tags: add /tag_versions page.

app/controllers/tag_versions_controller.rb

@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+
+class TagVersionsController < ApplicationController
+  respond_to :html, :xml, :json
+
+  def index
+    tag_id = params[:tag_id] || params[:search][:tag_id]
+    tag_name = params[:search][:name_matches]
+    updater_id = params[:updater_id] || params[:search][:updater_id]
+    updater_name = params[:search][:updater_name]
+
+    @tag = Tag.find(tag_id) if tag_id
+    @tag = Tag.find_by_name(tag_name) if tag_name
+    @updater = User.find(updater_id) if updater_id
+    @updater = User.find_by_name(updater_name) if updater_name
+
+    if request.format.html?
+      @tag_versions = authorize TagVersion.visible(CurrentUser.user).paginated_search(params, defaults: { tag_id: @tag&.id, updater_id: @updater&.id, order: "updated_at" }, count_pages: true)
+      @tag_versions = @tag_versions.includes(:tag, :updater, :previous_version)
+    else
+      @tag_versions = authorize TagVersion.visible(CurrentUser.user).paginated_search(params, defaults: { tag_id: @tag&.id, updater_id: @updater&.id })
+    end
+
+    respond_with(@tag_versions)
+  end
+
+  def show
+    @tag_version = authorize TagVersion.find(params[:id])
+
+    respond_with(@tag_version) do |format|
+      format.html { redirect_to tag_versions_path(search: { id: @tag_version.id }) }
+    end
+  end
+end

app/helpers/application_helper.rb

@@ -198,8 +198,8 @@ module ApplicationHelper
     link_to ip_addr.to_s, ip_addresses_path(search: { ip_addr: ip, group_by: "user" }), **options
   end
 
-  def link_to_search(search)
-    link_to search, posts_path(tags: search)
+  def link_to_search(tag, **options)
+    link_to tag.name, posts_path(tags: tag.name), class: tag_class(tag), **options
   end
 
   def link_to_wiki(text, title = text, **options)

app/logical/concerns/version_for.rb

@@ -78,6 +78,11 @@ module VersionFor
     previous_version.nil?
   end
 
+  # True if this version was updated after it was created (it was a merged edit).
+  def revised?
+    updated_at > created_at
+  end
+
   # Return a hash of changes made by this edit (compared to the previous version, or to another version).
   #
   # The hash looks like `{ attr => [old_value, new_value] }`.

app/models/tag_version.rb

@@ -4,4 +4,39 @@ class TagVersion < ApplicationRecord
   include VersionFor
 
   version_for :tag
+
+  def self.name_matches(name)
+    where_like(:name, Tag.normalize_name(name))
+  end
+
+  def self.search(params)
+    q = search_attributes(params, :id, :created_at, :updated_at, :version, :name, :category, :is_deprecated, :tag, :updater, :previous_version)
+
+    if params[:name_matches].present?
+      q = q.name_matches(params[:name_matches])
+    end
+
+    case params[:order]
+    when "created_at", "created_at_desc"
+      q = q.order(created_at: :desc, id: :desc)
+    when "created_at_asc"
+      q = q.order(created_at: :asc, id: :asc)
+    when "updated_at", "updated_at_desc"
+      q = q.order(updated_at: :desc, id: :desc)
+    when "updated_at_asc"
+      q = q.order(updated_at: :asc, id: :asc)
+    when "id", "id_desc"
+      q = q.order(id: :desc)
+    when "id_asc"
+      q = q.order(id: :asc)
+    else
+      q = q.apply_default_order(params)
+    end
+
+    q
+  end
+
+  def category_name
+    TagCategory.reverse_mapping[category].capitalize
+  end
 end

app/policies/tag_version_policy.rb

@@ -0,0 +1,4 @@
+# frozen_string_literal: true
+
+class TagVersionPolicy < ApplicationPolicy
+end

