From 38f811a24e9611c53105931399a4de9625923817 Mon Sep 17 00:00:00 2001
From: Yasutake Yohei <yohei@yasutakeyohei.com>
Date: Sat, 4 Jul 2026 23:20:31 +0900
Subject: og画像: タイトルハッシュによるキャッシュで再生成をスキップ
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---
 src/pages/og/[slug].png.ts | 37 ++++++++++++++++++++++++++++++++++++-
 1 file changed, 36 insertions(+), 1 deletion(-)

(limited to 'src')

diff --git a/src/pages/og/[slug].png.ts b/src/pages/og/[slug].png.ts
index 2b95898..1047647 100644
--- a/src/pages/og/[slug].png.ts
+++ b/src/pages/og/[slug].png.ts
@@ -1,6 +1,12 @@
 import satori from "satori";
 import { Resvg } from "@resvg/resvg-js";
-import { readFileSync, existsSync, readdirSync } from "node:fs";
+import {
+  readFileSync,
+  existsSync,
+  readdirSync,
+  writeFileSync,
+  mkdirSync,
+} from "node:fs";
 import path from "node:path";
 
 const contentDir = "src/content/docs";
@@ -136,6 +142,29 @@ export async function GET({ params }: { params: { slug: string } }) {
     title = `${reiwa}${month}定例会`;
   }
 
+  // Check cache: if title hash matches, return cached PNG
+  const distDir = path.join(process.cwd(), "dist", "og");
+  const cacheFile = path.join(distDir, `${slug}.png`);
+  const cacheJsonPath = path.join(distDir, ".og-cache.json");
+
+  let cache: Record<string, string> = {};
+  if (existsSync(cacheJsonPath)) {
+    cache = JSON.parse(readFileSync(cacheJsonPath, "utf-8"));
+  }
+
+  const { createHash } = await import("node:crypto");
+  const titleHash = createHash("md5").update(title).digest("hex");
+
+  if (existsSync(cacheFile) && cache[slug] === titleHash) {
+    const cachedBuffer = readFileSync(cacheFile);
+    return new Response(cachedBuffer, {
+      headers: {
+        "Content-Type": "image/png",
+        "Cache-Control": "public, max-age=31536000, immutable",
+      },
+    });
+  }
+
   const svg = await satori(
     {
       type: "div",
@@ -264,6 +293,12 @@ export async function GET({ params }: { params: { slug: string } }) {
   const resvg = new Resvg(svg, { fitTo: { mode: "width", value: 1200 } });
   const pngBuffer = resvg.render().asPng();
 
+  // Save to cache
+  if (!existsSync(distDir)) mkdirSync(distDir, { recursive: true });
+  writeFileSync(cacheFile, pngBuffer);
+  cache[slug] = titleHash;
+  writeFileSync(cacheJsonPath, JSON.stringify(cache, null, 2));
+
   return new Response(pngBuffer, {
     headers: {
       "Content-Type": "image/png",
-- 
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