From 1bfad5f0d028862cab06bb259e83eed6d1f9395e Mon Sep 17 00:00:00 2001
From: Anton Bulakh <him@necauq.ua>
Date: Sun, 5 Jan 2025 01:22:08 +0200
Subject: [PATCH] fix(backlinks): Improve backlink perf and fix aliased
 backlinks

Backlink calculation is quadratic, similar to breadcrumbs before the
fix.

Apply a similar fix here.

Also added alias resolution, so this depends on `file.data.aliases`
from #1681, but that can be commented out easily if needed.
---
 quartz/components/Backlinks.tsx | 40 ++++++++++++++++++++++++++++-----
 1 file changed, 35 insertions(+), 5 deletions(-)

diff --git a/quartz/components/Backlinks.tsx b/quartz/components/Backlinks.tsx
index e99055e31b2e7..5301161d19a5b 100644
--- a/quartz/components/Backlinks.tsx
+++ b/quartz/components/Backlinks.tsx
@@ -1,6 +1,6 @@
 import { QuartzComponent, QuartzComponentConstructor, QuartzComponentProps } from "./types"
 import style from "./styles/backlinks.scss"
-import { resolveRelative, simplifySlug } from "../util/path"
+import { FullSlug, resolveRelative, SimpleSlug, simplifySlug } from "../util/path"
 import { i18n } from "../i18n"
 import { classNames } from "../util/lang"
 
@@ -15,14 +15,44 @@ const defaultOptions: BacklinksOptions = {
 export default ((opts?: Partial<BacklinksOptions>) => {
   const options: BacklinksOptions = { ...defaultOptions, ...opts }
 
+  let backlinks: Map<SimpleSlug, Array<{ slug: FullSlug; title: string }>> | undefined
+
   const Backlinks: QuartzComponent = ({
     fileData,
     allFiles,
     displayClass,
     cfg,
   }: QuartzComponentProps) => {
-    const slug = simplifySlug(fileData.slug!)
-    const backlinkFiles = allFiles.filter((file) => file.links?.includes(slug))
+    if (!backlinks) {
+      backlinks = new Map()
+
+      const aliasMap = new Map<SimpleSlug, SimpleSlug>()
+      for (const file of allFiles) {
+        for (const alias of file.aliases ?? []) {
+          aliasMap.set(simplifySlug(alias), simplifySlug(file.slug!))
+        }
+      }
+
+      for (const file of allFiles) {
+        const seen = new Set<SimpleSlug>()
+        for (let link of file.links ?? []) {
+          link = aliasMap.get(link) ?? link
+          // avoid aliased duplicates
+          if (seen.has(link)) {
+            continue
+          }
+          seen.add(link)
+          let ref = backlinks.get(link)
+          if (!ref) {
+            backlinks.set(link, (ref = []))
+          }
+          ref.push({ slug: file.slug!, title: file.frontmatter?.title! })
+        }
+      }
+    }
+
+    const backlinkFiles = backlinks.get(simplifySlug(fileData.slug!)) ?? []
+
     if (options.hideWhenEmpty && backlinkFiles.length == 0) {
       return null
     }
@@ -33,8 +63,8 @@ export default ((opts?: Partial<BacklinksOptions>) => {
           {backlinkFiles.length > 0 ? (
             backlinkFiles.map((f) => (
               <li>
-                <a href={resolveRelative(fileData.slug!, f.slug!)} class="internal">
-                  {f.frontmatter?.title}
+                <a href={resolveRelative(fileData.slug!, f.slug)} class="internal">
+                  {f.title}
                 </a>
               </li>
             ))