Change admin UI for hashtags and add back whitelisted trends (#11490)

Fix #271

Add back the `GET /api/v1/trends` API with the caveat that it does
not return tags that have not been allowed to trend by the staff.

When a hashtag begins to trend (internally) and that hashtag has
not been previously reviewed by the staff, the staff is notified.

The new admin UI for hashtags allows filtering hashtags by where
they are used (e.g. in the profile directory), whether they have
been reviewed or are pending reviewal, they show by how many people
the hashtag is used in the directory, how many people used it
today, how many statuses with it have been created today, and it
allows fixing the name of the hashtag to make it more readable.

The disallowed hashtags feature has been reworked. It is now
controlled from the admin UI for hashtags instead of from
the file `config/settings.yml`

28 files changed, 258 insertions, 173 deletions

diff --git a/app/controllers/admin/dashboard_controller.rb b/app/controllers/admin/dashboard_controller.rb
index e74e4755f..70afdedd7 100644
--- a/app/controllers/admin/dashboard_controller.rb
+++ b/app/controllers/admin/dashboard_controller.rb
@@ -27,7 +27,7 @@ module Admin
       @saml_enabled          = ENV['SAML_ENABLED'] == 'true'
       @pam_enabled           = ENV['PAM_ENABLED'] == 'true'
       @hidden_service        = ENV['ALLOW_ACCESS_TO_HIDDEN_SERVICE'] == 'true'
-      @trending_hashtags     = TrendingTags.get(7)
+      @trending_hashtags     = TrendingTags.get(10, filtered: false)
       @profile_directory     = Setting.profile_directory
       @timeline_preview      = Setting.timeline_preview
       @spam_check_enabled    = Setting.spam_check_enabled
diff --git a/app/controllers/admin/tags_controller.rb b/app/controllers/admin/tags_controller.rb
index e9f4f2cfa..0e9dda302 100644
--- a/app/controllers/admin/tags_controller.rb
+++ b/app/controllers/admin/tags_controller.rb
@@ -4,41 +4,49 @@ module Admin
   class TagsController < BaseController
     before_action :set_tags, only: :index
     before_action :set_tag, except: :index
-    before_action :set_filter_params
 
     def index
       authorize :tag, :index?
     end
 
-    def hide
-      authorize @tag, :hide?
-      @tag.account_tag_stat.update!(hidden: true)
-      redirect_to admin_tags_path(@filter_params)
+    def show
+      authorize @tag, :show?
     end
 
-    def unhide
-      authorize @tag, :unhide?
-      @tag.account_tag_stat.update!(hidden: false)
-      redirect_to admin_tags_path(@filter_params)
+    def update
+      authorize @tag, :update?
+
+      if @tag.update(tag_params.merge(reviewed_at: Time.now.utc))
+        redirect_to admin_tag_path(@tag.id)
+      else
+        render :show
+      end
     end
 
     private
 
     def set_tags
-      @tags = Tag.discoverable
-      @tags.merge!(Tag.hidden) if filter_params[:hidden]
+      @tags = filtered_tags.page(params[:page])
     end
 
     def set_tag
       @tag = Tag.find(params[:id])
     end
 
-    def set_filter_params
-      @filter_params = filter_params.to_hash.symbolize_keys
+    def filtered_tags
+      scope = Tag
+      scope = scope.discoverable if filter_params[:context] == 'directory'
+      scope = scope.reviewed if filter_params[:review] == 'reviewed'
+      scope = scope.pending_review if filter_params[:review] == 'pending_review'
+      scope.reorder(score: :desc)
     end
 
