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// Package gemtext implements shared logic related to gemtext files.
package gemtext
import (
"bufio"
"bytes"
"errors"
"fmt"
"html"
"io"
"strings"
)
// HTMLTranslator is used to translate a gemtext file into equivalent HTML DOM
// elements.
type HTMLTranslator struct {
// RenderHeading, if given can be used to override how headings are
// rendered. The level indicates which heading level is being rendered: 1,
// 2, or 3.
RenderHeading func(w io.Writer, level int, text string) error
// RenderLink, if given, can be used to override how links are rendered.
RenderLink func(w io.Writer, url, label string) error
}
// HTML contains the result of a translation from gemtext. The Body will be the
// translated body itself, and Title will correspond to the first primary header
// of the gemtext file, if there was one.
type HTML struct {
Title string
Body string
}
// Translate will read a gemtext file from the Reader and return it as an HTML
// document.
func (t HTMLTranslator) Translate(src io.Reader) (HTML, error) {
var (
r = bufio.NewReader(src)
w = new(bytes.Buffer)
title string
pft, list bool
writeErr error
)
sanitizeText := func(str string) string {
return html.EscapeString(strings.TrimSpace(str))
}
write := func(fmtStr string, args ...any) {
if writeErr != nil {
return
}
_, writeErr = fmt.Fprintf(w, fmtStr, args...)
}
loop:
for {
if writeErr != nil {
return HTML{}, fmt.Errorf("writing line: %w", writeErr)
}
line, err := r.ReadString('\n')
switch {
case errors.Is(err, io.EOF):
break loop
case err != nil:
return HTML{}, fmt.Errorf("reading next line: %w", err)
case strings.HasPrefix(line, "```"):
if !pft {
write("<pre>\n")
pft = true
} else {
write("</pre>\n")
pft = false
}
continue
case pft:
write(html.EscapeString(line))
continue
case len(strings.TrimSpace(line)) == 0:
continue
}
// list case is special, because it requires a prefix and suffix tag
if strings.HasPrefix(line, "*") {
if !list {
write("<ul>\n")
}
write("<li>%s</li>\n", sanitizeText(line[1:]))
list = true
continue
} else if list {
write("</ul>\n")
list = false
}
switch {
case strings.HasPrefix(line, "=>"):
var (
line = strings.TrimSpace(line[2:])
urlStr = line
label = urlStr
)
if i := strings.IndexAny(urlStr, " \t"); i > -1 {
urlStr, label = urlStr[:i], sanitizeText(urlStr[i:])
}
if t.RenderLink == nil {
write("<p><a href=\"%s\">%s</a></p>\n", urlStr, label)
} else {
writeErr = t.RenderLink(w, urlStr, label)
}
case strings.HasPrefix(line, "###"):
text := sanitizeText(line[3:])
if t.RenderHeading == nil {
write("<h3>%s</h3>\n", text)
} else {
writeErr = t.RenderHeading(w, 3, text)
}
case strings.HasPrefix(line, "##"):
text := sanitizeText(line[2:])
if t.RenderHeading == nil {
write("<h2>%s</h2>\n", text)
} else {
writeErr = t.RenderHeading(w, 2, text)
}
case strings.HasPrefix(line, "#"):
text := sanitizeText(line[1:])
if title == "" {
title = text
}
if t.RenderHeading == nil {
write("<h1>%s</h1>\n", text)
} else {
writeErr = t.RenderHeading(w, 1, text)
}
case strings.HasPrefix(line, ">"):
write("<blockquote>%s</blockquote>\n", sanitizeText(line[1:]))
default:
line = strings.TrimSpace(line)
write("<p>%s</p>\n", line)
}
}
return HTML{
Title: title,
Body: w.String(),
}, nil
}
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