refactor: repository pattern for data access

src/db/connection.js

@@ -0,0 +1,88 @@
+import fs from 'node:fs';
+import path from 'node:path';
+import Database from 'better-sqlite3';
+import { warn } from '../logger.js';
+
+function isProcessAlive(pid) {
+  try {
+    process.kill(pid, 0);
+    return true;
+  } catch {
+    return false;
+  }
+}
+
+function acquireAdvisoryLock(dbPath) {
+  const lockPath = `${dbPath}.lock`;
+  try {
+    if (fs.existsSync(lockPath)) {
+      const content = fs.readFileSync(lockPath, 'utf-8').trim();
+      const pid = Number(content);
+      if (pid && pid !== process.pid && isProcessAlive(pid)) {
+        warn(`Another process (PID ${pid}) may be using this database. Proceeding with caution.`);
+      }
+    }
+  } catch {
+    /* ignore read errors */
+  }
+  try {
+    fs.writeFileSync(lockPath, String(process.pid), 'utf-8');
+  } catch {
+    /* best-effort */
+  }
+}
+
+function releaseAdvisoryLock(lockPath) {
+  try {
+    const content = fs.readFileSync(lockPath, 'utf-8').trim();
+    if (Number(content) === process.pid) {
+      fs.unlinkSync(lockPath);
+    }
+  } catch {
+    /* ignore */
+  }
+}
+
+export function openDb(dbPath) {
+  const dir = path.dirname(dbPath);
+  if (!fs.existsSync(dir)) fs.mkdirSync(dir, { recursive: true });
+  acquireAdvisoryLock(dbPath);
+  const db = new Database(dbPath);
+  db.pragma('journal_mode = WAL');
+  db.pragma('busy_timeout = 5000');
+  db.__lockPath = `${dbPath}.lock`;
+  return db;
+}
+
+export function closeDb(db) {
+  db.close();
+  if (db.__lockPath) releaseAdvisoryLock(db.__lockPath);
+}
+
+export function findDbPath(customPath) {
+  if (customPath) return path.resolve(customPath);
+  let dir = process.cwd();
+  while (true) {
+    const candidate = path.join(dir, '.codegraph', 'graph.db');
+    if (fs.existsSync(candidate)) return candidate;
+    const parent = path.dirname(dir);
+    if (parent === dir) break;
+    dir = parent;
+  }
+  return path.join(process.cwd(), '.codegraph', 'graph.db');
+}
+
+/**
+ * Open a database in readonly mode, with a user-friendly error if the DB doesn't exist.
+ */
+export function openReadonlyOrFail(customPath) {
+  const dbPath = findDbPath(customPath);
+  if (!fs.existsSync(dbPath)) {
+    console.error(
+      `No codegraph database found at ${dbPath}.\n` +
+        `Run "codegraph build" first to analyze your codebase.`,
+    );
+    process.exit(1);
+  }
+  return new Database(dbPath, { readonly: true });
+}