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Merge pull request #332 from commonmark/footnotes-extension
Footnotes extension
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‎commonmark-ext-footnotes/pom.xml‎

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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<parent>
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<groupId>org.commonmark</groupId>
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<artifactId>commonmark-parent</artifactId>
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<version>0.22.1-SNAPSHOT</version>
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</parent>
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<artifactId>commonmark-ext-footnotes</artifactId>
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<name>commonmark-java extension for footnotes</name>
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<description>commonmark-java extension for footnotes using [^1] syntax</description>
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<dependencies>
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<dependency>
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<groupId>org.commonmark</groupId>
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<artifactId>commonmark</artifactId>
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</dependency>
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<dependency>
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<groupId>org.commonmark</groupId>
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<artifactId>commonmark-test-util</artifactId>
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<scope>test</scope>
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</dependency>
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</dependencies>
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</project>

‎commonmark-ext-footnotes/src/main/java/module-info.java‎

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module org.commonmark.ext.footnotes {
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exports org.commonmark.ext.footnotes;
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requires org.commonmark;
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}

‎commonmark-ext-footnotes/src/main/java/org/commonmark/ext/footnotes/FootnoteDefinition.java‎

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package org.commonmark.ext.footnotes;
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import org.commonmark.node.CustomBlock;
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/**
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* A footnote definition, e.g.:
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* <pre><code>
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* [^foo]: This is the footnote text
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* </code></pre>
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* The {@link #getLabel() label} is the text in brackets after {@code ^}, so {@code foo} in the example. The contents
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* of the footnote are child nodes of the definition, a {@link org.commonmark.node.Paragraph} in the example.
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* <p>
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* Footnote definitions are parsed even if there's no corresponding {@link FootnoteReference}.
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*/
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public class FootnoteDefinition extends CustomBlock {
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private String label;
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public FootnoteDefinition(String label) {
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this.label = label;
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}
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public String getLabel() {
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return label;
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}
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}
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‎commonmark-ext-footnotes/src/main/java/org/commonmark/ext/footnotes/FootnoteReference.java‎

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package org.commonmark.ext.footnotes;
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import org.commonmark.node.CustomNode;
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/**
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* A footnote reference, e.g. <code>[^foo]</code> in <code>Some text with a footnote[^foo]</code>
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* <p>
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* The {@link #getLabel() label} is the text within brackets after {@code ^}, so {@code foo} in the example. It needs to
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* match the label of a corresponding {@link FootnoteDefinition} for the footnote to be parsed.
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*/
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public class FootnoteReference extends CustomNode {
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private String label;
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public FootnoteReference(String label) {
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this.label = label;
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}
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public String getLabel() {
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return label;
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}
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}

‎commonmark-ext-footnotes/src/main/java/org/commonmark/ext/footnotes/FootnotesExtension.java‎

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package org.commonmark.ext.footnotes;
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import org.commonmark.Extension;
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import org.commonmark.ext.footnotes.internal.*;
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import org.commonmark.parser.Parser;
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import org.commonmark.parser.beta.InlineContentParserFactory;
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import org.commonmark.renderer.NodeRenderer;
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import org.commonmark.renderer.html.HtmlRenderer;
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import org.commonmark.renderer.markdown.MarkdownNodeRendererContext;
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import org.commonmark.renderer.markdown.MarkdownNodeRendererFactory;
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import org.commonmark.renderer.markdown.MarkdownRenderer;
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import java.util.Set;
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/**
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* Extension for footnotes with syntax like GitHub Flavored Markdown:
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* <pre><code>
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* Some text with a footnote[^1].
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*
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* [^1]: The text of the footnote.
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* </code></pre>
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* The <code>[^1]</code> is a {@link FootnoteReference}, with "1" being the label.
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* <p>
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* The line with <code>[^1]: ...</code> is a {@link FootnoteDefinition}, with the contents as child nodes (can be a
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* paragraph like in the example, or other blocks like lists).
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* <p>
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* All the footnotes (definitions) will be rendered in a list at the end of a document, no matter where they appear in
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* the source. The footnotes will be numbered starting from 1, then 2, etc, depending on the order in which they appear
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* in the text (and not dependent on the label). The footnote reference is a link to the footnote, and from the footnote
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* there is a link back to the reference (or multiple).
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* <p>
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* There is also optional support for inline footnotes, use {@link #builder()} and then set {@link Builder#inlineFootnotes}.
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*
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* @see <a href="https://docs.github.com/en/get-started/writing-on-github/getting-started-with-writing-and-formatting-on-github/basic-writing-and-formatting-syntax#footnotes">GitHub docs for footnotes</a>
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*/
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public class FootnotesExtension implements Parser.ParserExtension,
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HtmlRenderer.HtmlRendererExtension,
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MarkdownRenderer.MarkdownRendererExtension {
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private final boolean inlineFootnotes;
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private FootnotesExtension(boolean inlineFootnotes) {
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this.inlineFootnotes = inlineFootnotes;
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}
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/**
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* The extension with the default configuration (no support for inline footnotes).
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*/
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public static Extension create() {
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return builder().build();
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}
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public static Builder builder() {
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return new Builder();
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}
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@Override
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public void extend(Parser.Builder parserBuilder) {
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parserBuilder
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.customBlockParserFactory(new FootnoteBlockParser.Factory())
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.linkProcessor(new FootnoteLinkProcessor());
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if (inlineFootnotes) {
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parserBuilder.linkMarker('^');
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}
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}
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@Override
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public void extend(HtmlRenderer.Builder rendererBuilder) {
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rendererBuilder.nodeRendererFactory(FootnoteHtmlNodeRenderer::new);
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}
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@Override
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public void extend(MarkdownRenderer.Builder rendererBuilder) {
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rendererBuilder.nodeRendererFactory(new MarkdownNodeRendererFactory() {
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@Override
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public NodeRenderer create(MarkdownNodeRendererContext context) {
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return new FootnoteMarkdownNodeRenderer(context);
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}
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@Override
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public Set<Character> getSpecialCharacters() {
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return Set.of();
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}
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});
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}
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public static class Builder {
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private boolean inlineFootnotes = false;
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/**
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* Enable support for inline footnotes without definitions, e.g.:
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* <pre>
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* Some text^[this is an inline footnote]
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* </pre>
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*/
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public Builder inlineFootnotes(boolean inlineFootnotes) {
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this.inlineFootnotes = inlineFootnotes;
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return this;
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}
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public FootnotesExtension build() {
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return new FootnotesExtension(inlineFootnotes);
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}
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}
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}

