From 05bd82df2497523d5e0388ecb53ca9b58cbb9e7d Mon Sep 17 00:00:00 2001
From: Maxime Cannoodt <Maxime.Cannoodt@UGent.be>
Date: Tue, 23 Aug 2022 11:15:11 +0200
Subject: [PATCH] feat: :sparkles: render footnote at bottom of page

---
 webapp/CHANGELOG.md                           |  3 +
 .../lib/components/MarkdownRenderer.svelte    | 34 ++++++++++-
 webapp/src/lib/marked/extensions.ts           | 59 ++++++++++++++++++-
 .../src/lib/marked/renderers/Footnote.svelte  | 35 +++++++++++
 .../lib/marked/renderers/FootnoteRef.svelte   | 13 ++++
 webapp/src/lib/util/scrollToId.ts             |  6 ++
 6 files changed, 147 insertions(+), 3 deletions(-)
 create mode 100644 webapp/src/lib/marked/renderers/Footnote.svelte
 create mode 100644 webapp/src/lib/marked/renderers/FootnoteRef.svelte
 create mode 100644 webapp/src/lib/util/scrollToId.ts

diff --git a/webapp/CHANGELOG.md b/webapp/CHANGELOG.md
index 8e603ba..4f6eebe 100644
--- a/webapp/CHANGELOG.md
+++ b/webapp/CHANGELOG.md
@@ -1,5 +1,8 @@
 # Changelog
 
+## [2022-08-23]
+
+- feat: ✨ Footnotes are rendered as they are in the Obsidian client.
 ## [2022-08-16]
 
 - fix: 🐛 Fix highlights not rendering correctly when mixed with other  formatting. ([issue #19](https://github.com/mcndt/noteshare.space/issues/19))
diff --git a/webapp/src/lib/components/MarkdownRenderer.svelte b/webapp/src/lib/components/MarkdownRenderer.svelte
index 60183d8..8073865 100644
--- a/webapp/src/lib/components/MarkdownRenderer.svelte
+++ b/webapp/src/lib/components/MarkdownRenderer.svelte
@@ -15,15 +15,24 @@
 	import MathBlock from '$lib/marked/renderers/MathBlock.svelte';
 	import ListItem from '$lib/marked/renderers/ListItem.svelte';
 	import Code from '$lib/marked/renderers/Code.svelte';
+	import FootnoteRef from '$lib/marked/renderers/FootnoteRef.svelte';
+	import Footnote from '$lib/marked/renderers/Footnote.svelte';
 
 	export let plaintext: string;
 	let ref: HTMLDivElement;
+	let footnotes: HTMLDivElement[];
+	let footnoteContainer: HTMLDivElement;
 
 	// @ts-ignore: typing mismatch
 	marked.use({ extensions: extensions });
 
 	const options = { ...marked.defaults, breaks: true };
 
+	function onParsed() {
+		setTitle();
+		parseFootnotes();
+	}
+
 	/**
 	 * Searches for the first major header in the document to use as page title.
 	 */
@@ -37,6 +46,19 @@
 			}
 		}
 	}
+
+	/*
+	 * find all elements inside "ref" that have the data-footnote attribute
+	 */
+	function parseFootnotes() {
+		footnotes = Array.from(ref.querySelectorAll('[data-footnote]'));
+	}
+
+	$: if (footnotes?.length > 0 && footnoteContainer) {
+		footnotes.forEach((footnote) => {
+			footnoteContainer.appendChild(footnote);
+		});
+	}
 </script>
 
 <div
@@ -47,7 +69,7 @@ prose-strong:font-bold prose-a:font-normal prose-blockquote:font-normal prose-bl
 prose-blockquote:first:before:content-[''] prose-hr:transition-colors"
 >
 	<SvelteMarkdown
-		on:parsed={setTitle}
+		on:parsed={onParsed}
 		renderers={{
 			heading: Heading,
 			list: List,
@@ -60,9 +82,17 @@ prose-blockquote:first:before:content-[''] prose-hr:transition-colors"
 			blockquote: Blockquote,
 			'math-inline': MathInline,
 			'math-block': MathBlock,
-			code: Code
+			code: Code,
+			'footnote-ref': FootnoteRef,
+			footnote: Footnote
 		}}
 		source={plaintext}
 		{options}
 	/>
+
+	<!-- footnote container -->
+	{#if footnotes?.length > 0}
+		<hr />
+		<div bind:this={footnoteContainer} />
+	{/if}
 </div>
diff --git a/webapp/src/lib/marked/extensions.ts b/webapp/src/lib/marked/extensions.ts
index 6b3a792..9faddd1 100644
--- a/webapp/src/lib/marked/extensions.ts
+++ b/webapp/src/lib/marked/extensions.ts
@@ -117,11 +117,68 @@ const MathBlock = {
 	}
 };
 
