 
-  def was_deleted
-    is_deleted && !previous.is_deleted
+  def was_deleted(type)
+    other = self.send(type)
+    if type == "previous"
+      is_deleted && !other.is_deleted
+    else
+      !is_deleted && other.is_deleted
+    end
   end
 
-  def was_undeleted
-    !is_deleted && previous.is_deleted
+  def was_undeleted(type)
+    other = self.send(type)
+    if type == "previous"
+      !is_deleted && other.is_deleted
+    else
+      is_deleted && !other.is_deleted
+    end
   end
 
   def self.available_includes

app/views/application/_diff_list.html.erb

@@ -2,11 +2,11 @@
 
 <%= tag.ul class: [*ul_class] do %>
   <% diff.added.each do |item| %>
-    <%= tag.li item, class: ["added", ("obsolete" if item.in?(diff.obsolete_added)), *li_class] %>
+    <%= tag.li item, class: ["added", *li_class] %>
   <% end %>
 
   <% diff.removed.each do |item| %>
-    <%= tag.li item, class: ["removed", ("obsolete" if item.in?(diff.obsolete_removed)), *li_class] %>
+    <%= tag.li item, class: ["removed", *li_class] %>
   <% end %>
 
   <% diff.changed.each do |old, new| %>

app/views/artist_commentary_versions/_listing.html.erb

@@ -19,13 +19,13 @@
       <% if !commentary_version.unchanged_empty?(:original_title) %>
         <b>Title:</b>
         <div class="commentary-body-section">
-          <%= diff_body_html(commentary_version, commentary_version.previous, :original_title) %>
+          <%= commentary_version_field_diff(commentary_version, params[:type], :original_title) %>
         </div>
       <% end %>
       <% if !commentary_version.unchanged_empty?(:original_description) %>
         <b>Description:</b>
         <div class="commentary-body-section">
-          <%= diff_body_html(commentary_version, commentary_version.previous, :original_description) %>
+          <%= commentary_version_field_diff(commentary_version, params[:type], :original_description) %>
         </div>
       <% end %>
     <% end %>
@@ -33,18 +33,18 @@
       <% if !commentary_version.unchanged_empty?(:translated_title) %>
         <b>Title:</b>
         <div class="commentary-body-section">
-          <%= diff_body_html(commentary_version, commentary_version.previous, :translated_title) %>
+          <%= commentary_version_field_diff(commentary_version, params[:type], :translated_title) %>
         </div>
       <% end %>
       <% if !commentary_version.unchanged_empty?(:translated_description) %>
         <b>Description:</b>
         <div class="commentary-body-section">
-          <%= diff_body_html(commentary_version, commentary_version.previous, :translated_description) %>
+          <%= commentary_version_field_diff(commentary_version, params[:type], :translated_description) %>
         </div>
       <% end %>
     <% end %>
     <% t.column "Changes", width: "3%" do |commentary_version| %>
-      <%= status_diff_html(commentary_version) %>
+      <%= status_diff_html(commentary_version, params[:type]) %>
     <% end %>
     <% t.column "Updated", width: "10%" do |commentary_version| %>
       <div>

app/views/artist_commentary_versions/index.html.erb

@@ -2,6 +2,8 @@
   <div id="a-index">
     <h1>Artist Commentary History</h1>
 
+    <%= render "versions/types" %>
+
     <%= render "posts/partials/common/inline_blacklist" %>
 
     <%= render "listing" %>

app/views/artist_versions/_listing.html.erb

@@ -4,17 +4,17 @@
       <% t.column "Name", td: {class: "diff-body"} do |artist_version| %>
         <%= link_to artist_version.name, artist_path(artist_version.artist_id) %>
         <%= link_to "»", artist_versions_path(search: {artist_id: artist_version.artist_id}, anchor: "artist-version-#{artist_version.id}") %>
-        <%= artist_version_name_diff(artist_version) %>
+        <%= artist_version_name_diff(artist_version, params[:type]) %>
       <% end %>
       <% t.column "Other Names", td: {class: "diff-body"} do |artist_version| %>
-        <%= artist_version_group_name_diff(artist_version) %>
-        <%= artist_version_other_names_diff(artist_version) %>
+        <%= artist_version_group_name_diff(artist_version, params[:type]) %>
+        <%= artist_version_other_names_diff(artist_version, params[:type]) %>
       <% end %>
       <% t.column "URLs", td: {class: "col-expand"} do |artist_version| %>
-        <%= artist_version_urls_diff(artist_version) %>
+        <%= artist_version_urls_diff(artist_version, params[:type]) %>
       <% end %>
       <% t.column "Changes" do |artist_version| %>
-        <%= status_diff_html(artist_version) %>
+        <%= status_diff_html(artist_version, params[:type]) %>
       <% end %>
       <% t.column "Updated" do |artist_version| %>
         <%= link_to_user artist_version.updater %>

