import sqlite3, json, time
                import paho.mqtt.client as mqtt
                db = sqlite3.connect("local_queue.db")
                db.execute("""
                    CREATE TABLE IF NOT EXISTS readings (
                        id INTEGER PRIMARY KEY AUTOINCREMENT,
                        device_id TEXT, value REAL, unit TEXT,
                        measured_at INTEGER, synced INTEGER DEFAULT 0
                    )
                """)
                def record_reading(device_id: str, value: float, unit: str):
                    # 不論網路狀態，先寫入本地資料庫，確保資料不遺失
                    db.execute(
                        "INSERT INTO readings (device_id, value, unit, measured_at) VALUES (?, ?, ?, ?)",
                        (device_id, value, unit, int(time.time() * 1000))
                    )
                    db.commit()
                def is_network_available() -> bool:
                    try:
                        mqtt_client.reconnect()
                        return True
                    except Exception:
                        return False
                def sync_pending_readings():
                    # 網路恢復後，依原始量測時間排序，批次補傳未同步記錄
                    pending = db.execute(
                        "SELECT id, device_id, value, unit, measured_at FROM readings WHERE synced = 0 ORDER BY measured_at ASC"
                    ).fetchall()
                    for row in pending:
                        record_id, device_id, value, unit, measured_at = row
                        payload = {
                            "deviceId": device_id,
                            "value": value,
                            "unit": unit,
                            "measuredAt": measured_at,   # 原始量測時間，非上傳時間
                            "syncedAt": int(time.time() * 1000)
                        }
                        try:
                            mqtt_client.publish(f"atlantis/ramp-ops/{device_id}/data", json.dumps(payload), qos=1)
                            db.execute("UPDATE readings SET synced = 1 WHERE id = ?", (record_id,))
                            db.commit()
                        except Exception:
                            break  # 網路又斷線，停止本輪同步，等下次重試
                def main_loop():
                    while True:
                        pressure = read_bluetooth_transmitter()
                        record_reading("HYD-CART-07", pressure, "bar")
                        if is_network_available():
                            sync_pending_readings()
                        time.sleep(5)