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html.go
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html.go
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package html
import (
"fmt"
"html"
"io"
"sort"
"strings"
"github.com/alecthomas/chroma"
)
// Option sets an option of the HTML formatter.
type Option func(f *Formatter)
// Standalone configures the HTML formatter for generating a standalone HTML document.
func Standalone(b bool) Option { return func(f *Formatter) { f.standalone = b } }
// ClassPrefix sets the CSS class prefix.
func ClassPrefix(prefix string) Option { return func(f *Formatter) { f.prefix = prefix } }
// WithClasses emits HTML using CSS classes, rather than inline styles.
func WithClasses(b bool) Option { return func(f *Formatter) { f.Classes = b } }
// TabWidth sets the number of characters for a tab. Defaults to 8.
func TabWidth(width int) Option { return func(f *Formatter) { f.tabWidth = width } }
// PreventSurroundingPre prevents the surrounding pre tags around the generated code.
func PreventSurroundingPre(b bool) Option {
return func(f *Formatter) {
if b {
f.preWrapper = nopPreWrapper
} else {
f.preWrapper = defaultPreWrapper
}
}
}
// WithPreWrapper allows control of the surrounding pre tags.
func WithPreWrapper(wrapper PreWrapper) Option {
return func(f *Formatter) {
f.preWrapper = wrapper
}
}
// WithLineNumbers formats output with line numbers.
func WithLineNumbers(b bool) Option {
return func(f *Formatter) {
f.lineNumbers = b
}
}
// LineNumbersInTable will, when combined with WithLineNumbers, separate the line numbers
// and code in table td's, which make them copy-and-paste friendly.
func LineNumbersInTable(b bool) Option {
return func(f *Formatter) {
f.lineNumbersInTable = b
}
}
// LinkableLineNumbers decorates the line numbers HTML elements with an "id"
// attribute so they can be linked.
func LinkableLineNumbers(b bool, prefix string) Option {
return func(f *Formatter) {
f.linkableLineNumbers = b
f.lineNumbersIDPrefix = prefix
}
}
// HighlightLines higlights the given line ranges with the Highlight style.
//
// A range is the beginning and ending of a range as 1-based line numbers, inclusive.
func HighlightLines(ranges [][2]int) Option {
return func(f *Formatter) {
f.highlightRanges = ranges
sort.Sort(f.highlightRanges)
}
}
// BaseLineNumber sets the initial number to start line numbering at. Defaults to 1.
func BaseLineNumber(n int) Option {
return func(f *Formatter) {
f.baseLineNumber = n
}
}
// New HTML formatter.
func New(options ...Option) *Formatter {
f := &Formatter{
baseLineNumber: 1,
preWrapper: defaultPreWrapper,
}
for _, option := range options {
option(f)
}
return f
}
// PreWrapper defines the operations supported in WithPreWrapper.
type PreWrapper interface {
// Start is called to write a start <pre> element.
// The code flag tells whether this block surrounds
// highlighted code. This will be false when surrounding
// line numbers.
Start(code bool, styleAttr string) string
// End is called to write the end </pre> element.
End(code bool) string
}
type preWrapper struct {
start func(code bool, styleAttr string) string
end func(code bool) string
}
func (p preWrapper) Start(code bool, styleAttr string) string {
return p.start(code, styleAttr)
}
func (p preWrapper) End(code bool) string {
return p.end(code)
}
var (
nopPreWrapper = preWrapper{
start: func(code bool, styleAttr string) string { return "" },
end: func(code bool) string { return "" },
}
defaultPreWrapper = preWrapper{
start: func(code bool, styleAttr string) string {
return fmt.Sprintf("<pre%s>", styleAttr)
},
end: func(code bool) string {
return "</pre>"
},
}
)
// Formatter that generates HTML.
type Formatter struct {
standalone bool
prefix string
Classes bool // Exported field to detect when classes are being used
preWrapper PreWrapper
tabWidth int
lineNumbers bool
lineNumbersInTable bool
linkableLineNumbers bool
lineNumbersIDPrefix string
highlightRanges highlightRanges
baseLineNumber int
}
type highlightRanges [][2]int
func (h highlightRanges) Len() int { return len(h) }
func (h highlightRanges) Swap(i, j int) { h[i], h[j] = h[j], h[i] }
func (h highlightRanges) Less(i, j int) bool { return h[i][0] < h[j][0] }
func (f *Formatter) Format(w io.Writer, style *chroma.Style, iterator chroma.Iterator) (err error) {
return f.writeHTML(w, style, iterator.Tokens())
}
// We deliberately don't use html/template here because it is two orders of magnitude slower (benchmarked).