     def filter_params
-      params.permit(:hidden)
+      params.slice(:context, :review).permit(:context, :review)
+    end
+
+    def tag_params
+      params.require(:tag).permit(:name, :trendable, :usable, :listable)
     end
   end
 end
diff --git a/app/controllers/api/v1/trends_controller.rb b/app/controllers/api/v1/trends_controller.rb
new file mode 100644
index 000000000..bcea9857e
--- /dev/null
+++ b/app/controllers/api/v1/trends_controller.rb
@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+class Api::V1::TrendsController < Api::BaseController
+  before_action :set_tags
+
+  respond_to :json
+
+  def index
+    render json: @tags, each_serializer: REST::TagSerializer
+  end
+
+  private
+
+  def set_tags
+    @tags = TrendingTags.get(limit_param(10))
+  end
+end
diff --git a/app/controllers/settings/preferences_controller.rb b/app/controllers/settings/preferences_controller.rb
index 742c97cdb..d548072a8 100644
--- a/app/controllers/settings/preferences_controller.rb
+++ b/app/controllers/settings/preferences_controller.rb
@@ -56,7 +56,7 @@ class Settings::PreferencesController < Settings::BaseController
       :setting_advanced_layout,
       :setting_use_blurhash,
       :setting_use_pending_items,
-      notification_emails: %i(follow follow_request reblog favourite mention digest report pending_account),
+      notification_emails: %i(follow follow_request reblog favourite mention digest report pending_account trending_tag),
       interactions: %i(must_be_follower must_be_following must_be_following_dm)
     )
   end
diff --git a/app/helpers/admin/filter_helper.rb b/app/helpers/admin/filter_helper.rb
index 0bda25974..506429e10 100644
--- a/app/helpers/admin/filter_helper.rb
+++ b/app/helpers/admin/filter_helper.rb
@@ -5,15 +5,16 @@ module Admin::FilterHelper
   REPORT_FILTERS       = %i(resolved account_id target_account_id).freeze
   INVITE_FILTER        = %i(available expired).freeze
   CUSTOM_EMOJI_FILTERS = %i(local remote by_domain shortcode).freeze
-  TAGS_FILTERS         = %i(hidden).freeze
+  TAGS_FILTERS         = %i(context review).freeze
   INSTANCES_FILTERS    = %i(limited by_domain).freeze
   FOLLOWERS_FILTERS    = %i(relationship status by_domain activity order).freeze
 
   FILTERS = ACCOUNT_FILTERS + REPORT_FILTERS + INVITE_FILTER + CUSTOM_EMOJI_FILTERS + TAGS_FILTERS + INSTANCES_FILTERS + FOLLOWERS_FILTERS
 
   def filter_link_to(text, link_to_params, link_class_params = link_to_params)
-    new_url = filtered_url_for(link_to_params)
+    new_url   = filtered_url_for(link_to_params)
     new_class = filtered_url_for(link_class_params)
+
     link_to text, new_url, class: filter_link_class(new_class)
   end
 
diff --git a/app/mailers/admin_mailer.rb b/app/mailers/admin_mailer.rb
index 9ab3e2bbd..8abce5f05 100644
--- a/app/mailers/admin_mailer.rb
+++ b/app/mailers/admin_mailer.rb
@@ -24,4 +24,14 @@ class AdminMailer < ApplicationMailer
       mail to: @me.user_email, subject: I18n.t('admin_mailer.new_pending_account.subject', instance: @instance, username: @account.username)
     end
   end
+
+  def new_trending_tag(recipient, tag)
+    @tag      = tag
+    @me       = recipient
+    @instance = Rails.configuration.x.local_domain
+
+    locale_for_account(@me) do
+      mail to: @me.user_email, subject: I18n.t('admin_mailer.new_trending_tag.subject', instance: @instance, name: @tag.name)
+    end
+  end
 end
diff --git a/app/models/application_record.rb b/app/models/application_record.rb
index 83134d41a..c1b873da6 100644
--- a/app/models/application_record.rb
+++ b/app/models/application_record.rb
@@ -2,5 +2,16 @@
 
 class ApplicationRecord < ActiveRecord::Base
   self.abstract_class = true
+
   include Remotable
+
+  def boolean_with_default(key, default_value)
+    value = attributes[key]
+
+    if value.nil?
+      default_value
+    else
+      value
+    end
+  end
 end
diff --git a/app/models/tag.rb b/app/models/tag.rb
index c7f0af86d..6a02581fa 100644
--- a/app/models/tag.rb
+++ b/app/models/tag.rb
@@ -3,11 +3,16 @@
 #
 # Table name: tags
 #
-#  id         :bigint(8)        not null, primary key
-#  name       :string           default(""), not null
-#  created_at :datetime         not null
-#  updated_at :datetime         not null
-#  score      :integer
+#  id                  :bigint(8)        not null, primary key
+#  name                :string           default(""), not null
+#  created_at          :datetime         not null
+#  updated_at          :datetime         not null
+#  score               :integer
+#  usable              :boolean
+#  trendable           :boolean
+#  listable            :boolean
+#  reviewed_at         :datetime
+#  requested_review_at :datetime
 #
 
 class Tag < ApplicationRecord
@@ -22,16 +27,17 @@ class Tag < ApplicationRecord
   HASHTAG_RE = /(?:^|[^\/\)\w])#(#{HASHTAG_NAME_RE})/i
 
   validates :name, presence: true, format: { with: /\A(#{HASHTAG_NAME_RE})\z/i }
+  validate :validate_name_change, if: -> { !new_record? && name_changed? }
 
