atom/link.go

package atom

import (
	"errors"
	"fmt"
	"strings"
)

type Link struct {
	*CommonAttributes
	Title    string      `xml:"title,attr,omitempty"`
	Content  string      `xml:",any"` // undefinedContent in RFC4287
	Href     IRI         `xml:"href,attr"`
	Rel      string      `xml:"rel,attr,omitempty"`
	Type     MediaType   `xml:"type,attr,omitempty"`
	HrefLang LanguageTag `xml:"hreflang,attr,omitempty"`
	Length   uint        `xml:"length,attr,omitempty"`
}

// NewLink creates a new Link. It returns a *Link and an error.
func NewLink(href, content string) (*Link, error) {
	return &Link{Href: IRI(href), Content: content}, nil
}

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

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

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

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

	if l.Content == "" {
		return errors.New("content element of link empty")
	}

	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
}