easy-going-rails/lib/hot/constants.rb

require 'dotenv'

module Hot
  # Hot Live Constants
  module Constants
    include SemanticLogger::Loggable
    HOTENV = {} # rubocop:disable Style/MutableConstant
    LISTENERS = {} # rubocop:disable Style/MutableConstant

    class << self
      def initialize
        @old_definitions = {}
        @hot_definitions = {}

        logger.level = :fatal
        load_definitions
        load_values
        logger.level = :info
      end

      def load_definitions
        logger.debug('--load_definitions3')

        new_definitions = Dotenv.parse('.env.sample')

        definitions_to_actualize = {}
        @old_definitions.merge(new_definitions) do |key, old_value, new_value|
          definitions_to_actualize[key] = new_value if new_value != old_value
        end
        definitions_to_actualize.each { |key, value| define_method(:actualize, key, value) }

        @old_definitions = new_definitions

        definitions_to_remove = @hot_definitions.except(*new_definitions.keys)
        definitions_to_remove.each_pair do |key, dkey|
          logger.info("remove method <#{dkey}>")
          singleton_class.undef_method(dkey)
          @hot_definitions.delete(key)
        end

        definitions_to_add = new_definitions.except(*@hot_definitions.keys)
        definitions_to_add.each { |key, value| define_method(:add, key, value) }
      end

      def load_values
        logger.debug('--load_values')

        new_env = Dotenv.parse
        constants_to_delete = HOTENV.except(*new_env.keys)
        constants_to_delete.each do |name, _|
          # FIXME: default should read default and type from @old_definitions
          type, default = @old_definitions[name]
          logger.info("constant <#{name}> reverts to default value <#{default}> of type <#{type}>")
        end

        constants_to_add = new_env.except(*HOTENV.keys)
        constants_to_add.each do |constant|
          logger.info("constant to add <#{constant}>")
        end

        HOTENV.replace new_env
        LISTENERS.each_pair { |k, b| perform_change(k, b) }
      end

      def on_change(key, &block)
        LISTENERS[key.downcase.to_sym] = block
        perform_change(key, block)
      end

      private

      def define_method(mode, key, value)
        dkey = key.downcase
        method = infer_method_from_value(value)

        inferred_type = method.name.to_s.split('_')[1]
        logger.info("#{mode} method <#{dkey}> of type <#{inferred_type}> with default value <#{value}> ")

        singleton_class.define_method(dkey) { method.call(key, value) }
        @hot_definitions.store(key, dkey)
      end

      def perform_change(key, block)
        old_value = nil # TODO: remember last previous value
        new_value = method(key).call
        block.call(new_value, old_value)
      end

      def load_boolean(key, default) = HOTENV.fetch(key, default).to_s.downcase == 'true'
      def load_integer(key, default) = HOTENV.fetch(key, default).to_i
      def load_string(key, default) = HOTENV.fetch(key, default)

      def infer_method_from_value(value)
        case value.downcase
        when /^(true|false)$/ then method(:load_boolean)
        when /^\d+$/ then method(:load_integer)
        else method(:load_string)
        end
      end
    end

    initialize # done once on first require, cause this is just a module (not a class!)
  end
end