-  scope :discoverable, -> { joins(:account_tag_stat).where(AccountTagStat.arel_table[:accounts_count].gt(0)).where(account_tag_stats: { hidden: false }).order(Arel.sql('account_tag_stats.accounts_count desc')) }
-  scope :hidden, -> { where(account_tag_stats: { hidden: true }) }
+  scope :reviewed, -> { where.not(reviewed_at: nil) }
+  scope :pending_review, -> { where(reviewed_at: nil).where.not(requested_review_at: nil) }
+  scope :discoverable, -> { where.not(listable: false).joins(:account_tag_stat).where(AccountTagStat.arel_table[:accounts_count].gt(0)).order(Arel.sql('account_tag_stats.accounts_count desc')) }
   scope :most_used, ->(account) { joins(:statuses).where(statuses: { account: account }).group(:id).order(Arel.sql('count(*) desc')) }
 
   delegate :accounts_count,
            :accounts_count=,
            :increment_count!,
            :decrement_count!,
-           :hidden?,
            to: :account_tag_stat
 
   after_save :save_account_tag_stat
@@ -48,6 +54,40 @@ class Tag < ApplicationRecord
     name
   end
 
+  def usable
+    boolean_with_default('usable', true)
+  end
+
+  alias usable? usable
+
+  def listable
+    boolean_with_default('listable', true)
+  end
+
+  alias listable? listable
+
+  def trendable
+    boolean_with_default('trendable', false)
+  end
+
+  alias trendable? trendable
+
+  def requires_review?
+    reviewed_at.nil?
+  end
+
+  def reviewed?
+    reviewed_at.present?
+  end
+
+  def requested_review?
+    requested_review_at.present?
+  end
+
+  def trending?
+    TrendingTags.trending?(self)
+  end
+
   def history
     days = []
 
@@ -117,4 +157,8 @@ class Tag < ApplicationRecord
     return unless account_tag_stat&.changed?
     account_tag_stat.save
   end
+
+  def validate_name_change
+    errors.add(:name, I18n.t('tags.does_not_match_previous_name')) unless name_was.mb_chars.casecmp(name.mb_chars).zero?
+  end
 end
diff --git a/app/models/trending_tags.rb b/app/models/trending_tags.rb
index 211c8f1dc..e9b9b25e3 100644
--- a/app/models/trending_tags.rb
+++ b/app/models/trending_tags.rb
@@ -10,20 +10,28 @@ class TrendingTags
     include Redisable
 
     def record_use!(tag, account, at_time = Time.now.utc)
-      return if disallowed_hashtags.include?(tag.name) || account.silenced? || account.bot?
+      return if account.silenced? || account.bot? || !tag.usable? || !(tag.trendable? || tag.requires_review?)
 
       increment_historical_use!(tag.id, at_time)
       increment_unique_use!(tag.id, account.id, at_time)
-      increment_vote!(tag.id, at_time)
+      increment_vote!(tag, at_time)
     end
 
-    def get(limit)
-      key     = "#{KEY}:#{Time.now.utc.beginning_of_day.to_i}"
-      tag_ids = redis.zrevrange(key, 0, limit - 1).map(&:to_i)
-      tags    = Tag.where(id: tag_ids).to_a.each_with_object({}) { |tag, h| h[tag.id] = tag }
+    def get(limit, filtered: true)
+      tag_ids = redis.zrevrange("#{KEY}:#{Time.now.utc.beginning_of_day.to_i}", 0, limit - 1).map(&:to_i)
+
+      tags = Tag.where(id: tag_ids)
+      tags = tags.where(trendable: true) if filtered
+      tags = tags.each_with_object({}) { |tag, h| h[tag.id] = tag }
+
       tag_ids.map { |tag_id| tags[tag_id] }.compact
     end
 
+    def trending?(tag)
+      rank = redis.zrevrank("#{KEY}:#{Time.now.utc.beginning_of_day.to_i}", tag.id)
+      rank.present? && rank <= 10
+    end
+
     private
 
     def increment_historical_use!(tag_id, at_time)
@@ -38,33 +46,27 @@ class TrendingTags
       redis.expire(key, EXPIRE_HISTORY_AFTER)
     end
 
