Add persistent anonymous usage logging

deploy/server.mjs

@@ -1,10 +1,14 @@
-import { createReadStream, existsSync, statSync } from "node:fs";
+import { appendFile, createReadStream, existsSync, mkdirSync, statSync } from "node:fs";
+import { createHash } from "node:crypto";
 import { createServer } from "node:http";
 import { extname, join, normalize } from "node:path";
 
 const packagedRoot = join(process.cwd(), "public");
 const root = existsSync(join(packagedRoot, "index.html")) ? packagedRoot : join(process.cwd(), "out");
 const port = Number(process.env.APP_PORT || 3200);
+const dataDirectory = process.env.DATA_DIR || join(process.cwd(), "data");
+const usageLogPath = join(dataDirectory, "usage.jsonl");
+mkdirSync(dataDirectory, { recursive: true });
 const mimeTypes = {
   ".css": "text/css; charset=utf-8",
   ".html": "text/html; charset=utf-8",
@@ -17,8 +21,59 @@ const mimeTypes = {
   ".webp": "image/webp",
 };
 
+function sendJson(response, status, value) {
+  response.writeHead(status, { "Content-Type": "application/json; charset=utf-8", "Cache-Control": "no-store" });
+  response.end(JSON.stringify(value));
+}
+
+function writeUsageLog(request, response) {
+  let body = "";
+  request.setEncoding("utf8");
+  request.on("data", (chunk) => {
+    body += chunk;
+    if (body.length > 16_384) request.destroy();
+  });
+  request.on("end", async () => {
+    try {
+      const input = JSON.parse(body || "{}");
+      if (!['page_view', 'conversion'].includes(input.event)) {
+        sendJson(response, 400, { error: "Invalid event" });
+        return;
+      }
+      const entry = {
+        timestamp: new Date().toISOString(),
+        event: input.event,
+        client_hash: request.headers["x-forwarded-for"] || request.socket.remoteAddress
+          ? createHash("sha256").update(String(request.headers["x-forwarded-for"] || request.socket.remoteAddress)).digest("hex").slice(0, 16)
+          : undefined,
+        ...(input.event === "conversion" ? {
+          width: Math.max(8, Math.min(256, Number(input.width) || 0)),
+          height: Math.max(8, Math.min(256, Number(input.height) || 0)),
+          sampling_strategy: input.sampling_strategy === "dominant" ? "dominant" : "smooth",
+          color_limit: Math.max(2, Math.min(64, Number(input.color_limit) || 0)),
+          actual_colors: Math.max(0, Math.min(221, Number(input.actual_colors) || 0)),
+          bead_count: Math.max(0, Math.min(65_536, Number(input.bead_count) || 0)),
+          transparent_cells: Math.max(0, Math.min(65_536, Number(input.transparent_cells) || 0)),
+        } : {}),
+      };
+      await appendFile(usageLogPath, `${JSON.stringify(entry)}\n`, "utf8");
+      sendJson(response, 202, { ok: true });
+    } catch {
+      sendJson(response, 400, { error: "Invalid request" });
+    }
+  });
+}
+
 createServer((request, response) => {
   const pathname = decodeURIComponent(new URL(request.url || "/", "http://localhost").pathname);
+  if (pathname === "/api/usage" && request.method === "POST") {
+    writeUsageLog(request, response);
+    return;
+  }
+  if (pathname.startsWith("/api/")) {
+    sendJson(response, 404, { error: "Not found" });
+    return;
+  }
   const relativePath = normalize(pathname).replace(/^([/\\])+/, "");
   let filePath = join(root, relativePath || "index.html");