module SeedFu
  class Seeder
    def self.plant(model_class, *constraints, &block)
      constraints = [:id] if constraints.empty?
      seed = Seeder.new(model_class)
      seed.set_constraints(*constraints)
      yield seed
      seed.plant!
    end
  
    def initialize(model_class)
      @model_class = model_class
      @constraints = [:id]
      @data = {}
    end
  
    def set_constraints(*constraints)
      raise "You must set at least one constraint." if constraints.empty?
      @constraints = []
      constraints.each do |constraint|
        raise "Your constraint `#{constraint}` is not a column in #{@model_class}. Valid columns are `#{@model_class.column_names.join("`, `")}`." unless @model_class.column_names.include?(constraint.to_s)
        @constraints << constraint.to_sym
      end
    end
  
    def set_attribute(name, value)
      @data[name.to_sym] = value
    end
  
    def plant!
      record = get
      @data.each do |k, v|
        record.send("#{k}=", v)
      end
      record.save!
      puts " - #{@model_class} #{condition_hash.inspect}"
      record
    end
  
    def method_missing(method_name, *args) #:nodoc:
      if (match = method_name.to_s.match(/(.*)=$/)) && args.size == 1
        set_attribute(match[1], args.first)
      else
        super
      end
    end
  
    protected
  
    def get
      records = @model_class.find(:all, :conditions => condition_hash)
      raise "Given constraints yielded multiple records." unless records.size < 2
      if records.any?
        return records.first
      else
        return @model_class.new
      end
    end
  
    def condition_hash
      @data.reject{|a,v| !@constraints.include?(a)}
    end
  end
end


class ActiveRecord::Base
  # Creates a single record of seed data for use
  # with the db:seed rake task. 
  # 
  # === Parameters
  # constraints :: Immutable reference attributes. Defaults to :id
  def self.seed(*constraints, &block)
    SeedFu::Seeder.plant(self, *constraints, &block)
  end
end