36922b6e95
This makes the renderer preserve existing line breaks in blockquotes, provided they do not split paragraphs. Some clients/sites may use this to form semantic around line breaks (for instance, for poems). See #5.
399 lines
11 KiB
Go
399 lines
11 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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"bytes"
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"fmt"
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"io"
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"regexp"
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"strings"
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"time"
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"github.com/gomarkdown/markdown/ast"
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"github.com/olekukonko/tablewriter"
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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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quoteBrPrefix = []byte("\n> ")
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quotePrefix = []byte("> ")
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itemPrefix = []byte("* ")
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itemIndent = []byte{'\t'}
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preformattedToggle = []byte("```\n")
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)
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var meaningfulCharsRegex = regexp.MustCompile(`\A[\s]+\z`)
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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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w.Write(space)
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r.text(w, node)
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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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w.Write(space)
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r.text(w, node)
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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 node := node.AsContainer(); node != nil {
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for _, child := range node.Children {
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w.Write(quotePrefix)
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r.blockquoteText(w, child)
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// double linebreak to ensure Gemini clients don't merge
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// quotes; gomarkdown assumes separate blockquotes are
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// paragraphs of the same blockquote while we don't
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w.Write(lineBreak)
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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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const gemtextHeadingLevelLimit = 3
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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; Gemini spec allows 3 at
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// maximum before the space, therefore add one after 3 and keep padding
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bufLength := node.Level + 1
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spaceNeeded := node.Level > gemtextHeadingLevelLimit
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if spaceNeeded {
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bufLength++
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}
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heading := make([]byte, bufLength)
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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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if spaceNeeded {
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heading[gemtextHeadingLevelLimit] = ' '
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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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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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}
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}
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linksOnly := func() bool {
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for _, child := range children {
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// TODO: simplify
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if _, ok := child.(*ast.Link); ok {
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continue
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}
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if _, ok := child.(*ast.Image); ok {
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continue
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}
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if child, ok := child.(*ast.Text); ok {
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// any meaningful text?
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if meaningfulCharsRegex.Find(child.Literal) == nil {
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return false
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}
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continue
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}
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return false
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}
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return true
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}()
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noNewLine = linksOnly
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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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switch child := child.(type) {
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case *ast.Link, *ast.Image:
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if !linksOnly {
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r.text(w, child)
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}
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linkStack = append(linkStack, child)
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case *ast.Text, *ast.Code, *ast.Emph, *ast.Strong, *ast.Del:
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// the condition prevents text blocks consisting only of
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// line breaks and spaces and such from rendering
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if !linksOnly {
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r.text(w, child)
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}
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}
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}
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if !linksOnly {
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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 !linksOnly {
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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(preformattedToggle)
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w.Write(node.Literal)
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w.Write(preformattedToggle)
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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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r.text(w, para)
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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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return
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}
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if node := node.AsContainer(); node != nil {
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for _, child := range node.Children {
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r.text(w, child)
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}
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}
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}
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// TODO: this really should've been unified with text(), but having two
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// extra params for prefix/line breaks is not neat
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func (r Renderer) blockquoteText(w io.Writer, node ast.Node) {
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if node := node.AsLeaf(); node != nil {
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// pad every line break with blockquote symbol
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w.Write([]byte(bytes.ReplaceAll(node.Literal, lineBreak, quoteBrPrefix)))
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return
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}
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if node := node.AsContainer(); node != nil {
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for _, child := range node.Children {
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r.blockquoteText(w, child)
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}
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}
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}
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func extractText(node ast.Node) string {
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if node := node.AsLeaf(); node != nil {
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return strings.ReplaceAll(string(node.Literal), "\n", " ")
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}
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if node := node.AsContainer(); node != nil {
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b := strings.Builder{}
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for _, child := range node.Children {
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b.WriteString(extractText(child))
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}
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return b.String()
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}
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panic("encountered a non-leaf & non-container node")
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}
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func (r Renderer) tableHead(t *tablewriter.Table, node *ast.TableHeader) {
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if node := node.AsContainer(); node != nil {
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// should always have a single row consisting of at least one
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// cell but worth checking nonetheless; tablewriter only
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// supports a single header row as of now therefore ignore
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// second row and the rest
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if len(node.Children) > 0 {
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if row := node.Children[0].AsContainer(); row != nil {
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cells := make([]string, len(row.Children))
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for i, cell := range row.Children {
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cells[i] = extractText(cell)
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}
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t.SetHeader(cells)
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}
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}
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}
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}
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func (r Renderer) tableBody(t *tablewriter.Table, node *ast.TableBody) {
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if node := node.AsContainer(); node != nil {
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for _, row := range node.Children {
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if row := row.AsContainer(); row != nil {
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cells := make([]string, len(row.Children))
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for i, cell := range row.Children {
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cells[i] = extractText(cell)
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}
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t.Append(cells)
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}
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}
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}
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}
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func (r Renderer) table(w io.Writer, node *ast.Table, entering bool) {
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if entering {
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w.Write(preformattedToggle)
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// gomarkdown appears to only parse headings consisting of a
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// single line and always have a TableBody preceded by a single
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// TableHeader but we're better off not relying on it
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t := tablewriter.NewWriter(w)
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t.SetAutoFormatHeaders(false) // TODO: tablewriter options should probably be configurable
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if node := node.AsContainer(); node != nil {
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for _, child := range node.Children {
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switch child := child.(type) {
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case *ast.TableHeader:
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r.tableHead(t, child)
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case *ast.TableBody:
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r.tableBody(t, child)
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}
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}
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}
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t.Render()
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} else {
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w.Write(preformattedToggle)
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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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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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case *ast.Table:
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r.table(w, node, entering)
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noNewLine = false
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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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