module Shoebox
  class Storage
    UnknownResourceType = Class.new(StandardError)

    attr_reader :resource_types, :data

    def initialize(*resource_types)
      @resource_types = resource_types
      reset
    end

    def fetch(resource_type, resource_id, &value)
      validate_resource_type(resource_type)

      data[resource_type][resource_id] ||= value.call
    end

    def stash(resource_type, resource_id, value)
      validate_resource_type(resource_type)

      data[resource_type][resource_id] = value
    end

    def get(resource_type, resource_id)
      validate_resource_type(resource_type)

      data[resource_type][resource_id]
    end

    def reset
      @data = Hash.new
      resource_types.each do |resource_type|
        data[resource_type] = Hash.new
      end
    end

    private
    def data
      @data
    end

    def validate_resource_type(resource_type)
      unless resource_types.include?(resource_type)
        raise UnknownResourceType.new(
          "#{resource_type} is not a known resource type"
        )
      end
    end
  end
end