35b4168935
This part of spec says soft text wrapping is preferred to hard wrapping, to comply with that we replace the newlines in raw Markdown text with spaces.
324 lines
8.8 KiB
Go
324 lines
8.8 KiB
Go
// This file is part of gmnhg.
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// gmnhg is free software: you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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// gmnhg is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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// You should have received a copy of the GNU General Public License
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// along with gmnhg. If not, see <https://www.gnu.org/licenses/>.
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// Package gemini contains an implementation of markdown => text/gemini
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// renderer for github.com/gomarkdown/markdown.
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package gemini
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import (
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"bufio"
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"bytes"
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"fmt"
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"io"
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"strings"
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"time"
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"github.com/gomarkdown/markdown/ast"
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)
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var (
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lineBreak = []byte{'\n'}
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space = []byte{' '}
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linkPrefix = []byte("=> ")
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quotePrefix = []byte("> ")
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itemPrefix = []byte("* ")
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itemIndent = []byte{'\t'}
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)
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const timestampFormat = "2006-01-02 15:04"
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// Metadata provides data necessary for proper post rendering.
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type Metadata interface {
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Title() string
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Date() time.Time
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}
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// Renderer implements markdown.Renderer.
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type Renderer struct {
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Metadata Metadata
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}
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// NewRenderer returns a new Renderer.
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func NewRenderer() Renderer {
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return Renderer{}
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}
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// NewRendererWithMetadata returns a new Renderer initialized with post
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// metadata.
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func NewRendererWithMetadata(m Metadata) Renderer {
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return Renderer{Metadata: m}
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}
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func (r Renderer) link(w io.Writer, node *ast.Link, entering bool) {
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if entering {
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w.Write(linkPrefix)
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w.Write(node.Destination)
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for _, child := range node.Children {
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if l := child.AsLeaf(); l != nil {
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w.Write(space)
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w.Write(l.Literal)
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}
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}
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}
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}
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func (r Renderer) linkText(w io.Writer, node *ast.Link) {
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for _, text := range node.Children {
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// TODO: Renderer.linkText: link can contain subblocks
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if l := text.AsLeaf(); l != nil {
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w.Write(l.Literal)
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}
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}
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}
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func (r Renderer) imageText(w io.Writer, node *ast.Image) {
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for _, text := range node.Children {
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// TODO: Renderer.imageText: link can contain subblocks
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if l := text.AsLeaf(); l != nil {
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w.Write(l.Literal)
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}
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}
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}
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func (r Renderer) image(w io.Writer, node *ast.Image, entering bool) {
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if entering {
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w.Write(linkPrefix)
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w.Write(node.Destination)
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for _, sub := range node.Container.Children {
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if l := sub.AsLeaf(); l != nil {
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// TODO: Renderer.image: Markdown technically allows for
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// links inside image titles, yet to think out how to
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// render that :thinking:
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w.Write(space)
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w.Write(l.Literal)
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}
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}
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}
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}
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func (r Renderer) blockquote(w io.Writer, node *ast.BlockQuote, entering bool) {
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// TODO: Renderer.blockquote: needs support for subnode rendering;
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// ideally to be merged with paragraph
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if entering {
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if para, ok := node.Children[0].(*ast.Paragraph); ok {
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for _, subnode := range para.Children {
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if l := subnode.AsLeaf(); l != nil {
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reader := bufio.NewScanner(bytes.NewBuffer(l.Literal))
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for reader.Scan() {
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w.Write(quotePrefix)
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w.Write(reader.Bytes())
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w.Write(lineBreak)
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}
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}
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}
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}
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}
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}
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func (r Renderer) heading(w io.Writer, node *ast.Heading, entering bool) {
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if entering {
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// pad headings with the relevant number of #-s
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heading := make([]byte, node.Level+1)
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heading[len(heading)-1] = ' '
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for i := 0; i < len(heading)-1; i++ {
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heading[i] = '#'
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}
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w.Write(heading)
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for _, text := range node.Children {
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w.Write(text.AsLeaf().Literal)
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}
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} else {
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w.Write(lineBreak)
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}
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}
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func (r Renderer) paragraph(w io.Writer, node *ast.Paragraph, entering bool) (noNewLine bool) {
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if entering {
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children := node.Children
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linkStack := make([]ast.Node, 0, len(children))
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// current version of gomarkdown/markdown finds an empty
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// *ast.Text element before links/images, breaking the heuristic
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onlyElementWithGoMarkdownFix := func() bool {
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if len(children) == 2 {
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firstChild := children[0]
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_, elementIsText := firstChild.(*ast.Text)
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asLeaf := firstChild.AsLeaf()
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if elementIsText && asLeaf != nil && len(asLeaf.Literal) == 0 {
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children = children[1:]
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return true
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}
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}
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return false
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}()
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onlyElement := len(children) == 1 || onlyElementWithGoMarkdownFix
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onlyElementIsLink := func() bool {
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if len(children) == 1 {
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if _, ok := children[0].(*ast.Link); ok {
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return true
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}
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if _, ok := children[0].(*ast.Image); ok {
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return true
