FEATURE: tag group options: limit usage of one tag per group, tags in a group can't be used unless a prerequisite tag is used

app/assets/javascripts/discourse/components/tag-chooser.js.es6

@@ -36,12 +36,19 @@ export default Ember.TextField.extend({
     const site = this.site,
           self = this,
           filterRegexp = new RegExp(this.site.tags_filter_regexp, "g");
+    var limit = this.siteSettings.max_tags_per_topic;
+
+    if (this.get('unlimitedTagCount')) {
+      limit = null;
+    } else if (this.get('limit')) {
+      limit = parseInt(this.get('limit'));
+    }
 
     this.$().select2({
       tags: true,
       placeholder: I18n.t(this.get('placeholderKey') || 'tagging.choose_for_topic'),
       maximumInputLength: this.siteSettings.max_tag_length,
-      maximumSelectionSize: self.get('unlimitedTagCount') ? null : this.siteSettings.max_tags_per_topic,
+      maximumSelectionSize: limit,
       initSelection(element, callback) {
         const data = [];
 
@@ -92,7 +99,12 @@ export default Ember.TextField.extend({
         url: Discourse.getURL("/tags/filter/search"),
         dataType: 'json',
         data: function (term) {
-          const d = { q: term, limit: self.siteSettings.max_tag_search_results, categoryId: self.get('categoryId') };
+          const d = {
+            q: term,
+            limit: self.siteSettings.max_tag_search_results,
+            categoryId: self.get('categoryId'),
+            selected_tags: self.get('tags')
+          };
           if (!self.get('everyTag')) {
             d.filterForInput = true;
           }

app/assets/javascripts/discourse/models/tag-group.js.es6

@@ -20,7 +20,9 @@ const TagGroup = RestModel.extend({
     return Discourse.ajax(url, {
       data: {
         name: this.get('name'),
-        tag_names: this.get('tag_names')
+        tag_names: this.get('tag_names'),
+        parent_tag_name: this.get('parent_tag_name') ? this.get('parent_tag_name') : undefined,
+        one_per_topic: this.get('one_per_topic')
       },
       type: this.get('id') ? 'PUT' : 'POST'
     }).then(function(result) {

app/assets/javascripts/discourse/templates/tag-groups-show.hbs

@@ -1,13 +1,25 @@
 <div class="tag-group-content">
   <h1>{{text-field value=model.name}}</h1>
   <br/>
-  <div class="group-tags-list">
-    <label>{{i18n 'tagging.groups.tags_label'}}</label>
-    <br/>
-    {{tag-chooser tags=model.tag_names everyTag="false" unlimitedTagCount="true"}}
-  </div>
-  <br/>
+  <section class="group-tags-list">
+    <label>{{i18n 'tagging.groups.tags_label'}}</label><br/>
+    {{tag-chooser tags=model.tag_names everyTag="true" unlimitedTagCount="true"}}
+  </section>
+
+  <section class="parent-tag-section">
+    <label>{{i18n 'tagging.groups.parent_tag_label'}}</label>
+    {{tag-chooser tags=model.parent_tag_name everyTag="true" limit="1" placeholderKey="tagging.groups.parent_tag_placeholder"}}
+    <span class="description">{{i18n 'tagging.groups.parent_tag_description'}}</span>
+  </section>
+
+  <section class="group-one-per-topic">
+    <label>
+      {{input type="checkbox" checked=model.one_per_topic name="onepertopic"}}
+      {{i18n 'tagging.groups.one_per_topic_label'}}
+    </label>
+  </section>
+
   <button {{action "save"}} disabled={{model.disableSave}} class='btn'>{{i18n 'tagging.groups.save'}}</button>
-  <button {{action "destroy"}} class='btn btn-danger'><i class="fa fa-trash-o"></i> {{i18n 'tagging.groups.delete'}}</button>
+  <button {{action "destroy"}} disabled={{model.disableSave}} class='btn btn-danger'><i class="fa fa-trash-o"></i> {{i18n 'tagging.groups.delete'}}</button>
   <span class="saving {{unless model.savingStatus 'hidden'}}">{{model.savingStatus}}</span>
 </div>

