module BjnInventory

    class ByKey < Hash

        def escape_name(value)
            value.gsub(/[^a-zA-Z0-9_-]+/, '_')
        end

        def _field_groups(fields, device, sep='__')
            fields = [fields] unless fields.respond_to? :inject
            value_map = fields.map do |field|
                values = device[field]
                values = [values] unless values.respond_to? :map
                values.map { |val| escape_name(val) }
            end
            #
            # So now we have an array of arrays, eg.:
            # fields='region' =>
            # [['dc2']]
            #
            # fields=['roles', 'region'] =>
            # [['web', ['dc2']]
            #   'db'],
            #
            groups =
                if fields.length == 1
                    value_map.first
                else
                    driving_array, *rest = value_map
                    driving_array.product(*rest).map { |compound_value| compound_value.join(sep) }
                end
            groups
        end

        # This basically builds an ansible inventory given a hash of hostvars
        def to_groups(kwargs)
            group_by = kwargs[:group_by]

            if group_by.empty?
                raise ArgumentError, "Expected group_by either as keyword or as argument list"
            end

            logger = kwargs[:logger] || BjnInventory::DefaultLogger.new
            # We need at least one field to create groups
            separator = kwargs[:separator] || '__'

            groups = { }

            self.each do |name, device_hash|
                group_by.each do |group_field_spec|
                    group_field_spec = [group_field_spec] unless group_field_spec.respond_to? :all?
                    if group_field_spec.all? { |field| !device_hash[field].nil? && !device_hash[field].empty? }
                        field_groups = _field_groups(group_field_spec, device_hash, separator)
                        field_groups.each do |group_name|
                            groups[group_name] = [ ] unless groups.has_key? group_name
                            groups[group_name] << name
                        end
                    end
                end
            end

            # I can't really do children, they need to be generators and I'm not
            # about that right now. Save it for ansible.

            groups
        end


    end

end