Date of treatment for "CGM Sensor Insert" or "Pump Site Change" differs with 1h in CET

[Joerg-Schoemer]

In CEST everything worked fine, now in CET it is 1h to earlier calculated in UTC

[dhermanns]

Hi! You mean you set the time with nightguard and afterwards it differs by one hour?

[Joerg-Schoemer]

Yes, when I enter an event at 16.00h in Nightguard it appears at 15.00h in Nightscout

[dhermanns]

You should check your settings on your server side. Can't reproduce this here with my Setup and CET timezone.

[Joerg-Schoemer]

The event date should be in UTC (string with Z at the end of the date). What setting can be wrong on the server to miss interpret the date?

[dhermanns]

I'm not a cgm-remote-monitor expert. So maybe you ask this there. From a nightguard perspective, I'm creating Global (UTC) Time for the timestamp here:

https://github.com/nightscout/nightguard/blob/master/nightguard/DateExtension.swift#L70

Looks ok to me.

[Joerg-Schoemer]

Hi Dirk,

I've added a test to see what happens.

final class DateExtensionTest: XCTestCase {

    override func setUpWithError() throws {
        // Put setup code here. This method is called before the invocation of each test method in the class.
    }

    override func tearDownWithError() throws {
        // Put teardown code here. This method is called after the invocation of each test method in the class.
    }

    func testExample() throws {

        let now = Date.now

        let gmt = now.toGlobalTime()

        var utcIsoFormatter = Date.ISO8601FormatStyle()
        // utcIsoFormatter.timeZone = TimeZone.gmt

        print("\(now.formatted(utcIsoFormatter)) \(gmt.formatted(utcIsoFormatter))")

        var localIsoFormatter = Date.ISO8601FormatStyle()
        localIsoFormatter.timeZone = TimeZone.current

        print("\(now.formatted(localIsoFormatter)) \(gmt.formatted(localIsoFormatter))")

        XCTAssert(gmt != now)
    }

    func testPerformanceExample() throws {
        // This is an example of a performance test case.
        self.measure {
            // Put the code you want to measure the time of here.
        }
    }

}

when I run the test now is already in the TimeZone UTC. So when subtracting the TimeZone.current difference, which is 1h, the "GlobalTime" is GMT-1

A calculation is not needed, the formatter should be configured for the desired TimeZone.

[Joerg-Schoemer]

Hi Dirk,

after hours spend on created_at I've found the bug

REST API treatment created [
{
    eventType: 'Site Change',
    enteredBy: 'nightguard',
    created_at: '2023-12-04T18:10:00.000Z',
    mills: 1701709800000,
    utcOffset: 0,
    _id: 656e3bf536b9019ceaa8d8da
}
]

created_at looks good 👍🏻 but when creating a date from mills in JavaScript it is interpreted as:

date = new Date(1701709800000)
Mon Dec 04 2023 18:10:00 GMT+0100

converted to UTC 2023-12-04T17:10:00Z is one hour to early 👎🏻

The bug is in the calculation of the mills.