-    def increment_vote!(tag_id, at_time)
+    def increment_vote!(tag, at_time)
       key      = "#{KEY}:#{at_time.beginning_of_day.to_i}"
-      expected = redis.pfcount("activity:tags:#{tag_id}:#{(at_time - 1.day).beginning_of_day.to_i}:accounts").to_f
+      expected = redis.pfcount("activity:tags:#{tag.id}:#{(at_time - 1.day).beginning_of_day.to_i}:accounts").to_f
       expected = 1.0 if expected.zero?
-      observed = redis.pfcount("activity:tags:#{tag_id}:#{at_time.beginning_of_day.to_i}:accounts").to_f
+      observed = redis.pfcount("activity:tags:#{tag.id}:#{at_time.beginning_of_day.to_i}:accounts").to_f
 
       if expected > observed || observed < THRESHOLD
-        redis.zrem(key, tag_id.to_s)
+        redis.zrem(key, tag.id)
       else
-        score = ((observed - expected)**2) / expected
-        added = redis.zadd(key, score, tag_id.to_s)
-        bump_tag_score!(tag_id) if added
+        score    = ((observed - expected)**2) / expected
+        old_rank = redis.zrevrank(key, tag.id)
+
+        redis.zadd(key, score, tag.id)
+        request_review!(tag) if (old_rank.nil? || old_rank > 10) && redis.zrevrank(key, tag.id) <= 10 && !tag.trendable? && tag.requires_review? && !tag.requested_review?
       end
 
       redis.expire(key, EXPIRE_TRENDS_AFTER)
     end
 
-    def bump_tag_score!(tag_id)
-      Tag.where(id: tag_id).update_all('score = COALESCE(score, 0) + 1')
-    end
-
-    def disallowed_hashtags
-      return @disallowed_hashtags if defined?(@disallowed_hashtags)
-
-      @disallowed_hashtags = Setting.disallowed_hashtags.nil? ? [] : Setting.disallowed_hashtags
-      @disallowed_hashtags = @disallowed_hashtags.split(' ') if @disallowed_hashtags.is_a? String
-      @disallowed_hashtags = @disallowed_hashtags.map(&:downcase)
+    def request_review!(tag)
+      User.staff.includes(:account).find_each { |u| AdminMailer.new_trending_tag(u.account, tag).deliver_later! if u.allows_trending_tag_emails? }
     end
   end
 end
diff --git a/app/models/user.rb b/app/models/user.rb
index 6806c0362..b83e26af3 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -207,6 +207,10 @@ class User < ApplicationRecord
     settings.notification_emails['pending_account']
   end
 
+  def allows_trending_tag_emails?
+    settings.notification_emails['trending_tag']
+  end
+
   def hides_network?
     @hides_network ||= settings.hide_network
   end
diff --git a/app/policies/tag_policy.rb b/app/policies/tag_policy.rb
index c63de01db..aaf70fcab 100644
--- a/app/policies/tag_policy.rb
+++ b/app/policies/tag_policy.rb
@@ -5,11 +5,11 @@ class TagPolicy < ApplicationPolicy
     staff?
   end
 
-  def hide?
+  def show?
     staff?
   end
 
-  def unhide?
+  def update?
     staff?
   end
 end
diff --git a/app/validators/disallowed_hashtags_validator.rb b/app/validators/disallowed_hashtags_validator.rb
index ee06b20f6..d745b767f 100644
--- a/app/validators/disallowed_hashtags_validator.rb
+++ b/app/validators/disallowed_hashtags_validator.rb
@@ -4,24 +4,7 @@ class DisallowedHashtagsValidator < ActiveModel::Validator
   def validate(status)
     return unless status.local? && !status.reblog?
 
