diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
new file mode 100644
index 0000000..37a9318
--- /dev/null
+++ b/.github/workflows/main.yml
@@ -0,0 +1,27 @@
+name: Ruby
+
+on:
+  push:
+    branches:
+      - main
+
+  pull_request:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    name: Ruby ${{ matrix.ruby }}
+    strategy:
+      matrix:
+        ruby:
+          - '3.3.0'
+
+    steps:
+    - uses: actions/checkout@v4
+    - name: Set up Ruby
+      uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: ${{ matrix.ruby }}
+        bundler-cache: true
+    - name: Run the default task
+      run: bundle exec rake
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..9106b2a
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,8 @@
+/.bundle/
+/.yardoc
+/_yardoc/
+/coverage/
+/doc/
+/pkg/
+/spec/reports/
+/tmp/
diff --git a/.standard.yml b/.standard.yml
new file mode 100644
index 0000000..6d67c99
--- /dev/null
+++ b/.standard.yml
@@ -0,0 +1,3 @@
+# For available configuration options, see:
+#   https://github.com/standardrb/standard
+ruby_version: 3.0
diff --git a/Gemfile b/Gemfile
new file mode 100644
index 0000000..13a6c2f
--- /dev/null
+++ b/Gemfile
@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+source "https://rubygems.org"
+
+# Specify your gem's dependencies in state_machine_enum.gemspec
+gemspec
+
+gem "rake", "~> 13.0"
+
+gem "minitest", "~> 5.16"
+
+gem "standard", "~> 1.3"
diff --git a/Gemfile.lock b/Gemfile.lock
new file mode 100644
index 0000000..787f86e
--- /dev/null
+++ b/Gemfile.lock
@@ -0,0 +1,88 @@
+PATH
+  remote: .
+  specs:
+    state_machine_enum (0.1.0)
+      activesupport (>= 6.0)
+
+GEM
+  remote: https://rubygems.org/
+  specs:
+    activesupport (7.1.3.3)
+      base64
+      bigdecimal
+      concurrent-ruby (~> 1.0, >= 1.0.2)
+      connection_pool (>= 2.2.5)
+      drb
+      i18n (>= 1.6, < 2)
+      minitest (>= 5.1)
+      mutex_m
+      tzinfo (~> 2.0)
+    ast (2.4.2)
+    base64 (0.2.0)
+    bigdecimal (3.1.8)
+    concurrent-ruby (1.3.1)
+    connection_pool (2.4.1)
+    drb (2.2.1)
+    i18n (1.14.5)
+      concurrent-ruby (~> 1.0)
+    json (2.7.2)
+    language_server-protocol (3.17.0.3)
+    lint_roller (1.1.0)
+    minitest (5.23.1)
+    mutex_m (0.2.0)
+    parallel (1.24.0)
+    parser (3.3.2.0)
+      ast (~> 2.4.1)
+      racc
+    racc (1.8.0)
+    rainbow (3.1.1)
+    rake (13.2.1)
+    regexp_parser (2.9.2)
+    rexml (3.2.8)
+      strscan (>= 3.0.9)
+    rubocop (1.63.5)
+      json (~> 2.3)
+      language_server-protocol (>= 3.17.0)
+      parallel (~> 1.10)
+      parser (>= 3.3.0.2)
+      rainbow (>= 2.2.2, < 4.0)
+      regexp_parser (>= 1.8, < 3.0)
+      rexml (>= 3.2.5, < 4.0)
+      rubocop-ast (>= 1.31.1, < 2.0)
+      ruby-progressbar (~> 1.7)
+      unicode-display_width (>= 2.4.0, < 3.0)
+    rubocop-ast (1.31.3)
+      parser (>= 3.3.1.0)
+    rubocop-performance (1.21.0)
+      rubocop (>= 1.48.1, < 2.0)
+      rubocop-ast (>= 1.31.1, < 2.0)
+    ruby-progressbar (1.13.0)
+    standard (1.36.0)
+      language_server-protocol (~> 3.17.0.2)
+      lint_roller (~> 1.0)
+      rubocop (~> 1.63.0)
+      standard-custom (~> 1.0.0)
+      standard-performance (~> 1.4)
+    standard-custom (1.0.2)
+      lint_roller (~> 1.0)
+      rubocop (~> 1.50)
+    standard-performance (1.4.0)
+      lint_roller (~> 1.1)
+      rubocop-performance (~> 1.21.0)
+    strscan (3.1.0)
+    tzinfo (2.0.6)
+      concurrent-ruby (~> 1.0)
+    unicode-display_width (2.5.0)
+
+PLATFORMS
+  arm64-darwin-23
+  ruby
+
+DEPENDENCIES
+  minitest (~> 5.16)
+  rake (~> 13.0)
+  standard (~> 1.3)
+  state_machine_enum!
