class Species < ActiveRecord::Base
  set_primary_key :name
  
  create_table do
    string   'name'
    integer  'population'
    float    'diet_emission_intensity'
    string   'diet_emission_intensity_units'
    float    'weight'
    string   'weight_units'
    float    'marginal_dietary_requirement'
    string   'marginal_dietary_requirement_units'
    float    'fixed_dietary_requirement'
    string   'fixed_dietary_requirement_units'
    float    'minimum_weight'
    string   'minimum_weight_units'
    float    'maximum_weight'
    string   'maximum_weight_units'
  end
  
  scope :thoroughly_researched, :conditions => 'marginal_dietary_requirement IS NOT NULL'
  
  falls_back_on :diet_emission_intensity => lambda { weighted_average :diet_emission_intensity, :weighted_by => :population }, # kg CO2 / joule
                :marginal_dietary_requirement => lambda { Species.marginal_dietary_requirement_fallback },
                :fixed_dietary_requirement => 0, # force a zero intercept to be respectful of our tiny tiny animal friends
                :weight => lambda { weighted_average :weight, :weighted_by => :population } # kg

  class << self
    def [](name)
      find_by_name name.to_s
    end

    def marginal_dietary_requirement_fallback
      total_diet_size = thoroughly_researched.map(&:weighted_diet_size).sum
      total_population = thoroughly_researched.sum(:population)
      return 0.0 unless total_population > 0.0
      average_weight = thoroughly_researched.weighted_average(:weight, :weighted_by => :population)
      return 0.0 unless average_weight > 0.0
      (total_diet_size / total_population) / average_weight
    end
  end
  
  def diet_size
    return unless weight and marginal_dietary_requirement and fixed_dietary_requirement
    weight * marginal_dietary_requirement + fixed_dietary_requirement
  end
  
  def weighted_diet_size
    return unless _diet_size = diet_size and _population = population
    _diet_size * _population
  end
  
  def to_s
    name
  end
  
  def cat?
    eql? self.class[:cat]
  end
end