app/views/static/site_map.html.erb

@@ -48,9 +48,10 @@
         <li><h2>Tags</h2></li>
         <li><%= link_to_wiki "Help", "help:tags" %></li>
         <li><%= link_to_wiki "Cheat sheet", "help:cheatsheet" %></li>
+        <li><%= link_to("Listing", tags_path) %></li>
+        <li><%= link_to("History", tag_versions_path) %></li>
         <li><%= link_to("Aliases", tag_aliases_path) %></li>
         <li><%= link_to("Implications", tag_implications_path) %></li>
-        <li><%= link_to("Listing", tags_path) %></li>
         <li><%= link_to("AI Tags", ai_tags_path) %></li>
         <li><%= link_to("Related Tags", related_tag_path) %></li>
       </ul>

app/views/tag_versions/index.html.erb

@@ -0,0 +1,79 @@
+<div id="c-tag-versions">
+  <div id="a-index">
+    <% if @tag %>
+      <h1>Tag History: <%= link_to_search @tag %></h1>
+      <%= link_to "« Back", tag_versions_path, class: "text-xs" %>
+    <% elsif @updater %>
+      <h1>Tag History: <%= link_to_user @updater %></h1>
+      <%= link_to "« Back", tag_versions_path, class: "text-xs" %>
+    <% else %>
+      <h1>Tag History</h1>
+    <% end %>
+
+    <%= search_form_for(tag_versions_path) do |f| %>
+      <%= f.input :name_matches, label: "Tag", input_html: { value: @tag&.name, "data-autocomplete": "tag" } %>
+      <%= f.input :updater_name, label: "User", input_html: { value: @updater&.name, "data-autocomplete": "user" } %>
+      <%= f.input :order, collection: [%w[Newest updated_at], %w[Oldest updated_at_asc]], include_blank: true, selected: params[:search][:order] %>
+      <%= f.submit "Search" %>
+    <% end %>
+
+    <div id="p-<%= listing_type(:tag_id, :updater_id) %>-listing" class="mt-4">
+      <%= table_for @tag_versions, class: "striped autofit", width: "100%" do |t| %>
+        <% t.column "Tag" do |tag_version| %>
+          <span class="<%= tag_class(tag_version) %>">
+            <%= link_to_wiki "?", tag_version.tag.name %>
+            <%= link_to tag_version.tag.name, posts_path(tags: tag_version.tag.name) %>
+            <%= link_to "»", tag_versions_path(search: { tag_id: tag_version.tag_id }) %>
+          </span>
+        <% end %>
+
+        <% t.column "Change", td: { class: "col-expand" } do |tag_version| %>
+          <% if tag_version.first_version? && tag_version.created_at - tag_version.tag.created_at < 1.minute %>
+            Anonymous created <%= link_to_search tag_version %>.
+          <% elsif tag_version.first_version? %>
+            Anonymous updated <%= link_to_search tag_version %>.
+          <% else %>
+            <% if !tag_version.previous_version.is_deprecated? && tag_version.is_deprecated? %>
+              <%= link_to_user tag_version.updater %> deprecated <%= link_to_search tag_version %>.
+            <% elsif tag_version.previous_version.is_deprecated? && !tag_version.is_deprecated? %>
+              <%= link_to_user tag_version.updater %> undeprecated <%= link_to_search tag_version %>.
+            <% end %>
+
+            <% if tag_version.previous_version.category != tag_version.category %>
+              <%= link_to_user tag_version.updater %> changed <%= link_to_search tag_version %> from <%= tag_version.previous_version.category_name.downcase %> to <%= tag_version.category_name.downcase %>.
+            <% end %>
+          <% end %>
+        <% end %>
+
+        <% t.column "Date" do |tag_version| %>
+          <%= time_ago_in_words_tagged(tag_version.updated_at) %>
+        <% end %>
+
+        <% t.column "User" do |tag_version| %>
+          <%= link_to_user tag_version.updater %>
+          <%= link_to "»", tag_versions_path(search: { **search_params, updater_id: tag_version.updater_id }) %>
+        <% end %>
+
+        <% t.column column: "control" do |tag_version| %>
+          <%= render PopupMenuComponent.new do |menu| %>
+            <% if policy(tag_version.tag).update? %>
+              <% menu.item do %>
+                <%= link_to "Edit tag", edit_tag_path(tag_version.tag) %>
+              <% end %>
+            <% end %>
+
+            <% unless @tag %>
+              <% menu.item do %>
+                <%= link_to "Tag history", tag_versions_path(search: { tag_id: tag_version.tag_id }) %>
+              <% end %>
+            <% end %>
+          <% end %>
+        <% end %>
+      <% end %>
+    </div>
+
+    <%= numbered_paginator(@tag_versions) %>
+  </div>
+</div>
+
+<%= render "tags/secondary_links" %>

