web: add prerendered version.json endpoint for frontend metadata

web/src/routes/version.json/+server.ts

@@ -0,0 +1,58 @@
+import { error, json } from '@sveltejs/kit';
+import { readFile }    from 'node:fs/promises';
+import { join, parse } from 'node:path';
+import { existsSync }  from 'node:fs';
+import { cwd }         from 'node:process';
+
+const findFile = (file: string) => {
+    let dir = cwd();
+
+    while (dir !== parse(dir).root) {
+        if (existsSync(join(dir, file))) {
+            return dir;
+        }
+
+        dir = join(dir, '../');
+    }
+}
+
+const root = findFile('.git');
+const pack = findFile('package.json');
+
+export async function GET() {
+    if (!root) {
+        return error(500, 'no git repository root found');
+    } else if (!pack) {
+        return error(500, 'no package root found');
+    }
+
+    const readGit = (filename: string) => readFile(join(root, filename), 'utf8');
+
+    const commit = (await readGit('.git/logs/HEAD'))
+                    ?.split('\n')
+                    ?.filter(String)
+                    ?.pop()
+                    ?.split(' ')[1];
+
+    const branch = (await readGit('.git/HEAD'))
+                    ?.replace(/^ref: refs\/heads\//, '')
+                    ?.trim();
+
+    const remote = (await readGit('.git/config'))
+                    ?.split('\n')
+                    ?.find(line => line.includes('url = ') && line.endsWith('.git'))
+                    ?.split(':')[1]
+                    ?.replace(/\.git$/, '');
+
+    const { version } = JSON.parse(
+        await readFile(join(pack, 'package.json'), 'utf8')
+    );
+
+    if (!commit || !branch || !remote || !version) {
+        return error(500, 'failed to extract project metadata');
+    }
+
+    return json({ commit, branch, remote, version });
+}
+
+export const prerender = true;