Extract database operations into separate db.ts module

- src/db.ts: initDatabase, closeDatabase, storeMessage, getNewMessages
- Removes SQL from index.ts
- Database initialization happens once at startup

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/db.ts

@@ -0,0 +1,78 @@
+import Database from 'better-sqlite3';
+import fs from 'fs';
+import path from 'path';
+import { proto } from '@whiskeysockets/baileys';
+import { NewMessage } from './types.js';
+import { STORE_DIR } from './config.js';
+
+let db: Database.Database;
+
+export function initDatabase(): void {
+  const dbPath = path.join(STORE_DIR, 'messages.db');
+  fs.mkdirSync(path.dirname(dbPath), { recursive: true });
+
+  db = new Database(dbPath);
+  db.exec(`
+    CREATE TABLE IF NOT EXISTS chats (
+      jid TEXT PRIMARY KEY,
+      name TEXT,
+      last_message_time TEXT
+    );
+    CREATE TABLE IF NOT EXISTS messages (
+      id TEXT,
+      chat_jid TEXT,
+      sender TEXT,
+      content TEXT,
+      timestamp TEXT,
+      is_from_me INTEGER,
+      PRIMARY KEY (id, chat_jid),
+      FOREIGN KEY (chat_jid) REFERENCES chats(jid)
+    );
+    CREATE INDEX IF NOT EXISTS idx_timestamp ON messages(timestamp);
+  `);
+}
+
+export function closeDatabase(): void {
+  db.close();
+}
+
+export function storeMessage(msg: proto.IWebMessageInfo, chatJid: string, isFromMe: boolean): void {
+  if (!msg.key) return;
+
+  const content =
+    msg.message?.conversation ||
+    msg.message?.extendedTextMessage?.text ||
+    msg.message?.imageMessage?.caption ||
+    msg.message?.videoMessage?.caption ||
+    '';
+
+  const timestamp = new Date(Number(msg.messageTimestamp) * 1000).toISOString();
+  const sender = msg.key.participant || msg.key.remoteJid || '';
+  const msgId = msg.key.id || '';
+
+  db.prepare(`INSERT OR REPLACE INTO chats (jid, name, last_message_time) VALUES (?, ?, ?)`)
+    .run(chatJid, chatJid, timestamp);
+  db.prepare(`INSERT OR REPLACE INTO messages (id, chat_jid, sender, content, timestamp, is_from_me) VALUES (?, ?, ?, ?, ?, ?)`)
+    .run(msgId, chatJid, sender, content, timestamp, isFromMe ? 1 : 0);
+}
+
+export function getNewMessages(jids: string[], lastTimestamp: string): { messages: NewMessage[]; newTimestamp: string } {
+  if (jids.length === 0) return { messages: [], newTimestamp: lastTimestamp };
+
+  const placeholders = jids.map(() => '?').join(',');
+  const sql = `
+    SELECT id, chat_jid, sender, content, timestamp
+    FROM messages
+    WHERE timestamp > ? AND chat_jid IN (${placeholders})
+    ORDER BY timestamp
+  `;
+
+  const rows = db.prepare(sql).all(lastTimestamp, ...jids) as NewMessage[];
+
+  let newTimestamp = lastTimestamp;
+  for (const row of rows) {
+    if (row.timestamp > newTimestamp) newTimestamp = row.timestamp;
+  }
+
+  return { messages: rows, newTimestamp };
+}