script to convert go tour html to present file format

conv.go

package main

import (
	"bytes"
	"exp/html"
	"fmt"
	"io/ioutil"
	"log"
	"os"
	"regexp"
	"strings"
)

func main() {
	root, err := html.Parse(os.Stdin)
	if err != nil {
		log.Fatal(err)
	}
	f, err := os.Create("tour.article")
	if err != nil {
		log.Fatal(err)
	}
	defer f.Close()
	fmt.Fprintln(f, header)
	for n, s := range findAll(root, hasClass("slide")) {
		title := text(find(s, isTag("h2")))
		fmt.Fprintf(f, "* %v\n\n", title)
		fmt.Fprint(f, slideText(s))
		source := text(find(s, hasClass("source")))
		if source != "" {
			fn := "tour/" + filename(n, title)
			ioutil.WriteFile(fn, []byte(source), 0666)
			fmt.Fprintf(f, ".play %s\n\n", fn)
		}
	}
}

const header = `
A Tour of Go

The Go Authors
http://golang.org
`

var nonSafe = regexp.MustCompile(`[^a-z ]`)

func filename(n int, title string) string {
	title = strings.ToLower(title)
	title = nonSafe.ReplaceAllString(title, "")
	title = strings.TrimSpace(title)
	title = strings.Replace(title, " ", "-", -1)
	return fmt.Sprintf("%03d-%s.go", n, title)
}

func slideText(s *html.Node) string {
	var buf bytes.Buffer
	walk(s, func(n *html.Node) bool {
		switch {
		case isTag("p")(n):
			buf.WriteString(wrap(text(n)))
		case isTag("pre")(n) && !hasClass("source")(n):
			buf.WriteString(indent(text(n)))
			buf.WriteByte('\n')
		default:
			return true
		}
		return false
	})
	return buf.String()
}

func indent(s string) string {
	var buf bytes.Buffer
	for _, l := range strings.Split(s, "\n") {
		buf.WriteByte('\t')
		buf.WriteString(l)
		buf.WriteByte('\n')
	}
	return buf.String()
}

func wrap(s string) string {
	var buf bytes.Buffer
	var cont bool
	for _, l := range strings.Split(s, "\n") {
		l = strings.TrimSpace(l)
		if len(l) == 0 {
			if cont {
				buf.WriteByte('\n')
				buf.WriteByte('\n')
			}
			cont = false
		} else {
			if cont {
				buf.WriteByte(' ')
			}
			buf.WriteString(l)
			cont = true
		}
	}
	return buf.String()
}

func text(n *html.Node) string {
	var buf bytes.Buffer
	walk(n, func(n *html.Node) bool {
		if hasClass("appengineMode")(n) {
			return false
		}
		if n.Type == html.TextNode {
			buf.WriteString(n.Data)
		}
		return true
	})
	return buf.String()
}

type selector func(*html.Node) bool

func isTag(name string) selector {
	return func(n *html.Node) bool {
		return n.DataAtom.String() == name
	}
}

func hasClass(name string) selector {
	return func(n *html.Node) bool {
		for _, a := range n.Attr {
			if a.Key == "class" {
				for _, c := range strings.Fields(a.Val) {
					if c == name {
						return true
					}
				}
			}
		}
		return false
	}
}

func findAll(node *html.Node, fn selector) (nodes []*html.Node) {
	walk(node, func(n *html.Node) bool {
		if fn(n) {
			nodes = append(nodes, n)
		}
		return true
	})
	return
}

func find(n *html.Node, fn selector) *html.Node {
	var result *html.Node
	walk(n, func(n *html.Node) bool {
		if result != nil {
			return false
		}
		if fn(n) {
			result = n
			return false
		}
		return true
	})
	return result
}

func walk(n *html.Node, fn selector) {
	var w func(*html.Node, bool)
	w = func(n *html.Node, first bool) {
		if n == nil {
			return
		}
		if fn(n) {
			w(n.FirstChild, false)
		}
		if !first {
			w(n.NextSibling, false)
		}
		return
	}
	w(n, true)
}