+
+BUNDLED WITH
+   2.5.11
diff --git a/LICENSE.txt b/LICENSE.txt
new file mode 100644
index 0000000..4ac45c9
--- /dev/null
+++ b/LICENSE.txt
@@ -0,0 +1,21 @@
+The MIT License (MIT)
+
+Copyright (c) 2024 Stanislav Katkov
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..8d84422
--- /dev/null
+++ b/README.md
@@ -0,0 +1,60 @@
+# StateMachineEnum
+
+This concern adds a method called "state_machine_enum" useful for defining an enum using string values along with valid state transitions. Validations will be added for the state transitions and a proper enum is going to be defined. For example:
+
+```ruby
+state_machine_enum :state do |states|
+  states.permit_transition(:created, :approved_pending_settlement)
+  states.permit_transition(:approved_pending_settlement, :rejected)
+  states.permit_transition(:created, :rejected)
+  states.permit_transition(:approved_pending_settlement, :settled)
+end
+```
+
+## Installation
+
+Install the gem and add to the application's Gemfile by executing:
+
+    $ bundle add state_machine_enum
+
+If bundler is not being used to manage dependencies, install the gem by executing:
+
+    $ gem install state_machine_enum
+
+## Usage
+
+StateMachineEnum needs to be extended and then it could be used, as example in AR model.
+
+```
+class User < ApplicationRecord
+  include StateMachineEnum
+
+  state_machine_enum :state do |s|
+    s.permit_transition(:registered, :active)
+    s.permit_transition(:active, :banned)
+    s.permit_transition(:banned, :active)
+    s.permit_transition(:active, :deleted)
+  end
+end
+```
+
+And then it will offer bunch of convenient methods and callbacks that ensure proper state transitions.
+
+```
+user = User.new(state: 'registered')
+user.active?
+user.registered! # throws InvalidState error, because state can not transition to "registered".
+```
+## Development
+
+After checking out the repo, run `bin/setup` to install dependencies. Then, run `rake test` to run the tests. You can also run `bin/console` for an interactive prompt that will allow you to experiment.
+
+To install this gem onto your local machine, run `bundle exec rake install`. To release a new version, update the version number in `version.rb`, and then run `bundle exec rake release`, which will create a git tag for the version, push git commits and the created tag, and push the `.gem` file to [rubygems.org](https://rubygems.org).
+
+## Contributing
+
+Bug reports and pull requests are welcome on GitHub at https://github.com/cheddar-me/state_machine_enum.
+
+## License
+
+The gem is available as open source under the terms of the [MIT License](https://opensource.org/licenses/MIT).
diff --git a/Rakefile b/Rakefile
new file mode 100644
index 0000000..f32601d
--- /dev/null
+++ b/Rakefile
@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+require "bundler/gem_tasks"
+require "minitest/test_task"
+
+Minitest::TestTask.create
+
+require "standard/rake"
+
+task default: %i[test standard]
diff --git a/bin/console b/bin/console
new file mode 100755
index 0000000..278edb6
--- /dev/null
+++ b/bin/console
@@ -0,0 +1,11 @@
+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+require "bundler/setup"
+require "state_machine_enum"
+
+# You can add fixtures and/or initialization code here to make experimenting
+# with your gem easier. You can also use a different console, if you like.
