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package internal
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import (
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"bytes"
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"fmt"
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"io"
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"log"
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"strings"
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"golang.org/x/net/html"
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"golang.org/x/net/html/atom"
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)
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type Doc struct{}
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type Assets struct {
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Images []Asset
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Styles []Asset
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Scripts []Asset
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}
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type Asset struct{}
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// Merges an HTML document over top of a base template.
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//
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// <head>
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// - <title> of the new doc overrides the base <title> unless the base
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// contains {{content}}, in which case the new title is substituted
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// - <style> elements from the new doc are placed after any base <style>
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// - all other elements are appended to the base
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//
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// <body>
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// - the <header> and <footer> and <main> elemnts are merged.
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// in the base document, these elements may appear abitrarily nested inside
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// wrapper elements; mergehtml will reproduce that structure in the merged document.
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// if there are multiples, only the first will be used for merging.
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// if they do not appear in the base doc, they will be appended to the body (header: prepended).
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// in the source document, these elements will be removed from any
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// containing elements before merging. if there are multiples their contents
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// will be concatenated.
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// html5 allows multiple <main> elements if all but one are hidden. mergehtml does not.
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// - <script> elements are placed at the end of the body
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// - all other elements are appended to <main> if it exists, or <body> if not.
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//
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// any classes attached to the <body>, <header>, <footer>, or <main> will be merged.
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//
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// all scripts and images will be collected and returned in the Assets object
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//
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func Merge(base, doc io.Reader) (merged string, assets *Assets, _ error) {
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baseParsed, err := html.Parse(base)
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if err != nil {
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return "", nil, fmt.Errorf("couldn't parse base html: %w", err)
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}
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docParsed, err := html.Parse(doc)
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if err != nil {
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return "", nil, fmt.Errorf("couldn't parse doc: %w", err)
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}
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out := merge(baseParsed, docParsed)
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buf := new(bytes.Buffer)
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err = html.Render(buf, out)
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if err != nil {
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panic(err)
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}
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assets = new(Assets)
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return buf.String(), assets, nil
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}
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// merges doc into base. doc and base are modified in the process.
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func merge(base, doc *html.Node) (out *html.Node) {
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out, err := html.Parse(strings.NewReader("<!doctype html><html><head></head><body></body></html>"))
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if err != nil {
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panic("mergehtml: internal error: " + err.Error())
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}
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// TODO: title
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html := find(out, atom.Html)
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if html == nil {
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log.Panicf("no <html> in %v", out)
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}
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head := find(html, atom.Head)
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reparentChildren(head, find(find(base, atom.Html), atom.Head))
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reparentChildren(head, find(find(doc, atom.Html), atom.Head))
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body := find(html, atom.Body)
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if body == nil {
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log.Panicf("no <body> in %v", html)
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}
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baseBody := find(find(base, atom.Html), atom.Body)
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newBody := find(find(doc, atom.Html), atom.Body)
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reparentChildren(body, baseBody)
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header := findRec(body, atom.Header)
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footer := findRec(body, atom.Footer)
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main := findRec(body, atom.Main)
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if header == nil {
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header = createElement(atom.Header)
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body.InsertBefore(header, body.FirstChild)
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}
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for {
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n := findRec(newBody, atom.Header)
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if n == nil {
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break
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}
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reparentChildren(header, n)
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n.Parent.RemoveChild(n)
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}
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if footer == nil {
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footer = createElement(atom.Header)
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body.InsertBefore(footer, body.FirstChild)
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}
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for {
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n := findRec(newBody, atom.Footer)
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if n == nil {
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break
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}
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reparentChildren(footer, n)
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n.Parent.RemoveChild(n)
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}
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_ = main // TODO
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return out
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}
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func createElement(a atom.Atom) *html.Node {
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return &html.Node{DataAtom: a, Data: a.String(), Type: html.ElementNode}
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}
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// reparentChildren reparents all of src's child nodes to dst.
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func reparentChildren(dst, src *html.Node) {
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if src == nil {
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return
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}
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for {
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child := src.FirstChild
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if child == nil {
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break
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}
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src.RemoveChild(child)
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dst.AppendChild(child)
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}
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}
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func find(elem *html.Node, tagName atom.Atom) *html.Node {
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if elem != nil {
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for n := elem.FirstChild; n != nil; n = n.NextSibling {
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if n.DataAtom == tagName {
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return n
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}
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}
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}
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return nil
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}
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// Find the first element named tagName that is a descendent of the given HTML node.
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// Returns nil if no element found.
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func findRec(elem *html.Node, tagName atom.Atom) *html.Node {
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if elem != nil {
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for c := elem.FirstChild; c != nil; c = c.NextSibling {
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if c.Type == html.ElementNode && c.DataAtom == tagName {
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return c
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}
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if d := findRec(c, tagName); d != nil {
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return d
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}
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}
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}
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return nil
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}
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// clone returns a new node with the same type, data and attributes.
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// The clone has no parent, no siblings and no children.
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func clone(n *html.Node) *html.Node {
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m := &html.Node{
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Type: n.Type,
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DataAtom: n.DataAtom,
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Data: n.Data,
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Attr: make([]html.Attribute, len(n.Attr)),
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}
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copy(m.Attr, n.Attr)
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return m
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}
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