blob: 64be64b971c7550b9de916a167cb88b184ccd8e7 [file] [log] [blame]
// Copyright 2020 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Present2md converts legacy-syntax present files to Markdown-syntax present files.
//
// Usage:
//
// present2md [-w] [file ...]
//
// By default, present2md prints the Markdown-syntax form of each input file to standard output.
// If no input file is listed, standard input is used.
//
// The -w flag causes present2md to update the files in place, overwriting each with its
// Markdown-syntax equivalent.
//
// Examples
//
// present2md your.article
// present2md -w *.article
//
package main
import (
"bytes"
"flag"
"fmt"
"io"
"io/ioutil"
"log"
"net/url"
"os"
"strings"
"unicode"
"unicode/utf8"
"golang.org/x/tools/present"
)
func usage() {
fmt.Fprintf(os.Stderr, "usage: present2md [-w] [file ...]\n")
os.Exit(2)
}
var (
writeBack = flag.Bool("w", false, "write conversions back to original files")
exitStatus = 0
)
func main() {
log.SetPrefix("present2md: ")
log.SetFlags(0)
flag.Usage = usage
flag.Parse()
args := flag.Args()
if len(args) == 0 {
if *writeBack {
log.Fatalf("cannot use -w with standard input")
}
convert(os.Stdin, "stdin", false)
return
}
for _, arg := range args {
f, err := os.Open(arg)
if err != nil {
log.Print(err)
exitStatus = 1
continue
}
err = convert(f, arg, *writeBack)
f.Close()
if err != nil {
log.Print(err)
exitStatus = 1
}
}
os.Exit(exitStatus)
}
// convert reads the data from r, parses it as legacy present,
// and converts it to Markdown-enabled present.
// If any errors occur, the data is reported as coming from file.
// If writeBack is true, the converted version is written back to file.
// If writeBack is false, the converted version is printed to standard output.
func convert(r io.Reader, file string, writeBack bool) error {
data, err := ioutil.ReadAll(r)
if err != nil {
return err
}
if bytes.HasPrefix(data, []byte("# ")) {
return fmt.Errorf("%v: already markdown", file)
}
// Convert all comments before parsing the document.
// The '//' comment is treated as normal text and so
// is passed through the translation unaltered.
data = bytes.Replace(data, []byte("\n#"), []byte("\n//"), -1)
doc, err := present.Parse(bytes.NewReader(data), file, 0)
if err != nil {
return err
}
// Title and Subtitle, Time, Tags.
var md bytes.Buffer
fmt.Fprintf(&md, "# %s\n", doc.Title)
if doc.Subtitle != "" {
fmt.Fprintf(&md, "%s\n", doc.Subtitle)
}
if !doc.Time.IsZero() {
fmt.Fprintf(&md, "%s\n", doc.Time.Format("2 Jan 2006"))
}
if len(doc.Tags) > 0 {
fmt.Fprintf(&md, "Tags: %s\n", strings.Join(doc.Tags, ", "))
}
// Summary, defaulting to first paragraph of section.
// (Summaries must be explicit for Markdown-enabled present,
// and the expectation is that they will be shorter than the
// whole first paragraph. But this is what the blog does today.)
if strings.HasSuffix(file, ".article") && len(doc.Sections) > 0 {
for _, elem := range doc.Sections[0].Elem {
text, ok := elem.(present.Text)
if !ok || text.Pre {
// skip everything but non-text elements
continue
}
fmt.Fprintf(&md, "Summary:")
for i, line := range text.Lines {
fmt.Fprintf(&md, " ")
printStyled(&md, line, i == 0)
}
fmt.Fprintf(&md, "\n")
break
}
}
// Authors
for _, a := range doc.Authors {
fmt.Fprintf(&md, "\n")
for _, elem := range a.Elem {
switch elem := elem.(type) {
default:
// Can only happen if this type switch is incomplete, which is a bug.
log.Fatalf("%s: unexpected author type %T", file, elem)
case present.Text:
for _, line := range elem.Lines {
fmt.Fprintf(&md, "%s\n", markdownEscape(line, true))
}
case present.Link:
fmt.Fprintf(&md, "%s\n", markdownEscape(elem.Label, true))
}
}
}
// Invariant: the output ends in non-blank line now,
// and after printing any piece of the file below,
// the output should still end in a non-blank line.