app/views/artist_versions/index.html.erb

@@ -2,6 +2,8 @@
   <div id="a-index">
     <h1>Artist History</h1>
 
+    <%= render "versions/types" %>
+
     <%= render "listing" %>
 
     <%= numbered_paginator(@artist_versions, :search_count => params[:search]) %>

app/views/note_versions/_listing.html.erb

@@ -14,16 +14,16 @@
         <% end %>
       <% end %>
       <% t.column "Body", td: {class: "col-expand diff-body"} do |note_version| %>
-        <%= diff_body_html(note_version, note_version.previous, :body) %>
+        <%= note_version_body_diff(note_version, params[:type]) %>
       <% end %>
       <% t.column "Position (X,Y)", width: "5%", column: "position" do |note_version| %>
-        <%= note_version_position_diff(note_version) %>
+        <%= note_version_position_diff(note_version, params[:type]) %>
       <% end %>
       <% t.column "Size (WxH)", width: "5%", column: "size"  do |note_version| %>
-        <%= note_version_size_diff(note_version) %>
+        <%= note_version_size_diff(note_version, params[:type]) %>
       <% end %>
       <% t.column "Changes", width: "3%" do |note_version| %>
-        <%= status_diff_html(note_version) %>
+        <%= status_diff_html(note_version, params[:type]) %>
       <% end %>
       <% t.column "Updated", width: "10%" do |note_version| %>
         <div>

app/views/note_versions/index.html.erb

@@ -2,6 +2,8 @@
   <div id="a-index">
     <h1>Note History</h1>
 
+    <%= render "versions/types" %>
+
     <%= render "listing" %>
 
     <%= numbered_paginator(@note_versions) %>

app/views/pool_versions/_listing.html.erb

@@ -2,21 +2,21 @@
 
     <%= table_for @pool_versions, {class: "striped autofit", width: "100%"} do |t| %>
       <% t.column column: "diff", width: "3%" do |pool_version| %>
-        <%= link_to_if pool_version_show_diff(pool_version), "diff", diff_pool_version_path(pool_version.id) %>
+        <%= link_to_if pool_version_show_diff(pool_version, params[:type]), "diff", diff_pool_version_path(pool_version.id) %>
       <% end %>
       <% t.column "Pool", td: {class: "diff-body"} do |pool_version| %>
         <%= link_to pool_version.pretty_name, pool_path(pool_version.pool_id), class: "pool-category-#{pool_version.pool.category}" %>
         <%= link_to "»", pool_versions_path(search: { pool_id: pool_version.pool_id }, anchor: "pool-version-#{pool_version.id}"), class: "pool-category-#{pool_version.pool.category}" %>
-        <%= pool_version_name_diff(pool_version) %>
+        <%= pool_version_name_diff(pool_version, params[:type]) %>
       <% end %>
       <% t.column "Post Changes", td: { class: "col-expand" } do |pool_version| %>
-        <%= pool_version_post_diff(pool_version) %>
+        <%= pool_version_post_diff(pool_version, params[:type]) %>
       <% end %>
       <% t.column "Post Count" do |pool_version| %>
         <%= link_to pool_version.post_ids.size, pool_versions_path(search: { pool_id: pool_version.pool_id }) %>
       <% end %>
       <% t.column "Changes", td: {class: "col-expand"} do |pool_version| %>
-        <%= status_diff_html(pool_version) %>
+        <%= status_diff_html(pool_version, params[:type]) %>
       <% end %>
       <% t.column "Updated", width: "10%" do |pool_version| %>
         <div>

