/
renderer.go
375 lines (346 loc) · 10.4 KB
/
renderer.go
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// This file is part of gmnhg.
// gmnhg is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
// gmnhg is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
// You should have received a copy of the GNU General Public License
// along with gmnhg. If not, see <https://www.gnu.org/licenses/>.
// Package gemini contains an implementation of markdown => text/gemini
// renderer for github.com/gomarkdown/markdown.
package gemini
import (
"fmt"
"io"
"regexp"
"strings"
"time"
"github.com/gomarkdown/markdown/ast"
"github.com/olekukonko/tablewriter"
)
var (
lineBreak = []byte{'\n'}
space = []byte{' '}
linkPrefix = []byte("=> ")
quotePrefix = []byte("> ")
itemPrefix = []byte("* ")
itemIndent = []byte{'\t'}
preformattedToggle = []byte("```\n")
)
var meaningfulCharsRegex = regexp.MustCompile(`\A[\s]+\z`)
const timestampFormat = "2006-01-02 15:04"
// Metadata provides data necessary for proper post rendering.
type Metadata interface {
Title() string
Date() time.Time
}
// Renderer implements markdown.Renderer.
type Renderer struct {
Metadata Metadata
}
// NewRenderer returns a new Renderer.
func NewRenderer() Renderer {
return Renderer{}
}
// NewRendererWithMetadata returns a new Renderer initialized with post
// metadata.
func NewRendererWithMetadata(m Metadata) Renderer {
return Renderer{Metadata: m}
}
func (r Renderer) link(w io.Writer, node *ast.Link, entering bool) {
if entering {
w.Write(linkPrefix)
w.Write(node.Destination)
w.Write(space)
r.text(w, node)
}
}
func (r Renderer) image(w io.Writer, node *ast.Image, entering bool) {
if entering {
w.Write(linkPrefix)
w.Write(node.Destination)
w.Write(space)
r.text(w, node)
}
}
func (r Renderer) blockquote(w io.Writer, node *ast.BlockQuote, entering bool) {
// TODO: Renderer.blockquote: needs support for subnode rendering;
// ideally to be merged with paragraph
if entering {
if para, ok := node.Children[0].(*ast.Paragraph); ok {
w.Write(quotePrefix)
r.text(w, para)
}
}
}
const gemtextHeadingLevelLimit = 3
func (r Renderer) heading(w io.Writer, node *ast.Heading, entering bool) {
if entering {
// pad headings with the relevant number of #-s; Gemini spec allows 3 at
// maximum before the space, therefore add one after 3 and keep padding
bufLength := node.Level + 1
spaceNeeded := node.Level > gemtextHeadingLevelLimit
if spaceNeeded {
bufLength++
}
heading := make([]byte, bufLength)
heading[len(heading)-1] = ' '
for i := 0; i < len(heading)-1; i++ {
heading[i] = '#'
}
if spaceNeeded {
heading[gemtextHeadingLevelLimit] = ' '
}
w.Write(heading)
for _, text := range node.Children {
w.Write(text.AsLeaf().Literal)
}
} else {
w.Write(lineBreak)
}
}
func (r Renderer) paragraph(w io.Writer, node *ast.Paragraph, entering bool) (noNewLine bool) {
if entering {
children := node.Children
linkStack := make([]ast.Node, 0, len(children))
// current version of gomarkdown/markdown finds an empty
// *ast.Text element before links/images, breaking the heuristic
if len(children) >= 2 {
firstChild := children[0]
_, elementIsText := firstChild.(*ast.Text)
asLeaf := firstChild.AsLeaf()
if elementIsText && asLeaf != nil && len(asLeaf.Literal) == 0 {
children = children[1:]
}
}
linksOnly := func() bool {
for _, child := range children {
if _, ok := child.(*ast.Link); ok {
continue
}
if _, ok := child.(*ast.Image); ok {
continue
}
if child, ok := child.(*ast.Text); ok {
// any meaningful text?