//
// OTOH we need to be super careful about correct escaping...
func (f *Formatter) writeHTML(w io.Writer, style *chroma.Style, tokens []chroma.Token) (err error) { // nolint: gocyclo
css := f.styleToCSS(style)
if !f.Classes {
for t, style := range css {
css[t] = compressStyle(style)
}
}
if f.standalone {
fmt.Fprint(w, "<html>\n")
if f.Classes {
fmt.Fprint(w, "<style type=\"text/css\">\n")
err = f.WriteCSS(w, style)
if err != nil {
return err
}
fmt.Fprintf(w, "body { %s; }\n", css[chroma.Background])
fmt.Fprint(w, "</style>")
}
fmt.Fprintf(w, "<body%s>\n", f.styleAttr(css, chroma.Background))
}
wrapInTable := f.lineNumbers && f.lineNumbersInTable
lines := chroma.SplitTokensIntoLines(tokens)
lineDigits := len(fmt.Sprintf("%d", len(lines)))
highlightIndex := 0
if wrapInTable {
// List line numbers in its own <td>
fmt.Fprintf(w, "<div%s>\n", f.styleAttr(css, chroma.Background))
fmt.Fprintf(w, "<table%s><tr>", f.styleAttr(css, chroma.LineTable))
fmt.Fprintf(w, "<td%s>\n", f.styleAttr(css, chroma.LineTableTD))
fmt.Fprintf(w, f.preWrapper.Start(false, f.styleAttr(css, chroma.Background)))
for index := range lines {
line := f.baseLineNumber + index
highlight, next := f.shouldHighlight(highlightIndex, line)
if next {
highlightIndex++
}
if highlight {
fmt.Fprintf(w, "<span%s>", f.styleAttr(css, chroma.LineHighlight))
}
fmt.Fprintf(w, "<span%s%s>%*d\n</span>", f.styleAttr(css, chroma.LineNumbersTable), f.lineIDAttribute(line), lineDigits, line)
if highlight {
fmt.Fprintf(w, "</span>")
}
}
fmt.Fprint(w, f.preWrapper.End(false))
fmt.Fprint(w, "</td>\n")
fmt.Fprintf(w, "<td%s>\n", f.styleAttr(css, chroma.LineTableTD, "width:100%"))
}
fmt.Fprintf(w, f.preWrapper.Start(true, f.styleAttr(css, chroma.Background)))
highlightIndex = 0
for index, tokens := range lines {
// 1-based line number.
line := f.baseLineNumber + index
highlight, next := f.shouldHighlight(highlightIndex, line)
if next {
highlightIndex++
}
if highlight {
fmt.Fprintf(w, "<span%s>", f.styleAttr(css, chroma.LineHighlight))
}
if f.lineNumbers && !wrapInTable {
fmt.Fprintf(w, "<span%s%s>%*d</span>", f.styleAttr(css, chroma.LineNumbers), f.lineIDAttribute(line), lineDigits, line)
}
for _, token := range tokens {
html := html.EscapeString(token.String())
attr := f.styleAttr(css, token.Type)
if attr != "" {
html = fmt.Sprintf("<span%s>%s</span>", attr, html)
}
fmt.Fprint(w, html)
}
if highlight {
fmt.Fprintf(w, "</span>")
}
}
fmt.Fprintf(w, f.preWrapper.End(true))
if wrapInTable {
fmt.Fprint(w, "</td></tr></table>\n")
fmt.Fprint(w, "</div>\n")
}
if f.standalone {
fmt.Fprint(w, "\n</body>\n")
fmt.Fprint(w, "</html>\n")
}
return nil
}
func (f *Formatter) lineIDAttribute(line int) string {
if !f.linkableLineNumbers {
return ""
}
return fmt.Sprintf(" id=\"%s%d\"", f.lineNumbersIDPrefix, line)
}
func (f *Formatter) shouldHighlight(highlightIndex, line int) (bool, bool) {
next := false
for highlightIndex < len(f.highlightRanges) && line > f.highlightRanges[highlightIndex][1] {
highlightIndex++
next = true
}
if highlightIndex < len(f.highlightRanges) {
hrange := f.highlightRanges[highlightIndex]
if line >= hrange[0] && line <= hrange[1] {
return true, next
}
}
return false, next
}
func (f *Formatter) class(t chroma.TokenType) string {
for t != 0 {
if cls, ok := chroma.StandardTypes[t]; ok {
if cls != "" {
return f.prefix + cls
}
return ""
}
t = t.Parent()
}
if cls := chroma.StandardTypes[t]; cls != "" {
return f.prefix + cls
}
return ""
}
func (f *Formatter) styleAttr(styles map[chroma.TokenType]string, tt chroma.TokenType, extraCSS ...string) string {
if f.Classes {
cls := f.class(tt)
if cls == "" {
return ""
}
return fmt.Sprintf(` class="%s"`, cls)
}
if _, ok := styles[tt]; !ok {
tt = tt.SubCategory()
if _, ok := styles[tt]; !ok {
tt = tt.Category()
if _, ok := styles[tt]; !ok {
return ""
}
}
}
css := []string{styles[tt]}
css = append(css, extraCSS...)