+
+require "irb"
+IRB.start(__FILE__)
diff --git a/bin/setup b/bin/setup
new file mode 100755
index 0000000..dce67d8
--- /dev/null
+++ b/bin/setup
@@ -0,0 +1,8 @@
+#!/usr/bin/env bash
+set -euo pipefail
+IFS=$'\n\t'
+set -vx
+
+bundle install
+
+# Do any other automated setup that you need to do here
diff --git a/lib/state_machine_enum.rb b/lib/state_machine_enum.rb
new file mode 100644
index 0000000..88e0e20
--- /dev/null
+++ b/lib/state_machine_enum.rb
@@ -0,0 +1,127 @@
+# frozen_string_literal: true
+
+require_relative "state_machine_enum/version"
+require "active_support/concern"
+
+# This concern adds a method called "state_machine_enum" useful for defining an enum using
+# string values along with valid state transitions. Validations will be added for the
+# state transitions and a proper enum is going to be defined. For example:
+#
+#   state_machine_enum :state do |states|
+#     states.permit_transition(:created, :approved_pending_settlement)
+#     states.permit_transition(:approved_pending_settlement, :rejected)
+#     states.permit_transition(:created, :rejected)
+#     states.permit_transition(:approved_pending_settlement, :settled)
+#   end
+
+module StateMachineEnum
+  extend ActiveSupport::Concern
+
+  class StatesCollector
+    attr_reader :states
+    attr_reader :after_commit_hooks
+    attr_reader :common_after_commit_hooks
+    attr_reader :after_attribute_write_hooks
+    attr_reader :common_after_write_hooks
+
+    def initialize
+      @transitions = Set.new
+      @states = Set.new
+      @after_commit_hooks = {}
+      @common_after_commit_hooks = []
+      @after_attribute_write_hooks = {}
+      @common_after_write_hooks = []
+    end
+
+    def permit_transition(from, to)
+      @states << from.to_s << to.to_s
+      @transitions << [from.to_s, to.to_s]
+    end
+
+    def may_transition?(from, to)
+      @transitions.include?([from.to_s, to.to_s])
+    end
+
+    def after_inline_transition_to(target_state, &blk)
+      @after_attribute_write_hooks[target_state.to_s] ||= []
+      @after_attribute_write_hooks[target_state.to_s] << blk.to_proc
+    end
+
+    def after_committed_transition_to(target_state, &blk)
+      @after_commit_hooks[target_state.to_s] ||= []
+      @after_commit_hooks[target_state.to_s] << blk.to_proc
+    end
+
+    def after_any_committed_transition(&blk)
+      @common_after_commit_hooks << blk.to_proc
+    end
+
+    def validate(model, attribute_name)
+      return unless model.persisted?
+
+      was = model.attribute_was(attribute_name)
+      is = model[attribute_name]
+
+      unless was == is || @transitions.include?([was, is])
+        model.errors.add(attribute_name, "Invalid transition from #{was} to #{is}")
+      end
+    end
+  end
+
+  class InvalidState < StandardError
+  end
+
+  class_methods do
+    def state_machine_enum(attribute_name, **options_for_enum)
+      # Collect the states
+      collector = StatesCollector.new
+      yield(collector).tap do
+        # Define the enum using labels, with string values
+        enum_map = collector.states.map(&:to_sym).zip(collector.states.to_a).to_h
+        enum(attribute_name, enum_map, **options_for_enum)
+
+        # Define validations for transitions
+        validates attribute_name, presence: true
+        validate { |model| collector.validate(model, attribute_name) }
+
+        # Define inline hooks
+        before_save do |model|
+          _value_was, value_has_become = model.changes[attribute_name]
+          next unless value_has_become
+          hook_procs = collector.after_attribute_write_hooks[value_has_become].to_a + collector.common_after_write_hooks.to_a
+          hook_procs.each do |hook_proc|
+            hook_proc.call(model)
+          end
+        end
+
+        # Define after commit hooks
+        after_commit do |model|
+          _value_was, value_has_become = model.previous_changes[attribute_name]
+          next unless value_has_become
+          hook_procs = collector.after_commit_hooks[value_has_become].to_a + collector.common_after_commit_hooks.to_a