if meaningfulCharsRegex.Find(child.Literal) == nil {
return false
}
continue
}
return false
}
return true
}()
noNewLine = linksOnly
for _, child := range children {
// only render links text in the paragraph if they're
// combined with some other text on page
switch child := child.(type) {
case *ast.Link, *ast.Image:
if !linksOnly {
r.text(w, child)
}
linkStack = append(linkStack, child)
case *ast.Text, *ast.Code, *ast.Emph, *ast.Strong, *ast.Del:
// the condition prevents text blocks consisting only of
// line breaks and spaces and such from rendering
if !linksOnly {
r.text(w, child)
}
}
}
if !linksOnly {
w.Write(lineBreak)
}
// render a links block after paragraph
if len(linkStack) > 0 {
if !linksOnly {
w.Write(lineBreak)
}
for _, link := range linkStack {
if link, ok := link.(*ast.Link); ok {
r.link(w, link, true)
}
if image, ok := link.(*ast.Image); ok {
r.image(w, image, true)
}
w.Write(lineBreak)
}
}
}
return
}
func (r Renderer) code(w io.Writer, node *ast.CodeBlock) {
w.Write(preformattedToggle)
w.Write(node.Literal)
w.Write(preformattedToggle)
}
func (r Renderer) list(w io.Writer, node *ast.List, level int) {
// the text/gemini spec included with the current Gemini spec does
// not specify anything about the formatting of lists of level >= 2,
// as of now this will just render them like in Markdown
isNumbered := (node.ListFlags & ast.ListTypeOrdered) == ast.ListTypeOrdered
for number, item := range node.Children {
item, ok := item.(*ast.ListItem)
if !ok {
panic("rendering anything but list items is not supported")
}
// this assumes github.com/gomarkdown/markdown can only produce
// list items that contain a child paragraph and possibly
// another list; this might not be true but I can hardly imagine
// a list item that contains anything else
if l := len(item.Children); l >= 1 {
for i := 0; i < level; i++ {
w.Write(itemIndent)
}
if isNumbered {
w.Write([]byte(fmt.Sprintf("%d. ", number+1)))
} else {
w.Write(itemPrefix)
}
para, ok := item.Children[0].(*ast.Paragraph)
if ok {
r.text(w, para)
}
w.Write(lineBreak)
if l >= 2 {
if list, ok := item.Children[1].(*ast.List); ok {
r.list(w, list, level+1)
}
}
}
}
}
func (r Renderer) text(w io.Writer, node ast.Node) {
if node := node.AsLeaf(); node != nil {
// replace all newlines in text with spaces, allowing for soft
// wrapping; this is recommended as per Gemini spec p. 5.4.1
w.Write([]byte(strings.ReplaceAll(string(node.Literal), "\n", " ")))
return
}
if node := node.AsContainer(); node != nil {
for _, child := range node.Children {
r.text(w, child)
}
}
}
func extractText(node ast.Node) string {
if node := node.AsLeaf(); node != nil {
return strings.ReplaceAll(string(node.Literal), "\n", " ")
}
if node := node.AsContainer(); node != nil {
b := strings.Builder{}
for _, child := range node.Children {
b.WriteString(extractText(child))
}
return b.String()
}
panic("encountered a non-leaf & non-container node")
}
func (r Renderer) tableHead(t *tablewriter.Table, node *ast.TableHeader) {
if node := node.AsContainer(); node != nil {
// should always have a single row consisting of at least one
// cell but worth checking nonetheless; tablewriter only
// supports a single header row as of now therefore ignore
// second row and the rest
if len(node.Children) > 0 {
if row := node.Children[0].AsContainer(); row != nil {
cells := make([]string, len(row.Children))
for i, cell := range row.Children {
cells[i] = extractText(cell)
}
t.SetHeader(cells)
}
}
}
}
func (r Renderer) tableBody(t *tablewriter.Table, node *ast.TableBody) {
if node := node.AsContainer(); node != nil {
for _, row := range node.Children {
if row := row.AsContainer(); row != nil {
cells := make([]string, len(row.Children))
for i, cell := range row.Children {
cells[i] = extractText(cell)
}
t.Append(cells)
}
}
}
}
func (r Renderer) table(w io.Writer, node *ast.Table, entering bool) {
if entering {
w.Write(preformattedToggle)
// gomarkdown appears to only parse headings consisting of a
// single line and always have a TableBody preceded by a single
// TableHeader but we're better off not relying on it
t := tablewriter.NewWriter(w)
t.SetAutoFormatHeaders(false) // TODO: tablewriter options should probably be configurable
if node := node.AsContainer(); node != nil {
for _, child := range node.Children {
switch child := child.(type) {
case *ast.TableHeader:
r.tableHead(t, child)
case *ast.TableBody:
r.tableBody(t, child)
}
}
}
t.Render()
} else {
w.Write(preformattedToggle)
}
}
// RenderNode implements Renderer.RenderNode().
func (r Renderer) RenderNode(w io.Writer, node ast.Node, entering bool) ast.WalkStatus {
// despite most of the subroutines here accepting entering, most of
// them don't really need an extra pass
noNewLine := true
switch node := node.(type) {
case *ast.BlockQuote:
r.blockquote(w, node, entering)
noNewLine = false
case *ast.Heading:
r.heading(w, node, entering)
noNewLine = false
case *ast.Paragraph:
// blockquote wraps paragraphs which makes for an extra render
_, parentIsBlockQuote := node.Parent.(*ast.BlockQuote)
_, parentIsListItem := node.Parent.(*ast.ListItem)
if !parentIsBlockQuote && !parentIsListItem {
noNewLine = r.paragraph(w, node, entering)
}
case *ast.CodeBlock:
r.code(w, node)
// code block is not considered a wrapping element
w.Write(lineBreak)
case *ast.List:
// lists of level >= 2 are rendered recursively along with the
// first level; the list is a container
if _, parentIsDocument := node.Parent.(*ast.Document); parentIsDocument && !entering {
r.list(w, node, 0)
noNewLine = false
}
case *ast.Table:
r.table(w, node, entering)
noNewLine = false
}
if !noNewLine && !entering {
w.Write(lineBreak)
}
return ast.GoToNext
}
// RenderHeader implements Renderer.RenderHeader(). It renders metadata
// at the top of the post if any has been provided.
func (r Renderer) RenderHeader(w io.Writer, node ast.Node) {
if r.Metadata != nil {
// TODO: Renderer.RenderHeader: check whether date is mandatory
// in Hugo
w.Write([]byte(fmt.Sprintf("# %s\n\n%s\n\n", r.Metadata.Title(), r.Metadata.Date().Format(timestampFormat))))
}
}
// RenderFooter implements Renderer.RenderFooter().
func (r Renderer) RenderFooter(w io.Writer, node ast.Node) {}