-    @status = status
-    tags    = select_tags
-
-    status.errors.add(:text, I18n.t('statuses.disallowed_hashtags', tags: tags.join(', '), count: tags.size)) unless tags.empty?
-  end
-
-  private
-
-  def select_tags
-    tags = Extractor.extract_hashtags(@status.text)
-    tags.keep_if { |tag| disallowed_hashtags.include? tag.downcase }
-  end
-
-  def disallowed_hashtags
-    return @disallowed_hashtags if @disallowed_hashtags
-
-    @disallowed_hashtags = Setting.disallowed_hashtags.nil? ? [] : Setting.disallowed_hashtags
-    @disallowed_hashtags = @disallowed_hashtags.split(' ') if @disallowed_hashtags.is_a? String
-    @disallowed_hashtags = @disallowed_hashtags.map(&:downcase)
+    disallowed_hashtags = Tag.matching_name(Extractor.extract_hashtags(status.text)).reject(&:usable?)
+    status.errors.add(:text, I18n.t('statuses.disallowed_hashtags', tags: disallowed_hashtags.map(&:name).join(', '), count: disallowed_hashtags.size)) unless disallowed_hashtags.empty?
   end
 end
diff --git a/app/views/admin/dashboard/index.html.haml b/app/views/admin/dashboard/index.html.haml
index 77cc1a2a0..910896075 100644
--- a/app/views/admin/dashboard/index.html.haml
+++ b/app/views/admin/dashboard/index.html.haml
@@ -107,5 +107,5 @@
       %ul
         - @trending_hashtags.each do |tag|
           %li
-            = link_to "##{tag.name}", web_url("timelines/tag/#{tag.name}")
+            = link_to content_tag(:span, "##{tag.name}", class: !tag.trendable? && !tag.reviewed? ? 'warning-hint' : (!tag.trendable? ? 'negative-hint' : nil)), admin_tag_path(tag.id)
             %span.pull-right= number_with_delimiter(tag.history[0][:accounts].to_i)
diff --git a/app/views/admin/tags/_tag.html.haml b/app/views/admin/tags/_tag.html.haml
index 961b83f93..91af8e492 100644
--- a/app/views/admin/tags/_tag.html.haml
+++ b/app/views/admin/tags/_tag.html.haml
@@ -1,12 +1,16 @@
-%tr
-  %td
-    = link_to explore_hashtag_path(tag) do
+.directory__tag
+  = link_to admin_tag_path(tag.id) do
+    %h4
       = fa_icon 'hashtag'
       = tag.name
-  %td
-    = t('directories.people', count: tag.accounts_count)
-  %td
-    - if tag.hidden?
-      = table_link_to 'eye', t('admin.tags.unhide'), unhide_admin_tag_path(tag.id, **@filter_params), method: :post
-    - else
-      = table_link_to 'eye-slash', t('admin.tags.hide'), hide_admin_tag_path(tag.id, **@filter_params), method: :post
+
+      %small
+        = t('admin.tags.in_directory', count: tag.accounts_count)
+        &bull;
+        = t('admin.tags.unique_uses_today', count: tag.history.first[:accounts])
+
+        - if tag.trending?
+          = fa_icon 'fire fw'
+          = t('admin.tags.trending_right_now')
+
+    .trends__item__current= number_to_human tag.history.first[:uses], strip_insignificant_zeros: true
diff --git a/app/views/admin/tags/index.html.haml b/app/views/admin/tags/index.html.haml
index 4ba395860..5e4ee21f5 100644
--- a/app/views/admin/tags/index.html.haml
+++ b/app/views/admin/tags/index.html.haml
@@ -3,17 +3,19 @@
 
 .filters
   .filter-subset
-    %strong= t('admin.reports.status')
+    %strong= t('admin.tags.context')
     %ul
-      %li= filter_link_to t('admin.tags.visible'), hidden: nil
-      %li= filter_link_to t('admin.tags.hidden'), hidden: '1'
+      %li= filter_link_to t('generic.all'), context: nil
+      %li= filter_link_to t('admin.tags.directory'), context: 'directory'
 
-.table-wrapper
-  %table.table
-    %thead
-      %tr
-        %th= t('admin.tags.name')
-        %th= t('admin.tags.accounts')
-        %th
-    %tbody
-      = render @tags
+  .filter-subset
+    %strong= t('admin.tags.review')
+    %ul
+      %li= filter_link_to t('generic.all'), review: nil
+      %li= filter_link_to t('admin.tags.reviewed'), review: 'reviewed'
+      %li= filter_link_to safe_join([t('admin.accounts.moderation.pending'), "(#{Tag.pending_review.count})"], ' '), review: 'pending_review'
+
+%hr.spacer/
+
+= render @tags
+= paginate @tags
diff --git a/app/views/admin/tags/show.html.haml b/app/views/admin/tags/show.html.haml
new file mode 100644
index 000000000..27c8dc92b
--- /dev/null
+++ b/app/views/admin/tags/show.html.haml
@@ -0,0 +1,16 @@
+- content_for :page_title do
+  = "##{@tag.name}"
+
+= simple_form_for @tag, url: admin_tag_path(@tag.id) do |f|
+  = render 'shared/error_messages', object: @tag
+
+  .fields-group
+    = f.input :name, wrapper: :with_block_label
+
+  .fields-group
+    = f.input :usable, as: :boolean, wrapper: :with_label
+    = f.input :trendable, as: :boolean, wrapper: :with_label
+    = f.input :listable, as: :boolean, wrapper: :with_label
+
+  .actions
+    = f.button :button, t('generic.save_changes'), type: :submit
diff --git a/app/views/admin_mailer/new_trending_tag.text.erb b/app/views/admin_mailer/new_trending_tag.text.erb
new file mode 100644
index 000000000..f3087df37
--- /dev/null
+++ b/app/views/admin_mailer/new_trending_tag.text.erb
@@ -0,0 +1,5 @@
+<%= raw t('application_mailer.salutation', name: display_name(@me)) %>
+
+<%= raw t('admin_mailer.new_trending_tag.body', name: @tag.name) %>
+
+<%= raw t('application_mailer.view')%> <%= admin_tags_url(review: 'pending_review') %>
diff --git a/app/views/settings/preferences/notifications/show.html.haml b/app/views/settings/preferences/notifications/show.html.haml
index acc646fc3..f666ae4ff 100644
--- a/app/views/settings/preferences/notifications/show.html.haml
+++ b/app/views/settings/preferences/notifications/show.html.haml
@@ -15,6 +15,7 @@
       - if current_user.staff?
         = ff.input :report, as: :boolean, wrapper: :with_label
         = ff.input :pending_account, as: :boolean, wrapper: :with_label
+        = ff.input :trending_tag, as: :boolean, wrapper: :with_label
 
