Add command to filter by tag

app/models/command/filter_by_tag.rb

@@ -0,0 +1,18 @@
+class Command::FilterByTag < Command
+  store_accessor :data, :tag_id, :params
+
+  validates_presence_of :tag_id
+
+  def title
+    "Filter by tag ##{tag&.title || tag_id} "
+  end
+
+  def execute
+    redirect_to cards_path(**params.merge(tag_ids: [ tag_id ]))
+  end
+
+  private
+    def tag
+      Tag.find_by_id(tag_id)
+    end
+end

app/models/command/parser.rb

@@ -23,6 +23,8 @@ class Command::Parser
         Command::Assign.new(assignee_ids: assignees_from(command_arguments).collect(&:id), card_ids: cards.ids)
       when "/close"
         Command::Close.new(card_ids: cards.ids, reason: command_arguments.join(" "))
+      when /^#/
+        Command::FilterByTag.new(tag_id: tag_from(string).id, params: filter.as_params)
       when /^@/
         Command::GoToUser.new(user_id: assignee_from(command_name)&.id)
       else
@@ -44,6 +46,11 @@ class Command::Parser
       User.all.find { |user| user.mentionable_handles.include?(string_without_at) }
     end
 
+    def tag_from(string)
+      title = string.gsub(/^#/, "")
+      Tag.find_or_create_by!(title: title)
+    end
+
     def parse_free_string(string)
       if cards = multiple_cards_from(string)
         Command::FilterCards.new(card_ids: cards.ids, params: filter.as_params)

test/models/command/filter_by_tag_test.rb

@@ -0,0 +1,15 @@
+require "test_helper"
+
+class Command::FilterByCardTest < ActionDispatch::IntegrationTest
+  include CommandTestHelper
+
+  setup do
+    @tag = tags(:web)
+  end
+
+  test "redirects to the cards index filtering by cards" do
+    result = execute_command "##{@tag.title}"
+
+    assert_equal cards_path(indexed_by: "newest", tag_ids: [ @tag.id ]), result.url
+  end
+end