// If a blank line separator is needed, it should be printed
// before the block that needs separating, not after.
if len(doc.TitleNotes) > 0 {
fmt.Fprintf(&md, "\n")
for _, line := range doc.TitleNotes {
fmt.Fprintf(&md, ": %s\n", line)
}
}
if len(doc.Sections) == 1 && strings.HasSuffix(file, ".article") {
// Blog drops section headers when there is only one section.
// Don't print a title in this case, to make clear that it's being dropped.
fmt.Fprintf(&md, "\n##\n")
printSectionBody(file, 1, &md, doc.Sections[0].Elem)
} else {
for _, s := range doc.Sections {
fmt.Fprintf(&md, "\n")
fmt.Fprintf(&md, "## %s\n", markdownEscape(s.Title, false))
printSectionBody(file, 1, &md, s.Elem)
}
}
if !writeBack {
os.Stdout.Write(md.Bytes())
return nil
}
return ioutil.WriteFile(file, md.Bytes(), 0666)
}
func printSectionBody(file string, depth int, w *bytes.Buffer, elems []present.Elem) {
for _, elem := range elems {
switch elem := elem.(type) {
default:
// Can only happen if this type switch is incomplete, which is a bug.
log.Fatalf("%s: unexpected present element type %T", file, elem)
case present.Text:
fmt.Fprintf(w, "\n")
lines := elem.Lines
for len(lines) > 0 && lines[0] == "" {
lines = lines[1:]
}
if elem.Pre {
for _, line := range strings.Split(strings.TrimRight(elem.Raw, "\n"), "\n") {
if line == "" {
fmt.Fprintf(w, "\n")
} else {
fmt.Fprintf(w, "\t%s\n", line)
}
}
} else {
for _, line := range elem.Lines {
printStyled(w, line, true)
fmt.Fprintf(w, "\n")
}
}
case present.List:
fmt.Fprintf(w, "\n")
for _, item := range elem.Bullet {
fmt.Fprintf(w, " - ")
for i, line := range strings.Split(item, "\n") {
if i > 0 {
fmt.Fprintf(w, " ")
}
printStyled(w, line, false)
fmt.Fprintf(w, "\n")
}
}
case present.Section:
fmt.Fprintf(w, "\n")
sep := " "
if elem.Title == "" {
sep = ""
}
fmt.Fprintf(w, "%s%s%s\n", strings.Repeat("#", depth+2), sep, markdownEscape(elem.Title, false))
printSectionBody(file, depth+1, w, elem.Elem)
case interface{ PresentCmd() string }:
// If there are multiple present commands in a row, don't print a blank line before the second etc.
b := w.Bytes()
sep := "\n"
if len(b) > 0 {
i := bytes.LastIndexByte(b[:len(b)-1], '\n')
if b[i+1] == '.' {
sep = ""
}
}
fmt.Fprintf(w, "%s%s\n", sep, elem.PresentCmd())
}
}
}
func markdownEscape(s string, startLine bool) string {
var b strings.Builder
for i, r := range s {
switch {
case r == '#' && i == 0,
r == '*',
r == '_',
r == '<' && (i == 0 || s[i-1] != ' ') && i+1 < len(s) && s[i+1] != ' ',
r == '[' && strings.Contains(s[i:], "]("):
b.WriteRune('\\')
}
b.WriteRune(r)
}
return b.String()
}
// Copy of ../../present/style.go adjusted to produce Markdown instead of HTML.
/*
Fonts are demarcated by an initial and final char bracketing a
space-delimited word, plus possibly some terminal punctuation.
The chars are
_ for italic
* for bold
` (back quote) for fixed width.
Inner appearances of the char become spaces. For instance,
_this_is_italic_!
becomes
<i>this is italic</i>!
*/
func printStyled(w *bytes.Buffer, text string, startLine bool) {
w.WriteString(font(text, startLine))
}
// font returns s with font indicators turned into HTML font tags.
func font(s string, startLine bool) string {
if !strings.ContainsAny(s, "[`_*") {
return markdownEscape(s, startLine)
}
words := split(s)
var b bytes.Buffer
Word:
for w, word := range words {
words[w] = markdownEscape(word, startLine && w == 0) // for all the continue Word
if len(word) < 2 {
continue Word
}
if link, _ := parseInlineLink(word); link != "" {
words[w] = link
continue Word
}
const marker = "_*`"
// Initial punctuation is OK but must be peeled off.