+          hook_procs.each do |hook_proc|
+            hook_proc.call(model)
+          end
+        end
+
+        # Define the check methods
+        define_method(:"ensure_#{attribute_name}_one_of!") do |*allowed_states|
+          val = self[attribute_name]
+          return if Set.new(allowed_states.map(&:to_s)).include?(val)
+          raise InvalidState, "#{attribute_name} must be one of #{allowed_states.inspect} but was #{val.inspect}"
+        end
+
+        define_method(:"ensure_#{attribute_name}_may_transition_to!") do |next_state|
+          val = self[attribute_name]
+          raise InvalidState, "#{attribute_name} already is #{val.inspect}" if next_state.to_s == val
+        end
+
+        define_method(:"#{attribute_name}_may_transition_to?") do |next_state|
+          val = self[attribute_name]
+          return false if val == next_state.to_s
+          collector.may_transition?(val, next_state)
+        end
+      end
+    end
+  end
+end
diff --git a/lib/state_machine_enum/version.rb b/lib/state_machine_enum/version.rb
new file mode 100644
index 0000000..49ab2c2
--- /dev/null
+++ b/lib/state_machine_enum/version.rb
@@ -0,0 +1,5 @@
+# frozen_string_literal: true
+
+module StateMachineEnum
+  VERSION = "0.1.0"
+end
diff --git a/sig/state_machine_enum.rbs b/sig/state_machine_enum.rbs
new file mode 100644
index 0000000..6a3c77b
--- /dev/null
+++ b/sig/state_machine_enum.rbs
@@ -0,0 +1,4 @@
+module StateMachineEnum
+  VERSION: String
+  # See the writing guide of rbs: https://github.com/ruby/rbs#guides
+end
diff --git a/state_machine_enum.gemspec b/state_machine_enum.gemspec
new file mode 100644
index 0000000..c59e4f9
--- /dev/null
+++ b/state_machine_enum.gemspec
@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+require_relative "lib/state_machine_enum/version"
+
+Gem::Specification.new do |spec|
+  spec.name = "state_machine_enum"
+  spec.version = StateMachineEnum::VERSION
+  spec.authors = ["Stanislav Katkov"]
+  spec.email = ["skatkov@cheddar.me"]
+
+  spec.summary = "Define possible state transitions for a field"
+  spec.description = "Concern that makes it easy to define and enforce possibe state transitions for a field/object"
+  spec.homepage = "https://cheddar.me"
+  spec.license = "MIT"
+  spec.required_ruby_version = ">= 3.0.0"
+
+  # spec.metadata["allowed_push_host"] = "TODO: Set to your gem server 'https://example.com'"
+
+  spec.metadata["homepage_uri"] = spec.homepage
+  spec.metadata["source_code_uri"] = "https://github.com/cheddar-me/state_machine_enum"
+  #spec.metadata["changelog_uri"] = "TODO: Put your gem's CHANGELOG.md URL here."
+
+  # Specify which files should be added to the gem when it is released.
+  # The `git ls-files -z` loads the files in the RubyGem that have been added into git.
+  gemspec = File.basename(__FILE__)
+  spec.files = IO.popen(%w[git ls-files -z], chdir: __dir__, err: IO::NULL) do |ls|
+    ls.readlines("\x0", chomp: true).reject do |f|
+      (f == gemspec) ||
+        f.start_with?(*%w[bin/ test/ spec/ features/ .git .github appveyor Gemfile])
+    end
+  end
+  spec.bindir = "exe"
+  spec.executables = spec.files.grep(%r{\Aexe/}) { |f| File.basename(f) }
+  spec.require_paths = ["lib"]
+
+  spec.add_dependency "activesupport", ">= 6.0"
+end
diff --git a/test/test_helper.rb b/test/test_helper.rb
new file mode 100644
index 0000000..18a5dd3
--- /dev/null
+++ b/test/test_helper.rb
@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+
+$LOAD_PATH.unshift File.expand_path("../lib", __dir__)
+require "state_machine_enum"
+
+require "minitest/autorun"
diff --git a/test/test_state_machine_enum.rb b/test/test_state_machine_enum.rb
new file mode 100644
index 0000000..c5c1dc2
--- /dev/null
+++ b/test/test_state_machine_enum.rb
@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+require "test_helper"
+
+class TestStateMachineEnum < Minitest::Test
+  def test_that_it_has_a_version_number
+    refute_nil ::StateMachineEnum::VERSION
+  end
+
+  def test_it_does_something_useful
+    assert false
+  end
+end