feat(desktop): add resolve-env for runtime placeholder replacement

surfsense_desktop/src/resolve-env.ts

@@ -0,0 +1,69 @@
+// TODO: Placeholders are gone after the first run. Self-hosted users
+// cannot change their backend URL without reinstalling.
+
+import fs from 'fs';
+import path from 'path';
+
+const DEFAULTS: Record<string, string> = {
+  __NEXT_PUBLIC_FASTAPI_BACKEND_URL__: 'http://localhost:8000',
+  __NEXT_PUBLIC_FASTAPI_BACKEND_AUTH_TYPE__: 'LOCAL',
+  __NEXT_PUBLIC_ETL_SERVICE__: 'DOCLING',
+  __NEXT_PUBLIC_ELECTRIC_URL__: 'http://localhost:5133',
+  __NEXT_PUBLIC_ELECTRIC_AUTH_MODE__: 'insecure',
+  __NEXT_PUBLIC_DEPLOYMENT_MODE__: 'self-hosted',
+};
+
+function walk(dir: string, replacements: [string, string][]) {
+  let entries: fs.Dirent[];
+  try {
+    entries = fs.readdirSync(dir, { withFileTypes: true });
+  } catch {
+    return;
+  }
+  for (const entry of entries) {
+    const full = path.join(dir, entry.name);
+    if (entry.isDirectory()) {
+      walk(full, replacements);
+    } else if (entry.name.endsWith('.js')) {
+      let content = fs.readFileSync(full, 'utf8');
+      let changed = false;
+      for (const [placeholder, value] of replacements) {
+        if (content.includes(placeholder)) {
+          content = content.replaceAll(placeholder, value);
+          changed = true;
+        }
+      }
+      if (changed) {
+        fs.writeFileSync(full, content);
+      }
+    }
+  }
+}
+
+export function resolveEnv(standalonePath: string, overrides?: Record<string, string>) {
+  const replacements: [string, string][] = Object.entries(DEFAULTS).map(
+    ([placeholder, defaultValue]) => {
+      const envKey = placeholder.replace(/^__|__$/g, '');
+      const value = overrides?.[envKey] ?? process.env[envKey] ?? defaultValue;
+      return [placeholder, value];
+    }
+  );
+
+  console.log('[resolve-env] Replacing placeholders in standalone build:');
+  for (const [placeholder, value] of replacements) {
+    console.log(`  ${placeholder} -> ${value}`);
+  }
+
+  walk(path.join(standalonePath, '.next'), replacements);
+
+  const serverJs = path.join(standalonePath, 'server.js');
+  if (fs.existsSync(serverJs)) {
+    let content = fs.readFileSync(serverJs, 'utf8');
+    for (const [placeholder, value] of replacements) {
+      if (content.includes(placeholder)) {
+        content = content.replaceAll(placeholder, value);
+      }
+    }
+    fs.writeFileSync(serverJs, content);
+  }
+}