first := strings.IndexAny(word, marker)
if first == -1 {
continue Word
}
// Opening marker must be at the beginning of the token or else preceded by punctuation.
if first != 0 {
r, _ := utf8.DecodeLastRuneInString(word[:first])
if !unicode.IsPunct(r) {
continue Word
}
}
open, word := markdownEscape(word[:first], startLine && w == 0), word[first:]
char := word[0] // ASCII is OK.
close := ""
switch char {
default:
continue Word
case '_':
open += "_"
close = "_"
case '*':
open += "**"
close = "**"
case '`':
open += "`"
close = "`"
}
// Closing marker must be at the end of the token or else followed by punctuation.
last := strings.LastIndex(word, word[:1])
if last == 0 {
continue Word
}
if last+1 != len(word) {
r, _ := utf8.DecodeRuneInString(word[last+1:])
if !unicode.IsPunct(r) {
continue Word
}
}
head, tail := word[:last+1], word[last+1:]
b.Reset()
var wid int
for i := 1; i < len(head)-1; i += wid {
var r rune
r, wid = utf8.DecodeRuneInString(head[i:])
if r != rune(char) {
// Ordinary character.
b.WriteRune(r)
continue
}
if head[i+1] != char {
// Inner char becomes space.
b.WriteRune(' ')
continue
}
// Doubled char becomes real char.
// Not worth worrying about "_x__".
b.WriteByte(char)
wid++ // Consumed two chars, both ASCII.
}
text := b.String()
if close == "`" {
for strings.Contains(text, close) {
open += "`"
close += "`"
}
} else {
text = markdownEscape(text, false)
}
words[w] = open + text + close + tail
}
return strings.Join(words, "")
}
// split is like strings.Fields but also returns the runs of spaces
// and treats inline links as distinct words.
func split(s string) []string {
var (
words = make([]string, 0, 10)
start = 0
)
// appendWord appends the string s[start:end] to the words slice.
// If the word contains the beginning of a link, the non-link portion
// of the word and the entire link are appended as separate words,
// and the start index is advanced to the end of the link.
appendWord := func(end int) {
if j := strings.Index(s[start:end], "[["); j > -1 {
if _, l := parseInlineLink(s[start+j:]); l > 0 {
// Append portion before link, if any.
if j > 0 {
words = append(words, s[start:start+j])
}
// Append link itself.
words = append(words, s[start+j:start+j+l])
// Advance start index to end of link.
start = start + j + l
return
}
}
// No link; just add the word.
words = append(words, s[start:end])
start = end
}
wasSpace := false
for i, r := range s {
isSpace := unicode.IsSpace(r)
if i > start && isSpace != wasSpace {
appendWord(i)
}
wasSpace = isSpace
}
for start < len(s) {
appendWord(len(s))
}
return words
}
// parseInlineLink parses an inline link at the start of s, and returns
// a rendered Markdown link and the total length of the raw inline link.
// If no inline link is present, it returns all zeroes.
func parseInlineLink(s string) (link string, length int) {
if !strings.HasPrefix(s, "[[") {
return
}
end := strings.Index(s, "]]")
if end == -1 {
return
}
urlEnd := strings.Index(s, "]")
rawURL := s[2:urlEnd]
const badURLChars = `<>"{}|\^[] ` + "`" // per RFC2396 section 2.4.3
if strings.ContainsAny(rawURL, badURLChars) {
return
}
if urlEnd == end {
simpleURL := ""
url, err := url.Parse(rawURL)
if err == nil {
// If the URL is http://foo.com, drop the http://
// In other words, render [[http://golang.org]] as:
// <a href="http://golang.org">golang.org</a>
if strings.HasPrefix(rawURL, url.Scheme+"://") {
simpleURL = strings.TrimPrefix(rawURL, url.Scheme+"://")
} else if strings.HasPrefix(rawURL, url.Scheme+":") {
simpleURL = strings.TrimPrefix(rawURL, url.Scheme+":")
}
}
return renderLink(rawURL, simpleURL), end + 2
}
if s[urlEnd:urlEnd+2] != "][" {
return
}
text := s[urlEnd+2 : end]
return renderLink(rawURL, text), end + 2
}
func renderLink(href, text string) string {
text = font(text, false)
if text == "" {
text = markdownEscape(href, false)
}
return "[" + text + "](" + href + ")"
}