‎commonmark-ext-footnotes/src/main/java/org/commonmark/ext/footnotes/InlineFootnote.java‎

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package org.commonmark.ext.footnotes;
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import org.commonmark.node.CustomNode;
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public class InlineFootnote extends CustomNode {
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}

‎commonmark-ext-footnotes/src/main/java/org/commonmark/ext/footnotes/internal/FootnoteBlockParser.java‎

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package org.commonmark.ext.footnotes.internal;
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import org.commonmark.ext.footnotes.FootnoteDefinition;
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import org.commonmark.node.Block;
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import org.commonmark.node.DefinitionMap;
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import org.commonmark.parser.block.*;
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import org.commonmark.text.Characters;
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import java.util.List;
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/**
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* Parser for a single {@link FootnoteDefinition} block.
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*/
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public class FootnoteBlockParser extends AbstractBlockParser {
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private final FootnoteDefinition block;
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public FootnoteBlockParser(String label) {
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block = new FootnoteDefinition(label);
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}
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@Override
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public Block getBlock() {
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return block;
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}
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@Override
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public boolean isContainer() {
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return true;
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}
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@Override
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public boolean canContain(Block childBlock) {
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return true;
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}
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@Override
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public BlockContinue tryContinue(ParserState parserState) {
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if (parserState.getIndent() >= 4) {
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// It looks like content needs to be indented by 4 so that it's part of a footnote (instead of starting a new block).
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return BlockContinue.atColumn(4);
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} else {
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// We're not continuing to give other block parsers a chance to interrupt this definition.
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// But if no other block parser applied (including another FootnotesBlockParser), we will
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// accept the line via lazy continuation (same as a block quote).
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return BlockContinue.none();
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}
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}
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@Override
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public List<DefinitionMap<?>> getDefinitions() {
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var map = new DefinitionMap<>(FootnoteDefinition.class);
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map.putIfAbsent(block.getLabel(), block);
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return List.of(map);
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}
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public static class Factory implements BlockParserFactory {
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@Override
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public BlockStart tryStart(ParserState state, MatchedBlockParser matchedBlockParser) {
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if (state.getIndent() >= 4) {
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return BlockStart.none();
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}
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var index = state.getNextNonSpaceIndex();
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var content = state.getLine().getContent();
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if (content.charAt(index) != '[' || index + 1 >= content.length()) {
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return BlockStart.none();
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}
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index++;
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if (content.charAt(index) != '^' || index + 1 >= content.length()) {
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return BlockStart.none();
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}
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// Now at first label character (if any)
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index++;
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var labelStart = index;
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for (index = labelStart; index < content.length(); index++) {
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var c = content.charAt(index);
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switch (c) {
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case ']':
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if (index > labelStart && index + 1 < content.length() && content.charAt(index + 1) == ':') {
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var label = content.subSequence(labelStart, index).toString();
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// After the colon, any number of spaces is skipped (not part of the content)
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var afterSpaces = Characters.skipSpaceTab(content, index + 2, content.length());
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return BlockStart.of(new FootnoteBlockParser(label)).atIndex(afterSpaces);
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} else {
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return BlockStart.none();
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}
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case ' ':
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case '\r':
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case '\n':
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case '\0':
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case '\t':
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return BlockStart.none();
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}
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}
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return BlockStart.none();
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}
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}
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}

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