atom/link.go

package atom

import (
	"encoding/xml"
	"fmt"
	"strings"
)

type Link struct {
	XMLName xml.Name `xml:"link"`
	*CommonAttributes
	Title    string `xml:"title,attr,omitempty"`
	Href     string `xml:"href,attr"` // IRI
	Rel      string `xml:"rel,attr,omitempty"`
	Type     string `xml:"type,attr,omitempty"`     // MediaType
	HrefLang string `xml:"hreflang,attr,omitempty"` // LanguageTag
	Length   uint   `xml:"length,attr,omitempty"`
}

// NewLink creates a new Link. It returns a *Link.
func NewLink(href string) *Link {
	return &Link{Href: href}
}

// Check checks the Link for incompatibilities with RFC4287. It returns an
// error.
func (l *Link) Check() error {
	if l.Href == "" {
		return fmt.Errorf("href attribute of link %v empty", l)
	} else {
		if !isValidIRI(l.Href) {
			return fmt.Errorf("href attribute of link %v not correctly formatted", l)
		}
	}

	if l.Rel != "" {
		if strings.Contains(l.Rel, ":") && !isValidIRI(l.Rel) {
			return fmt.Errorf("rel attribute of link %v not correctly formatted", l)
		}
	}

	if l.Type != "" {
		if !isValidMediaType(l.Type) {
			return fmt.Errorf("type attribute of link %v invalid media type", l)
		}
	}

	if l.HrefLang != "" {
		if !isValidLanguageTag(l.HrefLang) {
			return fmt.Errorf("hreflang attribute of link %v invalid language tag", l)
		}
	}

	return nil
}

// hasAlternateDuplicateLinks checks whether multiple Links with Rel
// "alternate" also have Type and HrefLang in common. It returns a bool.
// atom:feed/entry elements MUST NOT contain more than one atom:link element
// with a rel attribute value of "alternate" that has the same combination of
// type and hreflang attribute values.
func hasAlternateDuplicateLinks(l []*Link) bool {
	linkMap := make(map[string]bool)

	for _, link := range l {
		if link.Rel == "alternate" {
			key := fmt.Sprint(link.Type, "|", link.HrefLang)
			if linkMap[key] {
				return true
			}
			linkMap[key] = true
		}
	}

	return false
}

// alternateRelExists checks whether multiple Links with Rel "alternate" exist.
// It returns a bool.
func alternateRelExists(l []*Link) bool {
	for _, link := range l {
		if link.Rel == "alternate" {
			return true
		}
	}

	return false
}