return fmt.Sprintf(` style="%s"`, strings.Join(css, ";"))
}
func (f *Formatter) tabWidthStyle() string {
if f.tabWidth != 0 && f.tabWidth != 8 {
return fmt.Sprintf("; -moz-tab-size: %[1]d; -o-tab-size: %[1]d; tab-size: %[1]d", f.tabWidth)
}
return ""
}
// WriteCSS writes CSS style definitions (without any surrounding HTML).
func (f *Formatter) WriteCSS(w io.Writer, style *chroma.Style) error {
css := f.styleToCSS(style)
// Special-case background as it is mapped to the outer ".chroma" class.
if _, err := fmt.Fprintf(w, "/* %s */ .%schroma { %s }\n", chroma.Background, f.prefix, css[chroma.Background]); err != nil {
return err
}
// Special-case code column of table to expand width.
if f.lineNumbers && f.lineNumbersInTable {
if _, err := fmt.Fprintf(w, "/* %s */ .%schroma .%s:last-child { width: 100%%; }",
chroma.LineTableTD, f.prefix, f.class(chroma.LineTableTD)); err != nil {
return err
}
}
// Special-case line number highlighting when targeted.
if f.lineNumbers || f.lineNumbersInTable {
targetedLineCSS := StyleEntryToCSS(style.Get(chroma.LineHighlight))
for _, tt := range []chroma.TokenType{chroma.LineNumbers, chroma.LineNumbersTable} {
fmt.Fprintf(w, "/* %s targeted by URL anchor */ .%schroma .%s:target { %s }\n", tt, f.prefix, f.class(tt), targetedLineCSS)
}
}
tts := []int{}
for tt := range css {
tts = append(tts, int(tt))
}
sort.Ints(tts)
for _, ti := range tts {
tt := chroma.TokenType(ti)
if tt == chroma.Background {
continue
}
styles := css[tt]
if _, err := fmt.Fprintf(w, "/* %s */ .%schroma .%s { %s }\n", tt, f.prefix, f.class(tt), styles); err != nil {
return err
}
}
return nil
}
func (f *Formatter) styleToCSS(style *chroma.Style) map[chroma.TokenType]string {
classes := map[chroma.TokenType]string{}
bg := style.Get(chroma.Background)
// Convert the style.
for t := range chroma.StandardTypes {
entry := style.Get(t)
if t != chroma.Background {
entry = entry.Sub(bg)
}
if entry.IsZero() {
continue
}
classes[t] = StyleEntryToCSS(entry)
}
classes[chroma.Background] += f.tabWidthStyle()
lineNumbersStyle := "margin-right: 0.4em; padding: 0 0.4em 0 0.4em;"
// All rules begin with default rules followed by user provided rules
classes[chroma.LineNumbers] = lineNumbersStyle + classes[chroma.LineNumbers]
classes[chroma.LineNumbersTable] = lineNumbersStyle + classes[chroma.LineNumbersTable]
classes[chroma.LineHighlight] = "display: block; width: 100%;" + classes[chroma.LineHighlight]
classes[chroma.LineTable] = "border-spacing: 0; padding: 0; margin: 0; border: 0; width: auto; overflow: auto; display: block;" + classes[chroma.LineTable]
classes[chroma.LineTableTD] = "vertical-align: top; padding: 0; margin: 0; border: 0;" + classes[chroma.LineTableTD]
return classes
}
// StyleEntryToCSS converts a chroma.StyleEntry to CSS attributes.
func StyleEntryToCSS(e chroma.StyleEntry) string {
styles := []string{}
if e.Colour.IsSet() {
styles = append(styles, "color: "+e.Colour.String())
}
if e.Background.IsSet() {
styles = append(styles, "background-color: "+e.Background.String())
}
if e.Bold == chroma.Yes {
styles = append(styles, "font-weight: bold")
}
if e.Italic == chroma.Yes {
styles = append(styles, "font-style: italic")
}
if e.Underline == chroma.Yes {
styles = append(styles, "text-decoration: underline")
}
return strings.Join(styles, "; ")
}
// Compress CSS attributes - remove spaces, transform 6-digit colours to 3.
func compressStyle(s string) string {
parts := strings.Split(s, ";")
out := []string{}
for _, p := range parts {
p = strings.Join(strings.Fields(p), " ")
p = strings.Replace(p, ": ", ":", 1)
if strings.Contains(p, "#") {
c := p[len(p)-6:]
if c[0] == c[1] && c[2] == c[3] && c[4] == c[5] {
p = p[:len(p)-6] + c[0:1] + c[2:3] + c[4:5]
}
}
out = append(out, p)
}
return strings.Join(out, ";")
}