app/assets/stylesheets/common/base/tagging.scss

@@ -222,6 +222,14 @@ header .discourse-tag {color: $tag-color !important; }
   .tag-group-content {
     width: 75%;
     float: right;
+    section {
+      margin-bottom: 20px;
+    }
+    label {
+      font-size: 1em;
+      display: inline-block;
+      margin-right: 10px;
+    }
   }
   .group-tags-list .tag-chooser {
     height: 150px !important;
@@ -233,4 +241,10 @@ header .discourse-tag {color: $tag-color !important; }
   .saving {
     margin-left: 20px;
   }
+  .parent-tag-section {
+    .tag-chooser {
+      width: 200px;
+      margin-right: 10px;
+    }
+  }
 }

app/controllers/tag_groups_controller.rb

@@ -69,7 +69,10 @@ class TagGroupsController < ApplicationController
     end
 
     def tag_groups_params
-      params[:tag_names] ||= []
-      params.permit(:id, :name, :tag_names => [])
+      result = params.permit(:id, :name, :one_per_topic, :tag_names => [], :parent_tag_name => [])
+      result[:tag_names] ||= []
+      result[:parent_tag_name] ||= []
+      result[:one_per_topic] = (params[:one_per_topic] == "true")
+      result
     end
 end

app/controllers/tags_controller.rb

@@ -117,7 +117,12 @@ class TagsController < ::ApplicationController
     tags_with_counts = DiscourseTagging.filter_allowed_tags(
       self.class.tags_by_count(guardian, params.slice(:limit)),
       guardian,
-      { for_input: params[:filterForInput], term: params[:q], category: category }
+      {
+        for_input: params[:filterForInput],
+        term: params[:q],
+        category: category,
+        selected_tags: params[:selected_tags]
+      }
     )
 
     tags = tags_with_counts.count.map {|t, c| { id: t, text: t, count: c } }
@@ -125,7 +130,7 @@ class TagsController < ::ApplicationController
     unused_tags = DiscourseTagging.filter_allowed_tags(
       Tag.where(topic_count: 0),
       guardian,
-      { for_input: params[:filterForInput], term: params[:q], category: category }
+      { for_input: params[:filterForInput], term: params[:q], category: category, selected_tags: params[:selected_tags] }
     )
 
     unused_tags.each do |t|

app/models/tag_group.rb

@@ -6,7 +6,19 @@ class TagGroup < ActiveRecord::Base
   has_many :category_tag_groups, dependent: :destroy
   has_many :categories, through: :category_tag_groups
 
+  belongs_to :parent_tag, class_name: 'Tag'
+
   def tag_names=(tag_names_arg)
     DiscourseTagging.add_or_create_tags_by_name(self, tag_names_arg)
   end
+
+  def parent_tag_name=(tag_names_arg)
+    if tag_names_arg.empty?
+      self.parent_tag = nil
+    else
+      if tag_name = DiscourseTagging.tags_for_saving(tag_names_arg, Guardian.new(Discourse.system_user)).first
+        self.parent_tag = Tag.find_by_name(tag_name) || Tag.create(name: tag_name)
+      end
+    end
+  end
 end

app/models/tag_group_membership.rb

@@ -1,4 +1,4 @@
 class TagGroupMembership < ActiveRecord::Base
   belongs_to :tag
-  belongs_to :tag_group, counter_cache: "tag_count"
+  belongs_to :tag_group, counter_cache: "tag_count" # TODO: remove counter cache
 end

app/serializers/tag_group_serializer.rb

@@ -1,7 +1,11 @@
 class TagGroupSerializer < ApplicationSerializer
-  attributes :id, :name, :tag_names
+  attributes :id, :name, :tag_names, :parent_tag_name, :one_per_topic
 
   def tag_names
     object.tags.pluck(:name).sort
   end
+
+  def parent_tag_name
+    [object.parent_tag.try(:name)].compact
+  end
 end