import time
import boto3
from boto3.dynamodb.conditions import Key

dynamodb = boto3.resource("dynamodb", region_name="ap-northeast-1")
table = dynamodb.Table("factory_temperature_history")
cloudwatch = boto3.client("cloudwatch", region_name="ap-northeast-1")

MONITORED_DEVICES = ["ATL-STT-001", "ATL-STT-002", "ATL-SDPT-001"]

def get_last_timestamp(device_id: str):
    response = table.query(
        KeyConditionExpression=Key("device_id").eq(device_id),
        ScanIndexForward=False,  # 依timestamp倒序，取得最新一筆
        Limit=1
    )
    items = response.get("Items", [])
    return int(items[0]["timestamp"]) if items else None

def lambda_handler(event, context):
    now = int(time.time())

    for device_id in MONITORED_DEVICES:
        last_ts = get_last_timestamp(device_id)

        if last_ts is None:
            minutes_since_last_data = 99999  # 從未收過資料
        else:
            minutes_since_last_data = (now - last_ts) / 60

        cloudwatch.put_metric_data(
            Namespace="ATLANTIS/FactoryIoT",
            MetricData=[
                {
                    "MetricName": "MinutesSinceLastData",
                    "Dimensions": [{"Name": "DeviceId", "Value": device_id}],
                    "Value": minutes_since_last_data,
                    "Unit": "None"
                }
            ]
        )
        print(f"裝置 {device_id}：距上次回報 {minutes_since_last_data:.1f} 分鐘")

    return {"statusCode": 200, "body": "心跳檢查完成"}