app/views/pool_versions/diff.html.erb

@@ -3,18 +3,26 @@
 
 <div id="c-pool-versions">
   <div id="a-diff">
-    <h1>Pool Version Comparison: <%= link_to @pool_version.pretty_name, pool_versions_path(search: { pool_id: @pool_version.pool_id }, anchor: "pool-version-#{@pool_version.id}"), class: "pool-category-#{@pool_version.pool.category}" %></h1>
+    <h1>Pool Version Comparison: <%= link_to @pool_version.pretty_name, pool_versions_path(search: { pool_id: @pool_version.pool_id }, type: params[:type], anchor: "pool-version-#{@pool_version.id}"), class: "pool-category-#{@pool_version.pool.category}" %></h1>
+
+    <%= render "versions/types" %>
 
     <% if @other_version.present? %>
-      <p>Showing differences between <%= compact_time @pool_version.updated_at %> (<%= link_to_user @pool_version.updater %>) and <%= compact_time @other_version.updated_at %> (<%= link_to_user @other_version.updater %>)</p>
+      <% if @pool_version.id != @other_version.id %>
+        <p>Showing differences between <%= compact_time @pool_version.updated_at %> (<%= link_to_user @pool_version.updater %>) and <%= compact_time @other_version.updated_at %> (<%= link_to_user @other_version.updater %>)</p>
 
-      <% if @pool_version.description != @other_version.description %>
-        <div class="diff-body">
-            <%= diff_body_html(@pool_version, @other_version, :description) %>
-        </div>
+        <% if @pool_version.description != @other_version.description %>
+          <div class="diff-body">
+              <%= diff_body_html(@pool_version, @other_version, :description) %>
+          </div>
+        <% else %>
+          <p><em>No changes to description.</em></p>
+        <% end %>
       <% else %>
-        <p><em>No changes to description.</em></p>
+        <p><em>Version is latest!</em></p>
       <% end %>
+    <% else %>
+      <p><em>No versions to compare!</em></p>
     <% end %>
   </div>
 </div>

app/views/pool_versions/index.html.erb

@@ -2,6 +2,8 @@
   <div id="a-index">
     <h1>Pool History</h1>
 
+    <%= render "versions/types" %>
+
     <%= render "listing" %>
 
     <%= numbered_paginator(@pool_versions) %>

app/views/post_versions/_listing.html.erb

@@ -18,10 +18,10 @@
         <%= link_to "#{post_version.post_id}.#{post_version.version}", post_versions_path(search: { post_id: post_version.post_id }, anchor: "post-version-#{post_version.id}") %>
       <% end %>
       <% t.column "Tags", td: {class: "col-expand"} do |post_version| %>
-        <%= post_version_diff(post_version) %>
+        <%= post_version_diff(post_version, params[:type]) %>
       <% end %>
       <% t.column "Changes" do |post_version| %>
-        <%= status_diff_html(post_version) %>
+        <%= status_diff_html(post_version, params[:type]) %>
       <% end %>
       <% t.column "Updated" do |post_version| %>
         <%= link_to_user post_version.updater %>

app/views/post_versions/index.html.erb

@@ -6,6 +6,8 @@
       <h1>Post History</h1>
     <% end %>
 
+    <%= render "versions/types" %>
+
     <%= search_form_for(post_versions_path, classes: "inline-form") do |f| %>
       <%= f.input :post_id, label: "Post", input_html: { value: params.dig(:search, :post_id) } %>
       <%= f.input :updater_name, label: "Updater", input_html: { "data-autocomplete": "user", value: params.dig(:search, :updater_name) } %>

app/views/versions/_types.html.erb

@@ -0,0 +1,6 @@
+<div id="version-comparisons">
+  <span>Version comparison:</span>
+  <ul id="version-comparisons-list">
+    <%= version_type_links(params) %>
+  </ul>
+</div>

app/views/wiki_page_versions/_listing.html.erb

@@ -2,7 +2,7 @@
   <%= form_tag(diff_wiki_page_versions_path, :method => :get) do %>
     <%= table_for @wiki_page_versions.includes(:updater, :tag), width: "100%" do |t| %>
       <% t.column column: "diff", width: "3%" do |wiki_page_version, i| %>
-        <%= link_to_if wiki_version_show_diff(wiki_page_version), "diff", diff_wiki_page_versions_path(otherpage: wiki_page_version.previous.try(:id), thispage: wiki_page_version.id) %>
+        <%= link_to_if wiki_version_show_diff(wiki_page_version, params[:type]), "diff", diff_wiki_page_versions_path(thispage: wiki_page_version.id, type: params[:type]) %>
       <% end %>
 