   .fields-group
     = f.simple_fields_for :notification_emails, hash_to_object(current_user.settings.notification_emails) do |ff|
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 6c1a34300..9b62aac3a 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -483,13 +483,14 @@ en:
       title: Account statuses
       with_media: With media
     tags:
-      accounts: Accounts
-      hidden: Hidden
-      hide: Hide from directory
-      name: Hashtag
+      context: Context
+      directory: In directory
+      in_directory: "%{count} in directory"
+      review: Review status
+      reviewed: Reviewed
       title: Hashtags
-      unhide: Show in directory
-      visible: Visible
+      trending_right_now: Trending right now
+      unique_uses_today: "%{count} posting today"
     title: Administration
     warning_presets:
       add_new: Add new
@@ -505,6 +506,9 @@ en:
       body: "%{reporter} has reported %{target}"
       body_remote: Someone from %{domain} has reported %{target}
       subject: New report for %{instance} (#%{id})
+    new_trending_tag:
+      body: 'The hashtag #%{name} is trending today, but has not been previously reviewed. It will not be displayed publicly unless you allow it to, or just save the form as it is to never hear about it again.'
+      subject: New hashtag up for review on %{instance} (#%{name})
   appearance:
     advanced_web_interface: Advanced web interface
     advanced_web_interface_hint: 'If you want to make use of your entire screen width, the advanced web interface allows you to configure many different columns to see as much information at the same time as you want: Home, notifications, federated timeline, any number of lists and hashtags.'
@@ -939,6 +943,8 @@ en:
     pinned: Pinned toot
     reblogged: boosted
     sensitive_content: Sensitive content
+  tags:
+    does_not_match_previous_name: does not match the previous name
   terms:
     body_html: |
       <h2>Privacy Policy</h2>
diff --git a/config/locales/simple_form.en.yml b/config/locales/simple_form.en.yml
index 10b30e627..6fdfc9d7b 100644
--- a/config/locales/simple_form.en.yml
+++ b/config/locales/simple_form.en.yml
@@ -48,6 +48,8 @@ en:
         text: This will help us review your application
       sessions:
         otp: 'Enter the two-factor code generated by your phone app or use one of your recovery codes:'
+      tag:
+        name: You can only change the casing of the letters, for example, to make it more readable
       user:
         chosen_languages: When checked, only toots in selected languages will be displayed in public timelines
     labels:
@@ -137,6 +139,11 @@ en:
         pending_account: Send e-mail when a new account needs review
         reblog: Send e-mail when someone boosts your status
         report: Send e-mail when a new report is submitted
+        trending_tag: Send e-mail when an unreviewed hashtag is trending
+      tag:
+        listable: Allow this hashtag to appear on the profile directory
+        trendable: Allow this hashtag to appear under trends
+        usable: Allow toots to use this hashtag
     'no': 'No'
     recommended: Recommended
     required:
diff --git a/config/navigation.rb b/config/navigation.rb
index 9b46da603..38668bbf7 100644
--- a/config/navigation.rb
+++ b/config/navigation.rb
@@ -38,7 +38,7 @@ SimpleNavigation::Configuration.run do |navigation|
       s.item :reports, safe_join([fa_icon('flag fw'), t('admin.reports.title')]), admin_reports_url, highlights_on: %r{/admin/reports}
       s.item :accounts, safe_join([fa_icon('users fw'), t('admin.accounts.title')]), admin_accounts_url, highlights_on: %r{/admin/accounts|/admin/pending_accounts}
       s.item :invites, safe_join([fa_icon('user-plus fw'), t('admin.invites.title')]), admin_invites_path
-      s.item :tags, safe_join([fa_icon('tag fw'), t('admin.tags.title')]), admin_tags_path
+      s.item :tags, safe_join([fa_icon('hashtag fw'), t('admin.tags.title')]), admin_tags_path, highlights_on: %r{/admin/tags}
       s.item :instances, safe_join([fa_icon('cloud fw'), t('admin.instances.title')]), admin_instances_url(limited: whitelist_mode? ? nil : '1'), highlights_on: %r{/admin/instances|/admin/domain_blocks|/admin/domain_allows}, if: -> { current_user.admin? }
       s.item :email_domain_blocks, safe_join([fa_icon('envelope fw'), t('admin.email_domain_blocks.title')]), admin_email_domain_blocks_url, highlights_on: %r{/admin/email_domain_blocks}, if: -> { current_user.admin? }
     end
diff --git a/config/routes.rb b/config/routes.rb
index 04424bbbd..60f7d2e05 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -243,13 +243,7 @@ Rails.application.routes.draw do
     end
 
