easy-going-rails/lib/live/definable.rb

require 'dotenv'

$definable_thread_group ||= ThreadGroup.new

module Live
  # offers typed constant defintions with default value, by using lots of introspecting...
  module Definable
    MAIN_CSS = 'app/assets/stylesheets/application.css'.freeze # useful to trigger :reload_all from RailsLiveReload

    def integer(default = 0) = define_type_from_callee(caller[0], :integer, default)
    def boolean(default = true) = define_type_from_callee(caller[0], :boolean, default) # rubocop:disable Style/OptionalBooleanParameter
    def string(default = '') = define_type_from_callee(caller[0], :string, default)

    def reload_from_env
      logger.debug('reload from env')

      changes = []
      new_env_values = env_values(cached: false)
      new_env_keys = new_env_values.keys

      new_env_values.each_pair { |constant, raw| changes << override(constant, raw) }
      definitions.except(*new_env_keys).each_pair { |constant, definition| changes << restore(constant, definition) }
      changes.compact!

      trigger_rolling_event(changes) if changes.any?
    end

    private

    def trigger_rolling_event(changes)
      ActiveSupport::Notifications.instrument('rolling.live_constant', changes:)
      FileUtils.touch(MAIN_CSS) if defined?(RailsLiveReload) # triggering RailsLiveReload
    rescue StandardError => e
      logger.error(e)
    end

    def override(constant, raw)
      return unless definitions.include?(constant)

      type = definitions[constant][:type]
      new_value = typed_value(type, raw, definitions[constant][:default])
      old_value = definitions[constant][:value]
      return if new_value == old_value

      define_value(constant, new_value)
      logger.warn "Constant overriden from environment:#{Semantic::AnsiColors::CLEAR} #{constant} = #{new_value.ai}"
      { kind: :overriden, constant:, type:, old_value:, new_value: }
    end

    def restore(constant, definition)
      new_value = definition[:default]
      old_value = definition[:value]
      return if old_value == new_value

      type = definition[:type]
      define_value(constant, new_value)
      logger.warn "Constant restored:#{Semantic::AnsiColors::CLEAR} #{constant} = #{new_value.ai}"
      { kind: :restored, constant:, type:, old_value:, new_value: }
    end

    def env_values(cached: true)
      return @env_values if @env_values && cached

      @env_values = Dotenv.parse(*Dotenv::Rails.files)
    end

    def logger = @logger ||= SemanticLogger[self]
    def definitions = @definitions ||= {}

    def define_value(constant, value)
      definitions[constant][:value] = value
      remove_const(constant)
      const_set(constant, value)
    end

    # origin (or caller[0]) helps fetching the constant name from source code introspection
    def define_type_from_callee(origin, type, default)
      @@class_origin ||= self # rubocop:disable Style/ClassVars
      @listener ||= start_listener

      file, line = origin.split(':')
      constant = introspect_constant_from_file(file, line.to_i - 1)
      raw_value = env_values.fetch(constant, nil)
      value = typed_value(type, raw_value, default)
      definitions[constant] = { type:, default:, value: }

      # puts("-- new definition #{constant}:#{definitions[constant]}")
      value
    end

    def start_listener
      $definable_thread_group.list.each(&:kill)
      $definable_thread_group.add(Thread.new do
        listener = Listen.to(Rails.root, only: /^\.env\.?/) do
          @@class_origin.reload_from_env
        rescue StandardError
          nil
        end
        listener.start
      end)
    end

    def typed_value(type, raw, default)
      return default if raw.nil?

      case type
      when :integer then raw.to_i
      when :boolean then raw.upcase == 'TRUE'
      else raw
      end
    end

    # returns current directory of this source code
    def dir_source_location
      return @dir_source_location if defined?(@dir_source_location)

      *paths, _ = Live.const_source_location(:Definable).first.split('/')
      @dir_source_location = paths.join('/')
    end

    def introspect_constant_from_file(file, line)
      *dir_file, _ = file.split('/')
      dir_file = dir_file.join('/')
      raise "unexpected directory: #{dir_file} != #{dir_source_location}" unless dir_file == dir_source_location

      @lines ||= File.readlines(file) # cached source code
      @lines[line].match(/\s*(.\w+)/)[1] # TODO: should be uppercase!
    end
  end
end