       <% if listing_type(:wiki_page_id, member_check: false, types: [:page, :global]) == :page %>
@@ -20,10 +20,10 @@
           <%= link_to wiki_page_version.title, wiki_page_version %>
           <%= link_to "»", wiki_page_versions_path(search: { wiki_page_id: wiki_page_version.wiki_page_id }) %>
         </span>
-        <%= wiki_version_title_diff(wiki_page_version) %>
+        <%= wiki_version_title_diff(wiki_page_version, params[:type]) %>
       <% end %>
       <% t.column "Changes", width: "5%" do |wiki_page_version| %>
-        <%= status_diff_html(wiki_page_version) %>
+        <%= status_diff_html(wiki_page_version, params[:type]) %>
       <% end %>
       <% t.column "Updated", width: "26%" do |wiki_page_version| %>
         <%= compact_time(wiki_page_version.updated_at) %>

app/views/wiki_page_versions/diff.html.erb

@@ -4,21 +4,33 @@
 <%= render "wiki_pages/sidebar" %>
 
 <% content_for(:content) do %>
-  <h1>Wiki Page Version Comparison:  <%= link_to @thispage.title, wiki_page_versions_path(search: { wiki_page_id: @thispage.wiki_page_id }, anchor: "wiki-page-version-#{@thispage.id}"), class: "tag-type-#{@thispage.wiki_page.category_name}" %></h1>
+  <h1>Wiki Page Version Comparison:  <%= link_to @thispage.title, wiki_page_versions_path(search: { wiki_page_id: @thispage.wiki_page_id }, type: params[:type], anchor: "wiki-page-version-#{@thispage.id}"), class: "tag-type-#{@thispage.wiki_page.category_name}" %></h1>
 
-  <p>Showing differences between <%= compact_time @thispage.updated_at %> (<%= link_to_user @thispage.updater %>) and <%= compact_time @otherpage.updated_at %> (<%= link_to_user @otherpage.updater %>)</p>
-
-  <% if wiki_version_show_other_names(@thispage, @otherpage) %>
-    <p><%= wiki_version_other_names_diff(@thispage, @otherpage) %></p>
-  <% else %>
-    <p><em>No changes to other names.</em></p>
+  <% if params[:type].present? %>
+    <%= render "versions/types" %>
   <% end %>
 
-  <% if @thispage.body != @otherpage.body %>
-    <div class="diff-body">
-      <%= diff_body_html(@thispage, @otherpage, :body) %>
-    </div>
+  <% if @otherpage.present? %>
+    <% if @thispage.id != @otherpage.id %>
+      <p>Showing differences between <%= compact_time @thispage.updated_at %> (<%= link_to_user @thispage.updater %>) and <%= compact_time @otherpage.updated_at %> (<%= link_to_user @otherpage.updater %>)</p>
+
+      <% if wiki_version_show_other_names(@thispage, @otherpage) %>
+        <p><%= wiki_version_other_names_diff(@thispage, @otherpage) %></p>
+      <% else %>
+        <p><em>No changes to other names.</em></p>
+      <% end %>
+
+      <% if @thispage.body != @otherpage.body %>
+        <div class="diff-body">
+          <%= diff_body_html(@thispage, @otherpage, :body) %>
+        </div>
+      <% else %>
+        <p><em>No changes to body.</em></p>
+      <% end %>
+    <% else %>
+      <p><em>Version is latest!</em></p>
+    <% end %>
   <% else %>
-    <p><em>No changes to body.</em></p>
+    <p><em>No versions to compare!</em></p>
   <% end %>
 <% end %>

app/views/wiki_page_versions/index.html.erb

@@ -3,6 +3,8 @@
 <% content_for(:content) do %>
   <h1>Wiki Page History</h1>
 
+  <%= render "versions/types" %>
+
   <%= render "listing" %>
 
   <%= numbered_paginator(@wiki_page_versions) %>