app/views/tags/_secondary_links.html.erb

@@ -1,6 +1,7 @@
 <% content_for(:secondary_links) do %>
   <%= quick_search_form_for(:name_matches, tags_path, "tags", autocomplete: "tag") %>
   <%= subnav_link_to "Tags", tags_path %>
+  <%= subnav_link_to "History", tag_versions_path %>
   <%= subnav_link_to("Aliases", tag_aliases_path) %>
   <%= subnav_link_to("Implications", tag_implications_path) %>
   <%= subnav_link_to "Request alias/implication", new_bulk_update_request_path %>

app/views/wiki_pages/_sidebar.html.erb

@@ -7,7 +7,8 @@
 
     <ul>
       <% unless @wiki_page.is_meta_wiki? %>
-        <li><%= link_to "Tag History", post_versions_path(search: { changed_tags: @wiki_page.title }) %></li>
+        <li><%= link_to "Tag History", tag_versions_path(search: { tag_id: @wiki_page.tag.id }) %></li>
+        <li><%= link_to "Post History", post_versions_path(search: { changed_tags: @wiki_page.title }) %></li>
       <% end %>
       <li><%= link_to "Wiki History", wiki_page_versions_path(search: { wiki_page_id: @wiki_page.id }) %></li>
       <% if Danbooru.config.forum_enabled?.to_s.truthy? %>

config/routes.rb

@@ -251,6 +251,7 @@ Rails.application.routes.draw do
   resources :tags
   resources :tag_aliases, only: [:show, :index, :destroy]
   resources :tag_implications, only: [:show, :index, :destroy]
+  resources :tag_versions, only: [:index, :show]
 
   get "/redeem", to: "upgrade_codes#redeem", as: "redeem_upgrade_codes"
   resources :upgrade_codes, only: [:create, :index] do

test/functional/tag_versions_controller_test.rb

@@ -0,0 +1,53 @@
+require 'test_helper'
+
+class TagVersionsControllerTest < ActionDispatch::IntegrationTest
+  context "The tag versions controller" do
+    context "index action" do
+      setup do
+        @user = create(:user)
+        @tag = create(:tag, name: "test", created_at: 6.months.ago, updated_at: 3.months.ago)
+        travel_to(4.hours.ago) { @tag.update!(category: Tag.categories.character, updater: @user) }
+        travel_to(3.hours.ago) { @tag.update!(is_deprecated: true, updater: @user) }
+        travel_to(2.hours.ago) { @tag.update!(is_deprecated: false, updater: @user) }
+      end
+
+      should "render" do
+        get tag_versions_path
+        assert_response :success
+      end
+
+      should "render for a tag" do
+        get tag_versions_path(search: { name_matches: @tag.name })
+        assert_response :success
+      end
+
+      should "render for a user" do
+        get tag_versions_path(search: { updater_id: @user.id })
+        assert_response :success
+      end
+
+      should "render for a json response" do
+        get tag_versions_path, as: :json
+        assert_response :success
+      end
+    end
+
+    context "show action" do
+      setup do
+        @user = create(:user)
+        @tag = create(:tag)
+        @tag.update!(category: Tag.categories.character, updater: @user)
+      end
+
+      should "render" do
+        get tag_version_path(@tag.versions.last)
+        assert_redirected_to tag_versions_path(search: { id: @tag.versions.last.id })
+      end
+
+      should "render for a json response" do
+        get tag_version_path(@tag.versions.last), as: :json
+        assert_response :success
+      end
+    end
+  end
+end