     resources :account_moderation_notes, only: [:create, :destroy]
-
-    resources :tags, only: [:index] do
-      member do
-        post :hide
-        post :unhide
-      end
-    end
+    resources :tags, only: [:index, :show, :update]
   end
 
   get '/admin', to: redirect('/admin/dashboard', status: 302)
@@ -311,6 +305,7 @@ Rails.application.routes.draw do
       resources :mutes,        only: [:index]
       resources :favourites,   only: [:index]
       resources :reports,      only: [:create]
+      resources :trends,       only: [:index]
       resources :filters,      only: [:index, :create, :show, :update, :destroy]
       resources :endorsements, only: [:index]
 
diff --git a/config/settings.yml b/config/settings.yml
index ad2970bb7..10180201f 100644
--- a/config/settings.yml
+++ b/config/settings.yml
@@ -43,6 +43,7 @@ defaults: &defaults
     digest: true
     report: true
     pending_account: true
+    trending_tag: true
   interactions:
     must_be_follower: false
     must_be_following: false
diff --git a/db/migrate/20190805123746_add_capabilities_to_tags.rb b/db/migrate/20190805123746_add_capabilities_to_tags.rb
new file mode 100644
index 000000000..43c7763b1
--- /dev/null
+++ b/db/migrate/20190805123746_add_capabilities_to_tags.rb
@@ -0,0 +1,9 @@
+class AddCapabilitiesToTags < ActiveRecord::Migration[5.2]
+  def change
+    add_column :tags, :usable, :boolean
+    add_column :tags, :trendable, :boolean
+    add_column :tags, :listable, :boolean
+    add_column :tags, :reviewed_at, :datetime
+    add_column :tags, :requested_review_at, :datetime
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index e3af9c31a..d1b6825b4 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 2019_07_29_185330) do
+ActiveRecord::Schema.define(version: 2019_08_05_123746) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -660,6 +660,11 @@ ActiveRecord::Schema.define(version: 2019_07_29_185330) do
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.integer "score"
+    t.boolean "usable"
+    t.boolean "trendable"
+    t.boolean "listable"
+    t.datetime "reviewed_at"
+    t.datetime "requested_review_at"
     t.index "lower((name)::text)", name: "index_tags_on_name_lower", unique: true
   end
 
diff --git a/spec/controllers/admin/tags_controller_spec.rb b/spec/controllers/admin/tags_controller_spec.rb
index 3af994071..5c1944fc7 100644
--- a/spec/controllers/admin/tags_controller_spec.rb
+++ b/spec/controllers/admin/tags_controller_spec.rb
@@ -10,62 +10,14 @@ RSpec.describe Admin::TagsController, type: :controller do
   end
 
