package atom

import (
	"encoding/xml"
	"errors"
)

type CommonAttributes struct {
	Base                string      `xml:"base,attr,omitempty"` // IRI
	Lang                string      `xml:"lang,attr,omitempty"` // LanguageTag
	UndefinedAttributes []*xml.Attr `xml:",attr,omitempty"`
}

// NewCommonAttributes creates a new set of CommonAttributes. It returns a
// *CommonAttributes.
func NewCommonAttributes() *CommonAttributes {
	return new(CommonAttributes)
}

// AddAttribute adds the Attribute to the CommonAttributes. It returns an error.
func (c *CommonAttributes) AddAttribute(name, value string) error {
	if name == "" {
		return errors.New("error adding attribute: name string empty")
	}
	if value == "" {
		return errors.New("error adding attribute: value string empty")
	}

	if c.UndefinedAttributes == nil {
		c.UndefinedAttributes = make([]*xml.Attr, 1)
		c.UndefinedAttributes[0] = &xml.Attr{Name: xml.Name{Local: name}, Value: value}
	} else {
		c.UndefinedAttributes = append(c.UndefinedAttributes, &xml.Attr{Name: xml.Name{Local: name}, Value: value})
	}

	return nil
}