+const footnoteRef = {
+	name: 'footnote-ref',
+	level: 'inline',
+	start(src: string) {
+		return src.indexOf('[^');
+	},
+
+	tokenizer(src: string) {
+		const match = src.match(/^\[\^([^\]]+)\]/);
+		if (match) {
+			return {
+				type: 'footnote-ref',
+				raw: match[0],
+				id: match[1].trim()
+			};
+		}
+		return false;
+	}
+};
+
+const footnote = {
+	name: 'footnote',
+	level: 'block',
+	start(src: string) {
+		return src.match(/^\[\^([^\]]+)\]:/)?.index;
+	},
+
+	tokenizer(src: string): any {
+		const matchFootnote = /^\[\^([^\]]+)\]: ?((?:[^\r\n]*))/;
+
+		const lines = src.split('\n');
+		const match = lines[0].match(matchFootnote);
+		if (match) {
+			// find all subsequent lines that are not a match with matchFootnote or blank
+			let i = 1;
+			while (i < lines.length && !lines[i].match(matchFootnote) && lines[i].trim() !== '') {
+				i++;
+			}
+			const raw = lines.slice(0, i).join('\n');
+
+			// const text equals raw without the [^id]: part
+			const text = raw.replace(/^\[\^([^\]]+)\]: ?/, '').trim();
+
+			return {
+				type: 'footnote',
+				raw: raw,
+				id: match[1].trim(),
+				// @ts-expect-error - marked types are wrong
+				tokens: this.lexer.blockTokens(text, [])
+			};
+		}
+		return false;
+	}
+};
+
 export default [
 	InternalLinkExtension,
 	InternalEmbedExtension,
 	TagExtension,
 	HighlightExtension,
 	MathBlock,
-	MathInline
+	MathInline,
+	footnoteRef,
+	footnote
 ];
diff --git a/webapp/src/lib/marked/renderers/Footnote.svelte b/webapp/src/lib/marked/renderers/Footnote.svelte
new file mode 100644
index 0000000..1c19ec4
--- /dev/null
+++ b/webapp/src/lib/marked/renderers/Footnote.svelte
@@ -0,0 +1,35 @@
+<script lang="ts">
+	import { scrollToId } from '$lib/util/scrollToId';
+
+	export let id: string;
+
+	let content: HTMLElement;
+	let returnRef: HTMLElement;
+
+	let refMoved = false;
+
+	$: if (content && returnRef) {
+		// Find the p element in content move the return link to the end of that p element
+		const p = content.querySelector('p');
+		if (p) {
+			p.appendChild(returnRef);
+			refMoved = true;
+		}
+	}
+</script>
+
+<div data-footnote class="flex gap-2 prose-p:my-0">
+	<p>{id}.</p>
+	<span bind:this={content} class="">
+		<slot />
+	</span>
+</div>
+
+<span bind:this={returnRef} class="ml-1 {refMoved ? 'inline' : 'hidden'}"
+	><a
+		on:click|preventDefault={() => scrollToId(`footnote-ref-${id}`)}
+		id="footnote-{id}"
+		href="#footnote-ref-{id}"
+		class="no-underline">⮥</a
+	></span
+>
diff --git a/webapp/src/lib/marked/renderers/FootnoteRef.svelte b/webapp/src/lib/marked/renderers/FootnoteRef.svelte
new file mode 100644
index 0000000..3e802fa
--- /dev/null
+++ b/webapp/src/lib/marked/renderers/FootnoteRef.svelte
@@ -0,0 +1,13 @@
+<script lang="ts">
+	import { scrollToId } from '$lib/util/scrollToId';
+
+	export let id: string;
+</script>
+
+<sup
+	><a
+		on:click|preventDefault={() => scrollToId(`footnote-${id}`)}
+		id="footnote-ref-{id}"
+		href="#footnote-{id}">[{id}]</a
+	></sup
+>
diff --git a/webapp/src/lib/util/scrollToId.ts b/webapp/src/lib/util/scrollToId.ts
new file mode 100644
index 0000000..28a6565
--- /dev/null
+++ b/webapp/src/lib/util/scrollToId.ts
@@ -0,0 +1,6 @@
+export function scrollToId(id: string) {
+	document.querySelector(`#${id}`)?.scrollIntoView();
+
+	// scroll 65px down to avoid the navbar
+	window.scrollBy(0, -65);
+}