   describe 'GET #index' do
-    before do
-      account_tag_stat = Fabricate(:tag).account_tag_stat
-      account_tag_stat.update(hidden: hidden, accounts_count: 1)
-      get :index, params: { hidden: hidden }
-    end
-
-    context 'with hidden tags' do
-      let(:hidden) { true }
-
-      it 'returns status 200' do
-        expect(response).to have_http_status(200)
-      end
-    end
-
-    context 'without hidden tags' do
-      let(:hidden) { false }
-
-      it 'returns status 200' do
-        expect(response).to have_http_status(200)
-      end
-    end
-  end
-
-  describe 'POST #hide' do
-    let(:tag) { Fabricate(:tag) }
+    let!(:tag) { Fabricate(:tag) }
 
     before do
-      tag.account_tag_stat.update(hidden: false)
-      post :hide, params: { id: tag.id }
-    end
-
-    it 'hides tag' do
-      tag.reload
-      expect(tag).to be_hidden
-    end
-
-    it 'redirects to admin_tags_path' do
-      expect(response).to redirect_to(admin_tags_path(controller.instance_variable_get(:@filter_params)))
-    end
-  end
-
-  describe 'POST #unhide' do
-    let(:tag) { Fabricate(:tag) }
-
-    before do
-      tag.account_tag_stat.update(hidden: true)
-      post :unhide, params: { id: tag.id }
-    end
-
-    it 'unhides tag' do
-      tag.reload
-      expect(tag).not_to be_hidden
+      get :index
     end
 
-    it 'redirects to admin_tags_path' do
-      expect(response).to redirect_to(admin_tags_path(controller.instance_variable_get(:@filter_params)))
+    it 'returns status 200' do
+      expect(response).to have_http_status(200)
     end
   end
 end
diff --git a/spec/policies/tag_policy_spec.rb b/spec/policies/tag_policy_spec.rb
index c7afaa7c9..c63875dc0 100644
--- a/spec/policies/tag_policy_spec.rb
+++ b/spec/policies/tag_policy_spec.rb
@@ -8,7 +8,7 @@ RSpec.describe TagPolicy do
   let(:admin)   { Fabricate(:user, admin: true).account }
   let(:john)    { Fabricate(:user).account }
 
-  permissions :index?, :hide?, :unhide? do
+  permissions :index?, :show?, :update? do
     context 'staff?' do
       it 'permits' do
         expect(subject).to permit(admin, Tag)
diff --git a/spec/validators/disallowed_hashtags_validator_spec.rb b/spec/validators/disallowed_hashtags_validator_spec.rb
index 8ec1302ab..9deec0bb9 100644
--- a/spec/validators/disallowed_hashtags_validator_spec.rb
+++ b/spec/validators/disallowed_hashtags_validator_spec.rb
@@ -3,42 +3,44 @@
 require 'rails_helper'
 
 RSpec.describe DisallowedHashtagsValidator, type: :validator do
+  let(:disallowed_tags) { [] }
+
   describe '#validate' do
     before do
-      allow_any_instance_of(described_class).to receive(:select_tags) { tags }
+      disallowed_tags.each { |name| Fabricate(:tag, name: name, usable: false) }
       described_class.new.validate(status)
     end
 
-    let(:status) { double(errors: errors, local?: local, reblog?: reblog, text: '') }
+    let(:status) { double(errors: errors, local?: local, reblog?: reblog, text: disallowed_tags.map { |x| '#' + x }.join(' ')) }
     let(:errors) { double(add: nil) }
 
-    context 'unless status.local? && !status.reblog?' do
+    context 'for a remote reblog' do
       let(:local)  { false }
       let(:reblog) { true }
 
-      it 'not calls errors.add' do
+      it 'does not add errors' do
         expect(errors).not_to have_received(:add).with(:text, any_args)
       end
     end
 
-    context 'status.local? && !status.reblog?' do
+    context 'for a local original status' do
       let(:local)  { true }
       let(:reblog) { false }
 
-      context 'tags.empty?' do
-        let(:tags) { [] }
+      context 'when does not contain any disallowed hashtags' do
+        let(:disallowed_tags) { [] }
 
-        it 'not calls errors.add' do
+        it 'does not add errors' do
           expect(errors).not_to have_received(:add).with(:text, any_args)
         end
       end
 
-      context '!tags.empty?' do
-        let(:tags) { %w(a b c) }
+      context 'when contains disallowed hashtags' do
+        let(:disallowed_tags) { %w(a b c) }
 
-        it 'calls errors.add' do
+        it 'adds an error' do
           expect(errors).to have_received(:add)
-            .with(:text, I18n.t('statuses.disallowed_hashtags', tags: tags.join(', '), count: tags.size))
+            .with(:text, I18n.t('statuses.disallowed_hashtags', tags: disallowed_tags.join(', '), count: disallowed_tags.size))
         end
       end
     end