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}
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}
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return false
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}()
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noNewLine = onlyElementIsLink
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for _, child := range children {
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// only render links text in the paragraph if they're
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// combined with some other text on page
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if link, ok := child.(*ast.Link); ok {
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if !onlyElement {
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r.linkText(w, link)
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}
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linkStack = append(linkStack, link)
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}
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if image, ok := child.(*ast.Image); ok {
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if !onlyElement {
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r.imageText(w, image)
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}
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linkStack = append(linkStack, image)
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}
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if text, ok := child.(*ast.Text); ok {
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r.text(w, text)
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}
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if inlineBlock, ok := child.(*ast.Code); ok {
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r.text(w, inlineBlock)
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}
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}
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if !onlyElementIsLink {
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w.Write(lineBreak)
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}
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// render a links block after paragraph
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if len(linkStack) > 0 {
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if !onlyElementIsLink {
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w.Write(lineBreak)
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}
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for _, link := range linkStack {
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if link, ok := link.(*ast.Link); ok {
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r.link(w, link, true)
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}
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if image, ok := link.(*ast.Image); ok {
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r.image(w, image, true)
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}
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w.Write(lineBreak)
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}
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}
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}
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return
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}
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func (r Renderer) code(w io.Writer, node *ast.CodeBlock) {
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w.Write([]byte("```\n"))
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w.Write(node.Literal)
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w.Write([]byte("```\n"))
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}
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func (r Renderer) list(w io.Writer, node *ast.List, level int) {
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// the text/gemini spec included with the current Gemini spec does
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// not specify anything about the formatting of lists of level >= 2,
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// as of now this will just render them like in Markdown
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isNumbered := (node.ListFlags & ast.ListTypeOrdered) == ast.ListTypeOrdered
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for number, item := range node.Children {
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item, ok := item.(*ast.ListItem)
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if !ok {
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panic("rendering anything but list items is not supported")
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}
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// this assumes github.com/gomarkdown/markdown can only produce
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// list items that contain a child paragraph and possibly
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// another list; this might not be true but I can hardly imagine
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// a list item that contains anything else
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if l := len(item.Children); l >= 1 {
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for i := 0; i < level; i++ {
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w.Write(itemIndent)
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}
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if isNumbered {
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w.Write([]byte(fmt.Sprintf("%d. ", number+1)))
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} else {
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w.Write(itemPrefix)
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}
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para, ok := item.Children[0].(*ast.Paragraph)
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if ok {
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text, ok := para.Children[0].(*ast.Text)
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if ok {
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r.text(w, text)
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}
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}
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w.Write(lineBreak)
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if l >= 2 {
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if list, ok := item.Children[1].(*ast.List); ok {
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r.list(w, list, level+1)
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}
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}
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}
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}
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}
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func (r Renderer) text(w io.Writer, node ast.Node) {
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if node := node.AsLeaf(); node != nil {
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// replace all newlines in text with spaces, allowing for soft
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// wrapping; this is recommended as per Gemini spec p. 5.4.1
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w.Write([]byte(strings.ReplaceAll(string(node.Literal), "\n", " ")))
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}
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}
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// RenderNode implements Renderer.RenderNode().
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func (r Renderer) RenderNode(w io.Writer, node ast.Node, entering bool) ast.WalkStatus {
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// despite most of the subroutines here accepting entering, most of
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// them don't really need an extra pass
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noNewLine := true
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switch node := node.(type) {
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case *ast.BlockQuote:
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r.blockquote(w, node, entering)
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noNewLine = false
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case *ast.Heading:
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r.heading(w, node, entering)
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noNewLine = false
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case *ast.Paragraph:
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// blockquote wraps paragraphs which makes for an extra render
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_, parentIsBlockQuote := node.Parent.(*ast.BlockQuote)
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_, parentIsListItem := node.Parent.(*ast.ListItem)
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if !parentIsBlockQuote && !parentIsListItem {
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noNewLine = r.paragraph(w, node, entering)
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}
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case *ast.CodeBlock:
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r.code(w, node)
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// code block is not considered a wrapping element
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w.Write(lineBreak)
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case *ast.List:
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// lists of level >= 2 are rendered recursively along with the
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// first level; the list is a container
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if _, parentIsDocument := node.Parent.(*ast.Document); parentIsDocument && !entering {
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r.list(w, node, 0)
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noNewLine = false
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}
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}
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if !noNewLine && !entering {
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w.Write(lineBreak)
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}
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return ast.GoToNext
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}
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// RenderHeader implements Renderer.RenderHeader(). It renders metadata
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// at the top of the post if any has been provided.
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func (r Renderer) RenderHeader(w io.Writer, node ast.Node) {
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if r.Metadata != nil {
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// TODO: Renderer.RenderHeader: check whether date is mandatory
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// in Hugo
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w.Write([]byte(fmt.Sprintf("# %s\n\n%s\n\n", r.Metadata.Title(), r.Metadata.Date().Format(timestampFormat))))
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}
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}
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// RenderFooter implements Renderer.RenderFooter().
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func (r Renderer) RenderFooter(w io.Writer, node ast.Node) {}
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