From a9566402049db84439cb5520f3ed6322ab35df90 Mon Sep 17 00:00:00 2001
From: Sarah Gerrard <gerrardsarah@gmail.com>
Date: Fri, 24 Apr 2026 10:29:30 -0700
Subject: [PATCH] fix mermaid diagrams

---
 src/components/markdown/CodeBlock.server.tsx |  15 +++
 src/components/markdown/CodeBlock.tsx        |  31 +++++
 src/components/markdown/MermaidBlock.tsx     | 131 +++++++++++++++++++
 3 files changed, 177 insertions(+)
 create mode 100644 src/components/markdown/MermaidBlock.tsx

diff --git a/src/components/markdown/CodeBlock.server.tsx b/src/components/markdown/CodeBlock.server.tsx
index 7bde2bad..5b8a4082 100644
--- a/src/components/markdown/CodeBlock.server.tsx
+++ b/src/components/markdown/CodeBlock.server.tsx
@@ -1,10 +1,25 @@
 import { CodeBlockView } from './CodeBlockView'
+import { MermaidBlock } from './MermaidBlock'
 import type { CodeBlockProps } from './codeBlock.shared'
 import { extractCodeBlockData } from './codeBlock.shared'
 import { renderCodeBlockData } from './renderCodeBlock.server'
 
 export async function CodeBlock(props: CodeBlockProps) {
   const { code, lang, title } = extractCodeBlockData(props)
+
+  if (lang === 'mermaid') {
+    return (
+      <MermaidBlock
+        className={props.className}
+        code={code}
+        isEmbedded={props.isEmbedded}
+        showTypeCopyButton={props.showTypeCopyButton}
+        style={props.style}
+        title={title}
+      />
+    )
+  }
+
   const rendered = await renderCodeBlockData({
     code,
     lang,
diff --git a/src/components/markdown/CodeBlock.tsx b/src/components/markdown/CodeBlock.tsx
index d1e5b7ab..39904d0a 100644
--- a/src/components/markdown/CodeBlock.tsx
+++ b/src/components/markdown/CodeBlock.tsx
@@ -2,6 +2,7 @@
 
 import * as React from 'react'
 import { CodeBlockView } from './CodeBlockView'
+import { MermaidBlock } from './MermaidBlock'
 import {
   buildPlainCodeBlockHtml,
   extractCodeBlockData,
@@ -30,6 +31,36 @@ function getRenderPromise(
 
 export function CodeBlock(props: CodeBlockProps) {
   const { code, lang, title } = extractCodeBlockData(props)
+
+  if (lang === 'mermaid') {
+    return (
+      <MermaidBlock
+        className={props.className}
+        code={code}
+        isEmbedded={props.isEmbedded}
+        showTypeCopyButton={props.showTypeCopyButton}
+        style={props.style}
+        title={title}
+      />
+    )
+  }
+
+  return (
+    <HighlightedCodeBlock code={code} lang={lang} props={props} title={title} />
+  )
+}
+
+function HighlightedCodeBlock({
+  code,
+  lang,
+  props,
+  title,
+}: {
+  code: string
+  lang: string
+  props: CodeBlockProps
+  title?: string
+}) {
   const [rendered, setRendered] = React.useState<RenderedCodeBlockData | null>(
     null,
   )
diff --git a/src/components/markdown/MermaidBlock.tsx b/src/components/markdown/MermaidBlock.tsx
new file mode 100644
index 00000000..8151d4c6
--- /dev/null
+++ b/src/components/markdown/MermaidBlock.tsx
@@ -0,0 +1,131 @@
+'use client'
+
+import * as React from 'react'
+import { twMerge } from 'tailwind-merge'
+import { CodeBlockView } from './CodeBlockView'
+import { buildPlainCodeBlockHtml } from './codeBlock.shared'
+
+type MermaidRenderState =
+  | {
+      status: 'loading'
+      svg?: undefined
+    }
+  | {
+      status: 'rendered'
+      svg: string
+    }
+  | {
+      status: 'error'
+      svg?: undefined
+    }
+
+function getIsDarkMode() {
+  return document.documentElement.classList.contains('dark')
+}
+
+function useIsDarkMode() {
+  const [isDark, setIsDark] = React.useState(false)
+
+  React.useEffect(() => {
+    const updateIsDark = () => setIsDark(getIsDarkMode())
+    updateIsDark()
+
+    const observer = new MutationObserver(updateIsDark)
+    observer.observe(document.documentElement, {
+      attributeFilter: ['class'],
+      attributes: true,
+    })
+
+    return () => observer.disconnect()
+  }, [])
+
+  return isDark
+}
+
+export function MermaidBlock({
+  className,
+  code,
+  isEmbedded,
+  showTypeCopyButton,
+  style,
+  title,
+}: {
+  className?: string
+  code: string
+  isEmbedded?: boolean
+  showTypeCopyButton?: boolean
+  style?: React.CSSProperties
+  title?: string
+}) {
+  const isDark = useIsDarkMode()
+  const reactId = React.useId()
+  const mermaidId = React.useMemo(
+    () => `mermaid-${reactId.replace(/[^a-zA-Z0-9_-]/g, '')}`,
+    [reactId],
+  )
+  const [renderState, setRenderState] = React.useState<MermaidRenderState>({
+    status: 'loading',
+  })
+
+  React.useEffect(() => {
+    let cancelled = false
+
+    async function renderMermaid() {
+      setRenderState({ status: 'loading' })
+
+      try {
+        const mermaid = (await import('mermaid')).default
+
+        mermaid.initialize({
+          securityLevel: 'strict',
+          startOnLoad: false,
+          theme: isDark ? 'dark' : 'default',
+        })
+
+        const { svg } = await mermaid.render(mermaidId, code)
+
+        if (!cancelled) {
+          setRenderState({ status: 'rendered', svg })
+        }
+      } catch {
+        if (!cancelled) {
+          setRenderState({ status: 'error' })
+        }
+      }
+    }
+
+    void renderMermaid()
+
+    return () => {
+      cancelled = true
+    }
+  }, [code, isDark, mermaidId])
+
+  if (renderState.status !== 'rendered') {
+    return (
+      <CodeBlockView
+        className={className}
+        copyText={code.trimEnd()}
+        htmlMarkup={buildPlainCodeBlockHtml(code)}
+        isEmbedded={isEmbedded}
+        lang="mermaid"
+        showTypeCopyButton={showTypeCopyButton}
+        style={style}
+        title={title}
+      />
+    )
+  }
+
+  return (
+    <div
+      className={twMerge(
+        'mermaid-block not-prose w-full max-w-full overflow-x-auto rounded-md border border-gray-500/20 bg-white p-4 dark:bg-gray-950 [&_svg]:mx-auto [&_svg]:max-w-none',
+        className,
+      )}
+      style={style}
+      role="img"
+      aria-label={title ?? 'Mermaid diagram'}
+      dangerouslySetInnerHTML={{ __html: renderState.svg }}
+    />
+  )
+}