dashboard_metrics.rb

class DashboardMetrics < MetricsDefinition

  metric "github stargazers" do |m|
    m.reason = "Hallo!"

    m.fetch_with do
      5
    end
  end

end

metric.rb

class Metric < ActiveRecord::Base
  attr_accessor :reason

  has_many :daily_metrics

  def fetch_with(block)
    @block = block
  end

  def fetch
    daily_metric = daily_metrics.where(date: Date.today).first_or_initialize

    value = @block.call

    daily_metric.value = value

    daily_metric.save
  end

end

metrics_definition.rb

class MetricsDefinition

  cattr_accessor :definition
  attr_accessor :metrics

  class << self

    def inherited(base)
      super
      MetricsDefinition.definition ||= self.new
    end

    def metric(name)

      m = Metric.new

      yield(m)

      MetricsDefinition.definition.metrics << m

    end

  end

  def initialize
    @metrics = []
  end

  def run_fetchers()
    @metrics.each do |m|
      m.fetch
    end
  end

end