package classes

import "strings"

// The sitemap document is written by hand in the exact format PHP's
// DOMDocument::saveXML (libxml2) produced for the PHP plugin: the XML
// declaration and the stylesheet processing instruction each followed by a
// newline, everything else on one line, an empty urlset self-closed,
// xhtml:link elements self-closed without a space. The standard library's
// XML encoder escapes and closes elements differently, so the writer is a
// strings.Builder.

// The urlset opening tag's attributes, in the order PHP set them.
const urlsetAttrs = ` xmlns="http://www.sitemaps.org/schemas/sitemap/0.9"` +
	` xmlns:xhtml="http://www.w3.org/1999/xhtml"` +
	` xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"` +
	` xsi:schemaLocation="http://www.sitemaps.org/schemas/sitemap/0.9 http://www.sitemaps.org/schemas/sitemap/0.9/sitemap.xsd"`

// textEscaper is libxml's escaping of text nodes: &, <, > and carriage
// return; quotes, tabs, newlines and UTF-8 stay literal.
var textEscaper = strings.NewReplacer("&", "&amp;", "<", "&lt;", ">", "&gt;", "\r", "&#13;")

// attrEscaper is libxml's escaping of attribute values: also the double
// quote, tab and newline; the single quote stays literal.
var attrEscaper = strings.NewReplacer(
	"&", "&amp;", "<", "&lt;", ">", "&gt;", `"`, "&quot;",
	"\r", "&#13;", "\t", "&#9;", "\n", "&#10;",
)

// EscapeText escapes s as libxml writes a text node.
func EscapeText(s string) string { return textEscaper.Replace(s) }

// EscapeAttr escapes s as libxml writes an attribute value.
func EscapeAttr(s string) string { return attrEscaper.Replace(s) }

// Alternate is one hreflang link of a sitemap URL.
type Alternate struct {
	Hreflang string
	Href     string
}

// URLEntry is one url element: Loc, an optional Lastmod, Changefreq and
// Priority as they are written, the alternates (written only when there are
// more than one) and Extra, pre-escaped child XML that AddItem listeners
// appended, written before the closing tag.
type URLEntry struct {
	Loc        string
	Lastmod    string
	Changefreq string
	Priority   string
	Alternates []Alternate
	Extra      []string
}

// writeURL appends one url element.
func writeURL(b *strings.Builder, e URLEntry) {
	b.WriteString("<url><loc>")
	b.WriteString(EscapeText(e.Loc))
	b.WriteString("</loc>")
	if e.Lastmod != "" {
		b.WriteString("<lastmod>")
		b.WriteString(EscapeText(e.Lastmod))
		b.WriteString("</lastmod>")
	}
	b.WriteString("<changefreq>")
	b.WriteString(EscapeText(e.Changefreq))
	b.WriteString("</changefreq><priority>")
	b.WriteString(EscapeText(e.Priority))
	b.WriteString("</priority>")
	if len(e.Alternates) > 1 {
		for _, a := range e.Alternates {
			b.WriteString(`<xhtml:link rel="alternate" hreflang="`)
			b.WriteString(EscapeAttr(a.Hreflang))
			b.WriteString(`" href="`)
			b.WriteString(EscapeAttr(a.Href))
			b.WriteString(`"/>`)
		}
	}
	for _, x := range e.Extra {
		b.WriteString(x)
	}
	b.WriteString("</url>")
}

// Serialize writes the sitemap document: the XML declaration, the
// stylesheet processing instruction pointing at stylesheet (written as it
// is, like libxml writes PI data) and the urlset with entries.
func Serialize(stylesheet string, entries []URLEntry) string {
	var b strings.Builder
	b.WriteString("<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n")
	b.WriteString(`<?xml-stylesheet type="text/xsl" href="`)
	b.WriteString(stylesheet)
	b.WriteString("\"?>\n<urlset")
	b.WriteString(urlsetAttrs)
	if len(entries) == 0 {
		b.WriteString("/>\n")
		return b.String()
	}
	b.WriteString(">")
	for _, e := range entries {
		writeURL(&b, e)
	}
	b.WriteString("</urlset>\n")
	return b.String()
}