feat: persistent cache for npm package data

src/utils/npm-info.spec.ts

@@ -2,6 +2,7 @@ import { execa } from "execa";
 import { npmInfo } from "./npm-info";
 
 jest.mock("execa");
+jest.mock("./persistent-cache");
 
 const mockExeca = execa as unknown as jest.Mock;
 

src/utils/npm-info.ts

@@ -1,5 +1,6 @@
 import { execa } from "execa";
 import { type PackageJson } from "../types";
+import { persistentCacheGet, persistentCacheSet } from "./persistent-cache";
 
 const cache = new Map<string, PackageJson>();
 
@@ -9,8 +10,14 @@ export async function npmInfo(pkg: string): Promise<PackageJson> {
 		return cached;
 	}
 
+	const persistent = await persistentCacheGet(pkg);
+	if (persistent) {
+		return persistent as PackageJson;
+	}
+
 	const result = await execa("npm", ["info", "--json", pkg]);
 	const pkgData = JSON.parse(result.stdout) as PackageJson;
 	cache.set(pkg, pkgData);
+	await persistentCacheSet(pkg, pkgData);
 	return pkgData;
 }

src/utils/persistent-cache.ts

@@ -0,0 +1,42 @@
+import fs from "node:fs/promises";
+import path from "node:path";
+import crypto from "node:crypto";
+import os from "node:os";
+
+const enabled = os.platform() === "linux";
+const cacheRoot = process.env.XDG_CACHE_HOME ?? path.join(os.homedir(), ".cache");
+const cacheDir = path.join(cacheRoot, "npm-pkg-lint");
+
+function getFilePath(key: string): string {
+	const hash = crypto.createHash("md5").update(key).digest("hex");
+	const filename = `${hash.slice(0, 2)}/${hash.slice(2)}.json`;
+	return path.join(cacheDir, filename);
+}
+
+export async function persistentCacheGet(key: string): Promise<unknown | null> {
+	if (!enabled) {
+		return null;
+	}
+
+	const filePath = getFilePath(key);
+	try {
+		const content = await fs.readFile(filePath, "utf-8");
+		return JSON.parse(content) as unknown;
+	} catch (err: unknown) {
+		if (err instanceof Error && "code" in err && err.code === "ENOENT") {
+			return null;
+		}
+		throw err;
+	}
+}
+
+export async function persistentCacheSet(key: string, data: unknown): Promise<void> {
+	if (!enabled) {
+		return;
+	}
+
+	const filePath = getFilePath(key);
+	const content = JSON.stringify(data, null, 2);
+	await fs.mkdir(path.dirname(filePath), { recursive: true });
+	await fs.writeFile(filePath, content, "utf-8");
+}