htmlhelp.go

package main

import (
	"regexp"
	"sort"
	"strings"

	"golang.org/x/net/html"
)

func AppendNodes(node *html.Node, children ...*html.Node) *html.Node {
	for _, c := range children {
		if c != nil {
			node.AppendChild(c)
		}
	}
	return node
}

func DocumentNode(doctype string, children ...*html.Node) *html.Node {
	node := &html.Node{Type: html.DocumentNode}
	node.AppendChild(&html.Node{Type: html.DoctypeNode, Data: doctype})
	return AppendNodes(node, children...)
}

func TextNode(data string) *html.Node {
	return &html.Node{Type: html.TextNode, Data: data}
}

func CommentNode(data string) *html.Node {
	return &html.Node{Type: html.CommentNode, Data: data}
}

// Return an element with given attributes and children.
func Element(tag string, attributes map[string]string, children ...*html.Node) *html.Node {
	node := &html.Node{Type: html.ElementNode, Data: tag}
	if len(attributes) > 0 {
		keys := make([]string, 0, len(attributes))
		for k := range attributes {
			keys = append(keys, k)
		}
		sort.Strings(keys)
		for _, k := range keys {
			node.Attr = append(node.Attr, html.Attribute{Key: k, Val: attributes[k]})
		}
	}
	return AppendNodes(node, children...)
}

////////////////////////////////////////////////////////////////////////////////

func FindNodeByTagAndAttrib(root *html.Node, tag, key, value string) *html.Node {
	// I unrolled a recursive function to use no recursion, or heap allocation,
	// only loops.  This is allowed by the existance of Parent pointer.
	if root == nil {
		return nil
	}
	node := root
	for {
		if node.Type == html.ElementNode && (tag == "" || node.Data == tag) {
			if key == "" {
				return node
			}
			for _, attr := range node.Attr {
				if attr.Key == key && attr.Val == value {
					return node
				}
			}
		}
		if node.FirstChild != nil {
			node = node.FirstChild
			continue
		}
		for {
			if node == root || node == nil {
				return nil
			}
			if node.NextSibling != nil {
				node = node.NextSibling
				break
			}
			node = node.Parent
		}
	}
}

func FindNodeByTag(node *html.Node, tag string) *html.Node {
	return FindNodeByTagAndAttrib(node, tag, "", "")
}

func FindNodeById(node *html.Node, id string) *html.Node {
	return FindNodeByTagAndAttrib(node, "", "id", id)
}

func FindNodeByAttribute(node *html.Node, key, value string) *html.Node {
	return FindNodeByTagAndAttrib(node, "", key, value)
}

var whitespaceRegexp = regexp.MustCompile("\\s+")

// Extract and combine all Text Nodes under given node.
func ExtractText(root *html.Node) string {
	if root == nil {
		return ""
	}
	var accumulator strings.Builder
	node := root
	for {
		if node.Type == html.TextNode {
			accumulator.WriteString(whitespaceRegexp.ReplaceAllString(node.Data, " "))
		}
		if node.Type == html.ElementNode {
			switch node.Data {
			case "br":
				accumulator.WriteString("\n")
			case "hr":
				accumulator.WriteString("\n* * *\n")
			case "p":
				accumulator.WriteString("\n\n")
			}
		}

		if node.FirstChild != nil {
			node = node.FirstChild
			continue
		}
		for {
			if node == root || node == nil {
				return accumulator.String()
			}
			if node.NextSibling != nil {
				node = node.NextSibling
				break
			}
			node = node.Parent
		}
	}
}

////////////////////////////////////////////////////////////////////////////////

func example(w io.Writer) error {
	return html.Render(w,
		DocumentNode("html",
			TextNode("\n"),
			Element("html", map[string]string{"lang": "en"},
				TextNode("\n"),
				Element("head", nil,
					TextNode("\n"),
					Element("meta", map[string]string{"charset": "utf-8"}),
					TextNode("\n"),
					CommentNode("\nthis is an example\n"),
					TextNode("\n"),
					Element("meta", map[string]string{
						"name": "viewport", "content": "width=device-width, initial-scale=1.0"}),
					TextNode("\n"),
					Element("title", nil, TextNode("Hello World!")),
					TextNode("\n"),
					Element("style", nil, TextNode("\nbody{font-family: sans-serif;}\n")),
					TextNode("\n"),
				),
				TextNode("\n"),
				Element("body", nil,
					Element("h1", nil, TextNode("Hello World!")),
				),
				TextNode("\n"),
			),
			TextNode("\n"),
		),
	)
}