module Prosperity
  class Metric 
    def self.scope(&block)
      if block_given?
        @scope = block.call
      else
        raise MissingScope.new if @scope.nil?
        @scope
      end
    end

    def self.sql(fragment = nil, &block)
      if fragment && block_given?
        raise ArgumentError, "Must pass string or block but not both"
      elsif fragment
        @sql = fragment
      elsif block_given?
        @sql = block.call
      elsif @sql.nil?
        raise MissingSql.new
      else
        @sql
      end
    end

    def self.option(name, &block)
      raise SqlMetricCannotHaveOption.new unless @sql.nil?
      @options ||= default_options
      if block_given?
        @options[name] = Metrics::Option.new(name, &block)
      else
        raise MissingScope.new
      end
    end

    def self.value_at(&block)
      if block_given?
        @value_at = block
      else
        @value_at or raise MissingValueAt
      end
    end

    def self.options
      @options ||= default_options
    end

    def self.group_by(column = nil)
      if column
        @group_by = column
      else
        @group_by || :created_at
      end
    end

    def self.aggregate(&block)
      if block_given?
        @aggregate = ::Prosperity::Aggregate::AggregateBuilder.new(&block).build
      else
        @aggregate || ::Prosperity::Aggregate::Count.new
      end
    end

    def self.extractors
      [Extractors::Interval, Extractors::Total, Extractors::Change].inject({}) do |h, ext|
        h[ext.key] = ext
        h
      end
    end

    def self.sql?
      @sql.present?
    end

    def self.ruby?
      @value_at.present?
    end

    def extractors
      self.class.extractors.values
    end

    def group_by
      self.class.group_by
    end

    def scope
      self.class.scope
    end

    def sql
      self.class.sql
    end

    def value_at
      self.class.value_at
    end

    def options
      self.class.options
    end

    def aggregate
      self.class.aggregate
    end

    def title
      self.class.to_s.gsub(/Metric$/, "").titleize
    end

    def id
      self.class.name
    end

    def sql?
      self.class.sql?
    end

    def ruby?
      self.class.ruby?
    end

    private

    def self.default_options
      o = Metrics::Option.new("default") do |scope|
        scope
      end
      {"default" => o}
    end
  end
end