mjacobus / nurse-rb

  class DependencyContainer

    class UndefinedDependency < RuntimeError; end

    class DependencyAlreadyDefined < RuntimeError; end

    def initialize

      @factories = {}

      @shared_factories = {}

      @instances = {}

    end

    def share(dependency, &block)

      ensure_undefined(dependency)

      shared_factories[to_key(dependency)] = block

      self

    end

    def set(dependency, &block)

      ensure_undefined(dependency)

      factories[to_key(dependency)] = block

      self

    end

    def defined?(dependency)

      key = to_key(dependency)

      shared_factories.key?(key) || factories.key?(key)

    end

    def get(dependency, &_block)

      key = to_key(dependency)

      if self.defined?(key)

        return from_shared_factories(key) || from_factories(key)

      end

      return yield if block_given?

      fail UndefinedDependency, "'#{dependency}' was not defined"

    end

    protected

    attr_reader :factories

    attr_reader :instances

    attr_reader :shared_factories

    def from_shared_factories(key)

      return unless shared_factories.key?(key)

      instances[key] ||= shared_factories[key].call(self)

    end

    def from_factories(key)

      factories[key].call(self) if factories.key?(key)

    end

    def ensure_undefined(dependency)

      return unless self.defined?(dependency)

      fail DependencyAlreadyDefined,

           "Dependency '#{dependency}' was already defined"

    end

    def to_key(object)

      object.to_s

    end

  end

end