mgsnova/feature

# Feature module provides all methods
# - to set a feature repository
# - to check if a feature (represented by a symbol) is active or inactive
# - for conditional block execution with or without a feature
# - to refresh the feature lists (request them from repository)
#
# @note all features not active will be handled has inactive
#
# Example usage:
#   repository = SimpleRepository.new
#   repository.add_active_feature(:feature_name)
#
#   Feature.set_repository(repository)
#   Feature.active?(:feature_name)
#   # => true
#   Feature.inactive?(:inactive_feature)
#   # => false
#
#   Feature.with(:feature_name) do
#     # code will be executed
#   end
#
module Feature
  require 'feature/repository'
  require 'feature/generators/install_generator'

  @repository = nil
  @active_features = nil

  # Set the feature repository
  # The given repository has to respond to method 'active_features' with an array of symbols
  #
  # @param [Object] repository the repository to get the features from
  # @param [Boolean|Integer] refresh optional (default: false) - auto refresh or refresh after given number of seconds
  #
  def self.set_repository(repository, refresh = false)
    unless repository.respond_to?(:active_features)
      raise ArgumentError, 'given repository does not respond to active_features'
    end

    @perform_initial_refresh = true
    @repository = repository
    if [true, false].include?(refresh)
      @auto_refresh = refresh
    else
      @auto_refresh = false
      @refresh_after = refresh
      @next_refresh_after = Time.now + @refresh_after
    end
  end

  # Refreshes list of active features from repository.
  # Useful when using an repository with external source.
  #
  def self.refresh!
    @active_features = @repository.active_features
    @next_refresh_after = Time.now + @refresh_after if @refresh_after
    @perform_initial_refresh = false
  end

  ##
  # Requests if feature is active
  #
  # @param [Symbol] feature
  # @return [Boolean]
  #
  def self.active?(feature)
    active_features.include?(feature)
  end

  # Requests if feature is inactive (or unknown)
  #
  # @param [Symbol] feature
  # @return [Boolean]
  #
  def self.inactive?(feature)
    !active?(feature)
  end

  # Execute the given block if feature is active
  #
  # @param [Symbol] feature
  #
  def self.with(feature)
    raise ArgumentError, "no block given to #{__method__}" unless block_given?

    yield if active?(feature)
  end

  # Execute the given block if feature is inactive
  #
  # @param [Symbol] feature
  #
  def self.without(feature)
    raise ArgumentError, "no block given to #{__method__}" unless block_given?

    yield if inactive?(feature)
  end

  # Return value or execute Proc/lambda depending on Feature status.
  #
  # @param [Symbol] feature
  # @param [Object] value / lambda to use if feature is active
  # @param [Object] value / lambda to use if feature is inactive
  #
  def self.switch(feature, l1, l2)
    if active?(feature)
      l1.instance_of?(Proc) ? l1.call : l1
    else
      l2.instance_of?(Proc) ? l2.call : l2
    end
  end

  # Return list of active feature flags.
  #
  # @return [Array] list of symbols
  #
  def self.active_features
    raise 'missing Repository for obtaining feature lists' unless @repository

    refresh! if @auto_refresh || @perform_initial_refresh || (@next_refresh_after && Time.now > @next_refresh_after)

    @active_features
  end
end